A-210
Cisco ONS 15530 Configuration Guide and Command Reference
78-14227-01, Cisco IOS Release 12.1(10)E2
AppendixA Command Reference
System Management Commands
Not all destinations respond correctly to a probe message by sending back a n ICMP port unreachable
message. A long sequence of TTL levels with only asterisks, terminating only when the maximum TTL
is reached, may indicate this problem.
There is a known problem with the way some hosts handle an ICMP TTL exceeded message. Some hosts
generate an ICMP message, but they reuse the TTL of the incoming packet. Because this is zero, the
ICMP packets do not make it back. When you trace the path to such a host, you may see a set of TTL
values with asterisks (*). Eventually, the TTL gets high enough that the ICMP message can ge t back. For
example, if the host is 6 hops away, traceroute times out in responses 6 through 11.
Examples The following example displays sample I P traceroute output in EXEC mode when a destinat ion host
name is specified. (See Table A- 43 for field descriptions.)
Switch> traceroute ip ABA.NYC.mil
Type escape sequence to abort.
Tracing the route to ABA.NYC.mil (26.0.0.73)
1 DEBRIS.CISCO.COM (131.108.1.6) 1000 msec 8 msec 4 msec
2 BARRNET-GW.CISCO.COM (131.108.16.2) 8 msec 8 msec 8 msec
3 EXTERNAL-A-GATEWAY.STANFORD.EDU (192.42.110.225) 8 msec 4 msec 4 msec
4 BB2.SU.BARRNET.NET (131.119.254.6) 8 msec 8 msec 8 msec
5 SU.ARC.BARRNET.NET (131.119.3.8) 12 msec 12 msec 8 msec
6 MOFFETT-FLD-MB.in.MIL (192.52.195.1) 216 msec 120 msec 132 msec
7 ABA.NYC.mil (26.0.0.73) 412 msec 628 msec 664 msec
Table A -44 describes the characters that can appear in traceroute output.
TableA-43 traceroute command Field Descriptions
Field Description
1 Indicates the sequence number of the system in the path to the
host.
DEBRIS.CISCO.COM Shows the host name of this system.
131.108.1.61 Shows the IP address of this system.
1000 msec 8 msec 4 msec Shows the round-trip time for each of the three probes that are
sent.
TableA-44 IP Trace Text Characters
Character Description
nn msec Indicates for each node the round-trip time in milliseconds for the
specified number of probes.
* Indicates that the probe timed out.
? Indicates an unknown packet type.
Q Indicates a source quench.
P Indicates that the protocol is unreachable.
N Indicates that the network is unreachable.
U Indicates that the port is unreachable.
H Indicates that the host is unreachable.