Unable to add allowed VLANs to TenGig trunk port

[bgfl-tech]

Hi,

I've got a ten gig interface on a 6509 running 12.2(33) configured as a trunk, but I've not been able to add any allowed VLANs as I've done before on other ten gig ports on different 6509 chassis. Am I missing something obvious?

I'm assuming that the reason I'm unable to set the encapsulation to dot1q is because the new hardware doens't support ISL, hence no need. The command to add the VLANs however doesn't get rejected, it just doesn't appear to do anything.

I've tried adding single VLANs and multiples, but no joy. Any ideas?

Here's what I've done:

SWITCH_1631(config)#default int t4/1
Interface TenGigabitEthernet4/1 set to default configuration

SWITCH_1631#sh ru int t4/12
Building configuration...
Current configuration : 65 bytes
!
interface TenGigabitEthernet4/12
 no ip address
 shutdown
end

SWITCH_1631(config)#int t4/1
SWITCH_1631(config-if)#switchport
SWITCH_1631(config-if)#switchport mode trunk
SWITCH_1631(config-if)#switchport trunk allowed vlan ?
  WORD    VLAN IDs of the allowed VLANs when this port is in trunking mode
  add     add VLANs to the current list
  all     all VLANs
  except  all VLANs except the following
  none    no VLANs
  remove  remove VLANs from the current list
SWITCH_1631(config-if)#switchport trunk allowed vlan add 700
SWITCH_1631(config-if)#
SWITCH_1631#sh vlan id 700
VLAN Name                             Status    Ports
---- -------------------------------- --------- -------------------------------
700  VLAN_NAME                        active    <snip>

SWITCH_1631#sh ru int t4/1
Building configuration...
Current configuration : 74 bytes
!
interface TenGigabitEthernet4/1
 switchport
 switchport mode trunk
end

[Steve Fuller · Accepted solution]

Hi,

If you're using the switchport trunk allowed vlan add 700 command isn't this just "adding" VLAN 700 to a trunk that by default allows all VLANs anyway?

What do you see when you run the show interface trunk command?

Regards

[bgfl-tech]

Steve,

Thanks for getting back to me. You're right that it is by default a dot1q trunk allowing all VLANs, therefore it should work for what I want to do.

Port                Mode         Encapsulation  Status        Native vlan

Gi3/39              on           802.1q         trunking      1
Te4/1               on           802.1q         trunking      1
Po1                 on           802.1q         trunking      50
Po2                 on           802.1q         trunking      50
Po3                 on           802.1q         trunking      50
Po4                 on           802.1q         trunking      50
Po5                 on           802.1q         trunking      50

Port                Vlans allowed on trunk

Gi3/39              15-16,20-23,30,401,608
Te4/1               1-4094
Po1                 10,13,20-21,25,30,50,52,61,70,600,700-701,950
Po2                 10,20,30,50,52,61,70,600,700-701,950
Po3                 10,20,30,50,61,70,600,700-701,950
Po4                 10,20,30,50,61,70,600,700-701,950
Po5                 2-3,10-23,25-26,30,35-36,40,50-53,56,58,61,65,70,77,101-102,145-146,155-158,401-402,600-602,608,700-701,800,950

The problem was that I've always been advised that best practise is to only allow the VLANs that are actually required on a trunk to avoid broadcasting traffic unnecessarily. I worked out what the issue was though, and it was a pretty simple one!

Once I saw that 1-4094 was allowed I tried "switchport trunk allowed vlan remove 700" which worked and left me with 1-699,701-4094.

Then I realised what the problem was  trying to use the "add" command when all possible VLANs had already been added. As soon as I got rid of it and used "switchport trunk allowed vlan 700" followed by "switchport trunk allowed vlan add 701" I was back in business.

So it was a very simple issue, but thank you Steve for pointing me in the right direction and confirming that all the VLANs were already allowed!

[DimaL]

ISL is not used in modern networks, it is old protocol. As was stated by Steve, all VLANS are allowed to pass by default via trunk.