Support Support Downloads Knowledge Base Apex Support Portal Community

Knowledge Base

Search our Knowledge Base sites to find answers to your questions.

Ask All Knowledge Base Sites All Knowledge Base Sites JunosE Defect (KA)Knowledge BaseSecurity AdvisoriesTechnical BulletinsTechnotes Sign in to display secure content and recently viewed articles

BGP route update message pre-pended AS number over 75 times (the limit of most BGP routers). How does JUNOS code treat such BGP update messages.



Article ID: KB14029 KB Last Updated: 04 Mar 2017Version: 2.0
BGP route update message pre-pended AS number over 75 times (the limit of most BGP routers). How does JUNOS code treat such BGP update messages?
BGP flaps and long AS number update messages are seen
On receiving such long prefixes, JUNOS code will just accept the long BGP update message and will pass it on.

One AS-path segment can have 255 AS-paths pre-pended in the update message. If there are more than 255 AS-paths pre-pended, another AS-path segment/sequence will be added in the same update message.
Thus, in one update messages, there can be more than 255 AS-paths appended and more. JUNOS code will just pass on such long update messages.

If any Notification message are seen in the BGP traceoptions with such messages, it is not because of the long AS number update messages.
JUNOS sends notification message to the peers and resets the BGP session only for malformed packets. This is usually like a BGP flap which will reset BGP peering. It might take a few moments before BGP establishes connections automatically with its peers.

To resolve any related issues with such BGP flapping with notification messages (code 3, subcode 11), do the following:
It is required to filter the particular prefix on the peer router, so that peer blocks the malformed BGP update message from being advertised to the JUNOS router.
The filtering needs to be done on the peer router since with JUNOS, filtering of routes can be done only in the outbound direction.
JUNOS code will accept all the routes from peer in the RIB tables and then run any filtering policies on them.
You can enable BGP traceoptions for any further troubleshooting of BGP flap conditions.
Comment on this article > Affected Products Browse the Knowledge Base for more articles related to these product categories. Select a category to begin.

Getting Up and Running with Junos

Getting Up and Running with Junos Security Alerts and Vulnerabilities Product Alerts and Software Release Notices Problem Report (PR) Search Tool EOL Notices and Bulletins JTAC User Guide Customer Care User Guide Pathfinder SRX High Availability Configurator SRX VPN Configurator Training Courses and Videos End User Licence Agreement Global Search