C-78
Troubleshooting
Diagnostic Tools
Figure C-26. Example of Incomplete Traceroute Due to Low Maxttl Setting
If A Network Condition Prevents Traceroute from Reaching the
Destination.
Common reasons for Traceroute failing to reach a destination
include:
■
Timeouts (indicated by one asterisk per probe, per hop; refer to
Figure C-26, above.)
■
Unreachable hosts
■
Unreachable networks
■
Interference from firewalls
■
Hosts configured to avoid responding
Executing traceroute where the route becomes blocked or otherwise fails
results in an output marked by timeouts for all probes beyond the last detected
hop. For example with a maximum hop count of 7 (
maxttl
= 7), where the route
becomes blocked or otherwise fails, the output appears similar to this:
Figure C-27. Example of Traceroute Failing to Reach the Destination Address
Traceroute does not reach
destination IP address
because of low
maxttl
setting.
The asterisk indicates there was a
timeout on the second probe to the third
hop.
At hop 3, the first and
third probes timed out
but the second probe
reached the router.
All further probes
within the
maxttl
timed-out without
finding a router or the
destination IP
address.
An asterisk indicates a timeout
without finding the next hop.
3500-5400-6200-8200-MCG-Jan08-K_13_01.book Page 78 Monday, January 28, 2008 10:04 AM