<div dir="ltr">thanks all, guys. :-) there're many posts and lots of information follows my initial post, i thought it might be better if i make a summary for what i have done so far and it might be easier for late-coming gurus to get the whole situation at a glance. so here it goes: scenario: i have a desktop (ip <a href="http://192.168.1.35">192.168.1.35</a>) and a lptop (ip <a href="http://192.168.1.36">192.168.1.36</a>) at home network. i installed openssh-server on both of them. i have the same user name on both PCs. my problem is: i can connect from desktop to laptop but not reversely. in another word, desktop to laptop, ok. laptop to desktop, no connection. what i have done following all the suggestions you guys provide: 1. i run "ssh localhost" on both PCs and they work fine. 2. "sudo /etc/init.d/ssh restart" on desktop. output is: * Starting OpenBSD Secure Shell server sshd [ OK ] still no connection from laptop to desktop after that. 3. "netstat -an | grep 22 | grep LISTEN" on desktop: ttcp6 0 0 :::22 :::* LISTEN unix 2 [ ACC ] STREAM LISTENING 21762 /tmp/orbit-zhengguo/linc-1b96-0-61f847b3223d1 unix 2 [ ACC ] STREAM LISTENING 22180 /tmp/orbit-zhengguo/linc-1bd8-0-14b173498db0 unix 2 [ ACC ] STREAM LISTENING 22232 /tmp/orbit-zhengguo/linc-1bd7-0-73832025dcb9 unix 2 [ ACC ] STREAM LISTENING 22304 /tmp/orbit-zhengguo/linc-1bb1-0-30dd8720b0dde unix 2 [ ACC ] STREAM LISTENING 22387 /tmp/orbit-zhengguo/linc-1be9-0-5e13ed25cd93a unix 2 [ ACC ] STREAM LISTENING 22567 /tmp/orbit-zhengguo/linc-1bdb-0-61f847bfa746 unix 2 [ ACC ] STREAM LISTENING 22572 /tmp/orbit-zhengguo/linc-1be3-0-5e13ed28b1c2 unix 2 [ ACC ] STREAM LISTENING 22577 /tmp/orbit-zhengguo/linc-1be1-0-c42a5caba2b unix 2 [ ACC ] STREAM LISTENING 22610 /tmp/orbit-zhengguo/linc-1bf3-0-68dc5c4b61bd2 unix 2 [ ACC ] STREAM LISTENING 22753 /tmp/orbit-zhengguo/linc-1c03-0-6ad3398c3d2b unix 2 [ ACC ] STREAM LISTENING 22812 /tmp/orbit-zhengguo/linc-1bec-0-21f17fadac7d2 unix 2 [ ACC ] STREAM LISTENING 22950 /tmp/orbit-zhengguo/linc-1c0f-0-62f5b1002ed58 unix 2 [ ACC ] STREAM LISTENING 28927 /tmp/gedit-svn.zhengguo.4040482822 same command on laptop: tcp6 0 0 :::22 :::* LISTEN unix 2 [ ACC ] STREAM LISTENING 21735 /tmp/orbit-zhengguo/linc-177a-0-3b77f1c4f2228 unix 2 [ ACC ] STREAM LISTENING 22252 /tmp/scim-bridge-0.3.0.socket-1000@localhost:0.0 unix 2 [ ACC ] STREAM LISTENING 22777 /tmp/orbit-zhengguo/linc-1801-0-354a40bdf22b0 unix 2 [ ACC ] STREAM LISTENING 22810 /tmp/orbit-zhengguo/linc-1803-0-28fd485411c25 4. To force to IPV4 on desktop: $ sudo vi /etc/ssh/sshd_config At the top, uncomment ListenAddress <a href="http://0.0.0.0">0.0.0.0</a> And then $ sudo /etc/init.d/ssh restart to no avail. still no connection 5. "ps -A | grep iptables" on desktop gives nothing. Does that mean iptables is not running? 6. "ps -A | grep fire" on desktop gives only firefox. guess that means my firestarter is not running. 7. "ssh -vv <a href="http://192.168.1.35">192.168.1.35</a>" on laptop gives following output: OpenSSH_4.7p1 Debian-8ubuntu1.2, OpenSSL 0.9.8g 19 Oct 2007 debug1: Reading configuration data /etc/ssh/ssh_config debug1: Applying options for * debug2: ssh_connect: needpriv 0 debug1: Connecting to <a href="http://192.168.1.35">192.168.1.35</a> [<a href="http://192.168.1.35">192.168.1.35</a>] port 22. debug1: connect to address <a href="http://192.168.1.35">192.168.1.35</a> port 22: Connection timed out ssh: connect to host <a href="http://192.168.1.35">192.168.1.35</a> port 22: Connection timed out also tried "telnet", "ping" the same address on laptop, doesn't work. since desktop to laptop works, so "ssh -vv <a href="http://192.168.1.36">192.168.1.36</a>" on desktop, as expected, get a lot of information and after i typing the password, connection established. so i didn't bother to post the output. 8. ifconfig of desktop: eth0 Link encap:Ethernet HWaddr 00:11:d8:40:66:76 inet addr:<a href="http://192.168.1.35">192.168.1.35</a> Bcast:<a href="http://192.168.1.255">192.168.1.255</a> Mask:<a href="http://255.255.255.0">255.255.255.0</a> inet6 addr: fe80::211:d8ff:fe40:6676/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:836 errors:0 dropped:0 overruns:0 frame:0 TX packets:756 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:722731 (705.7 KB) TX bytes:187887 (183.4 KB) Interrupt:21 Base address:0xe400 lo Link encap:Local Loopback inet addr:<a href="http://127.0.0.1">127.0.0.1</a> Mask:<a href="http://255.0.0.0">255.0.0.0</a> inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:2179 errors:0 dropped:0 overruns:0 frame:0 TX packets:2179 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:131320 (128.2 KB) TX bytes:131320 (128.2 KB) wlan0 Link encap:Ethernet HWaddr 00:30:f1:f8:c9:54 UP BROADCAST MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:0 (0.0 B) TX bytes:0 (0.0 B) wmaster0 Link encap:UNSPEC HWaddr 00-30-F1-F8-C9-54-00-00-00-00-00-00-00-00-00-00 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:0 (0.0 B) TX bytes:0 (0.0 B) ipconfig of laptop: eth0 Link encap:Ethernet HWaddr 00:14:22:e0:43:68 UP BROADCAST MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:0 (0.0 B) TX bytes:0 (0.0 B) Interrupt:19 eth1 Link encap:Ethernet HWaddr 00:13:ce:da:05:f0 inet addr:<a href="http://192.168.1.36">192.168.1.36</a> Bcast:<a href="http://192.168.1.255">192.168.1.255</a> Mask:<a href="http://255.255.255.0">255.255.255.0</a> inet6 addr: fe80::213:ceff:feda:5f0/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:59 errors:0 dropped:0 overruns:0 frame:0 TX packets:93 errors:0 dropped:0 overruns:0 carrier:1 collisions:0 txqueuelen:1000 RX bytes:5888059 (5.6 MB) TX bytes:2216268 (2.1 MB) Interrupt:18 Base address:0xe000 Memory:dcffd000-dcffdfff lo Link encap:Local Loopback inet addr:<a href="http://127.0.0.1">127.0.0.1</a> Mask:<a href="http://255.0.0.0">255.0.0.0</a> inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:2733 errors:0 dropped:0 overruns:0 frame:0 TX packets:2733 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:142640 (139.2 KB) TX bytes:142640 (139.2 KB) 9. "tracepath <a href="http://192.168.1.35">192.168.1.35</a>" from desktop is: 1: <a href="http://192.168.1.35">192.168.1.35</a> (<a href="http://192.168.1.35">192.168.1.35</a>) 0.125ms pmtu 16436 1: <a href="http://192.168.1.35">192.168.1.35</a> (<a href="http://192.168.1.35">192.168.1.35</a>) 0.085ms reached 1: <a href="http://192.168.1.35">192.168.1.35</a> (<a href="http://192.168.1.35">192.168.1.35</a>) 0.090ms reached Resume: pmtu 16436 hops 1 back 64 same command from laptop is: 1: UbuntuDell.local (<a href="http://192.168.1.36">192.168.1.36</a>) 0.127ms pmtu 1500 1: no reply 2: no reply 3: no reply 4: no reply 5: no reply 6: no reply 7: no reply 8: no reply 9: no reply 10: no reply 11: no reply 12: no reply 13: no reply 14: no reply 15: no reply 16: no reply 17: no reply 18: no reply 19: no reply 20: no reply 21: no reply 22: no reply 23: no reply 24: no reply 25: no reply 26: no reply 27: no reply 28: no reply 29: no reply 30: no reply 31: no reply Too many hops: pmtu 1500 Resume: pmtu 1500 10. sshd_config as follows: # Package generated configuration file # See the sshd(8) manpage for details # What ports, IPs and protocols we listen for Port 22 # Use these options to restrict which interfaces/protocols sshd will bind to #ListenAddress :: #ListenAddress <a href="http://0.0.0.0">0.0.0.0</a> Protocol 2 # HostKeys for protocol version 2 HostKey /etc/ssh/ssh_host_rsa_key HostKey /etc/ssh/ssh_host_dsa_key #Privilege Separation is turned on for security UsePrivilegeSeparation yes # Lifetime and size of ephemeral version 1 server key KeyRegenerationInterval 3600 ServerKeyBits 768 # Logging SyslogFacility AUTH LogLevel INFO # Authentication: LoginGraceTime 120 PermitRootLogin yes StrictModes yes RSAAuthentication yes PubkeyAuthentication yes #AuthorizedKeysFile %h/.ssh/authorized_keys # Don't read the user's ~/.rhosts and ~/.shosts files IgnoreRhosts yes # For this to work you will also need host keys in /etc/ssh_known_hosts RhostsRSAAuthentication no # similar for protocol version 2 HostbasedAuthentication no # Uncomment if you don't trust ~/.ssh/known_hosts for RhostsRSAAuthentication #IgnoreUserKnownHosts yes # To enable empty passwords, change to yes (NOT RECOMMENDED) PermitEmptyPasswords no # Change to yes to enable challenge-response passwords (beware issues with # some PAM modules and threads) ChallengeResponseAuthentication no # Change to no to disable tunnelled clear text passwords #PasswordAuthentication yes # Kerberos options #KerberosAuthentication no #KerberosGetAFSToken no #KerberosOrLocalPasswd yes #KerberosTicketCleanup yes # GSSAPI options #GSSAPIAuthentication no #GSSAPICleanupCredentials yes X11Forwarding yes X11DisplayOffset 10 PrintMotd no PrintLastLog yes TCPKeepAlive yes #UseLogin no #MaxStartups 10:30:60 #Banner /etc/<a href="http://issue.net">issue.net</a> # Allow client to pass locale environment variables AcceptEnv LANG LC_* Subsystem sftp /usr/lib/openssh/sftp-server UsePAM yes i was told it's ok. 11. "sudo iptables -L" on desktop: Chain INPUT (policy DROP) target prot opt source destination ACCEPT tcp -- <a href="http://250.Red-80-58-61.staticIP.rima-tde.net">250.Red-80-58-61.staticIP.rima-tde.net</a> anywhere tcp flags:!FIN,SYN,RST,ACK/SYN ACCEPT udp -- <a href="http://250.Red-80-58-61.staticIP.rima-tde.net">250.Red-80-58-61.staticIP.rima-tde.net</a> anywhere ACCEPT tcp -- <a href="http://254.Red-80-58-61.staticIP.rima-tde.net">254.Red-80-58-61.staticIP.rima-tde.net</a> anywhere tcp flags:!FIN,SYN,RST,ACK/SYN ACCEPT udp -- <a href="http://254.Red-80-58-61.staticIP.rima-tde.net">254.Red-80-58-61.staticIP.rima-tde.net</a> anywhere ACCEPT all -- anywhere anywhere ACCEPT icmp -- anywhere anywhere limit: avg 10/sec burst 5 DROP all -- anywhere <a href="http://255.255.255.255">255.255.255.255</a> DROP all -- anywhere <a href="http://192.168.1.255">192.168.1.255</a> DROP all -- <a href="http://BASE-ADDRESS.MCAST.NET/8">BASE-ADDRESS.MCAST.NET/8</a> anywhere DROP all -- anywhere <a href="http://BASE-ADDRESS.MCAST.NET/8">BASE-ADDRESS.MCAST.NET/8</a> DROP all -- <a href="http://255.255.255.255">255.255.255.255</a> anywhere DROP all -- anywhere <a href="http://0.0.0.0">0.0.0.0</a> DROP all -- anywhere anywhere state INVALID LSI all -f anywhere anywhere limit: avg 10/min burst 5 INBOUND all -- anywhere anywhere LOG_FILTER all -- anywhere anywhere LOG all -- anywhere anywhere LOG level info prefix `Unknown Input' Chain FORWARD (policy DROP) target prot opt source destination ACCEPT icmp -- anywhere anywhere limit: avg 10/sec burst 5 LOG_FILTER all -- anywhere anywhere LOG all -- anywhere anywhere LOG level info prefix `Unknown Forward' Chain OUTPUT (policy DROP) target prot opt source destination ACCEPT tcp -- <a href="http://192.168.1.35">192.168.1.35</a> <a href="http://250.Red-80-58-61.staticIP.rima-tde.net">250.Red-80-58-61.staticIP.rima-tde.net</a> tcp dpt:domain ACCEPT udp -- <a href="http://192.168.1.35">192.168.1.35</a> <a href="http://250.Red-80-58-61.staticIP.rima-tde.net">250.Red-80-58-61.staticIP.rima-tde.net</a> udp dpt:domain ACCEPT tcp -- <a href="http://192.168.1.35">192.168.1.35</a> <a href="http://254.Red-80-58-61.staticIP.rima-tde.net">254.Red-80-58-61.staticIP.rima-tde.net</a> tcp dpt:domain ACCEPT udp -- <a href="http://192.168.1.35">192.168.1.35</a> <a href="http://254.Red-80-58-61.staticIP.rima-tde.net">254.Red-80-58-61.staticIP.rima-tde.net</a> udp dpt:domain ACCEPT all -- anywhere anywhere DROP all -- <a href="http://BASE-ADDRESS.MCAST.NET/8">BASE-ADDRESS.MCAST.NET/8</a> anywhere DROP all -- anywhere <a href="http://BASE-ADDRESS.MCAST.NET/8">BASE-ADDRESS.MCAST.NET/8</a> DROP all -- <a href="http://255.255.255.255">255.255.255.255</a> anywhere DROP all -- anywhere <a href="http://0.0.0.0">0.0.0.0</a> DROP all -- anywhere anywhere state INVALID OUTBOUND all -- anywhere anywhere LOG_FILTER all -- anywhere anywhere LOG all -- anywhere anywhere LOG level info prefix `Unknown Output' Chain INBOUND (1 references) target prot opt source destination ACCEPT tcp -- anywhere anywhere state RELATED,ESTABLISHED ACCEPT udp -- anywhere anywhere state RELATED,ESTABLISHED LSI all -- anywhere anywhere Chain LOG_FILTER (5 references) target prot opt source destination Chain LSI (2 references) target prot opt source destination LOG_FILTER all -- anywhere anywhere LOG tcp -- anywhere anywhere tcp flags:FIN,SYN,RST,ACK/SYN limit: avg 1/sec burst 5 LOG level info prefix `Inbound ' DROP tcp -- anywhere anywhere tcp flags:FIN,SYN,RST,ACK/SYN LOG tcp -- anywhere anywhere tcp flags:FIN,SYN,RST,ACK/RST limit: avg 1/sec burst 5 LOG level info prefix `Inbound ' DROP tcp -- anywhere anywhere tcp flags:FIN,SYN,RST,ACK/RST LOG icmp -- anywhere anywhere icmp echo-request limit: avg 1/sec burst 5 LOG level info prefix `Inbound ' DROP icmp -- anywhere anywhere icmp echo-request LOG all -- anywhere anywhere limit: avg 5/sec burst 5 LOG level info prefix `Inbound ' DROP all -- anywhere anywhere Chain LSO (0 references) target prot opt source destination LOG_FILTER all -- anywhere anywhere LOG all -- anywhere anywhere limit: avg 5/sec burst 5 LOG level info prefix `Outbound ' REJECT all -- anywhere anywhere reject-with icmp-port-unreachable Chain OUTBOUND (1 references) target prot opt source destination ACCEPT icmp -- anywhere anywhere ACCEPT tcp -- anywhere anywhere state RELATED,ESTABLISHED ACCEPT udp -- anywhere anywhere state RELATED,ESTABLISHED ACCEPT all -- anywhere anywhere however, on laptop the same command has output: Chain INPUT (policy ACCEPT) target prot opt source destination Chain FORWARD (policy ACCEPT) target prot opt source destination Chain OUTPUT (policy ACCEPT) target prot opt source destination it seems empty. is it normal? ok, here're things i've done so far trying to get the connection but to no avail. any further suggestion are welcomed whole haertly. thanks again for all the help you've given to me. :-) </div>