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

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

Post by stefan.oedenko.. » Fri, 06 Jan 2006 22:37:12



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/csockets/simpleclient.c
http://homepage.uibk.ac.at/~c703350/csockets/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

 
 
 

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

Post by Tom » Sat, 07 Jan 2006 02:59:17


Different MTU settings perhaps ?

> 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/csockets/simpleclient.c
> http://homepage.uibk.ac.at/~c703350/csockets/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


 
 
 

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

Post by Joe Beanfis » Sat, 07 Jan 2006 03:39:02



> 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/csockets/simpleclient.c
> http://homepage.uibk.ac.at/~c703350/csockets/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.
 
 
 

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

Post by stefan.oedenko.. » Sat, 07 Jan 2006 19:29:39


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

 
 
 

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

Post by stefan.oedenko.. » Sat, 07 Jan 2006 18:53:25


Quote:> 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
 
 
 

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

Post by Postmaste » Mon, 09 Jan 2006 06:51:09



Quote:>> 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
 
 
 

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

Post by Rober » Mon, 09 Jan 2006 17:39:48



> 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

Smile... it increases your face value!

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

Post by Clifford Kit » Wed, 11 Jan 2006 00:13:06



> 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.

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

--

 
 
 

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

Post by Joe Beanfis » Wed, 11 Jan 2006 02:59:15



>> 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.
 
 
 

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

Post by R » Fri, 13 Jan 2006 01:20:54


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.