Understanding VLAN's

[Welby24]

I’ve got a couple question on VLAN’s. If I have a subnet for a location such as 10.96.100.x, with a mask of 255.255.252.0, and a gateway of 10.96.100.1.

This gives me access to four class C size blocks:

10.96.100.x
10.96.101.x
10.96.102.x
10.96.103.x

Know lets say that I want to place a layer 3 Switch at the top of my network, turn each of these blocks into their own VLAN (VLAN 2, 3, and 4,) and route between the VLAN’s.

Question 1: Prior to the VLAN’s my gateway for my entire subnet was 10.96.100.1. After configuring my VLAN’s, will each VLAN have a different gateway or do all of them still operate with their original gateway?

Question 2: Again, prior to VLAN’s I had one DHCP server for the entire subnet. Do I know need a different DHCP server for each VLAN or is there a way I can configure one server to provide DHCP service for all four VLAN’s?

 

[jneiberger]

#1: They will each have their own gateway. What is a default gateway, after all? It's the IP address of a routed (router) interface on the *local* LAN. Once you subdivide your /24 into multiple /22 subnets, 10.96.100.1 is no longer local to the other subnets and can no longer be the default gateway for the other subnets. Your router (the L3 switch in your design) will have four routed interfaces, and each interface will need to have an IP address from its associated subnet.

#2: Yes, a single DHCP server can do this. It just needs to be reconfigured so that it understands your new addressing scheme. You'll then need to configure IP helper addresses, along with IP directed broadcasts, to forward DHCP requests from other subnets to your DHCP server. (I just realized that I'm assuming you're using Cisco gear. If you're not, you'll have to figure that part out for yourself. <g>)

 

[jimbopalmer]

The Nortel gear I have used also uses Directed broadcast (broadcast to unicast and back conversion) to allow you to use 1 DHCP server for the whole network.

I tried to remain child-like, all I acheived was childish.

 

[rn4it]

udp helper, directed broad caset or udp profiles .... Welby24 you may need to look into your user giudes for your switch/routers to find the proper command to forward broadcast traffic to another vlan. Cisco calls this udp-helper and Extreme calls it udp-profile.