Directly from CCO... To forward the initial DHCP requests from the host to the appropriate DHCP server, you should apply the ip helper-address command to the interface which is receiving the broadcasts. After the broadcasts are received, the Cisco IOS looks at the configuration of the ip helper-address for that interface and forwards those requests in a unicast packet to the appropriate DHCP server whose IP address is specified in ip helper-address. After the DHCP server replies with the IP address, it sends the response to the interface on the router that originally forwarded the request. This is used as the outbound interface to send the DHCP server response to the host that originally requested the service. The router also automatically installs a host route for this address. http://www.cisco.com/warp/customer/794/routed_bridged_encap.html
HTH Dwayne -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf Of Gaz Sent: Tuesday, November 27, 2001 5:34 AM To: [EMAIL PROTECTED] Subject: Re: DHCP Question [7:27380] Dave said: "The only reason for this I can fathom is because the DHCP request is no longer a broadcast it now has the source address of the router interface that the helper address is setup on and it seems DHCP will take this into account when dishing out addresses." That's exactly the assumption I've always made, but I'm not totally convinced. I'd like to sniff the packet and actually see whether it's dependant upon the source address or something contained within the packet. As per usual IF I get chance I'll put a sniffer on. Anybody know for sure? Gaz wrote in message [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... > As mentioned in an earier reply..you must have your DHCP Scopes > correctly set up > > I've found that with NT4/W2k DHCP servers > that, If for example your DHCP server is set up to dish out addresses > in the > range of 192.168.1.1 to 100 mask 255.255.255.0 and it receives a > request for > an address directed from the helper routers interface which has an > address of 10.1.1.1 (which means your DHCP clients will be on the same > network) it will ignore that request. The only reason for this I can > fathom is because the DHCP request is no longer a broadcast it now has > the source address of the router interface that the helper address is > setup on and it seems DHCP will take this into account when dishing > out addresses. > > I've found that if a scope in the 10.1.1.0 range is setup on the > server my DHCP clients will recieve an IP address in the correct 10. > range with no problem. > > I have two scopes on my DHCP server > 172.16.60.1 - 172.16.61.254 Subnet 255.255.254.0 and 10.222.36.1 > -10.222.37.254 Subnet 255.255.254.0 > > my router interface configured to forward DHCP reqests is set up as follows > .. > ip address 10.222.36.2 255.255.254.0 > ip helper-address 155.131.60.40 (MY DHCP SERVER address ) > my DHCP clients never get an address from the wrong range if i disable > the 10.222.36.0 range my dhcp clients behind the router don't get an > address at all ... > > Hope this make sense and helps and if i'm talking pants please someone > put me straight ... > > Regards Dave Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=27447&t=27380 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
