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The first step is to designate which types of broadcast packets to forward. The first command says to forward broadcast UDP packets to the Bootp client port. This seems to cause broadcast NetBIOS name server and datagram distributor packets to be forwarded as well. We found that the next two commands will stop the NetBIOS forwarding.

SZT#conf t
Enter configuration commands, one per line.  End with CNTL/Z.

SZT(config)#ip fo udp bootpc
SZT(config)#no ip fo udp netbios-ns
SZT(config)#no ip fo udp netbios-dgm

The next step is to define to whom to forward the packets, the "ip helpers". First define which ethernet interface you wish to configure. The next thing we did was to get rid of all forwarding targets so that we could start with a clean slate. The last command defines the IP addresses of the forwarding targets. We only defined one but you can specify more (though I don't know how many).

SZT#conf t
Enter configuration commands, one per line. End with CNTL/Z.

SZT(config)#int e 1
SZT(config-if)#no ip help
SZT(config-if)#ip help

Finally, you need to notify the router that it is to act like a BOOTP relay agent. This means that, when the router forwards a broadcast Discover packet, it should put its IP address in the giaddr field of the BootP part of the packet. Without this the DHCP server can't know from which subnet(s) to allocate an IP address.

SZT#conf t
Enter configuration commands, one per line. End with CNTL/Z.

SZT(config)#ip b?

SZT(config)#ip bootp ?
server Enable BOOTP server

SZT(config)#ip bootp s
SZT(config)# Support Home

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