Communities BCP [was: RE: BGP Path Filtering]

Stephen J. Wilcox steve at telecomplete.co.uk
Fri May 16 22:01:16 UTC 2003


On Fri, 16 May 2003, Danny McPherson wrote:

> On 5/16/03 1:26 PM, "Jay Ford" <jay-ford at uiowa.edu> wrote:
> 
> > You can & definitely should strip those community values on announcements you
> > receive from EBGP peers.  Interesting things happen if you let others turn
> > your routing policy knobs when you think they can't reach them.\
> 
> Agreed.  
> 
> Likewise, when you receive communities (and MEDs, ugh!) [if possible] you
> should reset them (v. employing 'additive').  Unnecessary propagation and/or

Hmm.. assuming you're interconnecting at multiple points with the same ASN they 
will probably want to indicate to you where to send traffic to them using MEDs, 
if you go stripping them out you lose that info, check the peering policy.. this 
may put you in breach.

Even without a breach of policy the MED will help find the best path to a route 
thats identical at two points and if you take it out you lose that.

Altho I'd agree if you'd say to clear the communities and MEDs on egress, thats 
an okay thing to do.

Steve

> uniqueness of many attributes (especially transitive) can that go unnoticed
> often have a significant impact on efficiencies of BGP update packing --
> which subsequently impacts convergence, CPU & memory resource utilization,
> etc...
> 
> -danny 
> 
> 




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