Re: [mpls] [Bier] Encapsulation first nibble

[Xuxiaohu <[e-mail]>]

Hi Jeffrey,

> -----邮件原件-----
> 发件人: Jeffrey (Zhaohui) Zhang [mailto:[e-mail]]
> 发送时间: 2015年3月18日 21:53
> 收件人: Xuxiaohu; Antoni Przygienda; [e-mail]; Eric Rosen; BIER;
> IJsbrand Wijnands
> 抄送: [e-mail]; [e-mail]
> 主题: RE: [Bier] Encapsulation first nibble
> 
> Xiaohu,
> 
> > Following such logic (i.e., assign a nibble value specific to the new
> > encapsulation header), we would have to consider how many available
> > nibble values are there which can be used for future encapsulation
> > headers in the same way.
> 
> There are still quite a few values left; defining a new encapsulation is not lightly
> taken; adding a new IP version is not lightly taken either. Besides, there is this
> "reserved value 15" idea from Ice.

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.

> Coupled with the reasons that Eric gave:
> 
> > I think the proper direction is to use the MPLS entropy label, rather
> > than to have each router compute the entropy based on an analysis of
> > the next encapsulation header.
> >
> > So I don't think BIER justifies the use of a new MPLS special purpose
> > payload-protocol-identifier label.
> 
> I would think the encap-specific nibble is quite reasonable, and better than a
> special purpose label.

Due to the same reason as mentioned above, I wonder whether it's feasible to reserve a certain first nibble value as an encap-specific nibble in practice.

Best regards,
Xiaohu

> Jeffrey