Re: [Idr] AD Review of draft-ietf-idr-rfc5575bis-17 -> Updated Version -18 and Flowspec v6

Christoph Loibl <> Wed, 18 December 2019 07:11 UTC

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Date: Wed, 18 Dec 2019 08:11:37 +0100
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Cc: Alvaro Retana <>,,, "idr@ietf. org" <>
To: Jeffrey Haas <>
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Subject: Re: [Idr] AD Review of draft-ietf-idr-rfc5575bis-17 -> Updated Version -18 and Flowspec v6
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Hi Jeffrey, Alvaro!

I only pick out this single issue from the complete list, because I do not 100% agree with this statement:

> On 17.12.2019, at 23:09, Jeffrey Haas <> wrote:
>> If an unknown Flow Specification component exists, then the entire
>> NLRI cannot be "successfully parsed"...which results in not being able
>> to use treat-as-withdraw.  The text above leaves us with AFI/SAFI
>> disable, which is not extension-friendly.
> This is exactly my largest concern about flowspec right now.  There is no
> safe way to extend the spec at this point.
> There are two options available to us, IMO:
> 1. Flowspec v2, which we stalled out until 5575bis was done.
> 2. We decide that for 5575-bis that all future extensions MUST be encoded
> with a TLV format (length being mandatory).  And perhaps even protect a
> compliant extension with a capability.  This is a major change, but perhaps
> provides an upgrade path without waiting on v2.
>> NEW (suggestion)>
>>    An advertisement containing an unknown Flow Specification component
>> should be discarded as specified in Section 5.4 of [RFC7606].
> You can't parse it, therefore it's malformed.

In case of an unknown flowspec component the parser can run until decoding the component type (always the first byte of the component). When it reads a unknown type-value it can easily jump over the remaining bytes of the entire NLRI (the length of the the complete NLRI is encoded in the first bytes of the NLRI) without needing to understand what is in there, because it should treat it as withdraw. I do not see the problem. It is supposed to “ignore” the entire NLRI not only a single component of it. 


Christoph Loibl | CL8-RIPE | PGP-Key-ID: 0x4B2C0055 |