Cisco – Handling Multiple ‘ip helper-address’ Statements

ciscodhcp

I've discovered a subnet with two "ip helper-address" statements. This is not our normal configuration.

interface Vlan300
 ip address 10.1.3.2 255.255.255.0
 ip helper-address 10.2.1.10
 ip helper-address 10.3.1.10

Looking at our DHCP servers, it seems that there are leases coming from both of them.

I realize this is not recommended, and the two DHCP servers might not be aware of each other's lease assignments (I'm pretty sure they don't).

The question is, how is this handled by the Cisco switch (4510 Sup7 12.2)?

  • Is it the first DHCP server to respond?
  • Is it the first one, then the second one if the first one times out?
  • Is it round robin?

Best Answer

The ip helper-address command designates an address which broadcasts are forwarded to; it will send the original packet to each of those listed addresses.

If both reply, both replies are forwarded back to LAN.

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