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There are a few other protocols that use IP that are not all often considered to be part of the TCP/IP suite of protocols but may be run over IP. Some of them are more closely associated with the TCP/IP suite of protocols like RIP, IGMP, and OSPF while others are a little less well known.
A reference to these extra protocols is included here so that you the reader realize that more than just TCP and IP exist in the TCP/IP suite of protocols, and they may be examined by a firewall before being allowed to pass on. In addition to UDP and ICMP which are part of the TCP/IP suite of protocols, there are other protocols that an be legally carried by IP packets. Many of them are considered by a number of people to part of the original TCP/IP suite of protocols, but all of these may still be part of the payload in an IP packet.
When recalling the review of the IP packet header, you will recall the protocol field is an 8 bit field. This allows for a decimal value that can range from 0 to 255.
In rfc1700.txt, you can find other protocols assigned for use with IP, and their decimal number in addition to UDP, TCP and ICMP. Here is a copy of those from that list: (If you recall the protocol field in the IP packet that was discussed in the review of the IP packet header, these are the decimal numbers that communicate the the receiving machine what protocol is being carried in the data portion of the IP packet.)
Assigned Internet Protocol Numbers Decimal Keyword Protocol References ------- ------- -------- ---------- 0 Reserved [JBP] 1 ICMP Internet Control Message [RFC792,JBP] 2 IGMP Internet Group Management [RFC1112,JBP] 3 GGP Gateway-to-Gateway [RFC823,MB] 4 IP IP in IP (encapsulation) [JBP] 5 ST Stream [RFC1190,IEN119,JWF] 6 TCP Transmission Control [RFC793,JBP] 7 UCL UCL [PK] 8 EGP Exterior Gateway Protocol [RFC888,DLM1] 9 IGP any private interior gateway [JBP] 10 BBN-RCC-MON BBN RCC Monitoring [SGC] 11 NVP-II Network Voice Protocol [RFC741,SC3] 12 PUP PUP [PUP,XEROX] 13 ARGUS ARGUS [RWS4] 14 EMCON EMCON [BN7] 15 XNET Cross Net Debugger [IEN158,JFH2] 16 CHAOS Chaos [NC3] 17 UDP User Datagram [RFC768,JBP] 18 MUX Multiplexing [IEN90,JBP] 19 DCN-MEAS DCN Measurement Subsystems [DLM1] 20 HMP Host Monitoring [RFC869,RH6] 21 PRM Packet Radio Measurement [ZSU] 22 XNS-IDP XEROX NS IDP [ETHERNET,XEROX] 23 TRUNK-1 Trunk-1 [BWB6] 24 TRUNK-2 Trunk-2 [BWB6] 25 LEAF-1 Leaf-1 [BWB6] 26 LEAF-2 Leaf-2 [BWB6] 27 RDP Reliable Data Protocol [RFC908,RH6] 28 IRTP Internet Reliable Transaction [RFC938,TXM] 29 ISO-TP4 ISO Transport Protocol Class 4 [RFC905,RC77] 30 NETBLT Bulk Data Transfer Protocol [RFC969,DDC1] 31 MFE-NSP MFE Network Services Protocol [MFENET,BCH2] 32 MERIT-INP MERIT Internodal Protocol [HWB] 33 SEP Sequential Exchange Protocol [JC120] 34 3PC Third Party Connect Protocol [SAF3] 35 IDPR Inter-Domain Policy Routing Protocol [MXS1] 36 XTP XTP [GXC] 37 DDP Datagram Delivery Protocol [WXC] 38 IDPR-CMTP IDPR Control Message Transport Proto [MXS1] 39 TP++ TP++ Transport Protocol [DXF] 40 IL IL Transport Protocol [DXP2] 41 SIP Simple Internet Protocol [SXD] 42 SDRP Source Demand Routing Protocol [DXE1] 43 SIP-SR SIP Source Route [SXD] 44 SIP-FRAG SIP Fragment [SXD] 45 IDRP Inter-Domain Routing Protocol [Sue Hares] 46 RSVP Reservation Protocol [Bob Braden] 47 GRE General Routing Encapsulation [Tony Li] 48 MHRP Mobile Host Routing Protocol[David Johnson] 49 BNA BNA [Gary Salamon] 50 SIPP-ESP SIPP Encap Security Payload [Steve Deering] 51 SIPP-AH SIPP Authentication Header [Steve Deering] 52 I-NLSP Integrated Net Layer Security TUBA [GLENN] 53 SWIPE IP with Encryption [JI6] 54 NHRP NBMA Next Hop Resolution Protocol 55-60 Unassigned [JBP] 61 any host internal protocol [JBP] 62 CFTP CFTP [CFTP,HCF2] 63 any local network [JBP] 64 SAT-EXPAK SATNET and Backroom EXPAK [SHB] 65 KRYPTOLAN Kryptolan [PXL1] 66 RVD MIT Remote Virtual Disk Protocol [MBG] 67 IPPC Internet Pluribus Packet Core [SHB] 68 any distributed file system [JBP] 69 SAT-MON SATNET Monitoring [SHB] 70 VISA VISA Protocol [GXT1] 71 IPCV Internet Packet Core Utility [SHB] 72 CPNX Computer Protocol Network Executive [DXM2] 73 CPHB Computer Protocol Heart Beat [DXM2] 74 WSN Wang Span Network [VXD] 75 PVP Packet Video Protocol [SC3] 76 BR-SAT-MON Backroom SATNET Monitoring [SHB] 77 SUN-ND SUN ND PROTOCOL-Temporary [WM3] 78 WB-MON WIDEBAND Monitoring [SHB] 79 WB-EXPAK WIDEBAND EXPAK [SHB] 80 ISO-IP ISO Internet Protocol [MTR] 81 VMTP VMTP [DRC3] 82 SECURE-VMTP SECURE-VMTP [DRC3] 83 VINES VINES [BXH] 84 TTP TTP [JXS] 85 NSFNET-IGP NSFNET-IGP [HWB] 86 DGP Dissimilar Gateway Protocol [DGP,ML109] 87 TCF TCF [GAL5] 88 IGRP IGRP [CISCO,GXS] 89 OSPFIGP OSPFIGP [RFC1583,JTM4] 90 Sprite-RPC Sprite RPC Protocol [SPRITE,BXW] 91 LARP Locus Address Resolution Protocol [BXH] 92 MTP Multicast Transport Protocol [SXA] 93 AX.25 AX.25 Frames [BK29] 94 IPIP IP-within-IP Encapsulation Protocol [JI6] 95 MICP Mobile Internetworking Control Pro. [JI6] 96 SCC-SP Semaphore Communications Sec. Pro. [HXH] 97 ETHERIP Ethernet-within-IP Encapsulation [RXH1] 98 ENCAP Encapsulation Header [RFC1241,RXB3] 99 any private encryption scheme [JBP] 100 GMTP GMTP [RXB5] 101-254 Unassigned [JBP] 255 Reserved [JBP]