Help with VLAN and 3Com 3300 Switch

[Venger]

Have a client with a 3Com 3300 switch...they are trying to create a number
of VLAN's that tier into a single port...i.e.

Port 1 - VLAN 1,2,3,4
Port 2-4 - VLAN 1
Port 5-7 - VLAN 2
Port 8-10 - VLAN 3
Port 11-13 - VLAN 4

So that Port 1 appears on all VLAN's, but traffic is isolated from the
VLAN's to each other. This would allow a server for instance to reside here,
or a router, etc...

Thing is, this doesn't seem to work on the 3Com. If you assign a port to
more than one, it cannot see anything except in it's first VLAN.

Is this by design? Would it require the optional 3Com Layer-3 switching
module to properly work?

Even though it's a new switch, 3Com will not help saying they need a service
contract - pretty cruddy huh, especially on new gear.

Any help would be appreciated...email replies especially...

Thanks,

Venger

[mortime...@my-deja.com]

In article <dMt56.168671$IP1.6...@news1.giganews.com>,

The way 3Com equipment works (if I remember rightly) is this:

If you define a port to be a member of multiple VLANs, then you have
effectively defined it as an 802.1q trunk with the complication that
the first-defined VLAN is untagged. This is the "native" VLAN for this
port. Therefore any traffic which is received without 802.1q
encapsulation on that port is inferred to be a member of its native
VLAN and propagated out on other ports as necessary for the VLAN.
Likewise, any traffic received on any other port for the native VLAN is
propagated out of the trunk port untagged, if necessary. Other VLAN
traffic is propagated out of the port using 802.1q encapulation, which
is not normally understood by end stations.

The way to achieve what you are aiming at is to define the port as a
trunk port using 802.1q encapsulation on all its associated VLANs -
including the native one - and only using devices hanging off this port
which understand 802.1q encapsulation. A number of network cards and
operating systems are capable of supporting 802.1q, including NT,
Netware and Linux, and Intel and 3Com cards. However, be aware that
not all NICs have 802.1q-capable drivers for all operating systems.
Check compatibility matrices carefully.

An alternative - and more conventional - approach would also be to use
a router (i.e. layer 3 card) to route between VLANs, but it's not
strictly necessary for the problem you describe. In fact it has the
potential disadvantage that you will end up enabling routing between
all the VLANs and potentially introduce a security issue (which you may
have to address using access control filters), whereas the system you
describe will only allow inter-connection between the server VLAN and
all the others.

Hope this helps...

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