Hello,
We are seeing something strange..

We tag certain prefixes announced to us with bgp communities, eg. 11280:115 etc.
(ROS ver 5.21 as well as 5.26)

We use these communities in our bgp filters for prefix announcements.

e.g. chain=out-filter match-chain=XYZ invert-match=no action=accept set-bgp-prepend-path=""
chain=out-filter bgp-communities=11280:115 invert-match=no action=accept set-bgp-prepend-path=""
chain=out-filter invert-match=no action=discard set-bgp-prepend-path=""

The desire is to announce prefixes defined by filter Chain XYZ and all other prefixes which are tagged with bgp community 11280:115

However, we see prefixes which have other bgp community tags being announced... e.g. prefixes with community tag of 11280:135

Is this a BUG ? or Known Issue ? or am I using the wrong syntax in the above filter chain commands ?

Hello,
We are seeing something strange..

We tag certain prefixes announced to us with bgp communities, eg. 11280:115 etc.
(ROS ver 5.21 as well as 5.26)

We use these communities in our bgp filters for prefix announcements.

e.g. chain=out-filter match-chain=XYZ invert-match=no action=accept set-bgp-prepend-path=""
chain=out-filter bgp-communities=11280:115 invert-match=no action=accept set-bgp-prepend-path=""
chain=out-filter invert-match=no action=discard set-bgp-prepend-path=""

The desire is to announce prefixes defined by filter Chain XYZ and all other prefixes which are tagged with bgp community 11280:115

However, we see prefixes which have other bgp community tags being announced... e.g. prefixes with community tag of 11280:135

Is this a BUG ? or Known Issue ? or am I using the wrong syntax in the above filter chain commands ?

Is it because the certain prefix carry the community internet (0:0) ? as the 0:0 will match any filter. All my incoming prefix had been modified the community from what so ever to 65530:XXXX for router internal routing purpose, so that all community internet will be erased.

Is it because the certain prefix carry the community internet (0:0) ? as the 0:0 will match any filter. All my incoming prefix had been modified the community from what so ever to 65530:XXXX for router internal routing purpose, so that all community internet will be erased.

Thank you for replying on this thread...

I can tell you that this behavior is not due to Community 0:0, if I do a print route detail it shows all the Communities, in our case, we are choosing to add communities, rather than 'set communities' which removes community tags setup by others.

I have played with it some more and came to the conclusion that a filter, when using the community tag as the sole section criteria does not work well (when there are multiple community tags on the prefixes), it acts as if there is a problem (bug?) in the matching algorithm.

For the time-being I have been able to solve my problem, by doing a more selective filter, in which I am also using another Prefix list (i.e. match two criteria, predefined prefix list as well as the community tag), and that works as expected.