Question : VLAN 2 on 3Com 5500 with fiber SFP causes problems on default VLAN 1

We've always had a rather flat (i.e. limited routing) network, so we haven't done much with VLANs in the past.  We tried it once before, but encountered the same basic problem.  When I bring up the new VLAN 2 (i.e. enable the ports or physically link them), the "core network" (default VLAN 1) has trouble.  Connectivity appears fine (i.e. ping-able), but performance suffers greatly, behaving like a loop exists (although not so severe that the network crashes.)

Goal:
Create a segregated/separate VLAN for WiFi (192.168.1.x)

Internet comes in location 1 through a clustered pair of Watchguard x1250e firewalls.  This new VLAN interfaces with the firewall on an optional port (192.168.1.1).  Based on user credentials and SSL authentication at the firewall, access is either granted to the internet (primary purpose), the internet and core LAN, or denied.  I'm not concerned with that at this point, as it is the VLAN itself that is giving me trouble.  This simply illustrates that the VLAN should be completely separate (i.e. no routing) outside of the firewall.  The trouble is in delivering the VLAN 2 to another building via single mode fiber.

- I can ping the VLAN 2 interface on the 5500 at location 1 (192.168.1.2), from 10.210.x.x (core network)
- With the link up, I can ping the VLAN 2 interface on the 5500 at location 2 (192.168.1.3)
- I think STP may be causing the problem, especially since our aggregated link is broken at the moment (construction moving fiber.)

Part of the problem is that our 3Com 5500 (3CR17254-91) switches are the newer switches.  Our core switches are 3Com 4900 fiber switches, only one of which supports VLANs (original died, new one has new software on it,) preventing me from passing VLAN traffic over the WAN link.  An aggregated pair of single mode gigabit ports link these two buildings together.  Each 5500 is then linked via multimode to the 4900 in their respective buildings.

I thought it would be easier to simply create a second direct fiber link between the 5500 switches, assigned to VLAN 2.  Since it is a second physical link, there is the potential for a loop, but I can't see where that is possible in the programming.  Originally, the ports for this link between the 5500 switches was set as trunked, tagged VLAN 2.  I have since changed them to access ports, untagged VLAN 2, thinking that perhaps the switches were trying to route 10.210.x.x over the trunk for some reason.  No change in behavior.

Not being familiar with 3Com CLI, I have done most of the work on the 3Com switches via the GUI, which may be a great part of the problem.  And I have not yet poured over the programming as presented in the CLI.

We also have another network with a Cisco 3560 switch in location 2 and a 2950 in location 1, with their own fiber WAN link.  Plan B would be to create the VLAN on that equipment.

Attachments:

WiFi-VLAN.jpg (28 KB) (File Type Details) 

Diagram

3com5500Location1.txt (7 KB) (File Type Details) 

3Com 5500 Location 1 Programming

3com5500Location2.txt (8 KB) (File Type Details) 

3Com 5500 Location 2 Programming

Answer : VLAN 2 on 3Com 5500 with fiber SFP causes problems on default VLAN 1

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