[j-nsp] BGP Communities

[Felix Schueren]

Paul,

> When I do "show route community 11666:5000" I get a list of the proper
> prefixes as expected.  11666:5000 is our own network routes.  The same
> occurs when I list 11666:4000 which is customer network routes - displays
> the list correctly.  This confirms in my mind that the MX480 is receiving
> correct communities from neighboring iBGP boxes..
do you happen to have the same routes in OSPF or as a static or 
aggregate route? Do the above "show route" commands indicate that the 
BGP version of the to-be-exported routes are active? By default, JUNOS 
will only advertise _active_ BGP routes. With default preferences, 
basically, if you have the same prefix in any other protocol (static, 
aggregate and local count as "protocols" in junos) on the router, then 
the BGP route is not considered active.

To wit:

show route 192.168.0.0/19
192.168.0.0/19     *[Direct/0] 1w2d 16:59:18
                     > via x/y/z.n
                     [BGP/170] 1w2d 16:58:05, localpref 100, from a.b.c.d
                       AS path: I
this route would _not_ be exported by your community-driven export 
policy (or the default BGP policy), even though the only routes with 
communities would be the BGP route.

You can work around this problem by specifying "advertise-inactive" on 
the group or neighbor level, in which case the best BGP route will be 
chosen even when it's not active.

If "show route community x:y" shows a BGP route, a policy matching on 
"community x:y" will export it - if it is active or when 
advertise-inactive is set.

Incidentally, how does your community definition look like? "show route 
community x:y" matches on the raw numbers, but the policy action matches 
on a regex that defines the community, maybe the problem lies there. 
Please check the
policy-options community blocks or paste an example here.

Kind regards,

Felix

-- 
Felix Schüren
Head of Network

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