From: ccie2be (ccie2be@nyc.rr.com)
Date: Fri Mar 14 2003 - 14:29:25 GMT-3
Hi,
Like yourself, I've been trying to get myself up to speed on the 3550 and I
think I can answer your questions correctly. I hope that if I say something
that's wrong or not completely correct, somebody here on GroupStudy will
correct my thinking.
So here goes:
Re: L3 EthChannel - the concept is surprisingly simple - it's just a link
between 2 logical routed interfaces and because its L3, the 2 interfaces on
each end of the link share a common IP subnet. Its purpose is just to
provide greater bandwidth between the 2 devices and due to the nature of
EthChannel it also provides a level of redundacy and flexibility (depending
on how many ports you include in the EthChannel determines the bandwidth of
the link). The important thing to keep in mind with a L3 EthChannel is that
it can't be a trunk - the link will carry the traffic of only 1 vlan and
that traffic isn't tagged. In other words, a L3 EthChannel behaves just
like any Ethernet link between 2 routers except that it has greater
bandwidth.
To configure a L3 EtherChannel on a 3550, do the following:
1) Create the logical interface
conf t
int port-channel X
no switchport (Remember, by default ports are L2 -
this makes it L3)
ip addr x.x.x.x m.m.m.m
end ( I don't why or if this is
needed)
2) Assign ports to the logical interface
conf t
int range x-x (You can also assign ports 1 by 1 instead of
using the range keyword)
no ip addr (You already assigned the ip addr at the
logical interface level)
channel-group X mode xxx (where mode specifies type of PAgP
negotiation)
end (I still don't why or if this is needed)
Regarding your 2nd question, this is my understanding:
An SVI is a logical L3 interface just like a BVI. It's the way the L2 ports
in the same vlan as the SVI are able to communicate with devices on other
subnets whether or not those devices are connected to the switch or not.
Remember that when you create a SVI you associate that SVI with a particular
vlan. So, for example, say you have 6 ports in vlan 6 and you create a SVI
as follows:
conf t
interface vlan 6
no switchport
ip addr x.x.x.x m.m.m.m
no shutdown
end
Here's what happens when a packet starts from a PC connected to a port in
vlan 6 heading for a device in a different subnet. Once the packet hits the
switch its tranparently bridged to the SVI based on normal switch behavior.
Once it hits the SVI, the route process does a route table lookup and routes
the packet to its next hop destination which could be another SVI interface
or an actual physical L3 interface.
Again, this is only the way I understand it. It makes sense to me but I
could be wrong and if I am wrong, I hope somebody here will correct me.
Jim
----- Original Message -----
From: "cebuano" <cebu2ccie@cox.net>
To: <ccielab@groupstudy.com>
Sent: Friday, March 14, 2003 12:04 AM
Subject: Need clarification on SVI and Layer 3 Etherchannel
> Hi group.
> I need to clarify (and simplify) my studies on SVI and L3 Etherchannel.
> 1. What is the purpose of having a L3 (routed) Etherchannel? I hope it's
> not just to have a 800-Mb P2P link running IP routing.
> 2. Is SVI used only to route between VLAN's INTERNALLY in the same
> switch? The configuration guide seems to indicate this type of interface
> is used to "bridge" between VLANs internally thereby keeping the router
> doing inter-VLAN routing from doing the work. Can you "span" this
> VLAN-to-VLAN routing between two 3550s if they have a trunk connection?
>
> Thanks in advance for the replies.
>
> Elmer
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