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Why did ping work but any other connection fail in the following scenario?

We have the following network scenario: 2 Offices each with a Sonicwall NSA 3500 Each office has it's own network, with a unique subnet A:(192.168.10.X/24) and B:(192.168.20.X/24) A single VPN configured between the offices

Problem: An application client running on a system in network A couldn't connect to server on network B.

Tests: First tried ping, successful. Then tried telnet to port of app, failed. So logically, we thought there was a firewall rule blocking that port. But that wasn't it...

Solution: The problem actually was the default gateway was not correctly set on server B. Once we set that correctly the connection from network A to network B worked.

So how could ping work, even though the default gateway of the destination system was wrong? Shouldn't it have failed?

Oh, the client system was 2008R2 and server was a network appliance PTX

Thanks for your time.

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Perhaps a cached route somewhere? It really is impossible to answer though. To give you a answer with any certainty, I would need to what you had in your routing tables on both firewalls, and the routing table on the server and client. There are certainly cases where routing can work in one directly, but not the opposite if you do things wrong. –  Zoredache Jul 25 '13 at 22:31
Thanks, you are correct, it would be difficult with a complicated setup. Here's the rub, routing tables were simple on both hosts, default gateway, no other routes, that's what's so strange. The recipient device is a Lantronix Universal Device Server, and it had our old default gateway ip address, which is no longer functioning and there is nothing on the network with that old IP. We had no RIP, OSPF etc. on either firewall. That's why we are baffled, why ping worked, when without a proper default gateway on the recipient, it should have failed. –  Monte Ducay Jul 26 '13 at 1:12

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