INE Workbook Vol 1 IP Routing

Well, I am making slow progress on INE WB1. I've had about two hours each day on the train ride into work available to study. Some times I was too tired, other times I didn't feel like studying. I was able to get through a few of the IP routing sections and I would like to share my notes with you.


The first interesting scenario was using Policy Based Routing (PBR). The scenario asked to use an alternate route based on CDP reachability. This was a real head scratcher but it really only added two lines in my route map.

route-map Policy-Routing permit 10
 match ip address R3-R4
 set ip next-hop 155.1.0.5
 set ip next-hop verify-availability
 set ip default next-hop 155.1.146.4



Simply add set ip next-hop verify ability to check for CDP. When used with set ip default next-hop, you can re-route based on CDP availability. If you look at this and think it is not working, remember this is based on CDP.  CDP has a default hello of 60 seconds and a hold time of 180, so it will take at least three minutes for CDP reachability to fail and the default next-hop to kick in. So either be patient, or change the hello timer to 5 and hold timer to 10 seconds. 

Additionally, you can also use IP SLA/Enhanced Obj Tracking to verify reachability. Use the same verify availability command, enter the IP address you want to verify, set a sequence number (For checking multiple destinations, like route-maps, first match processes) and then select the tracking instance.

route-map Policy-Routing permit 20
 match ip address R3-R5
 set ip next-hop verify-availability 155.1.146.4 1 track 1
 set ip next-hop 155.1.146.4
 set ip default next-hop 155.1.0.5

Important Note: When using a local policy, traffic is sent based on the loopback's source address and not source interface like RIB lookups. This could negatively  impact protocols such as BGP.



Here is the 12.3 command reference as I couldn't find this under the 12.4 command reference.
http://www.cisco.com/en/US/docs/ios/12_3t/ip_route/command/reference/ip2_s1gt.html#wp1091258


I hope to post more later as I complete IP Routing in workbook 1.