[c-nsp] L3 vs. L2 trunk connections to a 6509 core. Easy router-head question.

[Mike Louis]

If you are going to use the 3560 as a L2 switch you can disable ip routing. You will need to define a management interface and default-gateway for the management vlan on the switch only. All VLANs including management will be L2 only. Do not configure VLAN SVI if you only want to use the 3560 as a layer 3 switch. Did you configure EIGRP on the 3560 as well? If so that may be why you are getting routing information via VLAN 3 to the 6509.

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Grant Moerschel
Sent: Monday, April 14, 2008 11:45 AM
To: cisco-nsp at puck.nether.net
Subject: [c-nsp] L3 vs. L2 trunk connections to a 6509 core. Easy router-head question.

I am trying to determine what is normal here.  This is the situation. I
have a 6509 Sup1a/MSFC2 running the latest CatOS/IOS for that hardware.
I run EIGRP. I have several VLANs on the core and use VTP.  When I trunk
a 2950 L2 switch to the core I specify VTP on the 2950. No problem. All
VLANs show up on the 2950.  For our eighth floor, for example, I trunk
V1, V8, and V100 and clear all other VLANs from the trunk. V100 is for
Voice and V8 is for most PCs for Data.  My assumption is that if an
access port is "switchport access vlan 8" and the PC is plugged in to
that port, he's on V8. To get off that broadcast network to some other
destination, he hits the gateway which is the L3 interface on the core
6509 MSFC2.  I get all this.

Here's the question.  If my access switch is a 3560 which is a Layer 3
switch, it seems that I have to have it participate in EIGRP to make it
work.  But this does not make sense because for this application I still
have a single trunk to the core from the 3560. If I trunk V1, V10, and
V100 from the 3560 to the 6509, doesn't communication just go down the
trunk to the 6509 L3 gateway?  For example, if my PC is on a 3560 V10
port and needs to hit something on V8, shouldn't the 3560 forward the
frame down the trunk to the 6509 which'll route onto V8, up V8's trunk
to that access switch and forward it out to the destination?   If I look
at my routes on the 3560, they all say "to get to V10 you must go
through the 6509 V1 layer 3 interface" (I hope that makes sense).

Should I turn off "ip routing" on the 3560 in order to mimic the setup
of the 2950 <----> 6509 trunk link?  What am I missing?

Thanks

~~~~
Grant P. Moerschel
WaveGard, Inc.
gm -at- wavegard -dot- com
~~~~


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