Using Traceroute - 3Com SuperStack II 3300 User Manual

Using traceRoute

The traceRoute feature allows you to track the route of an IP packet
through the network. TraceRoute information includes all the nodes in
the network that a packet passes through to get from its origin to its
destination. The traceRoute feature uses the IP time-to-live (TTL) field in
UDP probe packets to elicit an ICMP "Time Exceeded" message from
each gateway to a particular host.
There are two traceRoute commands available:
— Uses the host name or IP address to trace a route to a
traceRoute
host using the default options.
advancedTraceRoute
route to a host using the advanced options that you specify.
You can enter the host name as part of the command string or you can
supply the name in response to the prompt.
To track the route of an IP packet, the traceRoute feature launches UDP
probe packets with a small TTL value and then listens for an ICMP "Time
Exceeded" reply from a gateway. Probes start with a small TTL of one and
increase the value by one until one of the following events occurs:
The Layer 3 Module receives a "Port Unreachable" message,
indicating that the packet reached the host.
The probe exceeds the maximum number of hops (the default is 30
hops).
At each TTL setting, the Layer 3 Module launches three UDP probe
packets, and the traceRoute display prints a line showing the TTL value,
the address of the gateway, and the round trip time of each probe. If a
probe answers from different gateways, the traceRoute feature prints the
address of each responding system. If no response occurs in the three
second time-out interval, traceRoute prints an asterisk * for that probe.
Other characters that can appear in the display are:
— Indicates that the network is unreachable
!N
— Indicates that the host is unreachable
!H
— Indicates that the protocol is unreachable
!P
— Indicates that fragmentation is needed
!F
— Indicates an unknown packet type
!<n>
— Uses the host name or IP address to trace a
Using traceRoute 123