CCNA Networking · Quick Reference

Module 13 — ICMP Cheat Sheet

CCNA Networking

In one line: The Internet Control Message Protocol (ICMP) is a Layer 3 protocol used by IP devices to send error messages and operational information. Unlike TCP or UDP, ICMP is not used to ...

Key Ideas

1What is ICMP?. The Internet Control Message Protocol (ICMP) is a Layer 3 protocol used by IP devices to send error messages and operational information. Unlike TCP or UDP, ICMP is no...

2ICMPv4 Message Types. ICMPv4 defines many message types, but the CCNA exam focuses on three key categories: Echo Request/Reply (used by ping), Destination Unreachable, and Time Exceeded (us...

3ICMPv6 Messages. ICMPv6 is defined in RFC 4443 and provides all the error and informational messaging of ICMPv4, but also incorporates the Neighbor Discovery Protocol (NDP) — a critica...

4Using Ping. Ping (Packet Internet Groper) is the most fundamental network diagnostic tool. It uses ICMP Echo Requests (Type 8) and Echo Replies (Type 0) to test whether a destinat...

5Using Traceroute. Traceroute (or tracert on Windows) traces the exact path that packets take from source to destination. It reveals every router (hop) along the path along with the roun...

Code Examples

Router# ping 192.168.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.1.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/4 ms

Router# traceroute 8.8.8.8
Type escape sequence to abort.
Tracing the route to 8.8.8.8
VRF info: (vrf in name/id, vrf out name/id)
  1 192.168.1.1   4 msec  2 msec  3 msec
  2 10.0.0.1     12 msec 11 msec 13 msec
  3 172.16.0.1   18 msec 19 msec 17 ms...