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

[jason.plank at comcast.net]

Grant,

The concepts here are simple:

Layer 2: VLan only, no layer 3 interface.
Layer 3: Vlan and SVI created

Now, if you have a layer 2 vlan and no corresponding layer 3 SVI, your traffic won't be routed because there is no layer 3 interface to handle the routing. If your trunks are set up and the layer 3 is being serviced from the 6500, then that's the only place layer 3 should happen.

The easiest thing for you to do here, is post your configurations.

--
Regards,

Jason Plank
CCIE #16560
e: jason.plank at comcast.net

 -------------- Original message ----------------------
From: "Grant Moerschel" <gm at wavegard.com>
> The only SVI configured on the 3560 is the VLAN1 interface. Is this
> incorrect?  My assumption was that the V1 SVI, a default route for V1,
> and "no ip routing" was all that was needed but when I did that I
> couldn't talk with the other VLANs on the switch.  I may have overlooked
> something.
> 
> Given my description of the 3560 (routing on, one SVI for VLAN1, one
> trunk to the core), do you think that the local V8 traffic on the 3560
> is being routed via VLAN1 in contrast to being tagged and forwarded as
> VLAN8 via the trunk to the core?
> 
> -----Original Message-----
> From: Mike Louis [mailto:MLouis at nwnit.com] 
> Sent: Monday, April 14, 2008 12:11 PM
> To: Grant Moerschel; cisco-nsp at puck.nether.net
> Subject: RE: [c-nsp] L3 vs. L2 trunk connections to a 6509 core.
> Easyrouter-head question.
> 
> 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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