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Home > Archive > alt.certification.cisco > March 2003 > Strange VLAN Problem on switch
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Strange VLAN Problem on switch
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| I have a strange problem that I cannot fathom, maybe someone can help
please?
I have a 7204 router connected to a 3548 switch, one port of the switch
connects to another switch (2924). The router uses sub-interfaces and dot1q
encapsulated VLANS and feeds several of these to the first switch via a port
on the switch that is set into trunk mode.
The two switches connect to each other via ports that are also set into
trunk mode.
The problem is that setting up certain vlan ID's on the router works and I
can set an interface on the second switch to see the VLAN, but some don't -
it's as though the first switch doesn't 'learn' about new VLAN's I set up
and only passes the ones it already knows about.
There are no restrictions or filters in place, here's what I mean...
Do a 'show interface fa0/33' on the first switch (port 33 is the trunk port
connected to the second switch) :
Name: Fa0/33
Switchport: Enabled
Administrative mode: trunk
Operational Mode: trunk
Administrative Trunking Encapsulation: dot1q
Operational Trunking Encapsulation: dot1q
Negotiation of Trunking: Disabled
Access Mode VLAN: 0 ((Inactive))
Trunking Native Mode VLAN: 1 (default)
Trunking VLANs Enabled: ALL
Trunking VLANs Active: 1,101-108
Pruning VLANs Enabled: 2-1001
See the line that says which VLANs are Active - only 1,101-108
If I setup a VLAN with ID between 101 & 108 on the router, and use the
command 'switchport access vlan 101' on a port on the second switch - it
works fine, but try setting a VLAN ID on the router of say 109 and it
doesn't work.
Like the first switch isn't 'learning' about the new VLAN ID.
Any ideas or pointers would be appreciated - it's driving me mad !
Thanks,
Chris
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| Hansang Bae 2003-03-30, 8:24 pm |
| In article <b67qin$q76$1@localhost.localdomain>,
chris@NO.SPAM.PLEASE.caladan.net says...
> I have a strange problem that I cannot fathom, maybe someone can help
> please?
> I have a 7204 router connected to a 3548 switch, one port of the switch
> connects to another switch (2924). The router uses sub-interfaces and dot1q
> encapsulated VLANS and feeds several of these to the first switch via a port
> on the switch that is set into trunk mode.
> The two switches connect to each other via ports that are also set into
> trunk mode.
[snip]
> Like the first switch isn't 'learning' about the new VLAN ID.
> Any ideas or pointers would be appreciated - it's driving me mad !
Switches don't learn VLAN information unless you set one as a VTP server
and other others as VTP client. Personally, I find VTP a nuisance and
would prefer to set it up manually on each switch.
Also, the router terminates any and all VTP information. So your router
stops vtp propagation.
--
hsb
"Somehow I imagined this experience would be more rewarding" Calvin
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