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Posts Tagged ‘advantage’

When studying for your BSCI exam for the CCNP, you get your first taste of BGP. One of the major differences between BGP and the other protocols you’ve studied to date is that BGP uses attributes to describe paths, and to influence the selection of one path over the other.

In this free tutorial, we’re going to take a look at the Local Preference attribute and compare it to the Cisco-proprietary BGP attribute “weight”.

The Local Preference (LOCAL_PREF) attribute is used to influence how traffic will flow from one Autonomous System (AS) to another when multiple paths exist. For example, if AS 100 has two different paths to a destination network in AS 200, the LOCAL_PREF attribute can be used to influence the path selection.

The major difference between the Weight and LOCAL_PREF attributes is that when the LOCAL_PREF attribute is changed, that change is reflected throughout the AS. The new LOCAL_PREF value will be advertised to all other routers in the AS, as compared to the Weight attribute, which is locally significant only. If you change the Weight for a path on one router in an AS, the other routers in the AS will not learn of the change.
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Configuring RIPv2 and EIGRP authentication with key chains can be tricky at first, and the syntax isn’t exactly easy to remember. But for BSCI and CCNP exam success, we’ve got to be able to perform this task.

In a previous tutorial, we saw how to configure RIPv2 packet authentication, with both clear-text and MD5 authentication schemes. EIGRP authentication is much the same, and has the text and MD5 authentication options as well. But EIGRP being EIGRP, the command just has to be a little more detailed!

As with RIPv2, the authentication mode must be agreed upon by the EIGRP neighbors. If one router’s interface is configured for MD5 authentication and the remote router’s interface is configured for text authentication, the adjacency will fail even if the two interfaces in question are configured to use the same password.

We’ll now configure link authentication on the adjacency over an Ethernet segment. Below, you’ll see how to configure a key chain called EIGRP on both routers, use key number 1, and use the key-string BSCI. Run show key chain on a router to see all key chains.

R2(config)#key chain EIGRP

R2(config-keychain)#key 1

R2(config-keychain-key)#key-string BSCI

R2#show key chain

Key-chain EIGRP:

key 1 — text “BSCI”

accept lifetime (always valid) – (always valid) [valid now]
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BCMSN exam success and earning your CCNP certification requires you to add to your knowledge of VLAN configuration. When you studied for your CCNA exam, you learned how to place ports into a VLAN and what the purpose of VLANs was, but you may not be aware that there are two types of VLAN membership. To pass the BCMSN exam, you must know the details of both types.

In this tutorial, we’ll take a look at the VLAN type you are most familiar with, the “static VLAN”. As you know, VLANs are a great way to create smaller broadcast domains in your network. Host devices connected to a port belonging to one VLAN will receive broadcasts and multicasts only if they were originated by another host in that same VLAN. The drawback is that without the help of a Layer 3 switch or a router, inter-VLAN communication cannot occur.

The actual configuration of a static VLAN is simple enough. In this example, by placing switch ports 0/1 and 0/2 into VLAN 12, the only broadcasts and multicasts hosts connected to those ports will receive are the ones transmitted by ports in VLAN 12.

SW1(config)#int fast 0/1

SW1(config-if)#switchport mode access

SW1(config-if)#switchport access vlan 12
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In this CCNA case study, we’ll take some basic switching and trunking theory and put it into action. We have two routers (R2 and R3) along with two switches (SW1 and SW2). R2 is connected to SW1 at fast 0/2, and R3 is connected to SW2 at fast 0/3. Both routers have IP addresses on the 172.12.23.0 /24 network.

For these routers to be able to ping each other, the switches must be able to communicate. These are two 2950 switches, and they’re connected via two crossover cables. Before we worry about the router connectivity, let’s make sure the trunk link is up between the switches with the “show interface trunk” command.

SW2#show interface trunk

Port Mode Encapsulation Status Native vlan

Fa0/11 desirable 802.1q trunking 1

Fa0/12 desirable 802.1q trunking 1

< output truncated for clarity >

The default mode of these switches is for the ports to run in dynamic desirable trunking mode, so we didn’t even need to write a configuration to have the trunk form – it’s already there!

Show vlan brief reinforces the theory that by default, all switch ports are placed into VLAN 1 (except the trunk ports).

R2 and R3’s Ethernet addresses have already been configured, the trunk line is operational, and both ports are in VLAN 1. We’ll ping R2’s Ethernet interface from R3, and then R3’s Ethernet interface from R2 to verify IP connectivity.

R2#ping 172.23.23.3

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 172.23.23.3, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 4/4/8 ms

R3#ping 172.23.23.2

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 172.23.23.2, timeout is 2 seconds:
!!!!!
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