Hello to all,
I would like to clarify some of the process of MLS using the 6500
chassis. What actually gives you the performance increase is the PFC card
that is also installed on the supervisor module along with the MSFC. MLS
uses the MLSP protocol. This protocol is the communication layer between the
RP in the MLS process and the SE. The RP is the Route Processor and the SE
is the Switching Engine. Using the MLSP protocol the RP informs the SE of
the MAC Addresses of the L3 interfaces in the chassis. The SE caches this
information. The cache it uses is a shared cache that is used by the other
processes that can use the MLS process(Multicast and IPX). The cache is
configurable. The SE is the PFC with an ASIC for this task. When a packet is
at the ingress, the SE logic sees it and being that it is destined for a MAC
address that it knows about it keeps L3/L4 info. This is called a candidate
packet. After an egress interface decision process(CEF, Fast switching), the
packet is put back on the backplane. When the SE sees that the source is
from a mac address it knows about, it checks it cache, it will have a match,
via the candidate entry. This second packet is called an enabler packet.
After the enabler packet the SE ASIC, handles all of the L2 re write
information at the much higher speed, taking processor load of off the CPU
of the MSFC.
It is possible to have the RP located externally from the chassis. A
single RP can service multiple SE capable devices. A situation where you may
use this is if you have several 6500 using regular CatOS code(say 5.4 or
so). The supervisor modules do not have to have the MSFC, but can have the
PFC, so they are capable of MLS but they do not contain the necessary RP
logic. This is solved via the external router to perform the RP function and
to use the MLSP process to inform the SE which resides on the 6500 chassis
of the necessary information. Deployment could be a centralized router
function witch has an interface in the different respective vlans residing
in a particular switch or multiple switches. This allows the non L3 capable
switches to use the MLS process.
Thanks
Mark Anthony Clarke
Netigy
CCIE #5198, CCNP, Voice Specialist, LAN ATM Specialist
MCSE, CNA
-----Original Message-----
From: Tony Olzak <[EMAIL PROTECTED]>
Newsgroups: groupstudy.cisco
To: [EMAIL PROTECTED] <[EMAIL PROTECTED]>
Date: Saturday, July 15, 2000 11:34 PM
Subject: Re: Multilayer Switching vs. External Router
>In multilayer switching, say as in a 6500 series switch with a MSFC
>integrated into the supervisor, the performance is much better than using
an
>external router. The host hits their configured gateway (the IP address of
>the VLAN interface on the MSFC) and the MSFC creates a virtual path through
>the switching fabric for the source MAC address to hit the destination MAC
>address. Only the first packet has to go through the router. The rest of
the
>packets will traverse the virtual path that allows any packets from the
>original source to the destination to be multi-layer switched (does not
need
>to hit the router again). This virutal path stays up until the configured
>timeout expires and the virtual path goes away.
>
>This whole process allows the switch to effectively route the packets at
>layer 2 instead of layer 3. Using an external router, your packets would
>have to exit the switch, hit the router, then come back to the switch to
>their destination. See the difference?
>
>
>Tony Olzak, CCNP, MCSE
>
>jeongwoo park <[EMAIL PROTECTED]> wrote in message
>[EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
>> HI all
>> I have a quick question.
>> Why would one think that Multilayer Switching(such as
>> Catalyst 5000) is better than just external router, or
>> vice versa?
>> Is one faster than the other?
>>
>> Thanks in adv.
>>
>> jeongwoo
>>
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>
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