8.4 WAN Output

8.4 WAN Output

The output shown earlier for our small internet is adequate for examining the protocols in action, but more a realistic use of traceroute involves larger internets such as the worldwide Internet.

Figure 8.4 is from the host sun to the Network Information Center, the NIC.

Figure 8.4. traceroute from host sun to nic.ddn.mil.

Since running this example for inclusion in the text, the NIC for non-DDN sites (i.e., non-military) has moved from nic.ddn.mil to rs.internic.net, the new "InterNIC."

Once the datagrams leave the tuc.noao.edu network they enter the telcom.arizona.edu network. They then enter the NASA Science Internet, nsn.nasa.gov. The routers for TTLs 6 and 7 are at the Jet Propulsion Laboratory (JPL). The network sura.net in the output for TTL 11 is the Southeastern Universities Research Association Network. The name GSI at TTL 12 is Government Systems, Inc., the operator of the NIC.

The second RTT for the TTL of 6 (590) is more than double the other two RTTs (234 and 262). This illustrates the dynamics of IP routing. Something happened somewhere between the sending host and this router that slowed down this datagram. Also, we can't tell if it was the outbound datagram that got held up or the return ICMP error.

The RTT for the first probe with a TTL of 3 (204) is less than the RTT for the first probe with a TTL of 2 (233). Since each printed RTT is the total time from the sending host to that router, this can (and does) happen.

The example in Figure 8.5 is from the host sun to the author's publisher.

Figure 8.5. traceroute from host sun.tuc.noao.edu to aw.com .

This time the datagrams enter the regional network westnet.net (TTLs 6 and 7) after leaving the telcom.arizona.edu network. They then enter the NSFNET backbone, t3.ans.net , which is run by Advanced Network & Services. (T3 is the common abbreviation for the 45 Mbits/sec phone lines used by the backbone.) The final network is alter.net , the connection point to the Internet for aw.com .