Exam 642-901

I just passed Cisco's 642-901 exam - Building Scalable Cisco Internetworks. What interesting, though, is that I scored higher for OSPF than for BGP and EIGRP sections of the exam, even though I work with BGP and EIGRP every day. I guess I got overconfident in what I thought I knew. On the other hand, I knew my weak OSPF spots and payed more attention.

Etherchannel notes

If you initially issue the channel-group command under the physical interface, it automatically creates the port-channel interface. If you configured the port-channel interface before you channeled physical interfaces, remove the port-channel interface first. This is only relevant on Catalyst switches. The order of configuration changes on the 7500 router. You must configure the port-channel interface before you configure the channel group under the physical interface.

The order of configuration of a port channel in Catalyst 6500/6000 and 4500/4000 Cisco IOS Software is important. It is best to issue any switchport command before you issue the channel-group command in a physical interface.

When you issue the channel-group command prior to the switchport command on a physical interface (interface Gigabit Ethernet 1/1), the port-channel interface is created automatically and becomes a L3 interface. If you then issue the switchport command under the physical interface, the physical interface becomes a L2 interface. Also, the port-channel interface that you created earlier has no physical interface associated with it. Notice that the channel-group command is absent from under the physical interface. In this case, you must first issue the switchport command under the newly configured port-channel interface. Then, the physical port accepts the channel-group command again. In this case, the port channel has changed from a L3 interface to a L2 interface.

Consider, in contrast, if you issue the switchport command first on a physical interface and then add the channel-group command. In this case, the port-channel interface is automatically created and inherits all the configured switchport commands.

On a Catalyst 6500/6000 switch running Cisco IOS Software, all ports are L3 ports by default. On a Catalyst 4500/4000 switch running Cisco IOS Software, all ports are L2 ports by default.

SUP720-3C TCAM exeption

If you are running BGP on Catalyst 6500 or 7600 with SUP 72-3C and receiving full routing table from a peer, sooner rather than later you'll get this message
%CFIB-SP-7-CFIB_EXCEPTION: FIB TCAM exception, Some entries will be software switched
Meaning that your router's performance will be degraded, since some of the traffic processed by CPU as opposed to hardware. The only way to get out of this state is to reboot the router. Here is how to check whether your router is in exception state:

cisco-7600#show mls cef exception status
Current IPv4 FIB exception state = TRUE
Current IPv6 FIB exception state = FALSE
Current MPLS FIB exception state = FALSE

If you are not running IPv6 or MPLS you can postpone inevitable upgrade to 720-3CXL by allocating entire TCAM memory to IPv4 routes
cisco-7600#mls cef maximum-routes ip 239
reboot

To see TCAM utilization
cisco-7600##show platform hardware capacity | begin L3 Forwarding Resources
L3 Forwarding Resources
FIB TCAM usage: Total Used %Used
72 bits (IPv4, MPLS, EoM) 196608 184013 94%
144 bits (IP mcast, IPv6) 32768 3 1%


.....skipping the rest