-----邮件原件-----
发件人: Scott Brim [mailto:scott(_dot_)brim(_at_)gmail(_dot_)com]
发送时间: 2014年1月11日 0:32
收件人: Eggert, Lars
抄送: Joel Halpern; mpls(_at_)ietf(_dot_)org; Xuxiaohu; IETF
主题: Re: Last Call: <draft-ietf-mpls-in-udp-04.txt> (Encapsulating MPLS in UDP)
to Proposed Standard
I don't think it's right to try to solve this in MPLS, because MPLS is not a
forwarding protocol - it's a connectivity protocol. In any use of UDP,
congestion
control is either left to something above UDP or ignored (left to queue
management). Similarly, you want the client of MPLS to be responsible for
managing its traffic. MPLS gives you paths, it doesn't push packets over them.
Fully agree. The congestion control should be performed either by the UDP
tunnel itself or the client of MPLS. In the former case, it'd better to specify
the practical congestion control mechanisms (if there were any) in a generic
draft (e.g., RFC5405bis) and then any use of the UDP tunnel could refer to that
generic draft with regard to congestion control. In the latter case, if the
client of MPLS is TCP-friendly, that is great. Otherwise (e.g., circuit
emulation service), it shouldn't be deployed on the Internet at all, just as
has been pointed out in RFC3985, therefore there is no need for any specific
congestion control mechanism on the client.
"... In essence, this requirement states that it is
not acceptable to deploy an application (using PWE3 or any other
transport protocol) on the best-effort Internet, which consumes
bandwidth arbitrarily and does not compete fairly with TCP within an
order of magnitude." (quoted from Section 6.5 of RFC3985)
The above choice seems no conflict with the following congestion control
guidelines as quoted from Section 3.1.1 of RFC5405, as those non-TCP-friendly
traffic would be transported over a provisioned path, rather than on the
Internet.
"...Finally, some bulk transfer applications may choose not to implement
any congestion control mechanism and instead rely on transmitting
across reserved path capacity. This might be an acceptable choice
for a subset of restricted networking environments, but is by no
means a safe practice for operation in the Internet."
Best regards,
Xiaohu
Scott
On Fri, Jan 10, 2014 at 11:09 AM, Eggert, Lars <lars(_at_)netapp(_dot_)com>
wrote:
Hi,
On 2014-1-10, at 16:36, Joel M. Halpern <jmh(_at_)joelhalpern(_dot_)com>
wrote:
Maybe I am completely missing things, but this looks wrong.
If the MPLS LSP is carrying fixed rate pseudo-wires, adding
congestion control will make it more likely that the service won't
work. Is that really the goal?
We do not perform congestion control on MPLS LSPs.
Assuming that a UDP tunnel is carrying just MPLS and was established
just for MPLS, why would we expect it to behave differently than an
MPLS LSP running over the exact same path, carrying the exact same traffic?
we've been rehashing this discussion several times over the years, e.g., for
PWE, AMT, etc. In order to carry fixed-rate or otherwise
non-congestion-controlled traffic over unprovisioned general Internet paths,
there needs to be some sort of basic congestion control mechanism, like a
circuit breaker.
The whole point of running MPLS is to create networks in which paths are
provisionable, so this is usually not an issue. But if you start sticking
MPLS inside
of UDP, those packets can go anywhere on the net, so you need mechanisms to
control the rate of that traffic if it causes congestion, or at the very
least you
need to be able to stop the traffic if it creates severe congestion.
Lars