RFC 1122 INTRODUCTION October 1989 2.2 PROTOCOL WALK-THROUGH .................................. 21 2.3 SPECIFIC ISSUES ........................................ 21 2.3.1 Trailer Protocol Negotiation ...................... 21 2.3.2 Address Resolution Protocol -- ARP ................ 22 2.3.2.1 ARP Cache Validation ......................... 22 2.3.2.2 ARP Packet Queue ............................. 24 2.3.3 Ethernet and IEEE 802 Encapsulation ............... 24 2.4 LINK/INTERNET LAYER INTERFACE .......................... 25 2.5 LINK LAYER REQUIREMENTS SUMMARY ........................ 26 3. INTERNET LAYER PROTOCOLS .................................... 27 3.1 INTRODUCTION ............................................ 27 3.2 PROTOCOL WALK-THROUGH .................................. 29 3.2.1 Internet Protocol -- IP ............................ 29 3.2.1.1 Version Number ............................... 29 3.2.1.2 Checksum ..................................... 29 3.2.1.3 Addressing ................................... 29 3.2.1.4 Fragmentation and Reassembly ................. 32 3.2.1.5 Identification ............................... 32 3.2.1.6 Type-of-Service .............................. 33 3.2.1.7 Time-to-Live ................................. 34 3.2.1.8 Options ...................................... 35 3.2.2 Internet Control Message Protocol -- ICMP .......... 38 3.2.2.1 Destination Unreachable ...................... 39 3.2.2.2 Redirect ..................................... 40 3.2.2.3 Source Quench ................................ 41 3.2.2.4 Time Exceeded ................................ 41 3.2.2.5 Parameter Problem ............................ 42 3.2.2.6 Echo Request/Reply ........................... 42 3.2.2.7 Information Request/Reply .................... 43 3.2.2.8 Timestamp and Timestamp Reply ................ 43 3.2.2.9 Address Mask Request/Reply ................... 45 3.2.3 Internet Group Management Protocol IGMP ........... 47 3.3 SPECIFIC ISSUES ........................................ 47 3.3.1 Routing Outbound Datagrams ........................ 47 3.3.1.1 Local/Remote Decision ........................ 47 3.3.1.2 Gateway Selection ............................ 48 3.3.1.3 Route Cache .................................. 49 3.3.1.4 Dead Gateway Detection ....................... 51 3.3.1.5 New Gateway Selection ........................ 55 3.3.1.6 Initialization ............................... 56 3.3.2 Reassembly ........................................ 56 3.3.3 Fragmentation ..................................... 58 3.3.4 Local Multihoming ................................. 60 3.3.4.1 Introduction ................................. 60 3.3.4.2 Multihoming Requirements ..................... 61 3.3.4.3 Choosing a Source Address .................... 64 3.3.5 Source Route Forwarding ........................... 65 Internet Engineering Task Force