asa5505 dhcp question

[fran19422]

Hello, looking at the ASA5505 outside interface connection options I see there is one called "obtain address via dhcp".

I am trying to understand how this would work.

So you would have a modem connected between your firewall and the ISP. The modem connects to the ISP.

The ISP would issue an address via DHCP. The modem simply passes this DHCP address allocation through to the firewall behind it ?

Do you need to activate a special setting on your modem to allow that address through to the firewall ?

Thanks for any clarification.

[lcambron · Accepted solution]

Hello,

I guess this is something to confirm with your ISP.

They need to setup DHCP on their end.

Regards,

Felipe.

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[Marius Gunnerud · Accepted solution]

As Felipe has mentioned for configuration of your modem, which presumably is provided by your ISP, you would need to contact your ISP for the correct settings.

But generally speaking, you would need to configure your ASA 5505 outside interface to send dhcp requests, and in turn your ISP modem, router, etc. would respond with an IP address for your ASA.

The outside interface configuration would be as follows:

interface gig0/1

description OUTSIDE_INTERFACE

ip address dhcp setroute

The setroute keyword will automatically set the default route next hop, so you do not have to configure the default route each time your IP address changes.

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