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Re: [mpls] [Bier] Encapsulation first nibble

"Stewart Bryant (stbryant)" <stbryant@cisco.com> Thu, 19 March 2015 07:41 UTC

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From: "Stewart Bryant (stbryant)" <stbryant@cisco.com>
To: Ignas Bagdonas <ibagdona.ietf@gmail.com>
Thread-Topic: [Bier] Encapsulation first nibble
Thread-Index: AQHQYec1U0ed6cLwWkSulZECuVCa0p0jbFFW
Date: Thu, 19 Mar 2015 07:41:08 +0000
Message-ID: <95467337-1826-4C9E-888A-ABABE872CD56@cisco.com>
References: <55033E87.3030305@juniper.net> <5503403E.4050304@cisco.com> <1FEE3F8F5CCDE64C9A8E8F4AD27C19EE0831CB77@NKGEML512-MBS.china.huawei.com> <1FEE3F8F5CCDE64C9A8E8F4AD27C19EE0831CBB2@NKGEML512-MBS.china.huawei.com> <2E4BB27CAB87BF43B4207C0E55860F1827D3C5@eusaamb103.ericsson.se> <BY2PR05MB079ACD3AE28CC48B48C789ED4030@BY2PR05MB079.namprd05.prod.outlook.com> <1FEE3F8F5CCDE64C9A8E8F4AD27C19EE0831CCE9@NKGEML512-MBS.china.huawei.com> <BY2PR05MB07904EDBB62DAF1E826E107D4000@BY2PR05MB079.namprd05.prod.outlook.com> <1FEE3F8F5CCDE64C9A8E8F4AD27C19EE0831CEFD@NKGEML512-MBS.china.huawei.com>, <550A2B98.4010409@gmail.com>
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Cc: "mpls@ietf.org" <mpls@ietf.org>, BIER <bier@ietf.org>, "sfc@ietf.org" <sfc@ietf.org>, Antoni Przygienda <antoni.przygienda@ericsson.com>, "IJsbrand Wijnands (iwijnand)" <ice@cisco.com>, "Jeffrey (Zhaohui) Zhang" <zzhang@juniper.net>
Subject: Re: [mpls] [Bier] Encapsulation first nibble
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That is correct.

PWE3 took over the design after draft-martini had been widely adopted and deployed, otherwise PWs may well have been exclusively CW. The wide deployment of Ethernet PW without the CW means that PW OAM is more complicated than it would otherwise be - see the latest vcxo over GAL draft from PALS. It was asserted in the early days that there would not be a problem because there would never be an ethernet address issued that alias with the IPv4 first nibble. Well guess what happened? Yes they were and yes there was!

There is another way forward, require the inclusion of the ELI and exclusive use of ELI enabled LSPs, but in that case the packet size would go up by more than needed to fix BIER and the operational complexity would be significant, thus the cure would be worse than the disease.

Stewart 

Sent from my iPad

> On 19 Mar 2015, at 01:51, Ignas Bagdonas <ibagdona.ietf@gmail.com> wrote:
> 
> 
> Hi,
> 
> > Since the control word is optional when transporting Ethernet over MPLS, I wonder whether the idea of reserving the first nibble value of 15 is feasible in practice.
> 
> Not using a control word for ethernet PW is painful from operational perspective. Many deployed platforms will look past the labels without much context and if they happen to find 4 or 6 there, the behavior will range from blindly believing that it is in fact IPv4 or IPv6 packet to trying to validate certain fields or even checksums. Control word helps here, and if both sides have support, it should be used.
> 
> Ignas
>

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