[c-nsp] BGP blackhole community config

Mark Tinka mark.tinka at seacom.mu
Tue Jun 21 03:16:55 EDT 2016

On 21/Jun/16 08:55, Oliver Boehmer (oboehmer) wrote:

> this is not entirely correct: 

Hey Oli.

There you are. Long time no see :-).

> BGP routes don’t have a tag in Cisco’s implementation, so you can’t match against a tag when a route-map controls BGP path advertisements. You can use it when redistributing other route sources which do support tags (statics, etc.) into BGP:
> r1(config)#route-map FOO
> r1(config-route-map)#match tag 123
> r1(config-route-map)#exit
> this one works:
> r1(config)#router bgp 65001
> r1(config-router)#redistribute static route-map FOO
> r1(config-router)#
> this one doesn’t
> r1(config-router)#neighbor remote-as 65002
> r1(config-router)#neighbor route-map FOO out
> % "FOO" used as BGP outbound route-map, tag match not supported
> % not supported match will behave as route-map with no match
> r1(config-router)#

I suppose this makes sense, because in Junos, I can define a source
routing protocol for BGP to reference when writing an import or export
routing policy.

I tried this once in IOS and IOS XE, and I think the only source that
worked well for my use-case was "from Local". Other routing protocols
seemed to behave strangely. Same for IOS XR, which took me by surprise
considering RPL allows you to define source routing protocols.

In Junos, I can define the source protocol as being "Static", and then
adding "Tag" as another match condition within the same policy to
extract static routes that contain the specific tag. So I suppose the
actual limitation here is telling the route map to support "Static" as a
match condition.

Thanks for the tip, anyway. And good to see you back here :-).


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