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I was adding a new policy to both import and export list for BGP. Then I observed a bgp session reset. Can anyone explain this for me?

The only change I made was to prepend a new policy to reject everything advertised from the neighbor and advertise nothing to the neighbor.

e.g: old config: 

set protocols bgp group ext import policy-A
set protocols bgp group ext export policy-B

New config:

set protocols bgp group ext import nothing policy-A
set protocols bgp group ext export nothing policy-B
Bo Cao
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  • Did any answer help you? if so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could post and accept your own answer. – Ron Maupin Jan 04 '21 at 02:19

1 Answers1

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Well, there are 3 ways to update policy (apply a policy to our Adj-RIB-In):

  • hard reset - cause a full reset of session with a neighbor and apply policies to recieving routes;

  • soft reset - neighbors should support Route Refresh feature [ https://www.rfc-editor.org/rfc/rfc2918 ]. This feature uses special Refresh message which request to send a full neighbor's Adj-RIB-Out to us. This feature do not interrupt a forwarding plane;

  • soft reconfiguration - our router always stores full neighbor's Adj-RIB-Out in its Adj-RIB-In, so if we update a policies we don't even sending any request to neighbor and applies in on our Adj-RIB-In. This feature do not interrupt a forwarding plane. This feature enabled by default in Juniper Junos OS and works autimatically when we commit a configuration.

If we consider all of the above it was the soft reset which not interrupt router's forwarding plane or it was if one of neighbors don't supports Route Refresh and "soft reconfiguration" feature is disabled with "keep none" keyword.

Recently i wrote a small article about those features, but in russian language - http://sk1f3r.ru/bgp-softreset

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