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3com 4200g & 4500

3com 4200g & 4500

3com 4200g & 4500


I currently have an isp that provides a seamless bridge for our site to site communications.  Both sides are  This Will be cleaned up at a later date.

We are going to be moving to another ISP that has a much different configuration.

Site A we have fibre coming in and are have a media converter providing 2 vlans from the isp.  1 vlan is for the site to site and the other is for internet.

vlan 200 = site to site
vlan 201 = internet

Site B we do not have to configure any vlans it just requires a port with 100mbit and in access mode to get the site to site network.

My issues are with getting the site to site to work.

Site A = 3com 4200g
Site B = 3com 4500

So here is what I have done so far....

I have a spare 4500 so I was able to test this setup without interupting business.

on the 4200g we have the media converter(fibre) going into Trunked port 45 vlan 200.
on the 4200g we have port 44 set to access mode vlan 200
on the 4500 port 25 access mode(default vlan) is patched into port 44 of the 4200g.

Plug my laptop into the 4500 and I am able to connect to the other side no problem.

Once I patch the 4500 into another switch it kills the connectivity.

Setting all switches to vlan 200 is out of the question because we will be putting in vlans at a later date.

Does anybody know why I lose connectivity when I uplink this switch?

RE: 3com 4200g & 4500

I don't understand what your 4200g "trunked port 45 VLAN 200" is for.
But with the 4200g-4500 connection, what you are doing is bridging VLAN 200 on the 4200g and VLAN1 on the 4500.

Now I haven't ever tried bridging VLANs on any kind of 3COM switches, but on other switches I have found that some switches allow it and log errors while other switches disable ports if they detect a VLAN mis-match.
Check your switch logs.
If your switches don't allow bridging, then you have three choices:
 - Use VLAN 1 to connect the sites
 - Use VLAN 200 to connect the sites
 - change to a routed link and re-address averything at SiteB

RE: 3com 4200g & 4500

The trunked port 45 is because the isp that provides the site to site also provides internet addresses to us.  So we trunk the mediaconverter into the switch so that we can have access to both vlans that are on our 100mbit circuit.  vlan 200 being site to site and vlan 201 being our block of static ips for internet use.

Thanks for the feedback in regards to the logs, I bet that its going into some type of protection mode.  I'll do some more research and let you know,  thanks again.

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