Ccna routing and Switching Complete Study Guide

Protocol

Protocol Number

ICMP

1

IP in IP (tunneling)

4

TCP

6

UDP

17

EIGRP

88

OSPF

89

IPv6

41

GRE

47

Layer 2 tunnel (L2TP)

115

You can find a complete list of Protocol field numbers at 

www.iana.org/

assignments/protocol-numbers

.

Internet Control Message Protocol (ICMP)

Internet Control Message Protocol (ICMP) works at the Network layer and is used by 

IP for many different services. ICMP is basically a management protocol and messaging 

service provider for IP. Its messages are carried as IP datagrams. RFC 1256 is an annex to 

ICMP, which gives hosts extended capability in discovering routes to gateways.

ICMP packets have the following characteristics:

 

■

They can provide hosts with information about network problems.

 

■

They are encapsulated within IP datagrams.

---

112

 

Chapter 3 

■

  Introduction to TCP/IP 

The following are some common events and messages that ICMP relates to: