How to Display Routing Table Status
The -r option of netstat displays the IP routing table.
netstat -r produces the following sample display on machine tenere:
Routing tables Destination Gateway Flags Refcnt Use Interface temp8milptp elvis UGH 0 0 irmcpeb1-ptp0 elvis UGH 0 0 route93-ptp0 speed UGH 0 0 mtvb9-ptp0 speed UGH 0 0 . mtnside speed UG 1 567 ray-net speed UG 0 0 mtnside-eng speed UG 0 36 mtnside-eng speed UG 0 558 mtnside-eng tenere U 33 190248 le0 |
The first column shows the destination network, the second the router through which packets are forwarded. The U flag indicates that the route is up. The G flag indicates that the route is to a gateway. The H flag indicates that the destination is a fully qualified host address, rather than a network.
The Refcnt column shows the number of active uses per route, and the Use column shows the number of packets sent per route. Finally, the Interface column shows the network interface that the route uses.
Logging Network Problems
If you suspect a routing daemon malfunction, you can log its actions, including all packet transfers when you start up the routed daemon.
How to Log Network Problems
Become superuser.
Create a log file of routing daemon actions by typing the following command at a command-line prompt.
# /usr/sbin/in.routed /var/logfilename
Caution - On a busy network, this command can generate almost continuous
output.
Displaying Packet Contents
You can use snoop to capture network packets and display their contents. Packets can be displayed as soon as they are received, or saved to a file. When snoop writes to an intermediate file, packet loss under busy trace conditions is unlikely. snoop itself is then used to interpret the file. For information about using the snoop command, refer to the snoop(1M) man page.
The snoop command must be run by root (#) to capture packets to and from the default interface in promiscuous mode. In summary form, only the data that pertains to the highest-level protocol is displayed. For example, an NFS packet only displays NFS information. The underlying RPC, UDP, IP, and Ethernet frame information is suppressed but can be displayed if either of the verbose options is chosen.
The snoop capture file format is described in RFC 1761.
snoop server client rpc rstatd collects all RPC traffic between a client and server, and filters the traffic for rstatd.
Displaying Packet Contents Task Map
Table 4-9 Displaying Packet Contents Task Map
Task | Description | For Instructions, Go To ... |
|---|---|---|
Check all packets from your system | Involves using the netstat and snoop commands and interpreting the results | |
Capture snoop results to a file | Involves using the -o option of the snoop command | |
Check packets between server and client | Involves saving the results of the snoop command to a file and inspecting the results |
How to Check All Packets From Your System
Become superuser.
Type the following command at the command-line prompt to find the interfaces that are attached to the system.
# netstat -i
snoop normally uses the first non-loopback device (le0).
Type snoop.
Use Control-C to halt the process.
# snoop Using device /dev/le (promiscuous mode) maupiti -> atlantic-82 NFS C GETATTR FH=0343 atlantic-82 -> maupiti NFS R GETATTR OK maupiti -> atlantic-82 NFS C GETATTR FH=D360 atlantic-82 -> maupiti NFS R GETATTR OK maupiti -> atlantic-82 NFS C GETATTR FH=1A18 atlantic-82 -> maupiti NFS R GETATTR OK maupiti -> (broadcast) ARP C Who is 120.146.82.36, npmpk17a-82 ?Interpret the results.
In the example, client maupiti transmits to server atlantic-82 by using NFS file handle 0343. atlantic-82 acknowledges with OK. The conversation continues until maupiti broadcasts an ARP request that asks who is 120.146.82.36?
This example demonstrates the format of snoop. The next step is to filter snoop to capture packets to a file.
Interpret the capture file by using details that are described in RFC 1761.
How to Capture snoop Results to a File
Become superuser.
On the command line, type the following command.
# snoop -o filename
For example:
# snoop -o /tmp/cap Using device /dev/le (promiscuous mode) 30 snoop: 30 packets captured
By using this command, you have captured 30 packets in a file /tmp/cap. The file can be anywhere with enough disk space. The number of packets that are captured is displayed on the command line, enabling you to press Control-C to abort at any time.
snoop creates a noticeable networking load on the host machine, which can distort the results. To see the actual results, run snoop from a third system (see the next section).
On the command line, type the following command to inspect the file.
# snoop -i filename
For example:
# snoop -i /tmp/cap 1 0.00000 frmpk17b-082 -> 224.0.0.2 IP D=224.0.0.2 S=129.146.82.1 LEN=32, ID=0 2 0.56104 scout -> (broadcast) ARP C Who is 129.146.82.63, grail ? 3 0.16742 atlantic-82 -> (broadcast) ARP C Who is 129.146.82.76, honeybea ? 4 0.77247 scout -> (broadcast) ARP C Who is 129.146.82.63, grail ? 5 0.80532 frmpk17b-082 -> (broadcast) ARP C Who is 129.146.82.92, holmes ? 6 0.13462 scout -> (broadcast) ARP C Who is 129.146.82.63, grail ? 7 0.94003 scout -> (broadcast) ARP C Who is 129.146.82.63, grail ? 8 0.93992 scout -> (broadcast) ARP C Who is 129.146.82.63, grail ? 9 0.60887 towel -> (broadcast) ARP C Who is 129.146.82.35, udmpk17b-82 ? 10 0.86691 nimpk17a-82 -> 129.146.82.255 RIP R (1 destinations)
Refer to specific protocol documentation for detailed analysis and recommended parameters for ARP, IP, RIP and so forth. The Web contains a number of requests for comments.