Understanding DHCP on multiple subnets 2

[MattWray]

I am VLANing my hq network here this weekend. When doing so, I am using 1 DHCP server to host all the subnets. I understand how the DHCP server knows how to hand out addresses to the remote clients via IP Helper, but what I don't understand is how it knows not to hand out "wrong" addresses to local clients attached to the same VLAN/segment.

Can anyone help me to understand this? I've been trying to get my head around it for days now....

Thanks,

Matt Wray

GFH

http://www.sss-steel.com

 

[WhoKilledKenny]

When you say "wrong" do you mean duplicate addresses (because in same vlan)? DHCP verifies the address is not currently in use before sending the offer.

Since Windows NT 4.0 Service Pack 2 (SP2), it provides updated code to assist DHCP in detecting and flagging duplicate IP addresses. Functionality has been added both at the client and at the Windows NT DHCP server.

Hope I understand what you are asking.

 

[GlenJohnson]

The easiest thing I can think of is just read the link below.

http://www.freesoft.org/CIE/RFC/2131/24.htm

Glen A. Johnson
If you like fun and sun, check out Tek-Tips Florida Forum
"Creditors have better memories than debtors."
Benjamin Franklin (1706-1790); US author, diplomat and inventor.

 

[MattWray]

Thanks for the replies!

Kenny, no I didn't mean a duplicate address. Let me try to clarify. I have server A (dhcp server) on a 192.168.77.x network. VLAN A is 192.168.76.x and VLAN B is on 192.168.75.x.

Now I understand how VLAN A and B will get the correct IP's via IP helper through the Catalyst switch.

What I am confused on, is how the server knows not to give machines on the local segment a .76.x or .75.x address.

Glen, thanks for the link, but I really didn't follow it too well.. lol...



Thanks,

Matt Wray

GFH

http://www.sss-steel.com

 

[avilov]

If a request comes as a broadcast, than the client is on a local subnet. If it comes as an unicast with source IP from the clients subnet, than the client will be given IP from the that subnet.

 

[MattWray]

If a request comes as a broadcast, than the client is on a local subnet. If it comes as an unicast with source IP from the clients subnet, than the client will be given IP from the that subnet.

ok, that makes sense. And I take it the DHCP server will "just know" the local subnet because of the address of its own interface, is that right?

Thanks,

Matt Wray

GFH

http://www.sss-steel.com

 

[MTVW]

yep

 

[MattWray]

Got everything up and running this past weekend. Thank you all for the help, its nice to understand something before trying to implement it.






Thanks,

Matt Wray

GFH

http://www.sss-steel.com