Cisco ASA 5510 - Restrictions on IP Pools and DHCP usage

Posted on 2006-04-12
Last Modified: 2013-11-16
Hey folks,

I have been trying to configure a Cisco 5510 for basic Remote Access VPN, the problem I am having is trying to get IP's assigned to remote clients; unless I specifiy a range that doesn't seem to be recognized by the firewall in it's building blocks it won't allow a VPN client to connect.  I am pretty sure that this is due to the firewall seeing the IP as something internal and is rejecting it's assignment to a VPN client (in the case of trying to use part of an unused pre-existing internal range) or is trying to route to the IP and it's being routed back into the network instead of out the VPN interface.  I am pretty sure in the past on PIX' I have been able to do this with no problem, but I may be misremembering.

This leads to my second problem, that when I specify an internal DHCP server, the same behaviour is seen.  I can find nothing to indicate that ACE's need to be in place to allow this per se, but I can't find anything to say otherwise.

Anyone have any suggestions on how I should handle the config?  I'd prefer to use the internal DHCP server, but I am trying to determine if the ASA system needs explicit rules to allow the DHCP for VPNs or not.

I was configuring through the ASDM btw, thanks in advance for any thoughts on the matter!
Question by:docsteel
    LVL 20

    Accepted Solution

    I'll save you further grief in trying to get these two features to work together... ;)
    The VPN client pool & the DHCP range have nothing to do with each other.  DHCP will never give out IPs to your VPN clients - it's only used for providing IP info to clients that are local to the ASA box, & the VPN client pool is only for use by the remote VPN users.

    >...unless I specifiy a range that doesn't seem to be recognized by the firewall in it's building blocks...
      Right.  This is how Cisco's implementation of VPN works; unlike many other vendors' VPN configs, Cisco forces you to use a separate IP subnet that's different than any of the local subnets on your ASA appliance, PIX firewall, router, etc.  If you do, as you found out yourself, you'll run right into the brick wall of a routing loop.  Personally, I prefer Cisco's method, as it makes more sense from a routing standpoint, plus you don't have to eat up IP addresses for your local internal subnets, especially nice in situations where you don't have many (or any) IPs left to reserve for the VPN clients.

      As for specifics on the VPN configuration, I'll leave that to those who're more experienced on ASA, which essentially is running PIX 7.x software.  lrmoore is one of the uber gurus who can help with an ASA config & using the ASDM.
      If you're willing to try out the CLI, here are some CLI reference guides:
       "Configuring Remote Access VPNs":
       * the above taken from the main CLI config guide page:

    LVL 4

    Expert Comment

    I recently setup a remote access VPN on a ASA 5510 using Radius auth. After wasting tons of time trying to get the VPN working through the CLI, I finally just used the VPN wizard through ASDM. It worked like a charm. If you open a TAC case, good chance they'll point to to the VPN wizard too.
    LVL 4

    Expert Comment

    Let me point you to a working config. There's nothing wrong with the config as it was a client issue.

    Author Comment

    I appreciate everyones help on this, I really do.  I am using the wizard and I can connect up now, but the last issue is once I set up a pool of IP's that are not previously part of the network, should I NAT them on to the interfaces coming off the ASA to avoid having to setup routes on all the internal routers for the new pool?  Is this advisable?

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