Networking problem - Just how to do this?

Daniel Bond db at
Tue Jul 27 07:02:34 PDT 2010

mikel king wrote:
On Jul 19, 2010, at 11:45 PM, elekktretterr at 
<mailto:elekktretterr at> wrote:

The situation is like this:

DF Box is on a public IP -  - The box is connected to a switch,
and the switch is connected to the upstream router -
Now, I've also connected another router(Cisco ASA 5505) to the 
switch. Its
also got a public IP - - and the router will be used to establish
VPN connections to another network on the internet. The problem is I dont
have a "private network", the DF box is on a public IP.

So I aliased the network interface on the DF Box and gave it a 
private IP:

I'm kind of at loss as what to do next. Has anyone been in a similar
situation? Worst come worst i'll have to run another cable to the second
NIC on the DF Box and split the topology physically.
Do you have a second NIC in the DF box? The ASA5505 is a firewall 
security device and not a router therefore do not make the mistake in 
believing it will behave like a router. Cisco ASA's are persnickety 
devices and will only VPN from an insecure to a secure  interface. If 
your DF box had a second NIC that you could put on the ASA's secure 
interface (LAN) then you could VPN via the ASA. This is not optimal 
and only based on the assumption that you do not want to relocate the 
DF box completely behind the ASA which is the other option.

I hope that helps.

Mikel King
Senior Editor, BSD News Network
Columnist, BSD Magazine
6 Alpine Court,
Medford, NY 11763
o: 631.627.3055
Just to clarify, the ASA5505 *IS* a router, it will just not do 

You would have to put the machines you want to VPN on the inside like 
suggested, but you could also make an IPSEC tunnel connect directly to 
your office network from the DF machine. Or if you switch is capable of 
doing dot1q-vlans, you could have a seperate vlan-interface (virtual 
nic) on the DF machine connected to the inside of the ASA, and route 
what ever networks you want to access via VPN with static routes.

Best regards,

Daniel Bond.

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