Network/Troubleshooting: Difference between revisions
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*Check that the ethernet cable is plugged in or that you are connected to a wireless network. | *Check that the ethernet cable is plugged in or that you are connected to a wireless network. | ||
*Check that you have an IP address. | *Check that you have an IP address. | ||
** | **Windows: type <code>ipconfig /all</code> into the command prompt | ||
**Linux/UNIX based hosts: type | **macOS/Linux/UNIX based hosts: type <code>ifconfig -a</code> into a terminal | ||
==PING== | ==PING== | ||
PING is a network utility that sends ICMP packets to a specified host to test network connectivity. | PING is a network utility that sends ICMP packets to a specified host to test network connectivity. | ||
*Open up a command prompt | *Open up a command prompt / terminal and type <code>ping</code> followed by the hostname or IP address of the host you want to test connectivity to. | ||
bash$ ping google.com | bash$ ping google.com | ||
PING google.com (74.125.228.34) 56(84) bytes of data. | PING google.com (74.125.228.34) 56(84) bytes of data. | ||
Line 16: | Line 16: | ||
64 bytes from iad23s06-in-f2.1e100.net (74.125.228.34): icmp_seq=3 ttl=52 time=4.41 ms | 64 bytes from iad23s06-in-f2.1e100.net (74.125.228.34): icmp_seq=3 ttl=52 time=4.41 ms | ||
64 bytes from iad23s06-in-f2.1e100.net (74.125.228.34): icmp_seq=4 ttl=52 time=4.04 ms | 64 bytes from iad23s06-in-f2.1e100.net (74.125.228.34): icmp_seq=4 ttl=52 time=4.04 ms | ||
*Linux/ | *On Linux/UNIX, you may want to add the <code>-c</code> flag followed by a number to specify how many times to ping the destination host. | ||
If you are having trouble connecting to UMIACS services we would suggest you test against one of our publicly accessible hosts like <code> | If you are having trouble connecting to UMIACS services, we would suggest you test against one of our publicly accessible [[Nexus]] hosts like <code>nexuscml00.umiacs.umd.edu</code> or <code>nexuscfar00.umiacs.umd.edu</code>. | ||
<pre> | <pre> | ||
$ ping | -bash-4.2$ ping nexuscml00.umiacs.umd.edu | ||
PING | PING nexuscml00.umiacs.UMD.EDU (128.8.121.4) 56(84) bytes of data. | ||
64 bytes from | 64 bytes from nexuscml00.umiacs.umd.edu (128.8.121.4): icmp_seq=1 ttl=60 time=0.507 ms | ||
64 bytes from | 64 bytes from nexuscml00.umiacs.umd.edu (128.8.121.4): icmp_seq=2 ttl=60 time=0.335 ms | ||
64 bytes from | 64 bytes from nexuscml00.umiacs.umd.edu (128.8.121.4): icmp_seq=3 ttl=60 time=0.328 ms | ||
64 bytes from | 64 bytes from nexuscml00.umiacs.umd.edu (128.8.121.4): icmp_seq=4 ttl=60 time=0.379 ms | ||
</pre> | </pre> | ||
Line 52: | Line 52: | ||
15 4 ms 4 ms 5 ms iad23s06-in-f6.1e100.net [74.125.228.38] | 15 4 ms 4 ms 5 ms iad23s06-in-f6.1e100.net [74.125.228.38] | ||
Trace complete. | Trace complete. | ||
*Linux/UNIX: | *macOS/Linux/UNIX: | ||
**In a terminal type 'traceroute' followed by the hostname or IP address of the host you want to test the route to. | **In a terminal type 'traceroute' followed by the hostname or IP address of the host you want to test the route to. | ||
bash$ traceroute google.com | bash$ traceroute google.com | ||
Line 72: | Line 72: | ||
13 iad23s07-in-f8.1e100.net (74.125.228.72) 10.798 ms 13.383 ms 7.540 ms | 13 iad23s07-in-f8.1e100.net (74.125.228.72) 10.798 ms 13.383 ms 7.540 ms | ||
Again if | Again, if you are having trouble connecting to UMIACS services, we would suggest you test against one of our publicly accessible [[Nexus]] host such as <code>nexuscml00.umiacs.umd.edu</code> or <code>nexuscfar00.umiacs.umd.edu</code>. | ||
==Other Things to consider== | ==Other Things to consider== | ||
*Is your IP address manually set? | *Is your IP address manually set? | ||
**In order for networking to function properly a machine must have a unique IP address on its network. In many cases IP address are assigned automatically via the DHCP protocol, but it is also possible to manually set an IP address. If your machine happens to have a manually set IP address that conflicts with that of another host, networking issues may arise. | **In order for networking to function properly, a machine must have a unique IP address on its network. In many cases IP address are assigned automatically via the DHCP protocol, but it is also possible to manually set an IP address. If your machine happens to have a manually set IP address that conflicts with that of another host, networking issues may arise. | ||
*Are you behind a firewall? | *Are you behind a firewall? | ||
**Some establishments use firewalls to restrict certain types of traffic both in and out of their networks. If you are having trouble accessing a specific service, this might be the case. To get around this you can connect to the VPN, or use SSH tunneling. | **Some establishments use firewalls to restrict certain types of traffic both in and out of their networks. If you are having trouble accessing a specific service, this might be the case. To get around this you can connect to the VPN, or use SSH tunneling. | ||
*Other useful commands: | *Other useful commands: | ||
**dig | **<code>dig</code>: performs DNS lookups and displays the answers that are returned from the name server(s) that were queried | ||
**host | **<code>host</code>: simple utility for performing DNS lookups | ||
**netstat ( | **<code>netstat</code> (macOS/Linux/UNIX): shows network status | ||
**route print (Windows) | **<code>route print</code> (Windows): shows network routing tables | ||
==Change your default DNS server== | ==Change your default DNS server== | ||
Please see [[Network/Troubleshooting/DNS | DNS]] to change your default DNS server. | Please see [[Network/Troubleshooting/DNS | DNS troubleshooting]] to change your default DNS server. |
Latest revision as of 15:00, 28 August 2023
Occasionally network related issues may arise. The following outlines basic troubleshooting methods.
Check Network Connection
- Check that the ethernet cable is plugged in or that you are connected to a wireless network.
- Check that you have an IP address.
- Windows: type
ipconfig /all
into the command prompt - macOS/Linux/UNIX based hosts: type
ifconfig -a
into a terminal
- Windows: type
PING
PING is a network utility that sends ICMP packets to a specified host to test network connectivity.
- Open up a command prompt / terminal and type
ping
followed by the hostname or IP address of the host you want to test connectivity to.
bash$ ping google.com PING google.com (74.125.228.34) 56(84) bytes of data. 64 bytes from iad23s06-in-f2.1e100.net (74.125.228.34): icmp_seq=1 ttl=52 time=4.52 ms 64 bytes from iad23s06-in-f2.1e100.net (74.125.228.34): icmp_seq=2 ttl=52 time=4.17 ms 64 bytes from iad23s06-in-f2.1e100.net (74.125.228.34): icmp_seq=3 ttl=52 time=4.41 ms 64 bytes from iad23s06-in-f2.1e100.net (74.125.228.34): icmp_seq=4 ttl=52 time=4.04 ms
- On Linux/UNIX, you may want to add the
-c
flag followed by a number to specify how many times to ping the destination host.
If you are having trouble connecting to UMIACS services, we would suggest you test against one of our publicly accessible Nexus hosts like nexuscml00.umiacs.umd.edu
or nexuscfar00.umiacs.umd.edu
.
-bash-4.2$ ping nexuscml00.umiacs.umd.edu PING nexuscml00.umiacs.UMD.EDU (128.8.121.4) 56(84) bytes of data. 64 bytes from nexuscml00.umiacs.umd.edu (128.8.121.4): icmp_seq=1 ttl=60 time=0.507 ms 64 bytes from nexuscml00.umiacs.umd.edu (128.8.121.4): icmp_seq=2 ttl=60 time=0.335 ms 64 bytes from nexuscml00.umiacs.umd.edu (128.8.121.4): icmp_seq=3 ttl=60 time=0.328 ms 64 bytes from nexuscml00.umiacs.umd.edu (128.8.121.4): icmp_seq=4 ttl=60 time=0.379 ms
Trace Route
The traceroute tool utilizes the IP protocol to track the route one's packets take through a network. Traceroute is useful when trying to figure out why a host is unreachable because it shows where the connection failed.
- Windows:
- In a command prompt type "tracert" followed by the hostname or IP address of the host you want to test the route to.
C:\>tracert google.com Tracing route to google.com [74.125.228.38] over a maximum of 30 hops: 1 <1 ms <1 ms <1 ms gw-486.umiacs.umd.edu [192.168.86.1] 2 <1 ms <1 ms <1 ms umfirewall00.umiacs.umd.edu [128.8.120.17] 3 13 ms <1 ms <1 ms avw1hub-gw.umiacs.umd.edu [128.8.120.1] 4 1 ms <1 ms <1 ms vlan8.css-priv-r1.net.umd.edu [128.8.6.129] 5 <1 ms <1 ms <1 ms gi6-1.css-core-r1.net.umd.edu [128.8.0.117] 6 <1 ms <1 ms <1 ms gi3-2.css-fw-r1.net.umd.edu [128.8.0.82] 7 1 ms 2 ms 2 ms 128.8.0.226 8 2 ms 2 ms 2 ms 107-0-84-29-static.hfc.comcastbusiness.net [107.0.84.29] 9 3 ms 2 ms 2 ms xe-3-1-2-0-ar04.capitolhghts.md.bad.comcast.net [68.85.114.113] 10 5 ms 6 ms 4 ms pos-5-7-0-0-cr01.ashburn.va.ibone.comcast.net [68.86.90.85] 11 4 ms 4 ms 5 ms pos-0-2-0-0-pe01.ashburn.va.ibone.comcast.net [68.86.86.70] 12 4 ms 6 ms 4 ms 75.149.231.62 13 42 ms 4 ms 4 ms 209.85.252.80 14 5 ms 5 ms 5 ms 72.14.238.175 15 4 ms 4 ms 5 ms iad23s06-in-f6.1e100.net [74.125.228.38] Trace complete.
- macOS/Linux/UNIX:
- In a terminal type 'traceroute' followed by the hostname or IP address of the host you want to test the route to.
bash$ traceroute google.com traceroute: Warning: google.com has multiple addresses; using 74.125.228.72 traceroute to google.com (74.125.228.72), 64 hops max, 52 byte packets 1 10.109.160.1 (10.109.160.1) 1.329 ms 1.086 ms 1.232 ms 2 129-2-129-129.wireless.umd.edu (129.2.129.129) 2.780 ms 1.924 ms 2.127 ms 3 te1-6.css-core-r1.net.umd.edu (128.8.0.121) 2.514 ms 2.293 ms 1.863 ms 4 gi3-2.css-fw-r1.net.umd.edu (128.8.0.82) 2.429 ms 2.548 ms 2.284 ms 5 128.8.0.226 (128.8.0.226) 3.838 ms 3.465 ms 3.635 ms 6 107-0-84-29-static.hfc.comcastbusiness.net (107.0.84.29) 3.941 ms 3.445 ms 3.303 ms 7 xe-3-1-2-0-ar04.capitolhghts.md.bad.comcast.net (68.85.114.113) 3.522 ms 4.333 ms 3.441 ms 8 pos-5-1-0-0-cr01.ashburn.va.ibone.comcast.net (68.86.90.241) 7.269 ms pos-4-12-0-0-cr01.newyork.ny.ibone.comcast.net (68.86.90.173) 9.025 ms 7.192 ms 9 pos-0-4-0-0-pe01.ashburn.va.ibone.comcast.net (68.86.86.146) 5.236 ms 5.636 ms 6.229 ms 10 75.149.231.62 (75.149.231.62) 5.186 ms 5.113 ms 6.725 ms 11 209.85.252.46 (209.85.252.46) 6.836 ms 6.352 ms 78.371 ms 12 72.14.238.247 (72.14.238.247) 7.823 ms 7.616 ms 8.331 ms 13 iad23s07-in-f8.1e100.net (74.125.228.72) 10.798 ms 13.383 ms 7.540 ms
Again, if you are having trouble connecting to UMIACS services, we would suggest you test against one of our publicly accessible Nexus host such as nexuscml00.umiacs.umd.edu
or nexuscfar00.umiacs.umd.edu
.
Other Things to consider
- Is your IP address manually set?
- In order for networking to function properly, a machine must have a unique IP address on its network. In many cases IP address are assigned automatically via the DHCP protocol, but it is also possible to manually set an IP address. If your machine happens to have a manually set IP address that conflicts with that of another host, networking issues may arise.
- Are you behind a firewall?
- Some establishments use firewalls to restrict certain types of traffic both in and out of their networks. If you are having trouble accessing a specific service, this might be the case. To get around this you can connect to the VPN, or use SSH tunneling.
- Other useful commands:
dig
: performs DNS lookups and displays the answers that are returned from the name server(s) that were queriedhost
: simple utility for performing DNS lookupsnetstat
(macOS/Linux/UNIX): shows network statusroute print
(Windows): shows network routing tables
Change your default DNS server
Please see DNS troubleshooting to change your default DNS server.