My Account | View Cart | Wishlist | Checkout | About Us | Contact Us

Login

Categories

Posts Tagged ‘ccnp’

« Older Entries

CCNA 640-802: IP Addressing

Monday, June 7th, 2010 by sales@ciscokits.com

IP Addressing, conversions between binary and decimal

Today we will continue your preparation for the CCNA exam. We will talk about IP addressing and conversions between binary and decimal. Understanding how IP addressing works is a critical step in your preparation for Cisco’s CCNA exam because it will help you learn easily how routers take decisions to forward packets in your network.

IP addressing is the key function of every IP network to function. Today, when you say IP, you talk about IPv4. Soon, IPv6 will take its place, but now, every time when we’ll say IP we will talk about IPv4.

IP enables hosts to communicate with each other at the Network layer. In IPv4 each packet contains a source and destination address. That’s how the routers on the network knows where the packet is coming from and where they must forward the packet. The IP addresses fields are represented in 32 bits. Routers know how to interpret those numbers, but for a human to understand them would be too difficult. From our point of view, we use what’s called a dotted decimal address. A dotted decimal address is the human representation of the binary address. For example, the address 192.168.10.1 is a dotted decimal address. In its binary form, the address is 11000000101010000000101000000001. IP addresses have 4 octets. For example, 192 is the first octet, 168 the second, 10 the third and 1 the last octet. In its binary form, 11000000 is the first octet, 10101000 the second, 00001010 the third and 00000001 the last octet. Every octet, in its decimal form, can get a value from 0 to 255.

In the binary system there are only 1s and 0s. Depending on their position in the octet, they get different values. Each position is a power of 2. To get the decimal number you have to sum up those number.  

1

1

1

1

1

1

1

1

2^7 = 128

2^6 = 64

2^5 = 32

2^4 = 16

2^3 = 8

2^2 = 4

2^1 = 2

2^0 = 1

 

For example, we know that 10101000 is 168. But let’s see if we get the same number after we make the calculations.

2^7 * 1 + 2^6 * 0 + 2^5 * 1 + 2^4 * 0 + 2^3 * 1 + 2^2 * 0 + 2^1 * 0 + 2^0 * 0 = 128 + 32 + 8 = 168

Let’s now learn how to convert those numbers from decimal to binary. The decimal to binary conversion is similar to binary to decimal conversion. Keep in mind those powers of 2. When you calculate the binary value, you take those powers of 2 and compare them with your number. If your number is greater, you write down 1 and you subtract that power of 2 from the number. If your number is lower than the power of 2, you write down 0. You continue to make the calculations until you reach 2^0.

Let’s take the same number, 168, and convert it to binary.

168 is greater than 128. We write down 1 and we subtract 128 from 168. We get 40. 40 is lower than 64. We write 0 and we continue. 40 is greater than 32. We write 1 and we subtract 32 from 40, getting us 8. 8 is lower than 16. Write 0. We continue to 8, which is equal to 8. We write down 1 and from this point we can fill the remaining 3 spaces with 0s. Finally, we get 10101000.

168 >= 128?               1      168 – 128 = 40
40 >= 64?                   0
40 >= 32?                   1       40 – 32 = 8
8 >= 16?                     0
8 >= 8?                       1        8 – 8 = 0
0 >= 4?                       0
0 >= 2?                       0
0 >= 1?                       0

Try to practice these conversions. This is a requirement in the CCNA exam, and you may have to do some calculations. You can start for example to find out what’s the binary representation of 215? What about 110 or 16? Are you able to calculate the decimal value for 11010011, 00010110, 01110001?

We continue in our CCNA certification topic with the types of IP addresses.

In the range of a network, there are three types of IP addresses: network address, broadcast address and host address.

The network address is the address by which we refer a network. It is always the first address in an IP address range.

The broadcast address is a special address used to send data to all hosts on a network. It is always the last address in an IP address range.

The host address is the address assigned to a single host in a network. The value of the IP address must have a value between the network and the broadcast address.

We will discuss these types of addresses in the IP address components lesson.

An IPv4 host can communicate in different ways: unicast, broadcast and multicast.

In Unicast a host sends packets to only one host on the network and a host in other network.

Broadcast is the process of sending packets to all hosts in a network. Broadcast messages are not routed in other networks, allowing hosts to communicate on their network.

Multicast traffic is the traffic sent from one host to a selected group of hosts using a special IP address. Multicast is often used by routing protocols, in video and audio distribution and software distribution. In IPv4, there is a special block of addresses reserved for multicasting: 224.0.0.0 to 239.255.255.255.

IPv4 has 3 types of addresses: host addresses, multicast addresses and experimental addresses.

Host addresses are from 0.0.0.0 to 223.255.255.255 and are used for IPv4 hosts.

Multicast addresses, as stated above, are from 224.0.0.0 to 239.255.255.255 and are used for special purposes.

Experimental addresses are used only for research and experimentation and cannot be used in IPv4 networks. The range is from 240.0.0.0 to 255.255.255.254.

However, not all host addresses can be routed through the internet. There is a private address space used for communications in your internal network, which can be freely used by anyone. The private address blocks are: 10.0.0.0 to 10.255.255.255 (10.0.0.0/8), 172.16.0.0 to 172.31.255.255 (172.16.0.0/12) and 192.168.0.0 to 192.168.255.255 (192.168.0.0/16).

Although these addresses cannot be routed in the Internet, you can still have Internet connectivity. This process is called Network Address Translation (NAT). In this process, one or many hosts having private IP addresses are mapped to a router’s public IP address.

There are 4 more types of special addresses. The default route address is 0.0.0.0. This is used as a “catch all” route when a specific route is not available. The loopback address is by default 127.0.0.1, but the whole 127.0.0.1 to 127.255.255.255 is used. The loopback address is used by a host to communicate with himself. A link-local address is an address assigned automatically to a host which has no IP configuration present. The reserved space is from 169.254.0.0 to 169.254.255.255. There’s one more special type of address, called TEST-NET addresses. The reserved space, 192.0.2.0 to 192.0.2.255 is used for teaching and learning purposes. Unlike the experimental range of addresses, these addresses can be assigned to network devices.

Back in the days, when classless routing was not used, the IP addresses were classified in 5 different classes.

Class A addresses were the ones from 0.0.0.0 to 127.255.255.255. A class A network is has a default netmask of 255.0.0.0 allowing for up to 16,777,214 hosts per network ( 2^24 – 2). However, there’s possible to create only 128 network from the whole class A space. Or at least it was, back in the days, when classless routing was not used.

Class B addresses are from 128.0.0.0 to 191.255.255.255. The whole class B was able to create 16,384 networks (2^14) with a maximum number of 65,534 hosts per network (2^16 – 2). The default netmask si 255.255.0.0.

Class C networks were found within the 192.0.0.0 – 223.255.255.255 range. This class allowed for more networks -2,097,150 ( 2^21 ) but the maximum hosts per network was only 254 (2^8 – 2).

The class D and the class E address blocks are the same used today for multicasting, respectively the experimental addresses.

However, these days we use classless addressing. The process of assigning classless addresses is called subneting. We will learn you how to subnet on a separate, dedicated topic.

We hope we have found this introduction in IP addressing helpful. We must note that you must be able to effectively use IP addressing and convert the addresses between their decimal and binary forms when you’ll take the CCNA exam.

Tags: , , , , , , , , , , , ,
Posted in CiscoKits CCNA Blog | No Comments »

CCNA 640-802: Cisco 3 Layer Model

Wednesday, May 12th, 2010 by sales@ciscokits.com

Cisco Three Layered Hierarchical Model

Welcome to a new lesson from our Cisco CCNA certification exam preparation series. We would like to present you today Cisco’s 3 Layered Hierarchical Model.

Understanding hierarchy is important and it’s simple too. In real life we have all kinds of hierarchical models. For example, when you were in school, you, as a student, were at the bottom of the hierarchy. At the next level of the hierarchy were the teachers. Above the teacher there was one or many directors.

In the networking world, hierarchy helps you separate some parts of your network from others. When you design your network, you should use a hierarchical model to separate your network in different layers. Every layer of your network should perform only some functions. Avoid using network equipments as all-in-one equipments. For example, a border router, connected to your service provider, should do only the process of routing and some basic filtering maybe. Don’t use this router to implement QoS policies or VoIP services. This way, your network will be more predictable and you will be able to troubleshoot problems faster.

1

After years in the networking industry, Cisco developed its own hierarchical model, Cisco’s Three Layered Hierarchical Model. This is probably the most basic model ever known, and Cisco even developed its network in accordance with this model. Benefits of using Cisco’s hierarchical model are network stability, reliability and cost-effectiveness.

Cisco’s 3 Layered model consist from the core, the distribution and the access layers.

The Core layer is actually the backbone, or the core, of your network. This is the most critical layer because its purpose is to provide fault isolation and backbone connectivity. The core layer must be able to switch traffic at the highest speeds possible in a timely fashion. Also, at the core layer, the network must have a level of redundancy, used in case of link or hardware failure. You should not use this layer to create services for your users.

Because it has to be a fast and reliable layer of your network, you should not implement at this layer anything that can slow down the traffic, like ACLs, Inter-VLAN routing, packet filtering. Also, don’t add support for group access and do not expand the core layer. If your current devices are not supporting the traffic, upgrade them, instead of adding more devices.

When you design the Core layer of your network you must make sure it will be reliable, meaning you have to use technologies able to carry large amounts of traffic and also provide a high level of redundancy, such as FDDI, Fast/Gigabit Ethernet or ATM. Also, a good practice is to use routing protocols with lower convergence times to avoid downtimes. Again, you have to design this with speed in mind. At the Core layer you should have very little latency.

Examples of network equipments used in the core layer are: high speed WAN routers and switches, multiplexers, ATM networks, such as Cisco 7000, 7200, 7500 and 12000 series for WAN and Cisco 4000, 5000 and 6000 series for LAN.

In smaller networks you may see high-speed routers instead of switches at the core layer.

The Distribution layer is used as a communication point between the access and the core layer. Basically, this layer handles the routing, packet filtering, WAN access and determines how packets can reach the core if needed. This layer includes all OSI Layer 3 devices, such as routers and layer 3 switches.

At the distribution layer, generally you would implement:

  • Routing
  • ACLs, packet filtering and QoS
  • Security and network policies, including NAT and firewalls
  • Route Reflectors (RRs) to distribute routes across your network
  • Inter-VLAN routing
  • Workgroup functions

Examples of network equipments used at the distribution layer are: LAN routers, layer 3 switches, firewalls, VPN access router.

Finally, the Access layer, also called the desktop layer, focuses on connecting client devices, such as workstations, laptops, servers and peripherals on the internal network (same broadcast domain). If a host must access a resource in some other network, the Distribution layer handles to traffic to reach that network.  The access layer is used also to separate collision domains, filter MAC addresses and implement load balancing.

At this layer, the most used technology is Ethernet. Routing protocols are rarely used, instead static routing is often being seen.

As we already told you, this is the easiest hierarchical model and Cisco uses it in its network with great success. Although is not a big topic for your CCNA exam, you must know what are the layers of Cisco’s Three Layered Hierarchical Model and what is their purpose.

Tags: , , , , , , , , , , , , ,
Posted in CiscoKits CCNA Blog | No Comments »

CCNA Certification: WAN Concepts

Tuesday, March 2nd, 2010 by CiscoKits

Cisco CCNA Certification: WAN Concepts

We are welcoming you to a new lesson from our Cisco CCNA 640-802 exam preparation series. As outlined in the CCNA exam requirements, the CCNA candidate must have at least a basic understanding about WANs.

Wide Area Networks, or WANs for short, is a network that operates beyond the geographic scope of a LAN. A LAN is used to connected computers and network devices in a small geographic area, while WANs are extending to larger geographical areas. For example, you have one office located in USA and another office located in London. It would be impossible to create a LAN network between these two offices, but bigger services providers or carriers can be able to connect these two offices for you using WAN technologies. To operate, WANs use serial connections of various types.

WANs operate at OSI Layer 1 and Layer 2, specifically the Physical Layer and the Data Link Layer. To review, OSI Layer 1 describes how to provide electrical, mechanical and operational connections, while Layer 2 defines how data is encapsulated for transmission to a remote location and the mechanisms for transferring the resulting frames. Different technologies are used, such as Frame Relay and ATM. WAN access standards are defined and managed by a number of recognized authorities like, International Organization of Standardization (ISO), Telecommunication Industry Association (TIA) and Electronic Industries Alliance (EIA).

When you prepare for the CCNA exam, you must be able to describe some specific WAN terms. Some terms are related to the Physical Layer, some to the Data Link Layer and some about the WAN Switching methods. In this lesson we will discuss the terms related to the Physical Layer and the ones related to WAN Switching. The Data Link layer, specifically the encapsulation types and frame formats will be left for another lesson.

At the Physical Layer of a WAN you must be able to recognize and describe some key concepts:

  • Customer Premises Equipment (CPE) – is the device located in the premises of the subscriber (company) and connected to a service provider or carrier. The subscriber can either own or lease the equipment from the carrier. Example of CPE equipments are telephones, DSL and Cable modems, set-top boxes.
  • Data Communications Equipment (DCE) – sometimes called data circuit-terminating equipment, the DCE provides an interface to connect subscribers to the WAN cloud and consists of devices that put data on the local loop. Usually, the DCE equipment is a modem.
  • Data Terminal Equipment (DTE) – are the customer devices that pass the data from its network for transmission over the WAN. The DTE connects to the local loop through the DCE. The DTE device is usually a router.
  • Demarcation Point – is the border which separates the customer equipment from the service provider equipment. Physically, the Demarcation Point is usually the cabling junction box from the customer premises.
  • Local Loop – is the copper or fiber cable that connects the CPE at the subscriber to the Central Office (CO) of the service provider. Sometimes is called “last-mile”.
  • Central Office (CO) – is the service provider’s facility where local telephone cables link to long-haul, all-digital, fiber-optic communications lines through a system of switches and other equipments.

Several types of devices are used in WANs:

  • Modem – used to modulate an analog carrier signal to encode digital information and also demodulate the carrier signal to decode the transmitted information.
  • CSU/DSU – used by digital lines such as T1 or T3. The CSU provides termination for the digital signal and the DSU converts the line frames so the LAN can interpret them and vice versa.
  • WAN Switch – is a multiport internetworking device used by carriers able to switch WAN traffic types such as Frame Relay, ATM or X.25. They operate at the Data Link Layer.
  • Router – provides internetworking and WAN access interface ports used to connect to the service provider network, such as serial interfaces. Some types of interfaces require an external device such as a DSU/CSU or modem (analog, cable, DSL).
  • Core Router – is the router located in the middle or backbone of the WAN. The router must be able to support multiple types of interfaces and must be able to forward IP packets at full speed on those interfaces. The router must also support the routing protocols used in the core.

As we already told you, several authorities are handling the WAN standards. These protocols establish the codes and electrical parameters used by devices to communicate with each other. We will cover the most important ones, as requested by the Cisco CCNA exam.

  • EIA/TIA-232 – this protocol is able to signal speeds of up to 64kb/s using a 25-pin D-connector over short distances. It is also known as RS-232. The ITU-T V.24 specification is effectively the same.
  • EIA/TIA-449/530 – this is the faster version of EIA/TIA-232, being able to carry frames at speeds up to 2Mb/s. It uses a 36-pin D-connector and is also able to reach longer destinations. Also know as RS422 and RS-423.
  • EIA/TIA-612/613 – describes the High-Speed Serial Interface (HSSI) protocol, which provides speeds up to 52Mb/s using a 60-pin D-connector.
  • V.35 – ITU-T standard for synchronous connections between a network access device and a packet network using a 34-pin rectangular connector. Originally designed to support speeds up to 48kb/s, now supports speeds of up to 2.048Mb/s.
  • X.21 – ITU-T standard for synchronous digital communications. Uses a 15-pin D-connector.

WAN protocols are not able to run over LAN technologies, such as Ethernet and vice versa because the frame formats, encapsulation methods and the signaling at the physical layer differ from WAN to LAN.

WAN connections are generally grouped in three connection types: Point-to-Point, Circuit-switched and Packet-switches. In your preparation for the CCNA exam you must study Circuit-switched and Packet-switched technologies.

Circuit-switched networks are networks that are establishing a dedicated circuit between nodes and terminals before users may communicate. Let’s take for example a connection between two modems. The first one tries to make a connection with the other one by dialing its number. The dialed number is used to set the switches in the exchanges along the route of the call so that there is a continuous circuit between the two modems. However, the internal path between the exchanges is shared with a number of other connections. Time-division multiplexing (TDM) assures that a fixed capacity is allocated to each connection. Examples of Circuit-switched networks are the Public Switched Telephone Network (PSTN) and Integrated Services Digital Network (ISDN).

Packet-switched networks, unlike circuit-switched, route packets over a shared network. They do not require a circuit to be established and they allow multiple devices to communicate over the same channel. The switches are able to determine the link required to be used for forwarding the packet to the next switch or device using the addressing information found in each packet. The link determination can be made in two ways: connectionless or connection-oriented. Connectionless systems carry full addressing information in each packet and each switch must evaluate the address to be able to figure out where to send it, while connection-oriented systems are able to predetermine the route for a packet and each packet carries only an identifier. In packet switched networks, because the internal links are shared by many users, you may encounter delays and jitter (variability of delay).

The predetermined routes in a packet-switched network are called virtual circuits (VCs). A VC is a logical circuit between two network devices through the shared internal network. There are two types of VCs:

  • Permanent Virtual Circuit (PVC) – PVCs are used when data transfer between devices is constant.
  • Switched Virtual Circuit (SVC) – is an on-demand VC. The virtual circuit comes up when a data transfer begins and terminates when the transfer is complete. The first phase in a SVC is to establish the VC itself and then the data transfer begins. When the transfer completes, the VC disconnects from the remote device. SVCs are cheaper than PVCs.

Examples of packet-switched connections include: X.25, Frame Relay and ATM.

We will go deeper in this CCNA topic by studying different circuit-switched and packet-switched connections.

Analog dialup and ISDN are examples of circuit switched connections.

Analog dialup is using the traditional telephony copper cables. The data is modulated and demodulated by a modem and sent through the local loop to the CO. Advantages of using analog dialup are simplicity, available and low implement costs, but the main disadvantage is the low data rate, 56kb/s due to the PSTN network limitations. If your company needs a data connection only occasionally and is not sending or receiving large amounts of data, this connection may be adequate. However, voice and video traffic is not supposed to work at these lot bit rates.

Integrated Services Digital Network, or ISDN for short, are also circuit-switched networks. They allow a local loop to carry digital signals, resulting in higher data rates. ISDN turns the analog signals to time-division multiplexed (TDM) digital signals. TDM allows two or more signals to be transferred as subchannels in one communication channel. ISDN connections are using 64kb/s bearer channels (B) for voice or data and a signaling delta channel (D) for call setup and other purposes.

There are two types of ISDN interfaces:

  • Basic Rate Interface (BRI) – provides two 64 kb/s B channels and a 16kb/s D channel.
  • Primary Rate Interface (PRI) – allows for higher speeds. In North America, an ISDN PRI deliver 23 B channels at 64kb/s and one D channel, also at 64kb/s, totaling to 1.544MB/s, corresponding to a T1 connection. In the other parts of the world, PRI provides 30 B channels and one D channel, totaling to 2.048MB/s, corresponding to an E1 or a J1 connection.

Common packet-switched technologies used today include X.25, Frame Relay and ATM.

X.25 is a packet-switched technology mainly used these days for point-of-sale (POS) card readers. X.25 works at the Network Layer. Subscribers are provided with a network address. SVCs are established using call request packets and are identified using a channel number. Available speeds vary from 2400b/s to 2Mb/s, but they rarely exceed above 64kb/s. Due to the speed limitations, this type of networks are now being replaced by other technologies such as Frame Relay, ATM and ADSL.

Frame Relay is a protocol that works at the Data Link Layer, implementing flow control. Frame relay offers speeds up to 4Mb/s, and is able to carry both voice and data traffic. The VCs in Frame Relay are identified using an unique DLCI. You will find more details about Frame Relay in its dedicated lesson.

Asynchronous Transfer Mode (ATM) has a cell-based architecture. You may find someone referring to ATM as a cell-switched network. ATM cell are always 53 bytes, containing a 5 byte ATM header followed by 48 bytes of ATM payload. ATM networks are suitable for voice, video and data traffic. However, due to its small cells, it’s is less efficient than X.25 and Frame Relay and you need at least 20% more bandwidth than Frame Relay to carry the same amount of data. The biggest advantage of ATM is that it is able to operate at very high speeds – from T1/E1 to OC-12 (622Mb/s) and higher. In most cases, ATM uses PVCs, but can be configured as a SVCs too and allows multiple VCs on a single leased-line connection.

This concludes our lesson today. We hope you find it useful in your preparation for the CCNA exam. Understanding these key WAN concepts is very important, as well as for taking the CCNA certification but for real-life scenarios too.

Tags: , , , , , , , , , , , , , , ,
Posted in CiscoKits CCNA Blog | No Comments »

CCNA Certification 640-802: Open Shortest Path First – OSPF

Monday, January 25th, 2010 by CiscoKits

CCNA Certification: Open Shortest Path First – OSPF

 

Today we will talk about the OSPF dynamic routing protocol, as required for Cisco’s CCNA Exam. You should learn this protocol carefully, not only because Cisco requires a good knowledge for the CCNA certification, but you will find it in many network deployments today. From all Interior Gateway Protocols (IGPs), OSPF is probably the most common one.

 

OSPF (Open Shortest Path First) is probably the most widely-used Interior Gateway Protocol (IGP). The reason it became so popular is because it’s a link-state routing protocol. Link-state routing protocols are able to create the topology of your network by gathering information from all the other routers. By having the map of your network, the link-state protocol is able to select the best path to any destination in your network. Unlike distance vector routing protocols, link-state routing protocols are not sending periodic updates(this is an important CCNA concept to know), instead, after the network has converged, they advertise updates only when the topology changes. Having this behavior, OSPF is able to recalculate the routes very fast in case the topology changes or a link is failing.

               

As defined by RFC 2328, OSPF is using an arbitrary value called cost for its metric. Cisco decided to use bandwidth as the OSPF cost metric.

               

OSPF’s advantages are its fast convergence and its scalability, which allows for large network scenarios. Currently, OSPFv2 is used for IPv4 networks and OSPFv3 for IPv6 networks. OSPF also supports Variable-Length Subnet Masking (VLSM) and Classless Inter-Domain-Routing (CIDR).

               

OSPF uses areas to manage the network. Areas are 32-bit numbers. Those numbers can either be in decimal form or in octet-based dot-decimal notation, just like IPv4 addresses. Area 0 (or 0.0.0.0) represents the backbone of an OSPF network.

 

The OSPF package header is included in every OSPF packet. In the IP packet header, the protocol field is set to 89 and the destination address is set to the ALLSPFRouters address, 224.0.0.5.

 

The OSPF protocol is sending the following packet types:

1.Hello – used to discover the neighbors, establish the parameters on which the routers must agree, build adjacencies, elect Designated Router (DR) and Backup Designed Router (BDR).

2.DBD – Database Description is used to check if the database is synchronized between the sending and the receiving router.

3.LSR – Link-State Request is used to request specific link-state records.

4.LSU – Link-State Update packets are used to reply to LSRs and also to announce new informations or changes to the current topology.

5.LSAack – Link-State Acknowledgement is send by the receiving router to confirm the receipt of an LSU.

 

OSPF uses the Dijkstra’s shortest path first alhorithm (SPF) to create the SPF tree.

 

The default Administrative Distance is 110, which makes OSPF preferred over other IGPs, like IS-IS and RIP.

 

To protect your network routers from receiving unsolicited and bogus OSPF information, the protocol is able to encrypt and authenticate the routing information. This way, the routers will receive information only from routers configured with the same authentication information.

 

To enable OSPF on a router, you must enter router ospf process-id in the global configuration mode, where process-id is a number between 1 and 65535. This number does not have to be the same on all routers and can be randomly selected. Its influence takes place only locally and it’s not advertised on the network.

               

To announce a route through OSPF, the network network-address wildcard-mask area area-id command is used in router configuration mode. For example, to announce the network 192.168.0.0/24 you must enter network 192.168.0.0 0.0.0.255 area 0. The wildcard mask is calculated by subtracting the netmask from  255.255.255.255. For example, the wildcard mask for 255.255.255.224 is 0.0.0.31.

 

Router(config)#router ospf 1                                                    

Router(config-router)#network 192.168.0.0 0.0.0.255 area 0                          

Router(config-router)#network 10.0.0.0 0.0.0.31 area 0                          

 

OSPF has 3 methods to determine the router-id in the following order: 1) use the IP address configured with the router-id command; 2) use the highest IP address of any Loopback interface; 3) use the highest IP of any other interface. If you didn’t configure the router ID, you can find out which one is it with the show ip protocols command. However, if the Router ID is automatically assigned and you decide to change it with the router-id command, you must use the clear ip ospf process command. Please note that, if you decide to use a Loopback or a physical interface, the above command may not work and you may have to reload your router.

 

Router(config)#router ospf 1                                                       

Router(config-router)#router-id 192.168.0.1                                         

Router(config-router)#ctrl-Z                                                     

Router#clear ip ospf process                                                     

 

The metric of OSPF can be easily determined with the following formula: 10^8 / speed of the interface in bps. For example, the metric of an Ethernet interface is 10^8 / 10,000,000 bps = 10. The metric of T1 (1.544Mbps) is 10^8 / 1,544,000 bps = 64. Considering this formula, any Fast Ethernet or faster interface has a metric of 1. Also, please note that the value of the metric in OSPF from the router to a network is the accumulated value of all metrics until it reaches that network. For example, if R1 needs to get to R3 through R2, and the metric between R1 and R2 is 1 and the metric from R2 and R3 is 64, the total value of the metric is 65.

               

However, if you are using for example a serial interface, which is able to support a T1 link but you have only a 128kbps link, you must use the bandwidth or the ip ospf cost  interface command to set the appropriate value. Without it, OSPF may not be able to calculate the real cost and you may get an undesirable routing behavior.

 

Router(config)#interface serial 0/0/0                                             

Router(config-if)#bandwidth 128                                                 

 

Router(config)#interface serial 0/0/0                                           

Router(config-if)#ip ospf cost 781                                               

 

Of course, today’s networks have even higher speed links, and you may have for example 10GigE interfaces along with 1GigE and Fast Ethernet. The problem here is that the metric for all these interfaces will be 1 which can lead to an unexpected behavior. To solve this problem, you can adjust the reference-bandwidth (the value is in Mbits per second):

 

Router(config)#router ospf 1                                                    

Router(config-router)#auto-cost reference-bandwidth 10000        

This will conclude part 1 of our Cisco CCNA 640-802 Certification topic of OSPF.  Please come back next week to see the conclusion of this CCNA topic where we will discuss the challenges of PSPF in a mult-access environment.             

Tags: , , , , , , , , , , , , ,
Posted in CiscoKits CCNA Blog | No Comments »

CCNA Certification: EIGRP 640-802 Concepts

Tuesday, January 19th, 2010 by CiscoKits

EIGRP Concepts

In this lesson, we will introduce you to EIGRP, as requested by the Cisco CCNA certification exam.

Enhanced Interior Gateway Routing Protocol (EIGRP) is a Cisco proprietary, distance vector, classless routing protocol used for routing inside a network (IGP). In addition to other distance vector routing protocol, like RIP and IGRP, EIGRP has some unique features like: Reliable Transport Protocol (RTP), which provides reliable and unreliable delivery of EIGRP packets, Bounded Updates, Diffusing Update Algorithm (DUAL) to guarantee loop-free paths and backup paths, Neighbor and Topology Tables. EIGRP can operate as a classful routing protocol, as well as a classless one.

Unlike other distance vector routing protocols, EIGRP does not send periodic updates, so the route entries to not age out, instead, EIGRP uses a lightweight Hello protocol to monitor connection status with its neighbors.

Every EIGRP packet includes the EIGRP Packet Header. The important fields in this header are the Opcode field and the Autonomous System Number field. The Opcode specifies the packet type, which can be Update, Query, Reply and Hello. The Autonomous System (AS) Number specifies the EIGRP routing process. Unlike RIP, a Cisco router can run multiple instances of EIGRP. The AS number is used to track multiple instances of EIGRP.

Reliable Transport Protocol (RTP) is used by EIGRP for the delivery and reception of EIGRP packets. RTP sends packets to either unicast address or the reserved multicast address 224.0.0.10.

As we already told you, EIGRP uses five different packet types:

·         Hello packets – are used to discover neighbors and form adjacencies with them. These packets are multicast and use unreliable delivery and are sent typically every 5 seconds.

·         Update packets – are used to propagate the routing information. Update packets are sent only when a change in the topology occurs and only to those routers who require them. EIGRP update packets use reliable delivery and are sent to the multicast address when multiple routers require them, and to the unicast address when they are required by a single router.

·         Acknowledgement (ACK) packets – are sent when reliable delivery is used. They contain a nonzero acknowledgement number and are always sent to the unicast address.

·         Query and Replay packets – are used by DUAL when searching for networks and other tasks. Queries are sent to the multicast address and use reliable delivery, while replies are sent as unicast and they are also using reliable delivery.

In EIGRP, the default administrative distance (AD) is 170 when used as an Exterior Gateway Protocol (EGP), 90 when used as an IGP and 5 for EIGRP summary routes.

EIGRP also supports authentication to ensure the information transmitted over the network is authentic and from a trusted source.

To better understand EIGRP, we will use the following topology to configure an EIGRP network.

eigrp 

First, let’s configure the IP addresses on the interfaces of the routers.

R0(config)#int Fa0/0
R0(config-if)#ip addr 172.16.1.1 255.255.255.0
R0(config-if)#no shutdown
R0(config-if)#int Fa0/1
R0(config-if)#ip addr 192.168.1.1 255.255.255.0
R0(config-if)#no shutdown

R1(config)#int Fa0/0
R1(config-if)#ip addr 172.16.1.2 255.255.255.0
R1(config-if)#no shutdown
R1(config-if)#int Fa0/1
R1(config-if)#ip addr 192.168.2.1 255.255.255.0
R1(config-if)#no shutdown

R2(config)#int Fa0/0
R2(config-if)#ip addr 192.168.1.2 255.255.255.0
R2(config-if)#no shutdown

R3(config)#int Fa0/0
R3(config-if)#ip addr 192.168.2.2 255.255.255.0
R3(config-if)#no shutdown

Now, let’s enable EIGRP and specify what networks to advertise to our neighbors. We will use EIGRP autonomous system (AS) 1.

R0(config)#router eigrp 1
R0(config-router)#network 172.16.1.0 0.0.0.255
R0(config-router)#network 192.168.1.0

Optionally, in EIGRP, you can specify the wildcard bits when you chose to advertise a network. By default, when using the network command and a classful network address such as 172.16.1.0, all interfaces will be enabled for EIGRP. Although this is not our case, if you don’t want to enable all of them, you must specify the wildcard mask. To calculate the wildcard mask, you must substract the subnet mask from 255.255.255.255. For example, the wildcard mask for 255.255.255.252 is 255.255.255.255 – 255.255.255.252 = 0.0.0.3.

Let’s continue to configure the other routers now.

R1(config-router)#router eigrp 1
R1(config-router)#network 172.16.1.0
R1(config-router)#
*Mar  1 00:14:27.267: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 172.16.1.1 (FastEthernet0/0) is up: new adjacency
R1(config-router)#network 192.168.2.0

R2(config)#router eigrp 1
R2(config-router)#network 192.168.1.0
R2(config-router)#
*Mar  1 00:16:17.475: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 192.168.1.1 (FastEthernet0/0) is up: new adjacency

R3(config)#router eigrp 1
R3(config-router)#network 192.168.2.0
R3(config-router)#
*Mar  1 00:17:02.279: %DUAL-5-NBRCHANGE: IP-EIGRP(0) 1: Neighbor 192.168.2.1 (FastEthernet0/0) is up: new adjacency

Now, let’s check the routing table.

R3#show ip route
Codes: C – connected, S – static, R – RIP, M – mobile, B – BGP
       D – EIGRP, EX – EIGRP external, O – OSPF, IA – OSPF inter area
       N1 – OSPF NSSA external type 1, N2 – OSPF NSSA external type 2
       E1 – OSPF external type 1, E2 – OSPF external type 2
       i – IS-IS, su – IS-IS summary, L1 – IS-IS level-1, L2 – IS-IS level-2
       ia – IS-IS inter area, * – candidate default, U – per-user static route
       o – ODR, P – periodic downloaded static route

Gateway of last resort is not set


D    172.16.0.0/16 [90/307200] via 192.168.2.1, 00:00:35, FastEthernet0/0
D    192.168.1.0/24 [90/332800] via 192.168.2.1, 00:00:35, FastEthernet0/0
C    192.168.2.0/24 is directly connected, FastEthernet0/0

As you can see, the routing table is already populated with the routes. Let’s check the neighbors.

R0#show ip eigrp neighbors
IP-EIGRP neighbors for process 1
H   Address                 Interface       Hold Uptime   SRTT   RTO  Q  Seq
                                            (sec)         (ms)       Cnt Num
1   192.168.1.2             Fa0/1             10 00:04:27    8   200  0  4
0   172.16.1.2              Fa0/0             13 00:06:17    6   300  0  9

The fields of this command show you the following:

·         H column – lists the neighbors in the order they were learned.

·         Address – the IP address of the neighbor.

·         Interface – the local interface on which the Hello packet was received.

·         Hold – the current hold time. Every time a Hello packet is received, this value is reset to the maximum hold time for that interface and then counts down to zero. If zero is reached, the neighbor is considered down.

·         Uptime – amount of time since the neighbor was added to the neighbor table

·         SRTT (Smooth Round Trip Timer) and RT0 (Retransmit Interval ) – used by RTP to manage reliable EIGRP packets.

·         Queue Count – should always be zero, else EIGRP packets are waiting to be sent.

·         Sequence Number – used to track updates, queries and reply packets.

As with the other routing protocols, you can use the show ip protocols command to check detailed information about your routing protocols.

R0#show ip protocols
Routing Protocol is “eigrp 1”
  Outgoing update filter list for all interfaces is not set
  Incoming update filter list for all interfaces is not set
  Default networks flagged in outgoing updates
  Default networks accepted from incoming updates
  EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0
  EIGRP maximum hopcount 100
  EIGRP maximum metric variance 1
  Redistributing: eigrp 1
  EIGRP NSF-aware route hold timer is 240s
  Automatic network summarization is in effect
  Automatic address summarization:
    192.168.1.0/24 for FastEthernet0/0
    172.16.0.0/16 for FastEthernet0/1
      Summarizing with metric 281600
  Maximum path: 4
  Routing for Networks:
    172.16.1.0/24
    192.168.1.0
  Routing Information Sources:
    Gateway         Distance      Last Update
    (this router)         90      00:16:06
    172.16.1.2            90      00:11:56
  Distance: internal 90 external 170

When automatic summarization is enabled or at least one subnet was learned via EIGRP, EIGRP includes a summary route. Null0 is the interface used for summary routes. This is a “virtual” interface used only for advertising purposes.

R0#show ip route
Codes: C – connected, S – static, R – RIP, M – mobile, B – BGP
       D – EIGRP, EX – EIGRP external, O – OSPF, IA – OSPF inter area
       N1 – OSPF NSSA external type 1, N2 – OSPF NSSA external type 2
       E1 – OSPF external type 1, E2 – OSPF external type 2
       i – IS-IS, su – IS-IS summary, L1 – IS-IS level-1, L2 – IS-IS level-2
       ia – IS-IS inter area, * – candidate default, U – per-user static route
       o – ODR, P – periodic downloaded static route


Gateway of last resort is not set

     172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
D       172.16.0.0/16 is a summary, 00:37:40, Null0
C       172.16.1.0/24 is directly connected, FastEthernet0/0
C    192.168.1.0/24 is directly connected, FastEthernet0/1
D    192.168.2.0/24 [90/307200] via 172.16.1.2, 00:33:30, FastEthernet0/0

To calculate the preferred path on a network, EIGRP uses the following values in its composite metric:

·         Bandwidth

·         Delay

·         Reliability

·         Load

The default composite formula is: metric = [K1 * bandwidth + K3*delay]

By default, K1 and K3 are set to 1, and K2, K4 and K5 are set to 0. These values can be changed with metric weights tos k1 k2 k3 k4 k5 EIGRP router configuration command.

To find out the values used by EIGRP for the bandwidth, delay, reliability and load use the show interface interface interface-number command.

R0#show interface Fa0/0
FastEthernet0/0 is up, line protocol is up
  Hardware is Gt96k FE, address is c400.039f.0000 (bia c400.039f.0000)
  Internet address is 172.16.1.1/24
  MTU 1500 bytes, BW 10000 Kbit/sec, DLY 1000 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation ARPA, loopback not set
  Keepalive set (10 sec)
  Half-duplex, 10Mb/s, 100BaseTX/FX
  ARP type: ARPA, ARP Timeout 04:00:00

When you use Serial interfaces, the default bandwidth value may not match your real bandwidth which may cause EIGRP to not work properly. In this case, you have to manually configure the bandwidth value for your interface. Although, this is not our case, because we use FastEthernet interface, we will demonstrate you how to accomplish this, with the bandwidth kilobits interface configuration command.

R0(config)#interface Serial 0/0/0
R0(config-if)#bandwidth 1024

EIGRP is one of the most used Interior Gateway Protocols (IGP) used these days. In your preparation for your CCNA exam, you must know the basics of EIGRP and we hope you found this article useful for achieving the basic knowledge required for the CCNA certification exam. Remember that practice is best way to prepare for the CCNA exam, and we can provide you with many training resources, including labs prepared specially for the exam on which you can setup your own EIGRP enabled topologies.

Tags: , , , , , , , , , , , , , , ,
Posted in CiscoKits CCNA Blog | No Comments »

CCNA Certification 640-802: Inter-VLAN Routing

Tuesday, January 5th, 2010 by CiscoKits

Inter-VLAN Routing

Welcome to a new lesson from the Cisco CCNA exam preparation series. In this lesson, we will talk about Inter-VLAN routing and different methods to accomplish this. Inter-VLAN Routing is used to allow devices on separate VLANs communicate with each other.

Inter-VLAN Routing is the process of routing traffic between VLANs in a network. As we explained to you in the previous lesson about VLANs, VLANs are used to create logical networks from a physical network, isolating hosts from one VLAN from the ones in other VLANs. Most of the times, although you want to create different broadcast domain in your network by creating more logical networks, you want the hosts from those networks to communicate with each other, even if they are not belonging to the same VLAN.

A host belonging to a VLAN attached on a specific physical port, for example VLAN 10 in port FastEthernet0/10 is usually not able to communicate to a host attached to another VLAN, for example VLAN11 attached to port FastEthernet0/11. They belong to different networks, different broadcast domains and switches do not know how to forward packets from one network to another. The process of forwarding packets from a network to another is called routing and you must use a router to accomplish this.

In classic networks that are using multiple VLANs, routing is performed by connecting multiple physical interfaces on the router to multiple physical interfaces on the switch. The switch ports are connected to the router in access mode, and a different static VLAN is assigned to every interface. An access mode switch port can belong to only one VLAN and is usually used to connect to an end user device.

Usually, this is not a desired behavior because you end up using too many physical interfaces, and sooner or later you will run out of interfaces. A typical switch can have up to 48 ports. This means, you can use that switch to route traffic between VLANs for up to 48 VLANs. In smaller networks this may be enough, but in larger enterprise networks, 48 VLANs may not be enough.

“Router-on-a-stick ” is a type of router configuration in which you are able to use a single physical interface to route traffic between multiple VLANs. The router interface is configured as a trunk link and is connected to a trunk switch port. The router is accepting the tagged traffic on the trunk interface and routes it internally using subinterfaces. Trunk links are able to accept multiple VLANs on one physical interface. Switches are able to recognize the VLAN used for a specific packet through the use of encapsulation protocols that encapsulate or tag the frames. The protocols used are 802.1Q or Cisco’s proprietary Inter-Switch Link (ISL). To find out more about these encapsulation protocols check the Trunking Concepts lessons from our Cisco CCNA exam preparation series.

Subinterfaces are virtual interfaces associated with a single physical interface. These subinterfaces have their own IP address and VLAN assignment to be able to operate on a specific VLAN.

However, if your switch is capable of doing Layer 3 functions, you don’t need a router anymore. The switch will handle the Inter-VLAN routing decisions too. These switches are called multilayer switches .

The router acts as a Gateway for devices on a VLAN. The subinterface configured for a particular VLAN has an IP assigned from the range of IPs used in that VLAN. The other devices on the VLAN are sending packets for devices in other VLANs through the router. The router then, takes the routing decision and sends the packet to the destination.

Usually, when you configure a router, you assign IPs to interfaces, and once the IPs are assigned, the routing table shows how to reach the networks those IPs are part of.

Router(config)#interface Fa0/0
Router(config-if)#ip address 172.16.10.1 255.255.255.0
Router(config-if)#no shutdown
Router(config-if)#interface Fa0/1
Router(config-if)#ip address 172.16.30.1 255.255.255.0
Router(config-if)#no shutdown
Router(config-if)#end
Router#show ip route
Codes: C – connected, S – static, R – RIP, M – mobile, B – BGP
D – EIGRP, EX – EIGRP external, O – OSPF, IA – OSPF inter area
N1 – OSPF NSSA external type 1, N2 – O SPF NSSA external type 2
E1 – OSPF external type 1, E2 – OSPF external type 2
i – IS-IS, su – IS-IS summary, L1 – IS-IS level-1, L2 – IS-IS level-2
ia – IS-IS inter area, * – candidate default, U – per-user static route
o – ODR, P – periodic downloaded static route

Gateway of last resort is not set

172.16.0.0/24 is subnetted, 2 subnets
C 172.16.10.0/24 is directly connected, FastEthernet0/1
C 172.16.30.0/24 is directly connected, FastEthernet0/1

As you can see, the only chance to route traffic between those two networks is to connect both interfaces to the switch. This could be a solution if you have a small number of VLANs on your network and you are sure your network will never evolve, but if you have for example 120 VLANs what would you do?

The solution is to use subinterfaces. When you use subinterfaces,

Router(config)#interface Fa0/0.10
 Router(config-if)#encapsulation dot1q 10
Router(config-if)#ip address 172.16.10.1 255.255.255.0
Router(config-if)#interface Fa0/0.30
 Router(config-if)#encapsulation dot1q 30
Router(config-if)#ip address 172.16.30.1 255.255.255.0
 Router(config-if)#interface Fa0/0
Router(config-if)#no shutdown
Router(config-if)#end
Router#show ip route
Codes: C – connected, S – static, R – RIP, M – mobile, B – BGP
D – EIGRP, EX – EIGRP external, O – OSPF, IA – OSPF inter area
N1 – OSPF NSSA external type 1, N2 – OSPF NSSA external type 2
E1 – OSPF external type 1, E2 – OSPF external type 2
i – IS-IS, su – IS-IS summary, L1 – IS-IS level-1, L2 – IS-IS level-2
ia – IS-IS inter area, * – candidate default, U – per-user static route
o – ODR, P – periodic downloaded static route

Gateway of last resort is not set

172.16.0.0/24 is subnetted, 2 subnets
C 172.16.10.0/24 is directly connected, FastEthernet0/0.10
C 172.16.30.0/24 is directly connected, FastEthernet0/0.30

As you can see in this example, we use only the FastEthernet 0/0 interface for both VLANs. We have created the Fa0/0.10 and Fa0/0.30 subinterfaces, specified the encapsulation type dot1q which is IEEE’s 802.1Q, and the VLAN they belong to and we assigned an IP address. In this case, the physical interface, FastEthernet 0/0, does not need an IP address configuration, the only thing you must do is to use the no shutdown command so that the interfaces comes up.

If you use a multilayer switch, to enable to routing features you must also enable ip routing .

Switch(config)#ip routing

However, different issue may arise when you use Inter-VLAN Routing. A switch for example can have an incorrect VLAN assigned to a switch port or the switch port may be configured in access mode instead of trunk. A router also, can have the wrong VLAN assigned to an interface or subinterface or the wrong encapsulation type. Assigning an IP address belonging to a class not used in that specific VLAN will also cause Inter-VLAN routing to not function properly. If your network is not working as expected, these are the most common places to look for errors.

This concludes our lesson. When you’ll take your Cisco CCNA certification exam, you must be able to correctly configure and troubleshoot a network using Inter-VLAN Routing. Practicing is the best way to learn how things work and we hope you found our hands-on example a great starting point.

Tags: , , , , , , , , , , , , , , , , ,
Posted in CiscoKits CCNA Blog | No Comments »

CCNA Certification: VLAN Trunking Protocol (VTP) Part II

Saturday, December 26th, 2009 by CiscoKits

When you begin to configure your VTP enabled network you must first make sure that all switches you are going to configure are set to their default settings. A good advice is to configure at least two VTP servers on your network in case one VTP server fails. Also, all switches in a VTP domain must use the same version. Not configuring the VTP version correctly will result in no VTP communication between your switches.

 

On a VTP server you must make sure you configure the following key components:

·         VTP domain

·         VTP version

·         VLANs and trunk ports

 

On the VTP clients you must configure:

·         VTP client mode

·         VTP version

·         Trunks

·         Access ports 

 

First of all, we must make sure that the VTP server’s configuration is the default one.

 

S1#show vtp status

VTP Version                     : running VTP1 (VTP2 capable)

Configuration Revision          : 0

Maximum VLANs supported locally : 1005

Number of existing VLANs        : 7

VTP Operating Mode              : Server

VTP Domain Name                 :

VTP Pruning Mode                : Disabled

VTP V2 Mode                     : Disabled

VTP Traps Generation            : Disabled

MD5 digest                      : 0xFB 0xC2 0×38 0xC1 0×0D 0×1D 0×14 0×10

Configuration last modified by 0.0.0.0 at 0-0-0 00:00:00

 

Looks good. Now, let’s configure the VTP domain name and check again the output of show vtp status.

 

S1#configure terminal

S1(config)#vtp mode server

S1(config)#vtp domain cisco

Changing VTP domain name from NULL to cisco

S1(config)#vtp version 1

VTP mode already in V1

S1(config)#exit

S1#show vtp status

VTP Version                     : running VTP1 (VTP2 capable)

Configuration Revision          : 0

Maximum VLANs supported locally : 1005

Number of existing VLANs        : 7

VTP Operating Mode              : Server

VTP Domain Name                 : cisco

 

Good. We have configured a switch to act as a version 1 VTP server for the VTP Domain cisco. Next, you must create the VLANs and trunks. You can find more details about these operations in our VLAN and Trunking courses from the CCNA Certification series.

Please note that, every added VLAN increases the revision number with 1. The name of a VLAN also increases the revision number with 1. For example, if you have 3 VLANs, you will have 3 VLANs + 3 Names = Revision 6.

 

Next, let’s configure the VTP client switches. The configuration is identical on both switches.

 

The first step is to check if the configuration is the default one with show vtp status, as you did for the VTP server too. Now let’s configure the switch to act as a client.

 

S2#configure terminal

S2(config)#vtp mode client

Setting device to VTP CLIENT mode.

S2(config)#exit

S2#show vtp status

VTP Version                     : running VTP1 (VTP2 capable)

Configuration Revision          : 0

Maximum VLANs supported locally : 1005

Number of existing VLANs        : 7

VTP Operating Mode              : Client

 

The next step is to connect the Client switch to the server. After the switches are connected, check the show vtp status output again and show vtp counters to make sure those switches are exchanging information.

 

S2#show vtp status

VTP Version                     : running VTP1 (VTP2 capable)

Configuration Revision          : 6

Maximum VLANs supported locally : 1005

Number of existing VLANs        : 10

VTP Operating Mode              : Client

VTP Domain Name                 : cisco

 

S2#show vtp counters

VTP statistics:

Summary advertisements received    : 1

Subset advertisements received     : 1

Request advertisements received    : 0

Summary advertisements transmitted : 1

Subset advertisements transmitted  : 1

 

We see that the switch has successfully joined the cisco VTP domain,  got the configuration revision 6, and now has 10 configured VLANs.

The next step is to configure the access ports, for example:

 

 

S2(config)#interface Gi0/18

S2(config-if)#switchport access vlan 20

 

In VTP enabled networks you can encounter different errors. To troubleshoot them you must be sure you the output the the show commands. Common issues you may encounter can be:

·         The VTP version is not configured correctly

·         If you use a VTP password, the password mismatches on the other switches

·         You didn’t correctly configured the VTP mode

·         You don’t have a VTP server in your network.

·         The VTP domain is not configured correctly

·         Before you put the switch on the network, you didn’t reset the revision number

 

This concludes our lesson. We are proud to provide real life examples along with our Cisco CCNA certification courses. Not only you will take the certification exam, but you will also have a valuable hands-on experience.

Tags: , , , , , , , , , , , , ,
Posted in CiscoKits CCNA Blog | No Comments »

CiscoKits CCNA 640-802 Lab Workbook Download!

Monday, December 7th, 2009 by CiscoKits

CiscoKits CCNA 640-802 Lab Workbook Download!

Today is going to be a real short post introducing the ability to download our CCNA 640-802 Lab Workbook.  We have had many customers who do not want to wait for a physical copy to arrive via UPS.  I understand that as you want to get to doing your CCNA labs as quickly as possible.  So we are offering a solution in which you can purchase to download our CCNA 640-802 Lab Workbook.  Keep in mind, if you purchase the electronic download copy, you will not also receive a physical copy of the book.  If you want a physical copy of the book, you will order that from our main store here http://www.ciscokits.com/cisco-ccna-lab-workbook/

One of the nice things about the download version, is that you can download the CCNA Lab Workbook and preview some of the chapters that are not password protected.  If you like it, you can buy the electronic version or the physical version.  Now the choice is yours!  So without further ado, here is the link to the electronic version of our CCNA Lab workbook  http://www.ciscokits.com/ebooks/CiscoKits-CCNA-640-802-Lab-Workbook.zip

We hope you enjoy this new offering from CiscoKits assisting in your CCNA exam studies!

labworkbook

Tags: , , , , , , , , , , , , , ,
Posted in CiscoKits CCNA Blog | No Comments »

CCNA Certification: VLAN Trunking Protocol (VTP) Part I

Monday, November 30th, 2009 by CiscoKits

VLAN Trunking Protocol (VTP)

Welcome to a new lesson for your preparation for the CCNA certification exam. We would like to discuss today about VLAN Trunking Protocol (VTP).  We are going to again break this CCNA conept into two parts so you are not overwhemled.  VTP is very important to udnerstand completely to ensure you pass your CCNA certification exam.

VLAN Trunking Protocol (VTP) is Cisco’s proprietary protocol for managing VLAN networks. As the network grows, creating, modifying and deleting VLANs becomes a time consuming job for the newly CCNA certified administrator. VTP helps network administrators to accomplish this task in just a few minutes. The philosophy of VTP is that a router running as a VTP server should manage the VLAN configuration of the other routers on the network, called VTP clients. VTP can operate with 802.1Q as well as with ISL.

VTP can run in three different modes:

·         Server mode – in server mode you can create, remove and modify VLANs. VTP servers advertise their configuration to the VTP clients in the same VTP domain. The VLAN information is stored in NVRAM and it’s not lost after a reboot.

·         Client mode – clients only get the VLANs advertised by the VTP server. They are not able to modify, create or delete VLANs from their configuration. The VLAN configuration is not stored in NVRAM and will be lost at first reboot (of course, the switch will get the VLAN configuration back after it boots, from the VTP server)

·         Transparent mode – in this mode, the switch does not participate in the VTP domain. You are able to add, delete or modify VLANs from their configuration. The configuration of the VLANs will not be broadcasted over the network. With VTP version 2, a transparent switch is forwarding the VTP messages that he receives out its trunk ports.

 

The first thing you have to do when you begin studying VTP is to understand some key concepts. We will briefly present them to you, as requested by Cisco’s CCNA certification exam.

 

·         VTP Domain – consists of one or more interconnected switch which are sharing the same VLAN configuration. A router or a Layer 3 switch defines the boundary of a VTP domain.

·         VTP Advertisements – are used to distribute the VLAN configuration across the VTP domain.

·         VTP Modes – the modes a switch can be configured in the VTP domain, as described above.

·         VTP Server – a VTP server is used to advertise the VLAN configuration to all VTP enabled switches in the same VTP domain. This is the point where you are able to create, modify or delete the VLAN configuration.

·         VTP Client – is a VTP enabled switch which receives the VLAN information from a VTP Server. You are not able to create, modify or delete the VLAN configuration.

·         VTP Transparent – is a switches that’s not participating in the VTP domain, but forwards VTP advertisements to other switches in the network. VLANs created, modified or deleted on a transparent switch are affecting only that switch and are not broadcasted on the VTP domain.

·         VTP Pruning – By default, a switch sends broadcast, multicast and unknown unicast traffic through all trunk links. The VTP pruning increases network available bandwidth by sending traffic only on those trunk links that the traffic must use to reach the destination device.

 

When you check the VTP configuration on a switch you use the show vtp status command.

 

Switch#show vtp status

VTP Version                     : running VTP1 (VTP2 capable)

Configuration Revision          : 4

Maximum VLANs supported locally : 1005

Number of existing VLANs        : 7

VTP Operating Mode              : Server

VTP Domain Name                 :

VTP Pruning Mode                : Disabled

VTP V2 Mode                     : Disabled

VTP Traps Generation            : Disabled

MD5 digest                      : 0xFB 0xC2 0×38 0xC1 0×0D 0×1D 0×14 0×10

Configuration last modified by 192.168.1.2 at 3-1-93 00:20:31

Local updater ID is 192.168.1.2 on interface Gi0/1 (first layer3 interface found)

 

You can see here some information. The first line shows us the version of VTP the switch is running, currently 1. We can configure the switch to run VTP2 because, as you can see, it’s VTP2 capable. Next we have a configuration revision. The revision number is a 32-bit number that indicates the level of revision for a VTP frame. By default, the number is 0, and it’s incremented every time the configuration changes. We also can see that this switch is supporting 1005 VLANs configured locally, and we currently have 7 VLANs configured on the switch. We find in the next line that this switch is acting as a VTP server. The VTP Domain Name identifies the administrative domain for the switch. By default, VTP Pruning Mode, V2 Mode and Traps Generation are disabled. The MD5 digest is a 15-byte checksum of the VTP configuration.

 

VTP uses the destination MAC address 01-00-0C-CC-CC-CC, which is a reserved multicast address for VTP messages.

 

A VTP advertisement contains the following global informations:

·         VTP domain name – the name of the VTP domain

·         Updater identity and update timestamp – used by client switches to identify who sent the update and when the message was sent.

·         MD5 digest – used by client switches to compare if the checksums match. Also includes the Maximum Transmission Unit (MTU) for each VLAN.

·         Frame format – can be ISL or 802.1Q

 

Also, VTP advertisements carry the following VLAN information:

·         VLAN IDs (IEEE 802.1Q)

·         VLAN name

·         VLAN type

·         VLAN state

·         Additional VLAN configuration specific to the VLAN type

 

VTP is sending different type of advertisements:

·         Summary advertisements

o        Sent every 5 minutes by a VTP server or immediately after a configuration change has been made.

o        Informs VTP enabled switches of the current VTP configuration revision number.

·         Subset advertisements

o        Contains VLAN information.

o        Sent when you:

§         Create or delete a VLAN.

§         Suspend or activate a VLAN.

§         Change the name of a VLAN.

§         Change the MTU of a VLAN.

·         Request advertisements

o        Sent by a VTP client to a VTP server

o        Sent if:

§         The domain name has been change.

§         The switch receives a summary advertisement with a higher revision number than its own.

§         A subset message is missed.

§         The switch has been reset.

In part II of this topic, we will cover how to configure your VTP domains.  So stop back next week as we continue our Cisco CCNA certification study series.  We hope you find this information to be helpful to you in passing your CCNA exam.  If you have any suggestions on how we can improve our CCNA study series, please feel free to post your comments! :)

 

Tags: , , , , , , , , , , , , , ,
Posted in CiscoKits CCNA Blog | No Comments »

CCNA Certification: Trunking Concepts Part II

Sunday, November 22nd, 2009 by CiscoKits

Today we will pickup in our Cisco CCNA 640-802 Certification Series with Part II of Trunking Concepts.

In many real world scenarios after you receive your Cisco CCNA, you may have a lot of VLANs on a single interface. Removing them one by one will be a time consuming job. To accomplish this task faster use the no switchport trunk allow vlan (remove all VLANs configured on the trunk interface), no switchport trunk native vlan (resets the native VLAN back to 1), switchport mode access (puts the switch port back to access mode).

Trunking can cause a lot of headaches for network administrators. Problems can appear from different causes. Most common cases are when the Native VLAN mismatches, trunk mode mismatches, the allowed VLAN list configured on trunk ports is not configured correctly or the IP addresses of the devices at the both ends of the link are not configured correctly.

If the Native VLAN mismatches, the solution is to reconfigure the native VLAN correctly on the switch. You can then test the connectivity of the ends with the ping command.

Cisco uses its proprietary protcol, Dynamic Trunking Protocol (DTP) to negotiate the trunk links between the switches configured to support VLANs. If you forgot to enable the trunking port on at least one device, they will both negotiate in access mode. To solve this issue, use the switchport mode trunk interface configuration command on one switch. The other will re-negotiate the parameters and will discover that the connecting port is a trunk port. To check if a switch port is in trunk port, use the command show interfaces interface switchport and look for the line beginning with Administrative Mode. The Administrative Mode should be trunk.


Switch#show interfaces Fa0/1 switchport
Name: Fa0/1
Switchport:P Enabled
Administrative Mode: trunk

On a trunk port, you must configure what VLANs are allowed. The command used is switchport access trunk allowed vlan add vlan-id. If you forgot to add a VLAN to the trunk port, the frames from that VLAN will be discarded by the switch. First of all, you must check what VLANs are allowed with show interfaces trunk. If your VLAN is not in the list associated with the desired interface you must add it.


Switch#show interfaces trunk
Port   Mode  Encapsulation  Status    Native vlan
Fa0/1  on    802.1q         trunking  20
Port Vlans allowed on trunk
Fa0/1  10,20

In this example, the switch knows that in should receive frames for VLANs 10 and 20 on the FastEther0/1 interface. If the switch is the final destination of the packet, that’s correct. But if the device that should receive the packet is connected in FastEthernet0/2, this is not. You must also add the desired VLANs to the Fa0/2 interface.


Switch(config)#interface Fa0/2
Switch(config-if)#switchport trunk allowed vlan 10,20
Switch(config-if)#ctrl-Z
Switch#show interfaces trunk
Port   Mode  Encapsulation  Status    Native vlan
Fa0/1  on    802.1q         trunking  20
Fa0/2  on    802.1q         trunking  20
Port Vlans allowed on trunk
Fa0/1  10,20
Fa0/2  10,20

Now you can check both ends of the link with the ping command and everything should be just fine.

It is crucial in your preparation for Cisco’s CCNA 640-802 certification to understand how trunking works and how to troubleshoot it. We make our best to explain to you these CCNA concepts in the simplest terms possible and give you examples for an easier understanding.

Tags: , , , , , , , , , , , , , ,
Posted in CiscoKits CCNA Blog | No Comments »

« Older Entries