Which two ICMP types must be allowed in a firewall to enable traceroutes through the
firewall? (Choose two.)
A.
ICMP type=5.code=1
B.
ICMP type=11, code=0
C.
ICMP type=5.code=0
D.
ICMP type=1l.code=1
E.
ICMP type=3, code=12
F.
ICMP type=3, code=3
Explanation:
http://www.cisco.com/c/en/us/support/docs/ios-nx-os-software/ios-software-releases-
121-mainline/12778-ping-traceroute.html#traceroute
This is the first sequence of packets we send with a TTL=1. The first router, in this case
Router2 (12.0.0.2), drops the packet, and sends back to the source (12.0.0.1) a type=11
ICMP message. This corresponds to the Time Exceeded Message.
Jan 20 16:42:48.707: IP: s=12.0.0.1 (local), d=34.0.0.4 (Serial0), len 28,
sending
Jan 20 16:42:48.711: UDP src=35734, dst=33437
Jan 20 16:42:48.743: IP: s=23.0.0.3 (Serial0), d=12.0.0.1 (Serial0), len 56,
rcvd 3
Jan 20 16:42:48.747: ICMP type=11, code=0
!— ICMP Time Exceeded Message from Router3.
Jan 20 16:42:48.751: IP: s=12.0.0.1 (local), d=34.0.0.4 (Serial0), len 28,
sending
Jan 20 16:42:48.755: UDP src=36753, dst=33438
Jan 20 16:42:48.787: IP: s=23.0.0.3 (Serial0), d=12.0.0.1 (Serial0), len 56,
rcvd 3
Jan 20 16:42:48.791: ICMP type=11, code=0
Jan 20 16:42:48.795: IP: s=12.0.0.1 (local), d=34.0.0.4 (Serial0), len 28,
sending
Jan 20 16:42:48.799: UDP src=36561, dst=33439
Jan 20 16:42:48.827: IP: s=23.0.0.3 (Serial0), d=12.0.0.1 (Serial0), len 56,
rcvd 3
Jan 20 16:42:48.831: ICMP type=11, code=0
The same process occurs for Router3 (23.0.0.3) with a TTL=2:Jan 20 16:42:48.839: IP: s=12.0.0.1 (local), d=34.0.0.4 (Serial0), len 28,
sending
Jan 20 16:42:48.843: UDP src=34327, dst=33440
Jan 20 16:42:48.887: IP: s=34.0.0.4 (Serial0), d=12.0.0.1 (Serial0), len 56,
rcvd 3
Jan 20 16:42:48.891: ICMP type=3, code=3
!— Port Unreachable message from Router4.
Jan 20 16:42:48.895: IP: s=12.0.0.1 (local), d=34.0.0.4 (Serial0), len 28,
sending
Jan 20 16:42:48.899: UDP src=37534, dst=33441
Jan 20 16:42:51.895: IP: s=12.0.0.1 (local), d=34.0.0.4 (Serial0), len 28,
sending
Jan 20 16:42:51.899: UDP src=37181, dst=33442
Jan 20 16:42:51.943: IP: s=34.0.0.4 (Serial0), d=12.0.0.1 (Serial0), len 56,
rcvd 3
Jan 20 16:42:51.947: ICMP type=3, code=3