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VLAN automatically shutting down and more

Dear All,

I have some special problems with my network. I think i missed out something while configuring or my solution is not right.

First case:

I have a 3750 12S, thats with 12 Gigabit ethernet interfaces. One link from there is connected to 6509 at the data center and is configured as an ip link with addrs. i have default route on the 3750 pointing to the ip configured on 6509 for the p2p link. There is vlan 1 in series and vlan 25 in series configured on 3750

The is then connected directly to another location 'A' having 2950 L2 switch. The link between the 3750 and 2950 is a trunk.location A has vlan 1 configured in series and vlan 25 configured in series. Default g/w for the 2950 is the vlan 25 ip configured on the 3750. the problem is that at location A, thats the 2950, i can have only one vlan in up position at any time. when i gave no shut in int vlan 25, the connectivity breaks, next time i login, vlan 1 is in shut position. when i give no shut in vlan 1, vlan 25 goes to shut mode..... what could be the problem ? the 6509 acts as the root bridge for vlan 1 and the 3750 acts as the root bridge for vlan 25. i am running per vlan spanning tree.

Case 2:

The 6509 at data center is connected to a location having 2950 L2 switch. in the vlan 1 of 2950 i have configured ip and acts as g/w address for my PCs connected to it, and a secondary ip for the p2p link between 2950 and 6509. default gw for the 2950 is the ip configured in the 6509 for the p2p link. The problem is my 2950 switch can ping to my dns server (both when source ip as ip n/w and addrs in th extended ping) at data center placed in n/w. but any pc connected to the switch with g/w as the vlan 1 ip of the 2950, cannot ping to the dns server .......

can any body help with some advice

thanx in advance

lots of love


HCL Infosystems,



Re: VLAN automatically shutting down and more


The 2950 series switches only support 1 layer 3 interface, this is used for the management vlan. You can only have one interface vlan ... active. All other vlans should be layer 2. If you create a second interface vlan ... you will shut down a previously created one. If interface vlan ... is shut, you will not get any traffic to pass on this vlan.

You do not have to have IP presence on both of your VLANs on each device. As long as the vlans are consistant and are in the same domain, and at the core both vlans have IP presence all should work fine.

New Member

Re: VLAN automatically shutting down and more


so in the 2950 at location A i dont assign an IP for the int vlan 25 and instead assign an ip for the int vlan 25 configured on the 3750 switch, assign the PCs the same as their default g/w all shld work fine for, isn't it ?

Re: VLAN automatically shutting down and more

As long as both vlans can traverse the trunk at layer 2, and vlan 1 and 25 exist on both switches, you do not need to create an interface vlan 25. Just put the appropriate ip address on interface vlan 1, and ensure it is not shutdown.

If the PC plugs into a port on the 2950 that is assigned to be in vlan 25, configure the default gateway on the pc to be that of the interface vlan 25 on the 3750.

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