6509 and 4948 Switch Routing Question

[NPT_2]

We have a 6509 switch in our core that handles routing between dozens of VLANs with it's MSFC.  I'm connecting a remote Layer 3 4948 Switch to the 6509 via a Gigabit Fiber Link. 

The 4948 will be connected to servers on a couple subnets as well as an alternate internet connection that I would like to have the 4948 route between locally but also send traffic to the VLAN's on the 6509.  We are using EIGRP as our internal routing protocol. 

The question I'm running into is whether I can setup a trunk link between the 6509 and the 4948, VTP, and setup EIGRP to route only using one of the trunk VLANs and between the local VLANs (with SVIs) and routed ports or would it be best to just setup a routed port to connect to one VLAN on the 6509. 

The advantage I see if the trunk idea is feasible is that I can allocate certain ports to be access ports and go back to the 6509 to route and not be affected by local routing on the 4948.  I absolutely do not want the 4948 to take over routing of my entire network as it will be on the edge and the 6509 is the core switch/router. 

The advantage with using the 4948 connected to the 6509 as a routed port is that nothing on the 4948 will interface with the 6509 at Layer 2 and I can also keep VLAN's local to that switch.  On the downside though this would prevent me from setting up VLAN's that span across the network connected to the 6509 or other areas of the network. 

My other question is whether I should use the same EIGRP AS# on the 4948 so it interacts and shares routes with the 6509 or use a separate AS# to keep things isolated. 

Any thoughts or ideas on these questions? 

[Reza Sharifi]

Since the 6509 has all the SVIs for your vlans, I would just have a layer-3 connection from the 6509 to the 4948 and not span vlans across multiple devices. Also, there is no need to complicate things by having multiple EIGRP AS numbers. Use the same AS number for both devices.

HTH

[NPT_2]

Thanks for the advice.  

I would assume then I would simply assign one physical port on my 4948 with an IP address with the no switchport command and  then set the ip address configuration rather than assign a SVI identical to the subnet connected to on the 6509?

Then could I create a new VLAN on the 4948 for the servers with an SVI to point my servers to as their default gateway.  I could then use eigrp to get routes shared between the switches and across my network.  I'm assuming I could just assign the physical port on the 6509 to one of my vlans as an access port (old 6509 CATOS so I don't have the "no switchport" configuration option).  

Also, will it cause any problems if I have the same vlan setup on both switches (even though I'm not trunking them) as long as I don't use the same ip address space on each?

Does that sound about right?

Any other thoughts or suggestions?

Jim

[Reza Sharifi]

Jim,

You can do this in 2 ways. 

1- A routed port between the 6500 and 4900 with a /30 IP subnet and assign an IP to each device.

2-An access port belong to a unique vlan with SVIs and the IP on each side goes on the SVI.  This could also be a /30 or a bigger subnet. Since your 6509 does not support the command no switchport, then you need to use option 2.

And yes, you create a new vlan for your servers and the default gateway for your servers would be the 4900.  Add the vlans on each device to your EIGRP process and also add the /30 in between and you should be good to go.

HTH

[NPT_2]

I guess I'll have to go with option #2.  Would there be an issue using "no switchport" and an ip address on the physical interface on the 4900 (since this will only be one port) and an SVI interface on the 6509 with an ip address assigned to the SVI?  Would this route ok or cause issues?  

Jim

[Reza Sharifi]

That should not be an issue

The 4900 should not care if the other side is in a vlan or not (not trunk of course )

If it gives you any issue you can also add the same vlan to the 4900 side and give it an IP

HTH