Re: help needed with debugging tcp/ip over ax25

[walter harms <wharms@bfs.de>]

Am 04.02.2011 23:16, schrieb Guido Trentalancia:
> Hello everybody !
> 
> I am experiencing problems when trying to run TCP/IP over AX.25 on
> Linux.
> 
> I have two hosts 44.134.241.1 and 44.134.241.21, both of them are using
> Linux. The kiss interfaces are up and running and the ax25 interfaces
> have been configured.
> 
> The first machine is running a few servers, for example conversd on port
> 3600.
> 
> After a fresh reboot, the first machine is responding correctly to any
> TCP/IP connection, for example telnet 44.134.241.1 3600 (from the second
> machine) works correctly and leads to a connection and a successful
> telnet session.
> 
> However, after a while (kissattach is killed, the ax25 interface is
> brought down and then kissattach and the ax25 interface are restarted
> again on the first machine), the TCP/IP connection does not work
> anymore. In other words I can no longer telnet from the second machine
> to the first one.
> 
> The packets are still there, as shown in the logs below.
> 
> Output from tcpdump -i ax0 on the first machine:
> 
> 19:51:46.932089 IP 44.134.241.21.43675 > iz6rdb.ampr.org.convers: Flags
> [S], seq 2030721846, win 1024, options [mss 256,sackOK,TS val 149718 ecr
> 0,nop,wscale 6], length 0
> 19:51:46.932089 IP 44.134.241.21.43675 > iz6rdb.ampr.org.convers: Flags
> [S], seq 2030721846, win 1024, options [mss 256,sackOK,TS val 149718 ecr
> 0,nop,wscale 6], length 0
> 
> Output from tcpdump -i ax0 on the second machine:
> 
> 19:51:46.386898 IP 44.134.241.21.43675 > iz6rdb.ampr.org.trap-daemon:
> Flags [S], seq 2030721846, win 1024, options [mss 256,sackOK,TS val
> 149718 ecr 0,nop,wscale 6], length 0
> 19:51:49.388715 IP 44.134.241.21.43675 > iz6rdb.ampr.org.trap-daemon:
> Flags [S], seq 2030721846, win 1024, options [mss 256,sackOK,TS val
> 152720 ecr 0,nop,wscale 6], length 0
> 
> The output from axlisten -a (on both machines) also shows that packets
> are getting transmitted and received correctly.
> 
> But unfortunately, the first machine is not responding anymore !
> 
> Similar things can be said about ping or other TCP/IP connections (such
> as ssh).
> 
> It shouldn't be an iptables issue (as bringing iptables down does not
> improve things and in any case, everything is working fine just after a
> reboot).
> 
> However, it could be an arp issue because when the connection is
> working, on the first machine (the one which runs the servers that do
> not respond) I have the following line in arp:
> 
> 44.134.241.21    ax25    IZ6RDB-7   C     ax0
> 
> while, when the connection is not working, that line does not appear
> anymore in arp.
> 
> The following lines are also missing from the tcpdump output when the
> server is not replying:
> 
> 20:19:35.011128 arp who-has 44.134.241.21 tell iz6rdb.ampr.org
> 20:19:35.934448 arp reply 44.134.241.21 is-at IZ6RDB-7
> 20:19:35.934448 arp reply 44.134.241.21 is-at IZ6RDB-7
> 
> Any help would be greatly appreciated.
> 



did you try arp -s ?

re,
 wh