-----邮件原件-----
发件人: mpls [mailto:mpls-bounces(_at_)ietf(_dot_)org] 代表 Curtis Villamizar
发送时间: 2014年1月15日 9:14
收件人: Wesley Eddy
抄送: Scott Brim; Eggert, Lars; IETF discussion list; mpls(_at_)ietf(_dot_)org
主题: Re: [mpls] Last Call: <draft-ietf-mpls-in-udp-04.txt> (Encapsulating MPLS
in UDP) to Proposed Standard
In message <52D5642A(_dot_)7090103(_at_)mti-systems(_dot_)com>
Wesley Eddy writes:
On 1/14/2014 11:06 AM, Eggert, Lars wrote:
Hi,
On 2014-1-14, at 16:39, Scott Brim
<scott(_dot_)brim(_at_)gmail(_dot_)com> wrote:
Lars, I know we're repeating arguments from the last decade. The
choice is between (1) specifying congestion control around the
substrate UDP that can be turned off if it causes problems, or (2)
specifying nothing at this time and adding it later if operators
want it.
I guess if this can be written as a SHOULD, up to the implementor's
discretion, then okay.
I don't think we can leave this up to implementors discretion. We've had
IETF consensus that Internet communication requires congestion control at
least
since RFC2914. A circuit breaker mechanisms seems straightforward to
implement.
As is, I object to this document going forward. The minor benefits of
getting
some better load balancing for MPLS are far outweighed by the risks.
(I'm also going to shut up now, and let others speak. I think I've
said my bit.)
I'm in basic agreement.
Assuming we might all agree that there are conceivable scenarios where
a circuit breaker mechanism would be useful, is the real issue that we
don't all agree that it could be implemented in a way that's not
burdensome and doesn't degrade performance unnecessarily?
Or is there still fundamental disagreement about whether the scenarios
where the circuit breaker is useful are even valid?
A circuit breaker (drop all traffic on sign of congestion) at the MPLS over
UDP
level would be the worst thing you could specify and IMO it would guarentee
zero implementations.
A circuit breaker might be appropriate for TDM over PW but nothing else. This
makes sense because TDM cannot change its bandwidth so the only choice is to
shut it off. TDM over PW is an application that can run over MPLS (or GRE or
L2TP). The best place to put that circuit breaker (if anywhere at all) is in
TDM
over PW.
I couldn't agree more with Curtis's point. Since RFC3985 has already made a
detailed description of congestion considerations about PWs, it seems that the
simplest way is just to add a reference to that RFC in this doc, in addition to
the text I have proposed in a previous email. The advantage of this choice is:
since there is only one place where the congestion control mechanism for
MPLS/PW traffic is specified, it's much easier for operators and implementors
to refer. In addition, once a more practical congestion control mechanism was
found in the future, it only needs to update one RFC, rather than updating many
RFCs.
Best regards,
Xiaohu
Curtis
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