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kim
Beginner
Beginner

Option B - back-to-back eBGP VPNv4

Hi guys,

thanks for a great resource!

 

I'm looking at this document on the topic:

Cisco IOS-XR BGP with MPLS Designs 

 

It says in section 4 that in order to make the exchange (In image 3) work ASBR3 needs to have a dummy iBGP neighbor configured. The doc just says there in this instance is an issue with advertising the vpnv4 routes from ASBR3. It doesn't really explain why.

 

I realize that this is a corner case, since irl more routers would exist within the average AS.

 

I'm hoping someone can elaborate.

Appreciated, thanks.

Cheers

1 ACCEPTED SOLUTION

Accepted Solutions

Hi @kim ,

 

I ran the test with XRv 6.3.1 and it works like a charm.

 

Regards,

Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

View solution in original post

9 REPLIES 9
Harold Ritter
Cisco Employee

Hi @kim

 

I am not sure what the restriction was, but this restriction is not present in recent XR versions. I just ran a quick test and it worked like a charm without the dummy ibgp session on the middle ASBR.

 

Regards, 

Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

Hi @Harold Ritter,

thanks!

 

Well thats interesting, that an iBGP peer is needed to trick XR into passing eBGP routes - which version did you test on? Feels kind of like a bug i ran into once where the XE didn't populate forwarding tables if CDP wasnt turned on for a specific interface. I'll compare to my lab, just needed to reach a milestone in the workbook.

 

Cheers!

Hi @kim ,

 

I ran the test with XRv 6.3.1 and it works like a charm.

 

Regards,

Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

Hey

 

Wow, okay - i'm running 6.5.3, promising - well now i cant wait to test it. The doc was updated june last year...

 

Thanks again!

Cheers

Hi @kim ,

 

Let us know if you run into issues or questions while testing.

 

Regards,

Harold Ritter
Sr Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México
Paseo de la Reforma 222
Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México

Hey

 

Ok tested it, works perfectly here as well. Go figure. Wonder what section 4 was originally about.

Anyway, thanks guys 

 

Cheers

MHM Cisco World
Advocate

I know this issue solved but I want to mention something here 
If I am right this B2B inter-AS "option-B" so 
there is two way the AS exchange label 
1- config the LDP under the interface connect both AS
2- config the BGP to exchange label <- are this what is ask for??

Hey

Well even though it was solved, any input is appreciated!

 

This is option b though, Option B 

Option a is more like how you would build your bgp towards the end customer, just with the added label path maybe.

 

Cheers

OK let me review my note within two days I will inform you what I get
""why we use dummy iBGP with Inter-AS op.B IOS XR ?""