Help configuring Point-To-Point T1

I'm kind of confused on exactly what your situation is.

How are you connecting the 3560 to the external CSU/DSU? Do you have a router there too?

Are you wanting to create a VLAN trunk between the two switches? So that you could have a VLAN that spans across both offices? If so, then, I don't think you can really do that. A 802.1q VLAN trunk uses taking in the Ethernet header to identify which VLAN a packet belongs on. The Ethernet headers would be dropped before it goes onto the T1 serial link, because the T1 line does not use Ethernet as a L2 protocol - it uses PPP/HDLC/etc. You also wouldn't really want to have the VLAN going over the WAN because all of the broadcasts on that network would be needlessly forwarded over the WAN wasting bandwidth on the relatively low-bandwidth WAN connection.

You could certainly have VLAN's set up on both sides of the WAN, and use the routers to route between them, but each VLAN would only exist on one side of the WAN.

Sorry if I misunderstood your question.

Ok, here's my situation (with hopefully gorey enough details). Office 1 (current) : 1700 series router (1 WIC port) w/ Internet T1 Bunch of servers (staying put) VOIP PBX (staying put) w/ Voice T1 Currently unused Adtran CSU/DSU 3560 Switch A couple PCs

Office 2 (new): 2851 Router (2 VWIC ports) w/ Internet T1 3560 Switch Bunch of PCs that need server access to the servers at Office 1 Phones that need access to the VOIP PBX at Office 1

Here's what I was hoping to do:

VLAN for servers VLAN for PCs at Office 1 VLAN for PCs at Office 2 VLAN for VOIP stuff

I was hoping to use the 3560 to statically route between the VLANs at the offices by sending the traffic to the specific switchport. So as an example the 3560 in Office 2 would have the server VLAN setup and then have a route to the P-T-P switchport, etc.. Apparently this may not be possible.

What additional hw/reorganization would I need to make it possible?

Thanks.

Also, I emailed Cisco and they said I could use Transparent Bridging to connect the 2 networks over the PPP link.

OK, I think I understand what you're wanting to do now. If your switches support a dynamic routing protocol (even RIP should probably work OK in this case), it might make it a bit easier to configure because you wouldn't have to worry about tons of static routes.

The only places you have to worry about the VLAN's is on the 3560's. You only have to set up the local VLAN's on the local switch. So, the

3560 @ office 1 just needs Office 1's VLAN's added to its VLAN databaset. And the same for office 2.

You just have to configure the 3560's to route between those local VLAN's, and to have the attached router as its default gateway. Then, you have to set up static routes on the routers. So, office 1's router would have static routes to all of the office 1 VLAN's with the

3560's IP as the next hop. And office 2's router would have static routes to all of the office 2 VLAN's with the 3560 at office 2 as the next hop. Then on your routers you should set up static routes to the other office's VLAN's. You would add static routes on office 1's router to all of the VLAN's at office 2 with the office 2 router as the next hop and vice versa.

You should try to use a dynamic routing protocol if you can, it'll make it easier to configure, and easier to change your network structure later on. I think the 3560's should support RIP even if they have SMI, and RIP should work OK in this case. If you are using RIP, then you should just add each of the local VLAN's networks to RIP on each of the 3560's. And just add the networks (ie, the serial link and link to the 3560) that are directly connected to the routers to RIP on the routers at each office. And make sure RIP is enabled for all of the appropriate interfaces. If you have EMI on your 3560's, then I think you are even be able to use EIGRP or OSPF or something much more modern than RIP.

Hope that helps a little,

Oliver

Thanks Oliver. The only caveat is that I don't have another router @ Office 1 - right now it's just a 1720 with a WIC card for the existing T1. Cisco seems to insist that the following configuration works with bridging:

3560 -> 2851 -> p-t-p T1 -> Adtran CSU/DSU -> 3560. Have you ever heard of that?

-- James