Traceroute Output Characters

The following characters can be displayed as output for the traceroute command:

Character	Description
nn msec	For each node, the round-trip time in milliseconds for the specified number of probes
*	The probe timed out
A	Administratively prohibited (eg: access lists)
Q	Source quench (destination too busy)
I	User interrupted test
U	Port unreachable
H	Host unreachable
N	Network unreachable
P	Protocol unreachable
T	Timeout
?	Unknown packet type

Below shows the output of the traceroute command in which 11.11.11.11 is an invalid IP address in the sample network and another router (3.3.3.2) has a black hole Null0 route to 0.0.0.0/0.

Router#trace 11.11.11.11

Type escape sequence to abort.
Tracing the route to 11.11.11.11

  1 2.2.2.2 40 msec 68 msec 40 msec
  2 3.3.3.2 92 msec 24 msec 164 msec
  3 3.3.3.2 !H  *  !H
Router#
Router#debug ip icmp
ICMP packet debugging is on
Router#
Router#trace 11.11.11.11

Type escape sequence to abort.
Tracing the route to 11.11.11.11

  1 2.2.2.2 40 msec 16 msec 40 msec
  2 3.3.3.2 108 msec 72 msec 56 msec
  3 3.3.3.2 !H
00:27:17: ICMP: time exceeded rcvd from 2.2.2.2
00:27:17: ICMP: time exceeded rcvd from 2.2.2.2
00:27:17: ICMP: time exceeded rcvd from 2.2.2.2
00:27:17: ICMP: time exceeded rcvd from 3.3.3.2
00:27:17: ICMP: time exceeded rcvd from 3.3.3.2
00:27:17: ICMP: time exceeded rcvd from 3.3.3.2
00:27:18: ICMP: dst (2.2.2.1) host unreachable rcv from 3.3.3.2 *  !H
00:27:21: ICMP: dst (2.2.2.1) host unreachable rcv from 3.3.3.2
Router#

Below shows the output of the traceroute command in which RT2 is configured with an access control list that blocked the UDP traceroute packets initiated by RT1:

RT1#ping 10.10.10.2

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.10.10.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 24/43/68 ms
RT1#
======================================================================
RT2#conf t
Enter configuration commands, one per line.  End with CNTL/Z.
RT2(config)#access-list 1 permit 1.1.1.1
RT2(config)#int s0/0
RT2(config-if)#ip access-group 1 in
RT2(config-if)#
======================================================================
RT1#debug ip icmp
ICMP packet debugging is on
RT1#
RT1#ping 10.10.10.2

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.10.10.2, timeout is 2 seconds:
U
00:03:25.383: ICMP: dst (10.10.10.1) administratively prohibited unreachable rcv from 10.10.10.2.U
00:03:27.431: ICMP: dst (10.10.10.1) administratively prohibited unreachable rcv from 10.10.10.2.U
Success rate is 0 percent (0/5)
RT1#
00:03:29.467: ICMP: dst (10.10.10.1) administratively prohibited unreachable rcv from 10.10.10.2
RT1#
RT1#sh run | in 0.0.0.0
ip route 0.0.0.0 0.0.0.0 10.10.10.2
RT1#
RT1#trace 172.16.1.1

Type escape sequence to abort.
Tracing the route to 172.16.1.1

  1 10.10.10.2 !A
00:05:32.071: ICMP: dst (10.10.10.1) administratively prohibited unreachable rcv from 10.10.10.2 *  !A
RT1#
00:05:35.119: ICMP: dst (10.10.10.1) administratively prohibited unreachable rcv from 10.10.10.2
RT1#