Finding the network of a VLAN

I was recently asked where I work to add a cubicle port to a specific network (let's say, 192.168.101.x). I discovered which VLAN that switchport belonged to, but how do I discover which network the VLAN is in? There is a command for that, but I've forgotten it.

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DPG

What are you using for the vlan interfaces? A router or layer 3 switch?

pham0329

I'm a little confused. Why do you need to know what network that VLAN is on? Couldn't you just switch it over to the correct VLAN (assuming you know what VLAN you're suppose to switch it to)?

Look on one of your L3 switch and look at the vlan interface for that VLAN, or just plug in a PC to the port and look at the IP it gets. Or, the best solution, look at your network documentations! If you don't have one, now would be a good time to make one!

Cat5

There are about ten different VLANs set up on the access and distribution switches. I need to add this port on the 2950 switch to this network, which belongs to a particular VLAN. I can log in to the switch from my terminal, but I dont' have the keys to the switch closet at the moment in order to just plug in.

*Note - I did find the networks listed with the associated VLANs in the distribution switch through a program we use. I'm still curious as to that command I had seen once. If I find it, I'll post it here. Thanks.

**Note - found the command: show ip route | include <network> You can also put in part of the network (like 192.168.62).

WiseWun

Cat5 wrote: »

There are about ten different VLANs set up on the access and distribution switches. I need to add this port on the 2950 switch to this network, which belongs to a particular VLAN. I can log in to the switch from my terminal, but I dont' have the keys to the switch closet at the moment in order to just plug in.

*Note - I did find the networks listed with the associated VLANs in the distribution switch through a program we use. I'm still curious as to that command I had seen once. If I find it, I'll post it here. Thanks.

If it's Cisco, type the following command and you should see the network address for that vlan.

show interfaces vlan <vlan interface number>

Cat5

Here's my problem: the switch port is in the correct VLAN/network; I can plug a computer into the cubicle jack and get a link light fine, and the computer is set for DHCP, but I only get a 169.x.x.x IP address. I also get a link light on the switch in the closet (going through a patch panel). I had swapped out ethernet cables in the cubicle to test, but they're fine. He should be pulling an IP address from that network, but he's not. I wonder if it's a DHCP problem.....?

WiseWun

Cat5 wrote: »

Here's my problem: the switch port is in the correct VLAN/network; I can plug a computer into the cubicle jack and get a link light fine, and the computer is set for DHCP, but I only get a 169.x.x.x IP address. I also get a link light on the switch in the closet (going through a patch panel). I had swapped out ethernet cables in the cubicle to test, but they're fine. He should be pulling an IP address from that network, but he's not. I wonder if it's a DHCP problem.....?

Yes, it's def a DHCP issue. You get the 169 aka APIPA address when DHCP is not available. Did you force to renew the IP address? Another option is to give it a static IP.

Monkerz

Is the DHCP server setup on the L3 switch (PC's default gateway)? If not, does your VLAN interface have a helper address configured to forward DHCP requests?

Cat5

WiseWun wrote: »

Yes, it's def a DHCP issue. You get the 169 aka APIPA address when DHCP is not available. Did you force to renew the IP address? Another option is to give it a static IP.

Yes, I tried a release/renew, but the renew command just sat and sat... It wouldn't renew. I did make sure that the required VLAN is configured on every switch in the path (there's only three). I want to take the user's computer and jack it directly into the 2950 switch and see if he still can't get a valid IP. That'll tell me a lot more. Waiting to hear back from him.

Cat5

Found the problem. The 2950 switch connected to a 3750 switch, which has "vlans allowed 52" in there and no others, so my vlan couldn't get past it. I had to add my VLAN in there. Something to remember.