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Re: [mpls] [Bier] Encapsulation first nibble

"Zhaohui (Jeffrey) Zhang" <zzhang@juniper.net> Tue, 17 March 2015 17:36 UTC

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From: "Zhaohui (Jeffrey) Zhang" <zzhang@juniper.net>
To: Antoni Przygienda <antoni.przygienda@ericsson.com>, Xuxiaohu <xuxiaohu@huawei.com>, "stbryant@cisco.com" <stbryant@cisco.com>, Eric Rosen <erosen@juniper.net>, BIER <bier@ietf.org>
Thread-Topic: [Bier] Encapsulation first nibble
Thread-Index: AQHQXcZsT/NTuReqcUafEPAn7P7Hmp0a0zkAgAWxRoCAAAe/AIAAZCaAgAABcAA=
Date: Tue, 17 Mar 2015 17:35:40 +0000
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Subject: Re: [mpls] [Bier] Encapsulation first nibble
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Today those "heuristics" are typically used in very specific deployments where an operator knows well what kind of traffic is going through their MPLS infrastructure.

As Eric mentioned in the other message, a nibble value specific to BIER might be useful for other purpose than ECMP entropy, and if such a value is standardized (like value 0 and 1 that are reserved for PWs), then it helps reduce the clashing with random/hacky heuristics usages.

Jeffrey

> -----Original Message-----
> From: BIER [mailto:bier-bounces@ietf.org] On Behalf Of Antoni Przygienda
> Sent: Tuesday, March 17, 2015 1:16 PM
> To: Xuxiaohu; stbryant@cisco.com; Eric Rosen; BIER
> Cc: mpls@ietf.org; sfc@ietf.org
> Subject: Re: [Bier] Encapsulation first nibble
> 
> Not being much of an encapsulation, data plane guy myself, I wonder a tad
> how hacky those 'heuristics' are.  Last label indicates clearly a BIER
> header is following. For the LSRs that do not support BIER and do not
> parse the BIER encaps there is no reason to look 'behind the label'.
> Multiple sub-domains allow for clean separation of traffic with different
> properties if needed and with that there is even less reason for some kind
> of 'heuristic' DPI
> 
> Now, given some 'heuristics' are in place no matter what value we put into
> the nibble, sooner or later we'll collide with it no matter what value we
> pick since such 'heuristics' basically try to parse bits without
> understanding their context and with that can easily mistake an 'eye' for
> an 'I' or an 'aye'.
> 
> --- tony
> 
> 
> 
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