Tracing The Route To A Host - Digi PortServer II User Manual

Tracing the Route to a Host

Many problems that you will encounter when using PortServer II in a network may be
due to faults with external systems. This is especially true if you use PortServer II to
connect to the Internet, where data may pass through many systems between source
and destination. To assist in identifying problems with intermediate Gateways,
PortServer II includes a traceroute command.
This command attempts to trace the route that an IP packet follows to an Internet host.
It identifies intermediate hops by sending probe packets with a small TTL (Time To
Live) and listening for an ICMP Time Exceeded reply from each Gateway. The first
three probe packets that are sent have a TTL of one, then this value is incremented by
one for each subsequent group of three packets. When PortServer II receives an ICMP
Port Unreachable reply, a probe packet reached the host or the maximum of 30 hops
was reached.
The address of each responding gateway is logged, together with the time to reply to
each probe packet. If there is no response within the five second timeout interval, a
"no response line is printed ("* * * ").
Probe packets are in UDP format, with the destination port set to a value that should
ensure the Gateway host does not process them.
The syntax for the traceroute command is:
traceroute <host>
where <host> may be the name or the IP address of the target Internet host.
90030500B Troubleshooting Page 235