From: Aaron T. Woland (aaron.woland@ins.com)
Date: Tue Mar 14 2006 - 13:04:43 GMT-3
That is because the switch will not tag the native VLAN, and the router has
no way of identifying which Sub-Interface it would be destined for without
the tag.
So by putting the "native" keyword on the sub-interface, the router knows to
accept the untagged frames on that sub-interface.
Does that make sense, or should I re-word?
-Aaron
Aaron T. Woland | Consultant | INS | Email: aaron.woland@ins.com |
Website: www.ins.com
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
ccieben@cox.net
Sent: Monday, March 13, 2006 9:25 PM
To: ccielab@groupstudy.com
Subject: Native Vlan tag/no-tag question?
Hello,
I have the following attached to a 3550:
Port 0/1 - trunked back to a Router A. I am allowing Vlan 10 & 20 & stating
that 20 is native.
Port 0/5 - a Vlan 20 access port attached to Router B.
Router A & Router B are both on the same subnet.
With the 3550 in its normal state - Router A & Router B cannot ping each
other. Once I add the command:
3550(config)#vlan dot1q tag native
Router A & Router B are able to ping each other... I thought that command
would only be useful in an SP environment where 1Q/L2 tunneling was being
performed.
I thought these untagged packets were automatically part of vlan 20? What
is the logic of why these devices can't "speak".... can someone help me
understand the logic?
TIA - Ben
***Router A
interface Ethernet0/0.20
encapsulation dot1Q 20 native
ip address 172.16.17.1 255.255.255.0
end
***Router B
interface FastEthernet0/0
ip address 172.16.17.6 255.255.255.0
end
***3550
interface FastEthernet0/1
description to ROUTER-A
switchport trunk encapsulation dot1q
switchport trunk native vlan 20
switchport trunk allowed vlan 10,20
switchport mode trunk
end
interface FastEthernet0/5
description to ROUTER-B
switchport access vlan 20
switchport mode access
end
3550#show int trun
Port Mode Encapsulation Status Native vlan
Fa0/1 on 802.1q trunking 20
<snip>
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