Remote desktop connection over VPN - IP routing issues?

Question

I'm trying to get a remote desktop connection over VPN to work. The VPN connection authenticates fine, and the (Microsoft) RDC client gives an error about the machine being unavailable. The kicker is this was previously working for a day, only after I mucked about with the routing table for a few hours. (This is on a Mac, so it wasn't perhaps as seamless as Windows may be on this occasion)

To explain, when researching my initial problem I came across this forum post, which answered a similar question - by manually adding routing entries. Essentially, the solution provided was:

sudo route add -host [IP of target machine inside VPN] [IP given to you by the VPN]

This didn't work right off the bat, but I kept throwing numbers at it, and it eventually worked. You may have gathered that, although I have a rough understanding of gateways, I'm unfamiliar with mucking about with router tables. And I'm unsure why it started working, and why it stopped...

So, we have the following IPs:

• Internal home network - 192.168.1.2
• Assigned to me, for the VPN connection - 171.30.7.89 (with router 171.30.7.91)
• Machine I'm trying to remote to - 171.17.2.175

I'm using the Microsoft Remote Desktop Connection For Mac app, and the built-in VPN link.

Ping can resolve DNS names of machines on the company network fine (e.g. machine01.company.local -> 171.17.2.175), but doesn't return the ping. Nor does a ping to my IP, or the router.

My questions:

• What tools should/can I use to debug the router hops to see what link is missing?
• Any clues as to which IP gap it is that likely needs to be filled?

Answer 1

Don't know the structure of a route add in *nix, but... shouldn't be there the netmask of the destination? In Windows, thing is something like:

route add NETWORK_ip NETWORK_MASK GATEWAY_TO_BE_USED METRIC

Maybe taking a look to the command syntax could help.

Answer 2

On a mac, you can use traceroute from the terminal to see what route your traffic is taking:

$>traceroute 171.17.2.175

this would tell you if the traffic to your machine is going through the vpn. Also, when adding routes, try this:

$>sudo route add 171.17.2.0/24 171.30.7.89 

you may have to adjust the network address and network mask so that all IP address you need to access go through the vpn, something the IT dept that maintains the VPN should be able to help you with, but the above should at least get you connecting to your one machine.

UPDATE: On Windows, this is pretty much identical:

C:\Users\mmoor>route add 171.17.2.0/24 171.30.7.89
 OK!