Inter-As solution

Unanswered Question
Mar 20th, 2008


In the Inter-AS solution using the option 10b[ASBR-ASBR MBGP] can we have the label distribution method between the two AS to use EBGPV4+Label??

If, yes: any configuration example ???

I have this problem too.
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Harold Ritter Thu, 03/20/2008 - 12:05


With option 10b, the VPNv4 routes are learnt from the ASBR and you don't even need to learn labels for the other AS'es IPv4 addresses (PEs loopback).

Can you please let us know what problem you are trying to solve.


dara111983 Thu, 03/20/2008 - 15:23

Thanks Harold,

This would be applying if we are having the EBGP peering on connected interface IP network.

But, What if we are having the peering using the multihop feature between the Loopback's of the ASBR???



Harold Ritter Thu, 03/20/2008 - 18:10


eBGP between the ASBR using the loopback interface instead of the directly connected interface has been supported since 12.0(29)S.

Here's what needs to be configured.

- static routes on the multiple links between the ASBRs, for example:

ip route X.X.X.X Ethernet1/0 Y.Y.Y.Y

ip route X.X.X.X Ethernet0/0 Z.Z.Z.Z

- Configuring "mpls bgp forwarding" on the physical interfaces, in this case e0/0 and e1/0.

- Configuring the eBGP VPNv4 session using loopback interface as follow:

router bgp 200

bgp log-neighbor-changes

neighbor X.X.X.X remote-as 100

neighbor X.X.X.X disable-connected-check

neighbor X.X.X.X update-source Loopback0


address-family vpnv4

neighbor X.X.X.X activate

neighbor X.X.X.X send-community extended


dara111983 Fri, 03/21/2008 - 12:15

Thanks Harold,

One more query for the same setup,

Can we have the VPN label end to end preserved in this case, i.e, not resetting the entire label stack.

As we can have this in the case of MBGP between the RR's.

Can we do this with the ASBR-ASBR MBGP approach.



Harold Ritter Fri, 03/21/2008 - 13:48


With option 10b, the VPN label will always be swapped at the ASBRs. Do you see any issue with this.


dara111983 Fri, 03/21/2008 - 22:48

Thanks Harold,

No not any issue that setup works fine, what I was trying is to use the next-hop-unchanged @ ASBR for the VPNV4 prefixes from the AS1 towards AS2, sending the AS1 require prefixes in AS2 was willing to have an end-end LSP VPNv4 label unchanged.

It would be nice if you can elaborate a lil on the possibility of this.



Harold Ritter Sat, 03/22/2008 - 07:37


It is definitely possible to run the eBGP VPNv4 session on the ASBRs but this doesn't make your setup option 10b. It is still option 10c but with the eBGP VPNv4 runnning on the ASBRs rather than on the RRs.



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