[afnog] VLANs on Cisco Catalyst 2950

[Mark Tinka]

On Friday 26 May 2006 10:29, Patrick Okui wrote:

> each VLAN on the switch. Effectively we had to do an
> int vlan blah
> ip address 1.2.3.4 5.6.7.8

Hmmh, that's not really necessary. It's only important to assign 
one IP address to one VLAN interface, typically, the 
one/backbone from which you will be running daily maintenance 
routines.

It's not that necessary to have a VLAN interface for each 
configured VLAN on a(n IOS) switch.

> short of that and the switch would *not* trunk the traffic
> from that VLAN over the trunk port(s). crazy no?

Which switch-IOS version combination were you running when you 
faced this problem.

Ordinarily, in IOS, a switch will fail to trunk ports from 
another VLAN if that VLAN is not explicitly defined in the VLAN 
database (hence the need for VTP if you have multiple switches). 
However, the switch (if the VLAN database is properly populated) 
will still trunk ports even though a corresponding VLAN 
interface is not explicitly defined.

In addition, if ALL switch ports are in a VLAN and none of those 
VLANs is VLAN 1, your management VLAN interface will have to be 
from one of the configured VLANs on the switch - and you'll only 
need that one to manage the switch.

A VLAN interface is generally needed to manage the switch 
(telnet, ssh, snmp, e.t.c.), and is not a pre-requisite for 
Layer 2 functionality of the switch.

I can confirm this configuration on desktop switches including 
2924XL, 2950-T and 3750-TS, all running IOS's released this 
year.

Cheers,

Mark.
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