How to forward a TCP/UDP broadcast to another VLAN on a Cisco switch?

Question

I have client software which sends out a broadcast on some TCP and UDP port numbers. The broadcast it sends out is designed to look for the server. But the server is sitting on another VLAN so the broadcast ends. I've heard of ip-helper but have no idea what command to use to forward the broadcast to travel to the correct VLAN and find the server. Any help appreciated.

Solution 1

you can use the ip helper-address command on a vlan interface to forward all broadcasts in this vlan directly to a host (mostly used for dhcp) or to another broadcast address.

example: broadcasts in vlan 10 are send directly to host 10.1.2.1 in vlan 20:

interface vlan10
  ip address 10.1.1.254 255.255.255.0
  ip helper-address 10.1.2.1
!
interface vlan20
  ip address 10.1.2.254 255.255.255.0
!

example: broadcasts in vlan 10 are send to broadcast address of vlan 20

interface vlan10
  ip address 10.1.1.254 255.255.255.0
  ip helper-address 10.1.2.255
!
interface vlan20
  ip address 10.1.2.254 255.255.255.0
!

Solution 2

you'll want to look into the cisco command "ip directed-broadcast" to achieve want you want to do. note, this isn't a recommended configuration for security reasons.

Comments

[cpt_fink]

Only the default protocols are forwarded, if you need others then you can use the 'ip forward-protocol' command to specify what should be forwarded.