The MPLS WG Archive

[Curtis Villamizar <curtis@workhorse.fictitious.org>]

In message <EB6D4918A175D311971E00204840E2820ABD3B89@whq-msgusr-01.pit.comms.ma
rconi.com>, "Rutemiller, John" writes:
> 
> If it is not behaving properly, why should I expect it to reduce its
> sending rate?

If its MPLS-OAM that's a problem.  In ICMP, the egress barely looks at
the packets shuffles some header bits and sends it back to the sender.
The errant sender only overloads itself.

If the router was truly malicius, it would be better served adding and
withdrawing link adjacencies (as routers are sometimes prone to do).

> What device is going to report that the source is misbehaving? Only the
> egress can report this problem.

You are assuming the sender is completely brain damaged but is able to
keep all protocol adjacencies going and otherwise go unnoticed.

> > If an egress is overloaded with OAM, there may be *NO* errant LSP,
> > just too many perfectly fine LSPs each sending just a little too much
> > probe traffic.  There are limits to what you can get a microprocessor
> > to do in a given amount of time.
> 
> If the processor is only capable of processing N OAM messages per second,
> and it enables OAM processing on more LSPs than it can handle, it gets
> what it asked for. If it only allows as many OAM streams as it can handle,
> then only errant LSPs will overload it.

Doesn't it make sense to enable OAM for all revenue bearing LSPs?  If
so, the ISP does so and the router needs a way to handle this if an
overload inadvertently occurs.

> And besides, if ICMP can use a probe as the source, why can't MPLS-OAM
> also use a sink? The MPLS-OAM label can be switched just like anything
> else. I can just as easily switch it externally to a sink device. This
> will provide compatibility with existing equipment.

A probe refers to a "probe packet" not an adjunct spacecraft attached
to the ingress LSR that generates ICMP particles.

The dumb CPU in the ingress generates ICMP echo requests and gets echo
replies.  Since it determines its own load, non-uniform router
dumbness does not become an issue.  In other words, if some router
CPUs are older and slower than most, the slower ones don't fall over.

> John

Curtis