Section A-1. IP Protocol Numbers

A-1. IP Protocol Numbers

A higher-layer protocol is identified with an 8-bit field called Protocol in an IPv4 packet. Figure A-1 shows the IPv4 packet header format, with the Protocol field shaded.

Figure A-1. IPv4 Header Format Showing the Protocol Field

Cisco firewalls have keywords that can be used to specify certain IP protocols in access lists. These keywords are shown along with the IP protocol numbers in Table A-1.

Table A-2. Cisco Firewall Keywords for IP Protocols

Protocol Number	Firewall Keyword	IP Protocol Description
1	icmp	Internet Control Message Protocol (ICMP)
2	igmp	Internet Group Management Protocol (IGMP)
4	ipinip	IP-in-IP encapsulation
6	tcp	Transmission Control Protocol (TCP)
9	igrp	Interior Gateway Routing Protocol (IGRP)
17	udp	User Datagram Protocol (UDP)
47	gre or pptp	General Routing Encapsulation (GRE)
50	esp or ipsec	Encapsulating Security Payload (ESP)
51	ah	Authentication Header (AH)
58	icmp6	ICMP for IPv6
88	eigrp	Enhanced Interior Gateway Routing Protocol (EIGRP)
89	ospf	Open Shortest Path First (OSPF)
94	nos	Network Operating System (Novell NetWare)
103	pim	Protocol-Independent Multicast (PIM)
108	pcp	Payload Compression Protocol
109	snp	Sitara Networks Protocol