Native Vlan in trunk does not work

[scjlin]

Hi I have question regards to native vlan in the trunk port.
I have a Cat 4503 (Switch A) running CatOS and is running L2 switching only. It had a trunk port setup and connect to Cat 3750 (Switch B), and it had another turnk to another Cat 3750 (Switch C). I had setup all three switches's Native vlan in trunk to be Vlan 99 witch is for switch management vlan only. Now the problem is I can't ping switch B or switch C from Switch A. But I can ping switch B from C or C to B. However, other vlans reside in that trunk are working fine. Just native vlan seems does not work across from Switch A to Switch B.

Cat 4503 (switch A) <--> Cat 3750 (switch B) <--> Cat 3750 (switch C).


Thanks in advanced

SL

 

[vipergg]

Maybe you can post the configs , on catos it is as simple set vlan slot/port and this sets the port for native . Are you sure the trunk is working correctly on the catos box ? Do a show trunk on the catos and a show int trunk on the 3750. On catos the vtp domain name "must" match the vtp domain name on the 3750's for the trunk to work . Is the native vlan allowed across the trunk on both the catos and the 3750 ?

 

[scjlin]

Thanks for promptly reply:

Here is link to the show trunk from both 4500 and 3750.

http://www.deccax.dreamhosters.com/logs/show_trunk.txt

Yes, both are in same vtp domain, and set native as 99.

In switch _B the gi1/0/23 is to switch C and gi1/0/24 is connect to switch_A

THe vlan 100 works on between these 3 switches but not vlan 99.

Many thanks,


SL

 

[vipergg]

Make sure int Sc0 on the catos box is set in vlan 99 , do a "show int" on the catos and it should say 99 right before the address starts . should look like sc0: flags=63<UP,BROADCAST,RUNNING>
vlan 99 inet xxx.xxx.xxx.xxx netmask 255.255.255.128 broadcast xxx.xxx.xxx.xxx The trunk looks correct.

 

[scjlin]

The SC0 in Cat 4500 is not on vlan 99. the SC0 is on vlan 100.... Is there anyways I can get around it by keeping the same ip on SC0? IE, create another interface and reside in vlan 99?

many thanks,


SL

 

[vipergg]

Just change the SC0 to 99 if it is in the 99 subnet address range . The address is determined by the subnet address range , is the current address in the vlan 99 range or in the 100 vlan range . If it is in the 100 range then you would have to assign it an address and mask out of 99 range and set sco to vlan 99. If for some reason it is currently in the 99 range but the vlan is just set to 100 then just do a "set int sc0 99" command .

 

[scjlin]

Thanks for the tip. However after I change the sc0 interface to be vlan 99 and same network as switch B and switch C. I still can't ping across the trunk. It was working fine when switch A was native vlan in 100 and switch B native in vlan 1 (Yes, there is native mismatch, but traffic for vlan 99, and 100 works fine). Until I correct the native mismatch problem on both switches to be 99 than I lost the switch B and switch C in vlan 99 (Management vlan).

Many tanks

SL

 

[vipergg]

Hard to say much else without seeing how the catos is configured and the switch that is attached to the catos switch. If they are truly in vlan 99 on both sides and the addresses are ijn the same subnet it has to work . something still not configured correctly..

 

[123tech]

Hello,

Try entering this command on switch B (and then Switch C if it didn't work with the command on switch B alone).

vlan dot1q tag native

 

[scjlin]

I set the default trunk on both switch A and switch B to be native on 1, and now it works. However, I do like to set the native vlan on both switch to be vlan 900.....

Thanks for 123tech input on vlan dot1q tag native. I look it up, and I think this command is more like for when you have multiple vlans tunnel thought your native vlan and you tag the navtive vlan. But thanks for suggestion.

SL