802.1q header removed in catalyst?

Jun 15, 2006 4 Replies

Hello,



I have question, I'm trying to setup a 802.1q vlan lab envirement. I see PC 1 sending a ICMP package to the catalyst switch, it includes the 802.1q bytes. from the switch towards PC 2 I see the ICMP package comming out but with the 802.1q bytes removed.



On the catalyst I have a simple configuration:



Switch#show running-config Building configuration...



Current configuration: ! version 12.0 no service pad service timestamps debug uptime service timestamps log uptime no service password-encryption ! hostname Switch ! ! ! ! ! ! ! no spanning-tree vlan 1 ip subnet-zero ! ! ! interface FastEthernet0/1 ! interface FastEthernet0/2 ! interface FastEthernet0/3 ! interface FastEthernet0/4 ! interface FastEthernet0/5 ! interface FastEthernet0/6 ! interface FastEthernet0/7 ! interface FastEthernet0/8 switchport trunk encapsulation dot1q switchport trunk native vlan 666 switchport mode trunk ! interface FastEthernet0/9 switchport trunk encapsulation dot1q switchport trunk native vlan 666 switchport mode trunk ! interface FastEthernet0/10 ! interface FastEthernet0/11 ! interface FastEthernet0/12 ! interface VLAN1 no ip directed-broadcast no ip route-cache ! ! line con 0 transport input none stopbits 1 line vty 0 4 login line vty 5 15 login ! end


What is wrong, the 802.1q bytes should be in the header during the complete transport? From client till Destination?



Who can help me.


thx.



CU



Roel Villerius


I suppose that PC1 is sending frames with VLAN 666. You specified on Fa0/8 and Fa0/9 that the native VLAN is 666, the switch will remove this tag when forwarding a packet in the native VLAN.

Two solutions to have the tags : * use another native VLAN (by default it is VLAN 1) * use "vlan dot1q tag native" to tag the native VLAN.

Indeed there is no concept of native VLAN with ISL. All VLANs are systematically tagged.

Join the Discussion

Have something to add? Share your thoughts — no account required.

Didn't find your answer?

Ask the community — no account required