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New Member

Vlan Issue

I have a switch that is assigning IP's from different VLAN's. This is happening when a user is gone for more than a week. When they return they get a wrong IP from a different VLAN. this is very strange and I was wondering if anyone has seen this before.

11 REPLIES
New Member

Re: Vlan Issue

is the port that the user is connected to the switch it is assign as access or trunk port?

New Member

Re: Vlan Issue

It is a trunk port

New Member

Re: Vlan Issue

Make it an access port and assign the vlan that you want this pc to be connected.

New Member

Re: Vlan Issue

is the port that the user is connected to the switch it is assign as access or trunk port?

New Member

Re: Vlan Issue

It needs to be trunked port as IP phone is also conneted to it.

New Member

Re: Vlan Issue

Sorry my knowledge is up to there.May be you should ask someone more experience on that.

Thanks

New Member

Re: Vlan Issue

Hi kanwar,

Did you configured any DHCP on ur router?

Plz. make sure that port is trunk port / access port, if the user connected to particular port that port should be access port.

regards,

naidu.

New Member

Re: Vlan Issue

Hi Kanwar

Make sure encapsulation between switch and ip-phone are same. It is correct that switch port must be trunked and NOT access port.

HTH.

Cheers

Joe

Silver

Re: Vlan Issue

It's really not about trunks or access settings.

Station can only communicate with untagged frames - i.e. through NATIVE or ACCESS vlan (unless it's an unusual special case).

This station send untagged packet for a DHCP request. This packet is BROADCAST, so it ends up either on the DHCP server that is put into the same segment (if that's the case, look for DHCP misconfiguration). Or if there is helper-address set up on the SVI (router interface) of that segment, that converts that broadcast into UNICAST and sends it to a DHCP server. DHCP server than uses the SOURCE ADDRESS of the packet (in this case, the address of the SVI - the router interface) to find from which DHCP SCOPE to assign an address. If that's the case, look for SECONDARY ip addresses on SVI, or check subinterfaces - there has to be only one per VLAN. If there are more than one, all of them have to be in the same subnet (e.g. HSRP).

Hope this helps.

Please rate all helpful posts.

New Member

Re: Vlan Issue

Port settings are Native VLAN is 112 and trunk settings are 802.1q. This layer two port is connected with the core where Layer 3 settings are pointing to the DHCP server with the IP helper command. The DHCP server is also Pingable from the access switch too. The address it is getting is a public VLAN and is separated by firewall and control by an acl. It was working for a long time and nothing changed that would cause this.If you connect a laptop it gets a 192.168.100.X address and you can manually configure 192.168.112.x on that port and it works too. It looks like it is happening to only workstations that are off and send a new dhcp request.

New Member

Re: Vlan Issue

Thanks everyone. we found the problem. Outside network was linked to inside network.

Regards

Kaiser

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