IP Helper Address

As in any network, broadcasts are used to find and discover end systems. In a Layer 2 environment, you use broadcasts to find an end system's MAC address. Layer 3 of the TCP/IP model, IP also uses broadcasts for such services as sending IP datagrams to all hosts on a particular network. Broadcasts on any network consume CPU and bandwidth to reduce this even more. In an IP network, you use the IP helper address to change a broadcast into a more specific destination address so not all devices must view the IP data, which conserves bandwidth.

To save on bandwidth, all Cisco routers installed with Cisco Internet Operating System (IOS) software by default have an algorithm that dictates that not all broadcast packets be forwarded. So to allow the ability to forward packets wisely, you can use the IP helper address command to convert a broadcast into a more specific destination address. The command to enable an IP help address is as follows:


   ip helper-address 
   address

You can configure more than one helper address per interface on a Cisco router. The IP helper address forwards packets that are normally discarded by default to the following services:

  • Trivial File Transfer Protocol (TFTP)
  • Domain Name System (DNS)
  • BOOTP server
  • BOOTP client
  • NetBIOS Name Server
  • Dynamic Host Configuration Protocol (DHCP)

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