Re: [Lsr] Prefix Unreachable Announcement Use Cases

Robert Raszuk <> Tue, 17 November 2020 08:06 UTC

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From: Robert Raszuk <>
Date: Tue, 17 Nov 2020 09:05:59 +0100
Message-ID: <>
To: Aijun Wang <>
Cc: Jeff Tantsura <>, lsr <>, "Acee Lindem (acee)" <>
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Subject: Re: [Lsr] Prefix Unreachable Announcement Use Cases
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> Moreover it seems that it will just also prevent any local protection to
> locally bypass the failed destination.
> *[WAJ] No, It will trigger the local protection instead, not prevent.*
You missed my point.

I am talking about *local* protection in a sense of adjacent node(s) to the
PE/ASBR which failed. *Local* to the failure.

You are talking about *local* protection on ingress to the network. Let's
focus on this:

Q1 - You are installing a /dev/null route in a router. That means that any
packet sent to this destination will be dropped. How is this of any
protection ?

Q2 - What you may be actually trying to say is that by installing such PUA
into RIB you will via RIB let know those clients (ex: BGP) which track this
route that it is gone and that their possibly best path is no longer valid.
Sure that is one way to share such information between IGP and BGP. But
this needs to be described in the document that this is your intention.
Otherwise when you say you are installing a drop route in RIB & FIB I am
not sure how helpful that is (well other then transiently relaxing the
network to drop some traffic few router hops away).