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vlan problem on a school campus

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Tuukka Peltoniemi
Occasional Visitor

vlan problem on a school campus

hi!

i know they say that one who asks isn't stupid, but still this question makes me feel like one :)

my problem is as follows: i'm trying to set up vlan to an college campus. i have succesfully configured five different vlans throughout the campus switches (all our switches are procurves). as we are a part of bigger "educational"-network we don't have access to our router nor the dhcp-server which are configured from elsewhere. is it possible to set up vlan's succesfully without the ability to configure the router nor the dhcp-server?

current situation is that all the vlan's are brought to switch that is connected closest to router. when i configure computer to be a member of different vlan than vlan 1 (id = 1), that computer doesn't get it's ip-address. i read the discussions concerning this issue, but i didn't understand it well enough to know if this is possible. i tested and configured ip helper-address (in vlan id 20) to closest switch to point to our dhcp-server but it still doesnt get ip-add.

thanks in advance,
tuukka
3 REPLIES
Joel Belizario
Trusted Contributor
Solution

Re: vlan problem on a school campus

When you create a new VLAN you are creating a separate layer-2 broadcast domain so the only way traffic is getting there is via layer-3 routing.

Since VLAN 20 does not have an IP address it cannot communicate with VLAN 1. You will need to assign an IP address to VLAN 20 (let's say x.x.29.1) and then enable IP routing on the switch or configure your router to route between the VLANs.

Then you have to create a corresponding scope on your DHCP server (x.x.29.x) and add the ip helper-address (DHCP server IP) to VLAN 20.

So to answer your question, yes you will need assistance from whoever manages your router / DHCP or get authorization to make changes yourself.

Also, have a read of this document from Cisco regarding LAN switching and VLANs:

http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/lanswtch.htm

Hope this helps!
Mohieddin Kharnoub
Honored Contributor

Re: vlan problem on a school campus

Hi

Additionally to Joel,

You need to create a route to this Vlan 20 in your router so it will have access to outside world.

Say you created a Vlan20 with IP address, then place a PC in untagged port to Vlan20, you need to add a static route on the router saying, if yo uwant to go to Vlan20 with a.b.c.d IP address, then go to Vlan1 IP address.

Also, i noticed that you tagged port 50 to Vlan20, and i guess you are doing routing on the 2650 switch, otherwise if you want to go for routing between Vlans on the router, then all the Vlans should be tagged on Port50 except Vlan1 untagged.

Good Luck !!!
Science for Everyone
Tuukka Peltoniemi
Occasional Visitor

Re: vlan problem on a school campus

thanks for pointing out the direction ... i forgot to mention earlier that i don't need to have any communication between vlans (if dhcp connection isn't counted as one). but if i understood your replies correctly, this doesn't change the fact that i still need to get in touch with company that governs our router/dhcp-server!

thanks again,
tuukka