Accumulated IGP Metric Attribute (AIGP)

This topic is to discuss the following lesson:

I’m glad to be the first to say, GREAT LESSON man :+1:

Thanks @joseph!

AIGP is easy to configure but it does take time to explain what the issue is with “regular” BGP in a scenario with multiple IGPs, and how things like MED/AS Path won’t fix it.

Rene

One thing Rene, I noticed in the config on R1 at the end of the lesson, there are two route-maps.

image

I think the highlighted one needs to be removed.

Hello Joseph

Yes, I think you are correct! I’ll let Rene know.

Thanks!

Laz

Hi Rene,
First of all, thank you very much for sharing this post.

However in section 1.2.1.2, R4 keeping MED 30 and R5 keeping MED 40 they why would AS123 prefers path via R3-R5 ??
Please correct me if I misunderstood anything.

Hello Abhishek

Yes, you are correct, the configuration on the route map on R5 should be set metric 20 and not 40. I will let Rene know to correct this…

Thanks in advance!

Laz

A post was merged into an existing topic: Cisco ASA Anyconnect Remote Access VPN

Thanks @joseph, that route-map was a leftover. I removed it.

Rene

Hello @mandeabhi10,

Sorry for the confusion. R5 should set the metric to 20, like in the picture. I just fixed this.

Rene

Hi Rene,
Thank you for the post :slight_smile:

  1. In the second diagram of section 1.2, if we advertise R5 with high MED value then i think we can send traffic from AS 456 to AS123 via R4.
  2. In Same diagram if we use AS-PAth prepending then also i think we can achieve optimal path.
  3. After configruing AIGP, i belive lowest AIGRP metric will be prefered. However R1 chooses highest AIGRP metric and R6 chooses lowest AIGRP metric. ( I am little confused here )
  4. Could you also explain how AIGRP metric calculated in that diagram ?
    Correct if i misunderstood anything.

thanks again.

Hello Vinay

I’ll try to respond to each question specifically.

  1. Remember that the MED value influences how neighboring ASes enter your AS. Changing the MED value of R5 will not affect traffic from AS356 to AS123 in any way. It only affects traffic in the other direction.
  2. AS-Path prepending will not work, for the same reason that MED did not work.

For 3 and 4, I believe there is a typo in the lesson. The diagram shows the costs of the OSPF links between routers, but the configurations as well as the show output display different values. It is true that the lowest metric should be chosen, and according to the diagram it was (but not according to the show output.)

I will let Rene know of the typo. Thanks for being thorough and pointing that out!

I hope this has been helpful!

Laz