DHCP pool and multiple subnet

[maurizio.pederneschi]

Hi all,

I have two subnets (192.168.42.96/27 and 192.168.42.128/25) assigned to the same VLAN.

Is it possibile configuring a DHCP pool on a Cisco switch that can distribute IPs from more than one subnet?

Many thanks,

Maurizio

[Mark Malone]

Generally no , but there is a mutiple DHCP subnet feature supported in 12.4T but i never seen it on dist or access switches or used it , not sure what its available on but you can cehck the doc below and follow the guides it may give more info on it

What are you trying to do this on, what platform ?

https://www.cisco.com/c/en/us/td/docs/ios/12_2sr/12_2srb/feature/guide/srbmultd.html#wp1053389

[maurizio.pederneschi]

Hi Mark,

I have to implement VLANs segmentation on a LAN that actually is using a flat network (VLAN1 ).

I have to move the DHCP server to the Cisco 3650 and I would like to avoid the reassignment of IP addresses. So I'm trying to subnetting the actually addressing plan to satisfy our requirements.

For the server VLAN I need to reserve two subnet, 192.168.42.96/27 and 192.168.42.128/25. Some of the servers (and printers) have a reservation, others take an IP from the pool.

[Mark Malone · Accepted solution]

hmm just thinking could you not use the secondary address for something like that , the syntax was actually designed for changing ip address schemes , your better off taking a hit now in my opinion and do it right , create the vlans you need and move everything over in a maintenance window.

https://www.cisco.com/c/en/us/td/docs/ios/12_2/ip/configuration/guide/fipr_c/1cfipadr.html

[maurizio.pederneschi]

Hi Mark,

I think I will do so. Moving some of the clients or servers in ordero to obtain the segmentation that I want. So I will not need a dhcp pool with two subnets :)

[Mark Malone]

It will work better in the long run and be easier to maintain and troubleshoot , good luck with it

[Julio E. Moisa]

Hi Maurizio,

Please check these links:

https://supportforums.cisco.com/t5/lan-switching-and-routing/secondary-ip-address-and-dhcp/td-p/1836681

DHCP smart relay 

https://www.cisco.com/c/en/us/td/docs/ios/12_2/ip/configuration/guide/fipr_c/1cfdhcp.html#wp1010291

Hope it is useful

:-)