Re: [Idr] I-D Action: draft-ietf-idr-rs-bfd-02.txt

Nick Hilliard <> Thu, 20 April 2017 22:50 UTC

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Date: Thu, 20 Apr 2017 23:50:24 +0100
From: Nick Hilliard <>
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Subject: Re: [Idr] I-D Action: draft-ietf-idr-rs-bfd-02.txt
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Robert Raszuk wrote:
> Nick,
> I am very happy for you that your experience with published static MTU
> values is so great. Well if you go via your own switches with dark fiber
> I would not expect this to be any different. 
> If however you operate a distributed IX and use leased circuits from
> other carriers between your access switches you may be very surprised
> that suddenly your MTU get's reduced due to underlying carrier reroute
> to different links or applying say MPLS link protection. 
> We do see this occurring more and more these days and it is nasty to
> troubleshoot too if you have no proper tool running. So tactfully I
> recommend we do not close our minds to only those problems which one
> have seen in his own shop.

So what you're saying is that if someone builds infrastructure which is
identifiably unfit for its intended purpose, it might break in nasty but
entirely predictable ways.

At this stage, I think it's important to say that this draft is not
about MTUs, and that if you have core MTU problems on your inter-domain
l2 network, you have problems which are both bigger and not particularly
related to this draft.

> On the topic of ICMP or ARP it is your choice. I prefer to know that my
> upstream is down in say 2 sec rather then suffer from broken Internet
> link forever as my upstream provider will not run BFD session with an
> office fiber tail.

We're talking about bfd session brokering via route servers in
inter-domain routing situations, not residential / b2b access models.