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Posted by Paul Matthews on September 14, 2006, 12:25 pm
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dilan.weerasinghe@gmail.com wrote:
>Hi
>
>Can someone tell me if MPLS (multi protocol layer switching) and MLS
>(multi layer switching) are essentially the same thing?
They are way different.
Basically MPLS is the addition of a label to a packet such that only the label
need be read for a device to decide what to do with it. Initially this was to
try to speed things up as just a tag needed to be checked when routers did
stuff in CPU. The main advantage now is not performance as most ruters work in
hardware but separation. Through the MPLS network it is the label that needs to
be checked rather than the IP info.
That means an MPLS carrier could provide services to, say Microsoft and Cisco.
they could both use the same area of RFC1918 network addressing and be able to
function totally independantly.
MLS is Multi layer switching. The first packet in a flow will be processes in
CPU, and then a cache entry written to the switch engine so that subsequent
packets can be switched in hardware without having to trouble the CPU.
This is where thing like code red cause problems to the network. At the router
near the infected device traffic was being sent to random[1] addresses. These
were not previously in the cache and needed full lookup. If you had a router
with a large routing table *and* a default route the routing table was checked
then the packet was forwarded according to the default so it could cause the
same problem at the nest router. The real crippler was where a random address
hit a valid subnet within the network, and the taget router had to ARP for lots
of nonexistant addresses...
[1] I know it was not totlly random, but near enough...
P.
--
Paul Matthews
paul@cattytown.me.uk
http://www.hepcats.co.uk
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