Understanding VLANs

MarkJeffers · ‎05-22-2006

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?

Anand Narayana · ‎05-22-2006

answer for question 1.

YES, each VALN should have different gateway.

on layer3 switch configure vlan2 interface IP as 10.96.100.1, vlan 3 10.96.101.1 & vlan 4 as 10.96.102.1.

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answer for question 2.

you can configure DHCP server on layer3 switch itself, by the following.

ip dhcp pool department1

network 10.96.100.0 255.255.255.0

dns-server

domain-name test.com

default-router 10.96.100.1

ip dhcp pool department2

network 10.96.101.0 255.255.255.0

dns-server

domain-name test.com

default-router 10.96.101.1

ip dhcp pool department3

network 10.96.102.0 255.255.255.0

dns-server

domain-name test.com

default-router 10.96.102.1

ip dhcp-server 10.96.100.1

ip dhcp-server 10.96.101.1

ip dhcp-server 10.96.102.1

Note: on layer2 switch, specify the vlan on the ports, based on that, the pc will pick up the ip address from the respective DHCP pool.

hope this helps,

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