2960 VLAN Trunk configuration

Answered Question
Apr 22nd, 2008

I just got 2 new C2960 Switches and want to set up "switchport mode trunk" for f0/48 of sw1 connects to f0/47 of sw2. On sw1, I configured vtp mode as server and the domain name as c2960. and I think the encapuslation is 802.1q by default(it's not configurable). But,

1. once I connect two switches, sw2 got vtp domain even it's on server mode, but no VLAN advertisement recieved.

2. after configuring the vtp mode as client and the domain name as c2960 on sw2 which same as sw1, it sitll can't get the VLAN advert from sw1.

3. when I configure the duplex full for both trunking interfaces on sw1 and sw2, all the interfaces went down. I have to use duplex auto. why?

Please advise, thank you.

I have this problem too.
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Correct Answer by m_zabetian about 8 years 9 months ago

Check Version of VTP for each switch, also

check your trunk and make sure trunking is working

show vtp statu

show interfaces trunk

Correct Answer by Jon Marshall about 8 years 9 months ago

Can you check the revision number in the output of a "sh vtp status" on SW1 and ensure that it is higher than the revision number on SW2. If it is the same modify the vlan database on sw1.

Jon

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Correct Answer
Jon Marshall Tue, 04/22/2008 - 11:56

Can you check the revision number in the output of a "sh vtp status" on SW1 and ensure that it is higher than the revision number on SW2. If it is the same modify the vlan database on sw1.

Jon

David Lin Wed, 04/23/2008 - 06:26

Yes, I just realized the Revision issue. I changed it and now it's working fine.

Also, the duplex issue on giga interface doesn't happen again.I can use it for trunk now even I reset both 2 switches. Weird...

Correct Answer
m_zabetian Tue, 04/22/2008 - 12:08

Check Version of VTP for each switch, also

check your trunk and make sure trunking is working

show vtp statu

show interfaces trunk

lamav Tue, 04/22/2008 - 13:39

Hello:

Posting the switch configs may make it easier for us to analyze what's going on.

Thanks

Victor

ANDREW LEOPOLD Tue, 04/22/2008 - 14:33

Would suggest going back to basics:

1> all ports in auto mode is fine. validate they negotiate SAME speed and duplex.

2> have one in VTP server mode and the other in client mode.

3> both ports MUST have same native vlan on trunk. switchport trunk native vlan xxx.

4> insure both are encapsulated in dot1q. switchport trunk encapsulation dot1q.

5> insure both ports trunked. switchport mode trunk.

6> by default they should pass all vlans and I will leave it to you if you desire to restrict.

Suspect if you force duplex then it would be best to force speed. Otherwise, leave both speed and duplex in auto mode.

David Lin Wed, 04/23/2008 - 06:35

Yes, I did it. The problem is revision number. But the duplex issue on the ports doesn't happen after I successfully got VTP advert. I don't know why...

Thank you anyway.

glen.grant Tue, 04/22/2008 - 15:57

You are probably using a straight thru cable to connect the switches and the auto mdix function is being used. Auto mdix only works when the ports are set as auto . If you want to hardcode the ports get a crossover cable and use the "no mdix auto" command on those interfaces then you can hardcode speed and duplex.

David Lin Wed, 04/23/2008 - 06:42

I tried either straight cable and crossover cable are working now. Don't know why.

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