ASA 5540 DHCP server - how to serve more than 255 addresses

rwiechman · ‎01-03-2010

I have an internal lan set up as a /21. I'd like to serve dhcp to most all of them. The pool address seems to be limited to 255 clients. Is there any way around this?

Thanks, Roger

YANGCCIE4 · ‎01-03-2010

Hi,

If I understood your posting right,

you can change the subnet number to add the more host addresses in one subnet.

/24 subnet includes 253 hosts.

/23 subnet includes 510 hosts.

.....

so you can change the dhcp server settings to realize this proposal.

hope it helps

Yang

rwiechman · ‎01-03-2010

The internal address is already assigned a /21 (255.255.248.0 mask) which would allow 2046 hosts. (x.x.8.1-x.x.15.254 for instance).

However, at least using ASDM, it complains about larger than 255 if I use the range x.x.8.30 - x.x.15.254.

I have not tried using the command line to see if it will take multiple address range statements, but I suspect it wont.

Roger

vilaxmi · ‎01-03-2010

Hello,

One solution to your problem could be to create a second INSIDE interface (security-level = 100) on the ASA. Then you can make the new iterfcae as DHCP server in order to serve clients. Please keep in mind that for access from inside (behind old inside interface) to inside (behind new inside interface) would need additional U turn NAT configurations on ASA.

Thanks

Vijaya

YANGCCIE4 · ‎01-03-2010

Hi,

If I understood your posting right,

you can change the subnet number to add the more host addresses in one subnet.

/24 subnet includes 253 hosts.

/23 subnet includes 510 hosts.

.....

so you can change the dhcp server settings to realize this proposal. ---- in the dhcp pool xx + options.

hope it helps

Yang

J_Vansen_S · ‎04-01-2010

"so you can change the dhcp server settings to realize this proposal. ---- in the dhcp pool xx + options."

that does not seem to work.

Apprarently the ASA's command takes it in the format

dhcpd address 192.168.8.10-192.168.8.100 *interface*
dhcpd enable *interface*

no way to configure it as /23? /22?

Please advise

JORGE RODRIGUEZ · ‎04-02-2010

Roger, as far as I know DHCP feature has a limitation of address pool per interface , see guidelines, http://www.cisco.com/en/US/docs/security/asa/asa80/command/reference/d2.html#wp1904997

It is more pratical to used a local DHCP server for your requirements, if you have Windows AD server DHCP services is free, or you may find 3rd party freeware DHCP servers software out here. You may also look at dhcp relay feature , see same link above but you will stilll need stand alone DHCP server for that .

Regards

Jorge Rodriguez