dot1q trunking with C2600

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Nov 26th, 2007
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I have a 2600 connected via an ethernet interface to a 6500. I have configured a dot1q trunk between then but cannot ping across them. The C2600 can see that the 6500 is advertising the correct native VLAN, but the 6500 sees Native Vlan Unknown. Both sides are set to use a native VLAN of 10.


I get the following debug output.

debug ip packet

00:01:55: IP: tableid=0, s=x.x.x.x (local), d=y.y.y.y (Ethernet0/1.10), routed via RIB

00:01:55: IP: s=x.x.x.x (local), d=y.y.y.y (Ethernet0/1.10), len 100, sending

00:01:55: IP: s=x.x.x.x (local), d=y.y.y.y (Ethernet0/1.10), len 100, encapsulation failed.


debug arp

00:05:47: IP ARP: sent req src x.x.x.x 00b0.6418.2b81,

dst y.y.y.y 0000.0000.0000 Ethernet0/1.10


Any advice would be great ? I am running c2600-ik9o3s-mz.122-31

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keller.oliver Tue, 11/27/2007 - 01:34
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I had the same "encapsulation failed" error due to a mismatch of trunking protocol :


One site (older router) defaulted to ISL, the other (switch) did DOT1Q as expected.


use "show interface [interface] switchport" to get the trunk protocol information, output should look similar to this :


CoreSwitchA#sh int f0/9 sw

Name: Fa0/9

Switchport: Enabled

Administrative mode: trunk

Operational Mode: trunk

Administrative Trunking Encapsulation: dot1q

Operational Trunking Encapsulation: dot1q

Negotiation of Trunking: Disabled


... (omitted)




ATB,


Oliver



Kevin Dorrell Tue, 11/27/2007 - 01:53
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Could you post the configs on both sides please?


I do remember there was a bug in some versions of 12.2 relating to native VLAN. If I remember correctly, (which maybe I do not), the only way to do native VLAN was to configure the base Ethernet interface of the router with the IP address of the "native" VLAN. The native keyword on a sub-interface did not work.


Kevin Dorrell

Luxembourg


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