Routes advertisement issue

[#1]

Hello -

Good Day -


Refer to the attached diagram, we are receiving some 5 prefixes from Site-A having BGP-ASN 100 -and we are advertising the same prefixes in MPLS Cloud to reach Site - B - but due to same ASN of Site-A and MPLS Cloud - these prefixes are being dropped by MPLS Cloud due to common ASN.

We do not have access to Site-A router and ASN will not change.

MPLS Cloud are not changed ASN.


Someone please guide how to figure out with this issue - MPLS Carrier has confirmed AS-Overide is already in place -
 

[cofee]

MPLS Carrier has confirmed AS-Overide is already in place - Then why is it not working?

You may find this link useful:

https://supportforums.cisco.com/discussion/12197686/bgp-asn-path-issue

[Julio E. Moisa]

Is confirmed the as-override under the address-family related to the VRF?

[#4]

Yes - AS-Overide was under address-family ipv4 vrf.

[Julio E. Moisa]

Thank you

Is possible to know the configuration on the CE routers? 

Thank you. 

[#6]

Hi,

Thank you for your writing!

Please find below relevant Configurations also attached fine topology along with router Labels which I missed in last release.

In attached topology - RTR-1 is receiving some 5 Prefixes from its neighbor (Site-A) and objective is these Prefixes should be see by RTR-3 - the challenge I am facing is Site-A and MPLS Cloud has same ASN (AS-100) due to this MPLS could sees its own ASN with Prefixes and not advertising to RTR-3 - My carrier has confirmed AS-Overide is already in place but when this never with AS-Overide then I tried the same topology in GNS which give the same result and Prefixes not traversing over MPLS Cloud -

Hope above details and attached topology is sufficient to understand -

RTR-1

ip vrf BGP
 rd 1:1
 import ipv4 unicast map PREFIX-LIST
 route-target export 1:1
 route-target import 1:1

interface Loopback99
 ip vrf forwarding BGP
 ip address 10.72.255.237 255.255.255.255
!
router bgp 200
 bgp log-neighbor-changes
 neighbor 172.16.1.1 remote-as 300
 !
 address-family ipv4
  neighbor 172.16.1.1  activate
  neighbor 172.16.1.1  prefix-list PREFIX-LIST in
  auto-summary
 exit-address-family
 !
 address-family ipv4 vrf BGP
  neighbor 172.16.1.1  remote-as 65000
  neighbor 172.16.1.1  ebgp-multihop 3
  neighbor 172.16.1.1  activate
  neighbor 172.16.1.1  as-override
 exit-address-family
!
!
ip prefix-list PREFIX-LIST seq 5 permit 1.1.1.1/32
ip prefix-list PREFIX-LIST seq 15 permit 2.2.2.2/32
ip prefix-list PREFIX-LIST seq 25 permit 3.3.3.3/32
ip prefix-list PREFIX-LIST seq 30 permit 4.4.4.4/32
ip prefix-list PREFIX-LIST seq 35 permit 5.5.5.5/32

-------------------

RTR-2

router bgp 300
 bgp log-neighbor-changes
  neighbor 172.16.1.2 remote-as 65200
 neighbor 172.16.1.2 ebgp-multihop 255
 neighbor 172.16.1.2 update-source Loopback99
 neighbor 172.16.1.2 next-hop-self
 neighbor 172.16.1.2 soft-reconfiguration inbound
 neighbor <MPLS Cloud Peer IP> remote-as 100

sh ip bgp

     Network          Next Hop            Metric LocPrf Weight Path
 *>  1.1.1.1/32  10.72.255.237                          0 200  100 i
 *>  2.2.2.2/32  10.72.255.237                          0 200  100 i
 *>  3.3.3.3/32  10.72.255.237                          0 200  100 i
 *>  4.4.4.4/32  10.72.255.237                          0 200  100 i
 *>  5.5.5.5/32  10.72.255.237                          0 200  100 i

[cofee]

Please look at the gns3 file I sent. You mentioned you simulated your topology and that didn't work for you. Did you use gns3, if so can you share the config. file I want to take a look at it.

[#8]

yes - I saw that gns-3 file that you sent.

I can paste my configs but my topology contains over 21 routers and switches and several other things are running on it - which leads to confusion so refer the config I pasted above -

Regards,

[#9]

Hi,

Yes - MPLS carrier has confirmed AS-Overide is in place but this didn't fixed the issue - in order to figure-out this , I simulated scenario in GNS - and created MPLS Cloud in below topology -

RTR-1 (ASN-100) >>> RTR-2 (ASN-300) PE (ASN-100) ---- P ---- PE (ASN-100) >>> RTR-3-(ASN-300) 

I enabled AS-Overide on both PE neighbors towards RTR routers but prefixes on RTR-2 having ASN 100 didn't reach to RTR-3 - i don't know what went wrong - but i tried another solution mentioned below but that didnt worked -

on RTR-2 I created VRF named BGP and enabled AS-Overide under  address-family ipv4 vrf BGP but when I see bgp routes on RTR-2 I saw ASN-100 still seen with prefixes -

I will refer link you shared - however do you any any more idea in order to fix that trouble ?

Regards,

[cofee]

I was able to make it work using below configuration:

router bgp 100

neighbor x.x.x.x allowas-in

R4#sh ip bgp
BGP table version is 6, local router ID is 30.30.30.4
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
              r RIB-failure, S Stale, m multipath, b backup-path, x best-external, f RT-Filter
Origin codes: i - IGP, e - EGP, ? - incomplete

   Network          Next Hop            Metric LocPrf Weight Path
*> 1.1.1.1/32       30.30.30.3                             0 300 200 100 i
*> 2.2.2.2/32       30.30.30.3                             0 300 200 100 i
*> 3.3.3.3/32       30.30.30.3                             0 300 200 100 i
*> 4.4.4.4/32       30.30.30.3                             0 300 200 100 i
*> 5.5.5.5/32       30.30.30.3                             0 300 200 100 i

[#11]

In the topology in which router and neighbour you have configured "Allowas-in" - i tried will all the combination but never works - though i still see prefixes has AS-100 - so what happend last router RTR-3 did not receive all thoses prefixes having AS-100 tagged - 

I dont have a problem in receiving prefixes on RTR-2 from RTR-1 - the problem occurs when I am trying to see the prefixes on RTR-3 that are learned from RTR-1 - the cause is MPLS cloud has the same ASN that RTR-1 has so PE router is not advertising all those prefixes which comes with AS-100 - that is an normal behaviour in BGP i-e AS PATH loop detection.

But i'd like to see how you made this work? Let me know if you are able to see Prefixes on RTR-3 from ASN-100.

Regards.

[cofee]

Can you tell me who is router 3 in your topology? I don't see any names. Are you addressing router at site b as router 3?

[#13]

Please see attached - RTR-3 is Router -3

[cofee]

Attached is the working gns3 topology. Please let me know if you have any questions.

I removed the previous attachment, it was having some issues. I hope this one will work for you if you have the new image.

[#15]

Thank You for your Working and sharing simulation -

You topology is different then mine and there shouldn't be any issue since both are edge routers I am R-1 and R-4 are on same ASN but all middle routers are on different AS -and you Allowas-in should work -

In my Scenario -

Your R4 is "MPLS Cloud" and "MPLS Cloud" need to send all Prefixes that are received from Router-1 with ASN-100 to the adjacent router let say Router-5. and MPLS Cloud and Router-1 has same ASN -100.

If you could revise your topology and add one more router -5 and modify as stated above and see if this works for you.

Regards,