manipulate BGP routing over MPLS

[Ab26]

Hi, how can i manipulate BGP routing over MPLS. I have s subnet that's advertised by one router in 2 different VRFs and received on a single VRF (some internal issue with wrong design that I can't rectify at the moment).

This subnet is advertised twice from same router but in 2 different VRFs. Since it's over MPLS I can't find an easy way to do the manipulation on the advertising router so that the receiving router chooses the VRF I want. BTW in this case how does the best Neighbor Address been chosen?

router# sh ip bgp vrf VRF-X 10.10.10.0
BGP routing table information for VRF VRF-X, address family IPv4 Unicast
BGP routing table entry for 10.10.10.0/24, version 50027
Paths: (2 available, best #2)
Flags: (0x8008001a) (high32 00000000) on xmit-list, is in urib, is best urib route, is in HW
vpn: version 4630879, (0x00000000100002) on xmit-list

Advertised path-id 1, VPN AF advertised path-id 1
Path type: internal, path is valid, is best path, in rib
Imported from 192.168.5.11:1170:10.10.10.0/24
AS-Path: 65225 , path sourced external to AS
192.168.5.11 (metric 75) from 192.168.5.25 (192.168.5.25)
Origin IGP, MED 0, localpref 100, weight 0
Received label 1889
Extcommunity: RT:65225:22101 RT:65225:6006 SOO:65225:10555
Originator: 192.168.5.11 Cluster list: 192.168.5.25

Path type: internal, path is valid, not best reason: Neighbor Address
Imported from 192.168.5.11:1250:10.10.10.0/24
AS-Path: 65225 , path sourced external to AS
192.168.5.11 (metric 75) from 192.168.5.25 (192.168.5.25)
Origin IGP, MED 0, localpref 100, weight 0
Received label 744
Extcommunity: RT:65225:1250 RT:65225:22101 SOO:65225:10555
Originator: 192.168.5.11 Cluster list: 192.168.5.25

VRF advertise information:
Path-id 1 not advertised to any peer

VPN AF advertise information:
Path-id 1 not advertised to any peer

[paul driver]

Hello
Is this a duplicate post with this?

[Harold Ritter · Accepted solution]

Hi @Ab26 ,

From the advertising router, you can simply set the local preference to a higher value on the prefix from the VRF you want to be preferred. This will cause the receiving router to select the prefix from the VRF you want.

Regards,

[Ab26]

Thanks Harald ! you always provide the correct answers Would local preference be preferred over a route heard with more ASs in the path?
For the backup route we do AS-apend few more times
So in this case I want the received from correct VRF to be chosen even if it's received from a back route with more ASs. 

Furthermore, in this case where both routes received from the same router, do you know what Neighbor Address includes or how the first route is chosen over the second ?

[Giuseppe Larosa]

Hello @Ab26 ,

yes the VPNv4 prefix with higher local preference will be preferred even if it has a longer AS path attribute.

Local preference attribute is checked before checking AS path attribute.

You should be fine if you are able to increase over the default of 100 the local preference on the primary VRF.

Hope to help

Giuseppe

[Harold Ritter]

Hi @Ab26 ,

> Furthermore, in this case where both routes received from the same router, do you know what Neighbor Address includes > or how the first route is chosen over the second ?

The only difference I see between the two paths is the following:

Path1: Imported from 192.168.5.11:1170:10.10.10.0/24 (preferred)

Path2: Imported from 192.168.5.11:1250:10.10.10.0/24

So my guess is that the lowest value is selected, but it is always better not to let the path selection be decided on these last selection criteria, which are arbitrary, and use something like the local preference or the AS path prepending to make sure the path you want is selected.

Regards,

[MHM Cisco World]

!!! 

MHM