Question on IP Helper

[Eric Hansen]

Hello, setting up a new vlan and in adding the IP helper found out that we now have 2 PXE servers(Altiris) on another VLAN and need to account for both. Can there be 3 IP helpers with 2 of them being PXE servers? will that even work?

int vlan x

ip address <>

ip helper-address <DHCP server>

ip helper-address <PXE server 1>

ip helper-address <PXE server 2> ????

ip directed-broadcast 101

end

access-list 101 permit udp host <PXE server 1> any

access-list 101 permit udp host <PXE server 2> any

ip forward-protocol udp 402

thanks

e-

[mahmoodmkl · Accepted solution]

Hi

Yes u can have multiple helper-address uner u r interface.

Thanks

Mahmood

[Eric Hansen]

Any idea if they round robin or anyting like that? Or do they process like an ACL?, which would basically make the second PXS helper useless.

thanks!

e-

[Jon Marshall]

Eric

They are all used at the same time. So a DHCP request is sent by the router to each ip helper-address under the interface. Usually first one to reply to the router is the one used by the client.

Jon

[Amit Singh]

The Cisco IOS can have multiple addresses listed with ip helper address pointing to each of the dhcp servers. With multiple helper-addresses configured, both servers would see the packets, but only the primary server for the scope would normally respond. This would depend on the servers end to distinguish which server would be the primary, there is not anything on the router or Cisco IOS that you can actually do to specify the primary or failover dhcp server.

HTH,

-amit singh

[yuttana_su]

Hi, asingh2

How many "ip helper-address" command per one interface?

Thank you.