09-27-2011 03:56 AM - edited 03-01-2019 02:29 PM
Hi all.
I've just run into the following problem when configuring Dual Autonomous System Support for BGP.
We handle 2 AS numbers that we intend to merge.
R1 has the following config:
router bgp 10
no bgp default ipv4-unicast
bgp log-neighbor-changes
neighbor 192.168.0.2 remote-as 10
!
address-family ipv4
neighbor 192.168.0.2 activate
no auto-summary
no synchronization
exit-address-family
R2 is located in a different AS (As20) and we try to pretend it is in AS10 ( from R1 perspective). R2 config is as follows:
router bgp 20
no bgp default ipv4-unicast
bgp log-neighbor-changes
neighbor 192.168.0.1 remote-as 10
neighbor 192.168.0.1 local-as 10 no-prepend replace-as
!
address-family ipv4
neighbor 192.168.0.1 activate
no auto-summary
no synchronization
exit-address-
It seems that BGP session is properly established with this config. However as soon as we add a network command to originate a given prefix the bgp session goes down. We see the following when running a debug ip bgp:
*Mar 1 00:08:30.643: %BGP-3-NOTIFICATION: received from neighbor 192.168.0.1 3/3 (update missing required attributes) 0 bytes
*Mar 1 00:08:30.643: BGP: 192.168.0.1 went from Established to Closing *Mar 1 00:08:30.643: %BGP-3-NOTIFICATION: received from neighbor 192.168.0.1 3/3 (update missing required attributes) 0 bytes
*Mar 1 00:08:30.643: BGP: 192.168.0.1 went from Established to Closing
Then the BGP session is established again but it goes down inmediately.....
I haven't a clue about where the problem might be. Any suggestion?
Thanks
Flo.
09-27-2011 11:18 AM
Hi Flo,
it sounds like a buggy behavior.
Can you tell which platforms/IOS your routers are?
Can you also add some more chatty debugs (on the routers closing the session).
deb ip bgp events
deb ip bgp updates
Riccardo
09-28-2011 12:33 AM
Hi Riccardo
Thanks for your comments.
I've just run the ip bgp events/updates debug and this is what I can see in both sides:
R1 ( the router that receives the update)
*********************************************************************************
*Mar 1 00:06:38.803: BGP: 192.168.0.2 Update missing attributes, flags 0x7
*Mar 1 00:06:38.807: BGP: 192.168.0.2 reset due to BGP Notification sent
*Mar 1 00:06:38.807: %BGP-5-ADJCHANGE: neighbor 192.168.0.2 Down BGP Notification sent
*Mar 1 00:06:38.807: %BGP-3-NOTIFICATION: sent to neighbor 192.168.0.2 3/3 (update missing required attributes) 0 bytes
R1# FFFF FFFF FFFF FFFF FFFF FFFF FFFF FFFF 0035 0200 0000 1940 0101 0040 0204 0201 000A 4003 04C0 A800 0280 0404 0000 0000 2002 0202 02
*Mar 1 00:06:38.927: BGP: service reset requests
*Mar 1 00:06:38.927: BGP: service reset requests
R2(config)#router bgp 20
R2(config-router)#net
R2(config-router)#network 2.2.2.2 mask
R2(config-router)#network 2.2.2.2 mask 255.255.255.255
R2(config-router)#
*Mar 1 00:06:38.179: BGP(0): route 2.2.2.2/32 up
*Mar 1 00:06:38.179: BGP(0): nettable_walker 2.2.2.2/32 route sourced locally
*Mar 1 00:06:38.183: BGP(0): 192.168.0.1 send UPDATE (format) 2.2.2.2/32, next 192.168.0.2, metric 0, path Local
*Mar 1 00:06:38.251: %BGP-3-NOTIFICATION: received from neighbor 192.168.0.1 3/3 (update missing required attributes) 0 bytes
*Mar 1 00:06:38.255: BGP: 192.168.0.1 reset due to BGP Notification received
*Mar 1 00:06:38.255: %BGP-5-ADJCHANGE: neighbor 192.168.0.1 Down BGP Notification received
R2(config-router)#
*Mar 1 00:06:38.255: BGP: service reset requests
*Mar 1 00:06:38.259: BGP: service reset requests
*Mar 1 00:06:38.259: BGP: service reset requests
*Mar 1 00:06:38.259: BGP: service reset requests
R2(config-router)#
*Mar 1 00:06:39.675: BGP: Regular scanner event timer
*Mar 1 00:06:39.675: BGP: Performing BGP general scanning
*Mar 1 00:06:39.675: BGP(0): scanning IPv4 Unicast routing tables
*Mar 1 00:06:39.675: BGP(IPv4 Unicast): Performing BGP Nexthop scanning for general scan
*Mar 1 00:06:39.675: BGP(0): Future scanner version: 5, current scanner version: 4
*Mar 1 00:06:39.679: BGP(2): scanning VPNv4 Unicast routing tables
*Mar 1 00:06:39.679: BGP(VPNv4 Unicast): Performing BGP Nexthop scanning for general scan
*Mar 1 00:06:39.679: BGP(2): Future scanner version: 5, current scanner version: 4
*Mar 1 00:06:39.679: BGP(4): scanning IPv4 Multicast routing tables
*Mar 1 00:06:38.803: BGP: 192.168.0.2 Update missing attributes, flags 0x7
*Mar 1 00:06:38.807: BGP: 192.168.0.2 reset due to BGP Notification sent
*Mar 1 00:06:38.807: %BGP-5-ADJCHANGE: neighbor 192.168.0.2 Down BGP Notification sent
*Mar 1 00:06:38.807: %BGP-3-NOTIFICATION: sent to neighbor 192.168.0.2 3/3 (update missing required attributes) 0 bytes
R1# FFFF FFFF FFFF FFFF FFFF FFFF FFFF FFFF 0035 0200 0000 1940 0101 0040 0204 0201 000A 4003 04C0 A800 0280 0404 0000 0000 2002 0202 02
*Mar 1 00:06:38.927: BGP: service reset requests
*Mar 1 00:06:38.927: BGP: service reset requests
*********************************************************************************
R2 (router that is configured with the "local-as no-prepend replace-as"). As soon as I configured the network 2.2.2.2 mask 255.255.255.255 command to announce a loopback interface to the peer, everything is triggered. These are the debug messages:
***************************************************************************
R2(config)#router bgp 20
R2(config-router)#net
R2(config-router)#network 2.2.2.2 mask
R2(config-router)#network 2.2.2.2 mask 255.255.255.255
R2(config-router)#
*Mar 1 00:06:38.179: BGP(0): route 2.2.2.2/32 up
*Mar 1 00:06:38.179: BGP(0): nettable_walker 2.2.2.2/32 route sourced locally
*Mar 1 00:06:38.183: BGP(0): 192.168.0.1 send UPDATE (format) 2.2.2.2/32, next 192.168.0.2, metric 0, path Local
*Mar 1 00:06:38.251: %BGP-3-NOTIFICATION: received from neighbor 192.168.0.1 3/3 (update missing required attributes) 0 bytes
*Mar 1 00:06:38.255: BGP: 192.168.0.1 reset due to BGP Notification received
*Mar 1 00:06:38.255: %BGP-5-ADJCHANGE: neighbor 192.168.0.1 Down BGP Notification received
R2(config-router)#
*Mar 1 00:06:38.255: BGP: service reset requests
*Mar 1 00:06:38.259: BGP: service reset requests
*Mar 1 00:06:38.259: BGP: service reset requests
*Mar 1 00:06:38.259: BGP: service reset requests
R2(config-router)#
*Mar 1 00:06:39.675: BGP: Regular scanner event timer
*Mar 1 00:06:39.675: BGP: Performing BGP general scanning
*Mar 1 00:06:39.675: BGP(0): scanning IPv4 Unicast routing tables
*Mar 1 00:06:39.675: BGP(IPv4 Unicast): Performing BGP Nexthop scanning for general scan
*Mar 1 00:06:39.675: BGP(0): Future scanner version: 5, current scanner version: 4
*Mar 1 00:06:39.679: BGP(2): scanning VPNv4 Unicast routing tables
*Mar 1 00:06:39.679: BGP(VPNv4 Unicast): Performing BGP Nexthop scanning for general scan
*Mar 1 00:06:39.679: BGP(2): Future scanner version: 5, current scanner version: 4
*Mar 1 00:06:39.679: BGP(4): scanning IPv4 Multicast routing tables
***********************************************************************************
Regarding the IOS, I'm currently using Version 12.4(25d),
Cheers!
Flo.
09-28-2011 03:29 AM
I think I've just found out what the problem is. This feature is only available to eBGP and it is quite reasonable.
*****
This feature allows a router to appear to external peers as a member of another autonomous system for the purpose of autonomous system number migration.
*******
I've just configured it and it works. I think we can use a private AS and then we can remote the private as when advertising it to the internet.
Thanks for your help.
Flo.
09-28-2011 04:56 AM
indeed..and it makes perfect sense.
good that you spotted it
09-30-2011 02:18 AM
local-as is the best and least complex command when migration of AS is concern.
Regards,
Smitesh
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