From: Bryan Osoro (bosoro@xxxxxxxxxxx)
Date: Thu Nov 08 2001 - 00:09:04 GMT-3
Reason for this happening is normal
Dot1q in Cisco's implementation does NOT tag VLAN traffic on the "Native
VLAN" Native VLAN on ports is 1, by default. Therefore VLAN 2 and 3
traffic is getting to the router with Dot1q information in every frame,
and VLAN 1 is NOT getting tagged. The router considers VLAN 1 to not be
"encapsulated," and I bet if you had a debug ip packet detail on you'd
see encapsulation failed when the PC sends the ping to the router. Up
until 12.1 IOS could not do anything to fix this, now there is a native
vlan command that makes the router aware of the switches behavior.
Other fix is to change the native vlan on the switch to be some number
that is not in use (i.e. 888) or some random number.
-Bryan
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
steven.j.nelson@bt.com
Sent: Wednesday, November 07, 2001 8:20 AM
To: cchurch@USTA.com; erickbe@yahoo.com; ccielab@groupstudy.com
Subject: RE: VLAN trunking and 802.1Q
Guys
This should do the trick, note the table regarding dot1q support and IOS
versions.
http://www.cisco.com/warp/customer/473/50.shtml
Thanks
Steve
-----Original Message-----
From: Church, Chuck [mailto:cchurch@USTA.com]
Sent: 07 November 2001 14:32
To: 'Erick B.'; 'ccielab@groupstudy.com'
Subject: RE: VLAN trunking and 802.1Q
Erick,
Do a 'sh trunk':
WP-4006-1> sh trunk
* - indicates vtp domain mismatch
Port Mode Encapsulation Status Native vlan
-------- ----------- ------------- ------------ -----------
1/1 on dot1q trunking 1
1/2 auto dot1q trunking 1
2/1 auto dot1q trunking 1
2/2 auto dot1q trunking 1
If your trunk port doesn't show 'trunking' as a status, it won't work.
Try
setting the mode on both ends to on, rather than auto or desirable. Are
you
running fairly recent GD code on the router and switch?
Chuck
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Erick B.
Sent: Wednesday, November 07, 2001 1:45 AM
To: ccielab@groupstudy.com
Subject: VLAN trunking and 802.1Q
Hello there,
I've been playing around with some VLAN stuff lately
and have seen some odd behavior with trunking and I
can't find a answer so thought I'd see if anyone here
knew, because it is bugging me.
Real basic setup.
Cisco router with FE connecting to a switch. VLANs 1,
2, and 3. Workstation on switch in VLAN 2 and VLAN 3.
Dot1Q trunk with all VLANs defined. Sub-interfaces on
router for dot1q. Ping from PC in VLAN2 to VLAN3 and
don't get further then router interface for that VLAN.
Change to ISL encaps and everything works fine. Change
back to Dot1Q and things continue to work. Save
configs and reload switch and routers and things
continue to work.
I also had a similar thing when I didn't configure a
VLAN1 sub-interface on the router (just 2 and 3). Once
I added VLAN1 thing started working. Took VLAN1 away
for kicks and things still worked. Weird.
Any one have any thoughts???
Thanks, Erick
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