Multiple DHCP pools shared settings

[Gary Jeffers II]

Should the less-specific mask of POOL3 result in both POOL1 and POOL2 handing out dns-server 192.168.1.2?


ip dhcp pool POOL1
network 192.168.1.0 255.255.255.0
!
ip dhcp pool POOL2

network 192.168.2.0 255.255.255.0
!
ip dhcp pool POOL3
network 192.168.0.0 255.255.0.0
dns-server 192.168.1.2
!
ip dhcp excluded-address 192.168.1.1 192.168.1.10

[Petr Lapukhov 4xCCIE]

Hi,

Per Cisco IOS DHCP pool matching behavior the DHCP attributes are collected from all matching pool, with more specific match being preferred. Essentially, pools are grouped in "child-parent" manner and the attributes are collected by traversing the hierarchy. In your case, POOL3 will supply DNS server for requests matching POOLs 1 and 2 as any of these requests will also match POOL3.

If you have access to a live router, use the command "debug ip dhcp server linkage" on the server to see how the DHCP pools are linked in "child-parent" chains when a server receives the request. This helps in complex situations with multiple overlapping pools.


HTH

[Gary Jeffers II]

Thank you very much Petr. That answers my question perfectly. I'll test out that debug command