Re: [sidr] 4-byte vs 2 byte ASN (was re: I-D Action: draft-ietf-sidr-pfx-validate-03.txt)

"George, Wes" <> Wed, 02 November 2011 16:38 UTC

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From: "George, Wes" <>
To: Randy Bush <>
Date: Wed, 02 Nov 2011 12:38:35 -0400
Thread-Topic: [sidr] 4-byte vs 2 byte ASN (was re: I-D Action: draft-ietf-sidr-pfx-validate-03.txt)
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Subject: Re: [sidr] 4-byte vs 2 byte ASN (was re: I-D Action: draft-ietf-sidr-pfx-validate-03.txt)
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> -----Original Message-----
> From: Randy Bush []
> aven i, an old fuddy duddy, kinda assume that an AS number is two or
> four bytes, an ip address is ipv4 or ipv6, etc.  i can understand
> clarifying once in a document where it is critical to do so, but would
> not be inclined to make it explicit everywhere AS is used or ip address
> is used.
> randy
[WEG] And I agree with the notion that unless specified as one or the other, it means the combination. However, especially in documents dealing with the mechanics of wrangling the bits on the router, that is not an implementation detail I want to leave purely to assumption/interpretation. Doesn't have to be stated and restated ad infinitum, I simply mention the other docs because I wasn't 100% certain where it made the most sense to cover it.

Based on the comments thus far, sounds like the questions are:

Q1) is RFC4893 support a prerequisite for those routers supporting SIDR Origin and Path validation
A: Yes.
I believe that this needs to be explicitly documented, where is the most appropriate location?

Q2) Do we need to incorporate something like: "MUST validate the AS Path _after_ reconstruction using AS4_PATH in the case where routing information comes from a peer which doesn't recognize 4-byte ASNs" as John suggested?

Q3) do we need some sort of language recommending a method to handle AS23456 as an origin (or in a path in the case of BGPSec), especially if it does not coincide with valid AS4_PATH info?
Technically if we're saying 4893 is a prereq, this shouldn't happen, but I could see it as a possible attack vector if we don't explicitly cover it.

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