Redundant DHCP server
If you want to build a truly redundant LAN infrastructure, you should also have redundant DHCP servers. If you decide to do the DHCP address allocation locally (on the router), you should take care that the two routers acting as DHCP servers don't assign overlapping addresses.
If the address space assigned to a LAN is at least twice as large as the number of LAN-attached devices, you can use the ip dhcp excluded-addresses command to exclude half of the address pool on each router, for example:
ip dhcp pool LANAlternatively, you can rely on the ip dhcp ping packets command; the router will ping an IP address to check whether it's live before assigning it (by default, the router sends two pings with 500 millisecond timeout).
network 192.168.1.0 192.168.0.0 255.255.255.0
!
! Exclude router addresses
ip dhcp excluded-addresses 192.168.0.1 192.168.0.10
!
! Exclude half of the pool
ip dhcp excluded-addresses 192.168.0.128 192.168.0.255
Note: You can also inspect the conflicting IP addresses the router found with the show ip dhcp conflict command.
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5 comments:
Little mistake:
192.168.1.0 has to be 192.168.0.1
Actually, it has to be 192.168.0.0 :) ... although your suggestion will work as well. Fixed.
To use dhcp conflict logging, doesn't one have to have a storage location configured?
I generally configure "no ip dhcp conflict logging" as the router will broadcast for a tftp server to put the file on if left default. Or at least so I've been told.
"router(config)#ip dhcp database ?
WORD Uniform Resource Locator (URL)"
Hi All,
Is there any way to have some kind of redundancy between a windows dhcp server and a Cisco router ?
Thanks
You can use the same trick to achieve router/Windows redundancy, just make sure you use two separate address ranges.
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