[j-nsp] Junos BGP update generation inefficiency -cause for concern?

[Adam Vitkovsky]

Hi Saku,

> Saku Ytti [mailto:saku at ytti.fi]
> Sent: 18 May 2015 12:50
> 
> On 18 May 2015 at 14:00, Adam Vitkovsky <Adam.Vitkovsky at gamma.co.uk>
> wrote:
> 
> Hey Adam,
> 
> > Yes I'm thinking about "BGP Dynamic Update Peer-Groups"
> > - the improved BGP update message generation where the update-group
> > memberships is calculated automatically/dynamically by the system based
> on
> > common egress policies assigned to peers.
> > And of course the configuration using templates (i.e. session templates and
> > policy templates) and inheritance.
> > I've been relying on the above since ever in Cisco world and I miss that
> > much in Junos.
> 
> The update-groups are created dynamically in JunOS as far as I know.
> That is if you have BGP group where neighbors have unique export
> policies, you will have multiple update-groups in configuration group.
Yes that is my understanding, that there's definitely an update-group for each configuration group. 

> But I guess if you have two neighbors with same export policies in
> different configuration group, it likely won't share same
> update-group, haven't tested though.
Yeah that's the culprit right there that the update-group is based on the configuration group rather than the actual egress policy commonalities.

I also suspect that if you have two neighbours in a configuration group both with the same policy but attached directly to the peer there would be 3 update groups created one for the configuration group and one for each peer.

 
> I'm personally not too excited about templates in IOS, as I tend to
> have only like 3-5 peer-groups in IOS, and if I translate the config
> to template based, the amount of lines in my config increases. I think
> the break-even would require rather large amount of groups.
> --
>   ++ytti
Of course it depends on the use case and the divergence of routing policies among peers.

adam 
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