3550 stacking and vlan trunking

[DOUGLAS EVANS]

After reading some of the posts I'm a bit confused. Can I have a stack of four 3550 24 port switches, stacked with gigastack with the redundant link look like a single switch without clustering, have two Gigabit uplinks on in the top switch, one in the third switch, multiple vlans configured and vlan trunking on the uplinks ? (Uplinks will terminate on a 4507R)

Thanks

Devans

[milan.kulik]

Hi Douglas,

I'm glad to see your question.

My opinion is:

1) A stack of four 3550 24 port switches will never look like one switch even with clustering. You need to cluster the new 3750 switches to reach the true clustering features. The "clustering" on 2900/3500/2950/3550s is just a Cisco marketing game, the only real effect is displaying all the switches on one screen in CMS software.

2) Regarding VLANs:

Everything would work if you connect your stack in full-duplex mode, i.e using just one port on each GigaStack GBIC (it requires two GigaStack GBICs in each switch).

BUT when using BOTH ports on GigaStack GBIC the connection between particular switches changes to half-duplex bus and you are not able to establish trunks in the stack.

This is my personal opinion and I had an argue with one guy in this forum. He said trunking works even on half-duplex bus in stack.

Unfortunately I don't have multiple 3550s in my lab and so I can't test it to prove who's correct. Would you be able to test this problem?

Regards,

Milan

[milan.kulik]

I was not correct.

Trunking works on GigaStack half-duplex connection.

But it's necessary to use switchport mode trunk and switchport nonegotiate interface configuration commands.

See http://www.cisco.com/univercd/cc/td/doc/product/lan/c3550/12114ea1/3550scg/swvlan.htm#1096213 for details.

Regards,

Milan

[m.sir]

I have expirience whit this. You can trunk stacked switches. Normaly trunk all up links than RELOAD all switches after reboot you should see all configured VLANs from VTP server