From: Mark Lewis (markl11@xxxxxxxxxxx)
Date: Thu Sep 28 2000 - 03:45:39 GMT-3
Watch out! You've just given a definition of the 'no-advertise' community
attribute.
No-export - don't advertise to eBGP neighbors. (This route will not go
outside the AS).
No-advertise - don't advertise to ANY other routers (iBGP or eBGP).
Community attribute can also take the form of a number. You set (tag) the
route with a number & then filter later based upon that number.
You can have combinations - you can set 'no-export' on a route, and by using
the keyword 'additive' you can set additional community attributes on the
same route (ie. set community xxx additive).
Don't forget to send community attrib.s to neighbors (if thats what you
intend!). Use the command 'neighbor xxx send-community'.If you don't use it,
the community attrib. doesn't get sent!
Also, watch out for community attribute affecting the advetisement on
aggregate route with 'as-set' keyword. If one of the routes is,for example,
'no-export' - the attribute doesn't get sent (various
ways around this - resetting community of the route (use attribute map),
using an advertise map to control which routes make up the aggregate,etc).
Hope that helps,
Mark
>From: Kevin Baumgartner <kbaumgar@cisco.com>
>Reply-To: Kevin Baumgartner <kbaumgar@cisco.com>
>To: masalmon@cisco.com
>CC: ccielab@groupstudy.com
>Subject: Re: BGP community attribute
>Date: Wed, 27 Sep 2000 21:26:35 -0700 (PDT)
>
> Actually the examples of have seen more commonly used are setting
>the community no-export. What happens then is the route 0.0.0.0 will
>be sent to BGP neighbor router 2.2.2.2. Router 2.2.2.2 will not forward
>the 0.0.0.0 route on any neighbor routers.
>
> Also need to add "neighbor 2.2.2.2 send-community" in your configuration.
>
> A excellent book on BGP with configurations is Internal Routing
>Architecures by Bassam Halabi.
>
> Kevin
>
> >
> > Hey guys, I need some help with something. CAn someone explain for me
> > the community attribute. I understand that it can be used to control
> > which routes are sent by a downstream router to its downstream
> > router(s). However, see below really confuses me. Can someone explain
> > it? THanks.
> >
> > Assume that on Router C you want to set to 300 the community attribute
> > of outgoing updates for network 170.10.0.0. The following
> > commands apply a route map to outgoing updates on Router C:
> >
> > !Router C
> > router bgp 300
> > network 170.10.0.0
> > neighbor 2.2.2.2 remote-as 100
> > neighbor 2.2.2.2 route-map SETCOMMUNITY out
> > !
> > route-map SETCOMMUNITY permit 10
> > match ip address 1
> > set community 300
> > !
> > access-list 1 permit 0.0.0.0 255.255.255.255
> >
> >
> > Access list 1 denies any update for network 170.10.0.0 and permits
> > updates for any other network.
> >
> > FYI it is from the BGP section of the Cisco CD.
> > --
> >
> >
> >
> > Mark Salmon
> > Network Support Engineer
> > SBC OP HQ
> > Cisco Systems Inc
> > 8735 W. Higgins Road
> > Suite 300
> > Chicago IL 60631
> > Phone:773-695-8235
> > Pager:800-365-4578
> > email: masalmon@cisco.com
> > Empowering The Internet Generation.
> >
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