Manipulating EIGRP administrative distance

Unanswered Question
Sep 18th, 2008
User Badges:
  • Gold, 750 points or more

router 4 is learning route for 192.168.192.0/24 from both R2/R3 from EIGRP. I would R4 to use R3 as a backup instead. i need to change the AD on router R3 to send the 192.168.192.0/24 route to R4 with AD of 100 instead of 90.


I have created a prefix for 192.168.192.0/24 on R3 and used a route-map to try to change the AD, but cannot find any option. Also used offset-list on R3 by manipulating the composite metric and it worked, but dont like it.


any ideas on how to change the AD using policy routing?

  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
Loading.
Giuseppe Larosa Fri, 09/19/2008 - 02:41
User Badges:
  • Super Silver, 17500 points or more
  • Hall of Fame,

    Founding Member

Hello Francisco,

AD is a local node concept used by the process that mantain the IP routing table to make choices between different routing protocols offering a route for a prefix.


AD is never sent in any routing protocol update including EIGRP.

Even if you could change the AD on R3 it will never influence the AD used on R4.

Think of AD as similar to the BGP weight : it is local on the box and it is never advertised.


Offset-lists is the right tool for doing this job because they change the metric for selected routes, changing delay on R4 on the interface to R3 could achieve that R3 will be a backup for all routes (no selection)


I've given a look to ip routing protocol command reference and no set AD option is available.


A distance eigrp command is available within router eigrp process and can be used when you want to prefer a non EIGRP route over an EIGRP route but here both routes come from EIGRP and so you need to play on metric to prefer one over the other.


Hope to help

Giuseppe


francisco_1 Fri, 09/19/2008 - 02:54
User Badges:
  • Gold, 750 points or more

Giuseppe,


as usual, thanks for your prompt rely. much appreciated


On Router 3

access-list 10 permit 192.168.192.0 0.0.0.255


router eigrp 1

offset-list 10 out 9000000 (This will influence the route advertise from from R3 to R2/R4


R4 is now see 192.168.192.0 via R3 as the successor and backuo via R3.


I take it i dont need to do anthing else on R4/R2? The config above is ok? I only need to make the offset-list change on R3.right?


Giuseppe Larosa Fri, 09/19/2008 - 04:18
User Badges:
  • Super Silver, 17500 points or more
  • Hall of Fame,

    Founding Member

Hello Francisco,

yes I just wonder if you can even specify the outgoing interface if desired to be even more specific.


offset-list (EIGRP)

To add an offset to incoming and outgoing metrics to routes learned via Enhanced Interior Gateway Routing Protocol (EIGRP), use the offset-list command in router configuration mode. To remove an offset list, use the no form of this command.


offset-list {access-list-number | access-list-name} {in | out} offset [interface-type interface-number]


see


http://www.cisco.com/en/US/docs/ios/iproute/command/reference/irp_eig2.html#wp1012264


so you can be specific at interface level and on selected IP subnets.

this comes from the DV nature of EIGRP that can send different updates out different interfaces.

And yes, the job needs to be done only on R3.


Hope to help

Giuseppe




Actions

This Discussion