To make sure that you can establish an ssh connection to an NCAR system it is helpful to know that the basic network connectivity is working the way it needs to be in order for you to be successful. First, can your system resolve ( or translate ) the target host name into an IP address? Using most flavors of Unix you can determine if your system can resolve names using the "nslookup" command.
[WOMBATNET:/home/wombat]
$ nslookup chinookfe.ucar.edu
Server: isp.serv1.net
Address: 128.117.8.250
Non-authoritative answer:
Name: chinookfe.ucar.edu
Address: 128.117.215.218
Instead of using "nslookup" on a Linux-based system, use the "dig" command:
[WOMBATNET:/home/wombat]
$ dig chinookfe.ucar.edu
; <<>> DiG 9.1.3 <<>> chinookfe.ucar.edu
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 27383
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;chinookfe.ucar.edu IN A
;; ANSWER SECTION:
chinookfe.ucar.edu. 172800 IN A 128.117.215.218
;; Query time: 133 msec
;; SERVER: 128.117.8.250#53(128.117.8.250)
;; WHEN: Tue Jul 16 13:09:27 2002
;; MSG SIZE rcvd: 47
If for some reason you cannot use "nslookup" or "dig" to try to resolve the IP address for the target hostname, check your system's "/etc/hosts" file for a static entry. While using the "/etc/hosts" file may be practical, it is not, given the number of possible systems on the Internet, a very advisable solution. If in doubt about any of this, seek out the help of your local systems/network administrator.
After acquiring the IP address for the target, in this case chinookfe.ucar.edu, test basic connectivity using a "ping" command.
[WOMBATNET:/home/wombat]
$ ping chinookfe.ucar.edu
PING chinookfe.ucar.edu (128.117.215.218): 56 data bytes
64 bytes from 128.117.215.218: icmp_seq=0 ttl=254 time=0.271 ms
64 bytes from 128.117.215.218: icmp_seq=1 ttl=254 time=0.289 ms
64 bytes from 128.117.215.218: icmp_seq=2 ttl=254 time=0.318 ms
^C
--- chinookfe.ucar.edu ping statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/max/stddev = 0.271/0.283/0.318/0.024 ms
NOTE: Not all sites allow the use of the "ping" command. A failure of ping may be due to a firewall or special router configuration within your facility. If in doubt, check with your local systems/network administrator.
Along with "ping" another useful command available on most flavors of Unix and Linux is "traceroute". This allows you to understand, in case there is a network failure, where problems maybe occurring. In the following example we are able to "traceroute" from the WOMBATNET workstation locally to the remote host chinookfe at NCAR. Tracing the full route is logical given we were able to ping chinookfe from WOMBATNET in the previous example. Again "traceroute" usage maybe restricted for security purposes within your facility. If you have any doubts about network viability or appropriate tools to diagnose basic network connectivity, seek local assistance.
[WOMBATNET:/home/wombat]
$ traceroute chinookfe.ucar.edu
traceroute to chinookfe.ucar.edu (128.117.215.218), 30 hops max, 38 byte packets
1 WOMBATNET.net (211.254.12.1) 85.912 ms 83.795 ms 83.651 ms
2 fence12.isp.net (155.180.168.110) 88.850 ms 88.842 ms 84.221 ms
3 core6.oscar.widget.net (206.253.192.194) 84.656 ms 87.175 ms 84.422 ms
4 POS3-3.GW6.SEA1.ALTER.NET (157.130.191.113) 86.855 ms 84.720 ms 84.392 ms
5 * * *
6 unknown.Level3.net (64.159.3.206) 131.021 ms 134.525 ms 131.965 ms
7 mlrb-n243-72.ucar.edu (128.117.243.75) 121.082 ms 118.531 ms 118.160 ms
8 chinookfe.ucar.edu (128.117.215.218) 118.658 ms 119.274 ms 116.922 ms
If you have questions about this document, please contact SCD Customer Support. You can also reach us by telephone 24 hours a day, seven days a week at 303-497-1278. Additional contact methods: consult1@ucar.edu and during business hours in NCAR Mesa Lab Suite 39.