Re: [Idr] comments on draft-ietf-idr-rs-bfd

Robert Raszuk <robert@raszuk.net> Wed, 02 August 2017 10:49 UTC

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From: Robert Raszuk <robert@raszuk.net>
Date: Wed, 2 Aug 2017 12:49:40 +0200
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To: Gert Doering <gert@space.net>
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Subject: Re: [Idr] comments on draft-ietf-idr-rs-bfd
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Hi Gert,

Sure you can say that this is implementation detail ... but if you design
protocol right implementation becomes much easier.

Q:

Let's consider a scenario that RS client has a view with some bgp policy.
Now this client is using 1500 mtu lan and 9k mtu lan for ipv4 connectivity
via ix.

As reachability to next hops may be different for each lan are we going to
have two sessions of new safi between RS and said client ? Or are we in
this case going to put such client into two different contexts on RS ?

Cheers
R.


On Aug 2, 2017 5:32 AM, "Gert Doering" <gert@space.net>; wrote:

Hi,

On Wed, Aug 02, 2017 at 11:07:45AM +0200, Robert Raszuk wrote:
> Interesting ...
>
> Look at section 5 of yr draft:
>
> "The next hop field is the key for the NH-Reach NLRI type".
>
> As defined today your new NLRI encoding in MP_REACH does not have per
> client distinguisher. And if it is the NLRI key as the draft states good
> luck to have the next hop information it carries scoped to be per client.

It's an implemention decision on whether the RS sees this as global
or per-client thing.

Since RSs already today do many things in ways the original BGP specs
did not envision (like, per-client bestpath calculation) doing this
particular one globally does not sound (as said before) like the most
reasonable implementation decision.

OTOH, if the draft had a few more words on this (like, "It is RECOMMENDED
that next-hop reachability is considered a per-client value.  A route-server
MAY decide that a given next-hop should not be considered anymore for
any client if more than a configurable threshold of clients report
unreachability.") it would help to de-confuse readers.

Gert Doering
        -- NetMaster
--
have you enabled IPv6 on something today...?

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