malformed AS_Path if IBGP sessions confederation

[balaji_170]

Dear all,

intra-confederation labs -

   Ibgp router (R1 ) - propagate updates packets to intra-confederation neighbor (64512) and 64512 - member as sending notification errors to ibgp router R1 - with Malformed AS_Path

   R1   neighborship going down after receiving notification

i dont what exact root cause of this issuse

kindly check attached configuration files of both routers and wireshark traces and expalin it 

note:

ios : 7200

[Ivan Krimmel]

Hi Balaji,

what is the IOS version you're running?

I checked the config:

R1

router bgp 100

no synchronization

bgp log-neighbor-changes

neighbor 4.1.1.1 remote-as 100

neighbor 4.1.1.1 update-source Loopback0

R4

router bgp 64512

no synchronization

bgp log-neighbor-changes

bgp confederation identifier 100

bgp confederation peers 64513

neighbor 1.1.1.1 remote-as 100

neighbor 1.1.1.1 ebgp-multihop 2

neighbor 1.1.1.1 update-source Loopback0

I am not sure it is a valid config where you have confederation on one box and pretending to have iBGP on the other.

In the .cap we do see R4 is complaining to invalid AS-PATH, it expects to receive confederation-styled updates. You can either revert these two to a eBGP sesion, or add R1 to the confederation.

HTH,

Ivan.

[skarthic]

Few questions on your setup

- Are the two routers forming a intra confederation peers? If so both routers must be must have info on their BGP confederation id,confederation peers etc and there will be a EBGP neighborship between them

- Or is one of the router say R1 is in a different AS 100 and R4 is a router part of a confederation ? If thats the case both the routers must be configured for different AS.

It looks like a config issue as Ivan explained as R4 is in AS 100 and receives an update from a IBGP neighbor but in this case no confederation id is configured. So there comes the confusion for R4

[balaji_170]

thanks for your reply

kindly below details for my queries

Labs: snap shot - issuse marked also - after adv network in 101.1.0.0/16 in R1 - i absorved fluctuation in R4 and R5

(confederaion)

and i also attached my configuration files of each routers and traces for your reference

> router ios version : 7200

can please verify my configuration and confirm my configuration for confederation is right or not

or cisco ios 7200 defect

[cadet alain]

Hi,

I think your config is not good.

You should put R1-R2 in subAS 64512, R3-R4-R5 in subAS 64513 and you could use R3 as RR in this subAS with R4 and R5 as clients but that would save you only one BGP peering in this subAS.

Then you would have 1 intra-confed eBGP peering between R1 and R3.

Gonna pu the configs once I've verified all in GNS3.

Alain.

[balaji_170]

Hi alain,

My intention-  when  i  created confederation member -AS  (IBGP sessions)  and i advertise networks to it and observing fluctuations in link between Ibgp and Confederation peers

whether all IBGP sessions - should have confederation peers

[cadet alain]

Hi,

I don't understand what you mean.

Here is the config for what I suggested above:

R1:

router bgp 64512

bgp confederation identifier 100

bgp confederation peers 64513

neighbor 10.1.1.1 remote-as 64512

neighbor 3.1.1.1 remote-as 64513

neighbor 3.1.1.1 ebgp-multihop 2

neighbor 3.1.1.1 next-hop-self

neighbor 3.1.1.1 update-source Loopback0

neighbor 4.1.1.1 remote-as 64513

neighbor 4.1.1.1 ebgp-multihop 2

neighbor 4.1.1.1 next-hop-self

neighbor 4.1.1.1 update-source Loopback0

R2:

ip route 0.0.0.0 0.0.0.0 10.1.1.2

router bgp 64512

bgp confederation identifier 100

network 102.1.0.0 mask 255.255.0.0

neighbor 10.1.1.2 remote-as 64512

R3:

router bgp 64513

bgp confederation identifier 100

bgp confederation peers 64512

neighbor 1.1.1.1 remote-as 64512

neighbor 1.1.1.1 update-source Loopback0

neighbor 1.1.1.1 ebgp-multihop 2

neighbor 13.1.1.1 remote-as 64513

neighbor 13.1.1.1 route-reflector-client

neighbor 15.1.1.2 remote-as 64513

neighbor 15.1.1.2 route-reflector-client

R4:

router bgp 64513

bgp confederation identifier 100

bgp confederation peers 64512

neighbor 13.1.1.2 remote-as 64513

neighbor 1.1.1.1 remote-as 64512

neighbor 1.1.1.1 update-source Loopback0

neighbor 1.1.1.1 ebgp-multihop 2

R5:

router bgp 64513

bgp confederation identifier 100

neighbor 15.1.1.1 remote-as 64513

It should work this way

Regards.

Alain.

[balaji_170]

hi  alain

I  agreed with your configuration - it working fine (All IBGP's  - have intra confederation connectivity)

But my intention

In Same AS

One  router R1 AS (100) is having IBGP session with intra-Confederation R4 AS (64512) Member-AS

R1 trying to published routes to R4 (Confed) router received updates it sending notifcation error to R1

(traces i attached in first mail) - for your reference

> whether any specfic configuration required in Confed ( router ) to accept updates

[cadet alain]

Hi,

it wonk work as you want it to, in a confederation there are 3 types of BGP peerings: iBGP inside a subAS and intra-confed eBGP between routers in different subASes and finally normal eBGP between a border router in your confed and another AS.

So you'll have to do like I did before: every router must be part of a subAS

Regards.

Alain.

[balaji_170]

thanks for your reply

i understood my problem