A <= ping => B => OK A <= TCP => B => FAILS

Hi ng,

i've two linux systems (A and B).
I can successfully ping A from B and vice versa.

A simple TCP-Connection from A to B is failing.
I'm using the following TCP SimpleServer and SimpleClient Examples:
http://homepage.uibk.ac.at/~c703350/...simpleclient.c
http://homepage.uibk.ac.at/~c703350/...simpleserver.c

The TCP/IP stack should be ok, since a TCP connection with this program
is working from A<=>A and B<=>B and from A<=>C

Does anyone has a hint what could be the problem?

regards,
Stefan



stefan.oedenkoven@gmx.de

Different MTU settings perhaps ?


On Thu, 05 Jan 2006 05:37:12 -0800, stefan.oedenkoven wrote:

> Hi ng,
>
> i've two linux systems (A and B).
> I can successfully ping A from B and vice versa.
>
> A simple TCP-Connection from A to B is failing.
> I'm using the following TCP SimpleServer and SimpleClient Examples:
> http://homepage.uibk.ac.at/~c703350/...simpleclient.c
> http://homepage.uibk.ac.at/~c703350/...simpleserver.c
>
> The TCP/IP stack should be ok, since a TCP connection with this program
> is working from A<=>A and B<=>B and from A<=>C
>
> Does anyone has a hint what could be the problem?
>
> regards,
> Stefan

On Thu, 05 Jan 2006 08:37:12 -0500, <(E-Mail Removed)> wrote:

> Hi ng,
>
> i've two linux systems (A and B).
> I can successfully ping A from B and vice versa.
>
> A simple TCP-Connection from A to B is failing.
> I'm using the following TCP SimpleServer and SimpleClient Examples:
> http://homepage.uibk.ac.at/~c703350/...simpleclient.c
> http://homepage.uibk.ac.at/~c703350/...simpleserver.c
>
> The TCP/IP stack should be ok, since a TCP connection with this program
> is working from A<=>A and B<=>B and from A<=>C
>
> Does anyone has a hint what could be the problem?

Firewall on B perhaps? Or on A for that matter.

> Firewall on B perhaps? Or on A for that matter.

A and B are directly connected with a crosslink (A has two NICs). There
are no firewalls on this systems... some more ideas? or any hints how
to narrow it down?
regards,
Stefan

What i forgot to mention:

PCs:
A: x86, SuSe 8.2, MTU 1500
B: PowerPC, trimmed-down linux, MTU 1500
C: x86, WinXP, MTU 1500

Net:
C <= (192.168.10.205 company net) => A <= (172.16.10.X crosslink) => B

<(E-Mail Removed)> wrote in message
news:(E-Mail Removed) oups.com...
>> Firewall on B perhaps? Or on A for that matter.
>
> A and B are directly connected with a crosslink (A has two NICs). There
> are no firewalls on this systems... some more ideas? or any hints how
> to narrow it down?
> regards,
> Stefan
>

Ethereal

On Fri, 06 Jan 2006 02:29:39 -0800, stefan.oedenkoven wrote:

> What i forgot to mention:
>
> PCs:
> A: x86, SuSe 8.2, MTU 1500
> B: PowerPC, trimmed-down linux, MTU 1500
> C: x86, WinXP, MTU 1500
>
> Net:
> C <= (192.168.10.205 company net) => A <= (172.16.10.X crosslink) => B

Netmasks set correctly?

Can B talk to C?


--

Regards
Robert

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(E-Mail Removed) wrote:
> What i forgot to mention:

> PCs:
> A: x86, SuSe 8.2, MTU 1500
> B: PowerPC, trimmed-down linux, MTU 1500
> C: x86, WinXP, MTU 1500

Perhaps "trimmed-down linux" is configured to deny all TCP access
in hosts.deny or hosts.allow, the configuration files for tcpd.

> Net:
> C <= (192.168.10.205 company net) => A <= (172.16.10.X crosslink) => B

--
Clifford Kite Email: "echo xvgr_yvahk-(E-Mail Removed)|rot13"

On Fri, 06 Jan 2006 04:53:25 -0500, <(E-Mail Removed)> wrote:

>> Firewall on B perhaps? Or on A for that matter.
>
> A and B are directly connected with a crosslink (A has two NICs). There
> are no firewalls on this systems... some more ideas? or any hints how
> to narrow it down?

There needn't bee additional hardware for a firewall. Any Linux
system can be configured as a firewall. Check the iptables settings.

Since you are pinging between the two machines, we believe routing,
etc. to be ok. On the server machine I would do a netstat -an | more
-or- an lsof -i to make sure that the box is actually listening on the
right port, etc. to make a connection. If you don't see your
simpleserver listening to a particular port then there you go,
application never bound to port. if it is listening, then the next step
would be ethereal or tcpdump on both machines at the same time to see
if you are getting the inital SYN at the server and to see if the
server is sending the SYN/ACK. This should help you see were its
getting lost. You might try netcat (nc) as al alternative to the
simpleclient/simpleserver stuff.