Extreme congestion (was Re: inter-domain link recovery)
sean at donelan.com
Wed Aug 15 15:59:54 UTC 2007
On Wed, 15 Aug 2007, Fred Baker wrote:
> On Aug 15, 2007, at 8:35 AM, Sean Donelan wrote:
>> Or should IP backbones have methods to predictably control which IP
>> applications receive the remaining IP bandwidth? Similar to the telephone
>> network special information tone -- All Circuits are Busy. Maybe we've
>> found a new use for ICMP Source Quench.
> Source Quench wouldn't be my favored solution here. What I might suggest is
> taking TCP SYN and SCTP INIT (or new sessions if they are encrypted or UDP)
> and put them into a lower priority/rate queue. Delaying the start of new work
> would have a pretty strong effect on the congestive collapse of the existing
> work, I should think.
I was joking about Source Quench (missing :-), its got a lot of problems.
But I think the fundamental issue is who is responsible for controlling
the back-off process? The edge or the middle?
Using different queues implies the middle (i.e. routers). At best it
might be the "near-edge," and creating some type of shared knowledge
between past, current and new sessions in the host stacks (and maybe
middle-boxes like NAT gateways).
How fast do you need to signal large-scale back-off over what time period?
Since major events in the real-world also result in a lot of "new"
traffic, how do you signal new sessions before they reach the affected
region of the network? Can you use BGP to signal the far-reaches of
the Internet that I'm having problems, and other ASNs should start slowing
things down before they reach my region (security can-o-worms being
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