Networking Problem - Firewall blocking traffic from Ubuntu but allows Windows

[Markus Schönhaber]

Anoop John:

> * When these people try to acess the Wireless network in their office
> from Ubuntu, they get connected to the access point but their packets
> get stopped at a Symantec firewall that sits at the gateway.
> 
> Symptoms
> 
> * I can ping the firewall as well as other systems in the network.
> * tracepath stops at the firewall.

tracepath sends UDP packets as big as they can be to do PMTU detection.
If you lower the packet size (e. g. tracepath -l 100 ...) does that
change anything? Do you get replies when ping'ing a machine on the
internet that is known to respond to echo requests?
If the answer is "no" in both cases, that pretty much rules out a MTU
problem.

> * The same system when booted off from windows can access the internet

So, the most interesting question is: what is different between Ubuntu
and Windows? Does the machine get the same IP in both cases?

> * I tried changing MTU to 1492 and 1400 using NetworkManager but that
> didn't help
> 
> Network Layout
> 
> Wireless connection is via an Accesspoint connected to an L3 switch
> (Cisco L3 switch 4507) that forwards all traffic to the
> router/firewall (Symantec UTM box 5640) which is connected directly to
> the internet.

How is that box connected to the internet? The MTU of 1492 you mention
above suggests some kind of DSL/PPPoE.
Does it do NAT?

> Interestingly the firewall log records that the packets
> are being forwarded and not dropped when the connection is from Ubuntu
> or Windows.

What's the difference then between packets from Ubuntu and Windows? If
the Symantec Box does NAT, are the packets from Ubuntu NAT'ed too?

-- 
Regards
  mks