Traceroute; Using Traceroute; Traceroute Operation - 3Com corebuilder 3500 Implementation Manual

532 C 18: D
HAPTER EVICE

traceRoute

Using traceRoute

traceRoute Operation

M
ONITORING
Use the traceRoute feature to track the route of an IP packet through the
network. TraceRoute information includes all of the nodes in the network
through which a packet passes to get from its origin to its destination.
The traceRoute feature uses the IP time-to-live (TTL) field in User
Datagram Protocol (UDP) probe packets to elicit an ICMP Time Exceeded
message from each gateway to a particular host.
The system provides two traceRoute functions:
traceRoute — Uses the hostname or IP address to trace a route to a
host with default options
advancedTraceRoute — Uses the hostname or IP address to trace a
route to a host with the advanced traceRoute options that you specify
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 1 and
increase the value by 1 until one of the following events occurs:
The system receives a Port Unreachable message, indicating that the
packet reached the host.
The probe exceeds the maximum number of hops. The default is 30.
At each TTL setting, the system launches three UDP probe packets, and
the traceRoute display shows a line with 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 3-second time-out
interval, traceRoute displays an asterisk (*) for that probe. Other
characters that can be displayed include the following:
— Network is unreachable
!N
— Host is unreachable
!H
— Protocol is unreachable
!P
— Fragmentation is needed
!F
— Unknown packet type
!< n >