RFC 1812 Requirements for IP Version 4 Routers June 1995 4.2.2.11 Addressing: RFC 791 Section 3.2 ............... 47 4.2.3 SPECIFIC ISSUES .................................. 50 4.2.3.1 IP Broadcast Addresses ......................... 50 4.2.3.2 IP Multicasting ................................ 50 4.2.3.3 Path MTU Discovery ............................. 51 4.2.3.4 Subnetting ..................................... 51 4.3 INTERNET CONTROL MESSAGE PROTOCOL - ICMP ........... 52 4.3.1 INTRODUCTION ..................................... 52 4.3.2 GENERAL ISSUES ................................... 53 4.3.2.1 Unknown Message Types .......................... 53 4.3.2.2 ICMP Message TTL ............................... 53 4.3.2.3 Original Message Header ........................ 53 4.3.2.4 ICMP Message Source Address .................... 53 4.3.2.5 TOS and Precedence ............................. 54 4.3.2.6 Source Route ................................... 54 4.3.2.7 When Not to Send ICMP Errors ................... 55 4.3.2.8 Rate Limiting .................................. 56 4.3.3 SPECIFIC ISSUES .................................. 56 4.3.3.1 Destination Unreachable ........................ 56 4.3.3.2 Redirect ....................................... 57 4.3.3.3 Source Quench .................................. 57 4.3.3.4 Time Exceeded .................................. 58 4.3.3.5 Parameter Problem .............................. 58 4.3.3.6 Echo Request/Reply ............................. 58 4.3.3.7 Information Request/Reply ...................... 59 4.3.3.8 Timestamp and Timestamp Reply .................. 59 4.3.3.9 Address Mask Request/Reply ..................... 61 4.3.3.10 Router Advertisement and Solicitations ........ 62 4.4 INTERNET GROUP MANAGEMENT PROTOCOL - IGMP .......... 62 5. INTERNET LAYER - FORWARDING ......................... 63 5.1 INTRODUCTION ....................................... 63 5.2 FORWARDING WALK-THROUGH ............................ 63 5.2.1 Forwarding Algorithm ............................. 63 5.2.1.1 General ........................................ 64 5.2.1.2 Unicast ........................................ 64 5.2.1.3 Multicast ...................................... 65 5.2.2 IP Header Validation ............................. 67 5.2.3 Local Delivery Decision .......................... 69 5.2.4 Determining the Next Hop Address ................. 71 5.2.4.1 IP Destination Address ......................... 72 5.2.4.2 Local/Remote Decision .......................... 72 5.2.4.3 Next Hop Address ............................... 74 5.2.4.4 Administrative Preference ...................... 77 5.2.4.5 Load Splitting ................................. 79 5.2.5 Unused IP Header Bits: RFC-791 Section 3.1 ....... 79 5.2.6 Fragmentation and Reassembly: RFC-791, Section 3.2 ...................................... 80 5.2.7 Internet Control Message Protocol - ICMP ......... 80 Baker Standards Track