There is a vlan5 currently configured with an ip helper-address to forward the broadcast traffic to our DHCP on a different vlan. Works perfectly and everyone is happy.

interface Vlan5
 description Super Vlan 5
 ip address
 ip helper-address (dhcp)
 ip helper-address (netboot server, DeployStudio)

By default, DHCP packets are forwarded (with the ip helper-address), along with other common broadcast traffic.

I'm a little bit concern if that could cause any problems on the long term ? Is there any point to forward all the broadcast packets to the dhcp ? (useless since he doesn't need EVERYTHING when a machine is requesting to netboot ?)

Is there any way to decide which type of broadcast packets goes to which machine ?


ip-helper doesn't forward all broadcasts, just these UDP ports:

Protocol   UDP Port

Time      37
TACACS    49
DNS       53
BOOTP-S   67
BOOTP-C   68
TFTP      69
NetBIOS N 137
NetBIOS D 138
IEN-116   42

You can disable some of these with the command

no ip forward-protocol udp <port number>

But I don't know of a way to forward to different hosts.

  • It actually forwards the allowed protocols to all the addresses in ip helper-address statements on an interface.
    – Ron Maupin
    Oct 26 '18 at 16:27
  • Right, but you can't forward BOOTP to one host and NetBios to another.
    – Ron Trunk
    Oct 26 '18 at 16:35
  • Exactly, it sends any allowed to all the configured addresses.
    – Ron Maupin
    Oct 26 '18 at 16:38
  • @RonMaupin So I don't need to no ip forward-protocol udp the useless ones ? (let's say TACAS, since the DHCP doesn't care that kind of packet)
    – Tolsadus
    Oct 29 '18 at 8:07

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