Mark's clarification at the "higher" end of the spectrum is
excellent. Let me add some comments at the "lower" and "highest"
ends.
In selecting equipment, never look at performance alone. Look at
price-performance. I've had any number of situations where putting
two or more low-end routers or switches next to one another was more
cost-effective than moving to the next higher product family.
Now, consider a situation where you make extensive use of VLANs. You
have clients in one or more buildings, connected via campus fiber to
a server room where most servers are either dedicated to one VLAN, or
are VLAN aware. In such a configuration, you only need Layer 2
switching for most servers. Backup traffic passes over a dedicated
VLAN to which major servers are connected with a separate NIC.
Assume the users have very little or no Internet connectivity
requirement. They do need to reach a shared mail server. The largest
inter-VLAN requirement, however, is network management, ranging from
pinging, to SNMP polling, etc. from the management side, and
infrastructure functions from the client side: DHCP, DNS, etc.
Given very little inter-VLAN, routed traffic, it might very well be
cheaper to connect a free-standing 2600 to a Fast Ethernet port than
to use a high-performance "layer 3 switching module".
Distributing all layer 3 processing is still related to the points
that Mark makes. You are specializing functions in the box that is
best matched to the requirements. Indeed, a low-end box with
multiple fast Ethernet ports still might be the best choice for a
situation where you need lots and lots of 10/100 ports and the
switching is primarily among those ports.
At the highest end, the 12000 series is optimized for inter-ISP
forwarding, and will outperform a 6500 in the environments for which
it is designed. Again not optimized for campus applications, things
like the 5300/5800/AccessPath and Service Selection Gateway are
optimized for other workload patterns.
>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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