Odd, Native VLAN question

davegibelli · ‎01-30-2007

I have a 3745 with a 34 port ethernet card.

I configure port 2/0 as a trunk. I create interface vlan 1 and assign it an IP and no shut.

Now, port 2/0 is a trunk and it's up. But why is interface vlan 1 showing "up, down"?

The trunk has native vlan set to 1 by default so - interface vlan 1 should be "up, up" but is isn't!

Anyone explain why?

glen.grant · ‎01-30-2007

You have a port on that ethernet card that is vlan 1 and is connected before the SVI will go up/up , once you get one port in vlan connected the SVI will go up/up.

m-haddad · ‎01-30-2007

Hello,

TO have SVI go up you have to have one of the below cases:

1- One interface assigned to the vlan and in UP/UP state

2- You have a trunk port in Up/UP state

You case matches number 2. However, issue the command "show interface trunk" to check if the port has negotiated as trunk. Also, make sure that the trunk interface is in UP/UP state.

You need to wait for about 15 seconds after the trunk is up so that the SVI goes up.

One last thing to check is that if you layer 2 switch you cann't have to SVIs with IP addresses assigned and UP. One of them showed only be up.

Let me know if one of the above solves your problem and appreciate your rating,

Regards,

m-haddad · ‎01-30-2007

Hello,

TO have SVI go up you have to have one of the below cases:

1- One interface assigned to the vlan and in UP/UP state

2- You have a trunk port in Up/UP state

Your case matches number 2. However, issue the command "show interface trunk" to check if the port has negotiated as trunk. Also, make sure that the trunk interface is in UP/UP state.

You need to wait for about 15 seconds after the trunk is up so that the SVI goes up.

One last thing to check is that if you layer 2 switch you cann't have TWO SVIs with IP addresses assigned and UP. One of them showed only be up.

Let me know if one of the above solves your problem and appreciate your rating,

Regards,

davegibelli · ‎01-31-2007

As you say in case 2, I should see the SVI up but it isn't. I think this is a bug because the trunk is up and all other tagged VLAN SVI's are up.

Only the native VLAN is not coming up but there is an interface up because the native VLAN port is up.

glen.grant · ‎01-31-2007

Maybe you can post the trunk setup on both sides . I doubt it is bug .

m-haddad · ‎01-31-2007

What type of Switch is it?

If it is L2 switch you can have ONE SVI up!

Regards,

sundar.palaniappan · ‎01-31-2007

Dave,

Do a 'show int (trunk_port) switchport' and check whether vlan 1 is allowed on the trunk. Sometimes, pruning (manual or vtp pruning) mightn't be forwarding data on a trunk for a certain vlan.

HTH

Sundar