VLANS / DHCP

[cpc]

If you have multiple vlans and one dhcp server, what are the options for providing dhcp services to multiple vlans using a single server ?

 

[wybnormal]

UDP forwarding.. IP helper... No different then a "normal" router and passing broadcast based traffic.

Mike S
"Diplomacy; the art of saying 'nice doggie' till you can find a rock" Wynn Catlin

 

[AidanEnos]

if you go to

http://www.routergod.com

you can read a great article on this very topic entitled

"Trinity on IP-Helper Addresses"

AidanEnos

 

[marks66]

IP Helper will get you going.

However it's my understanding that the IP-Helper command will forward ALL broadcasts to the helper address. This is know to cause problems with Microsofts computer browsing elections.

To aviod having a DHCP server for each VLAN, and forwarding traffic , try a network card in the DHCP server that supports ISL trunking. Once connected to a Cisco switch as a trunk you can configure multiple interfaces on the DHCP so it has a presence in all VLANS. (Intel Pro 100 works OK)

Cheers

Mark

 

[wybnormal]

Whoops... it doesnt forward ALL broadcasts.. just ten of the most common. The issue with MS comes from both a timing issue ( timeout waiting for master browser) and how WINS is configured on the clients. Cisco has a nice white paper detailing the issues....

Cisco;s paper:

http://www.cisco.com/warp/public/473/winnt_dg.htm

IP Helper

http://www.cisco.com/univercd/cc/td/doc/cisintwk/ics/cs006.htm

Ports opened by ip helper:
Trivial File Transfer Protocol, Domain Name System, Time service, NetBIOS Name Server, NetBIOS Datagram Server, Boot Protocol, and Terminal Access Controller Access Control System.

MikeS "Diplomacy; the art of saying 'nice doggie' till you can find a rock" Wynn Catlin