rfc1716.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

Network Working Group                                P. Almquist, Author
Request for Comments: 1716                                    Consultant
Category: Informational                            F. Kastenholz, Editor
                                                      FTP Software, Inc.
                                                           November 1994


                  Towards Requirements for IP Routers

Status of this Memo

   This memo provides information for the Internet community.  This memo
   does not specify an Internet standard of any kind.  Distribution of
   this memo is unlimited.





































Almquist & Kastenholz                                           [Page i]

RFC 1716          Towards Requirements for IP Routers      November 1994


Table of Contents


0.  PREFACE .......................................................    1
1.  INTRODUCTION ..................................................    2
1.1  Reading this Document ........................................    4
1.1.1  Organization ...............................................    4
1.1.2  Requirements ...............................................    5
1.1.3  Compliance .................................................    6
1.2  Relationships to Other Standards .............................    7
1.3  General Considerations .......................................    8
1.3.1  Continuing Internet Evolution ..............................    8
1.3.2  Robustness Principle .......................................    9
1.3.3  Error Logging ..............................................    9
1.3.4  Configuration ..............................................   10
1.4  Algorithms ...................................................   11
2.  INTERNET ARCHITECTURE .........................................   13
2.1  Introduction .................................................   13
2.2  Elements of the Architecture .................................   14
2.2.1  Protocol Layering ..........................................   14
2.2.2  Networks ...................................................   16
2.2.3  Routers ....................................................   17
2.2.4  Autonomous Systems .........................................   18
2.2.5  Addresses and Subnets ......................................   18
2.2.6  IP Multicasting ............................................   20
2.2.7  Unnumbered Lines and Networks and Subnets ..................   20
2.2.8  Notable Oddities ...........................................   22
2.2.8.1  Embedded Routers .........................................   22
2.2.8.2  Transparent Routers ......................................   23
2.3  Router Characteristics .......................................   24
2.4  Architectural Assumptions ....................................   27
3.  LINK LAYER ....................................................   29
3.1  INTRODUCTION .................................................   29
3.2  LINK/INTERNET LAYER INTERFACE ................................   29
3.3  SPECIFIC ISSUES ..............................................   30
3.3.1  Trailer Encapsulation ......................................   30
3.3.2  Address Resolution Protocol - ARP ..........................   31
3.3.3  Ethernet and 802.3 Coexistence .............................   31
3.3.4  Maximum Transmission Unit - MTU ............................   31
3.3.5  Point-to-Point Protocol - PPP ..............................   32
3.3.5.1  Introduction .............................................   32
3.3.5.2  Link Control Protocol (LCP) Options ......................   33
3.3.5.3  IP Control Protocol (ICP) Options ........................   34
3.3.6  Interface Testing ..........................................   35
4.  INTERNET LAYER - PROTOCOLS ....................................   36
4.1  INTRODUCTION .................................................   36
4.2  INTERNET PROTOCOL - IP .......................................   36


Almquist & Kastenholz                                          [Page ii]

RFC 1716          Towards Requirements for IP Routers      November 1994


4.2.1  INTRODUCTION ...............................................   36
4.2.2  PROTOCOL WALK-THROUGH ......................................   37
4.2.2.1  Options: RFC-791 Section 3.2 .............................   37
4.2.2.2  Addresses in Options: RFC-791 Section 3.1 ................   40
4.2.2.3  Unused IP Header Bits: RFC-791 Section 3.1 ...............   40
4.2.2.4  Type of Service: RFC-791 Section 3.1 .....................   41
4.2.2.5  Header Checksum: RFC-791 Section 3.1 .....................   41
4.2.2.6  Unrecognized Header Options: RFC-791 Section 3.1 .........   41
4.2.2.7  Fragmentation: RFC-791 Section 3.2 .......................   42
4.2.2.8  Reassembly: RFC-791 Section 3.2 ..........................   43
4.2.2.9  Time to Live: RFC-791 Section 3.2 ........................   43
4.2.2.10  Multi-subnet Broadcasts: RFC-922 ........................   43
4.2.2.11  Addressing: RFC-791 Section 3.2 .........................   43
4.2.3  SPECIFIC ISSUES ............................................   47
4.2.3.1  IP Broadcast Addresses ...................................   47
4.2.3.2  IP Multicasting ..........................................   48
4.2.3.3  Path MTU Discovery .......................................   48
4.2.3.4  Subnetting ...............................................   49
4.3  INTERNET CONTROL MESSAGE PROTOCOL - ICMP .....................   50
4.3.1  INTRODUCTION ...............................................   50
4.3.2  GENERAL ISSUES .............................................   50
4.3.2.1  Unknown Message Types ....................................   50
4.3.2.2  ICMP Message TTL .........................................   51
4.3.2.3  Original Message Header ..................................   51
4.3.2.4  ICMP Message Source Address ..............................   51
4.3.2.5  TOS and Precedence .......................................   51
4.3.2.6  Source Route .............................................   52
4.3.2.7  When Not to Send ICMP Errors .............................   53
4.3.2.8  Rate Limiting ............................................   54
4.3.3  SPECIFIC ISSUES ............................................   55
4.3.3.1  Destination Unreachable ..................................   55
4.3.3.2  Redirect .................................................   55
4.3.3.3  Source Quench ............................................   56
4.3.3.4  Time Exceeded ............................................   56
4.3.3.5  Parameter Problem ........................................   57
4.3.3.6  Echo Request/Reply .......................................   57
4.3.3.7  Information Request/Reply ................................   58
4.3.3.8  Timestamp and Timestamp Reply ............................   58
4.3.3.9  Address Mask Request/Reply ...............................   59
4.3.3.10  Router Advertisement and Solicitations ..................   61
4.4  INTERNET GROUP MANAGEMENT PROTOCOL - IGMP ....................   61
5.  INTERNET LAYER - FORWARDING ...................................   62
5.1  INTRODUCTION .................................................   62
5.2  FORWARDING WALK-THROUGH ......................................   62
5.2.1  Forwarding Algorithm .......................................   62
5.2.1.1  General ..................................................   63
5.2.1.2  Unicast ..................................................   64


Almquist & Kastenholz                                         [Page iii]

RFC 1716          Towards Requirements for IP Routers      November 1994


5.2.1.3  Multicast ................................................   65
5.2.2  IP Header Validation .......................................   66
5.2.3  Local Delivery Decision ....................................   68
5.2.4  Determining the Next Hop Address ...........................   70
5.2.4.1  Immediate Destination Address ............................   71
5.2.4.2  Local/Remote Decision ....................................   71
5.2.4.3  Next Hop Address .........................................   72
5.2.4.4  Administrative Preference ................................   77
5.2.4.6  Load Splitting ...........................................   78
5.2.5  Unused IP Header Bits: RFC-791 Section 3.1 .................   79
5.2.6  Fragmentation and Reassembly: RFC-791 Section 3.2 ..........   79
5.2.7  Internet Control Message Protocol - ICMP ...................   80
5.2.7.1  Destination Unreachable ..................................   80
5.2.7.2  Redirect .................................................   82
5.2.7.3  Time Exceeded ............................................   84
5.2.8  INTERNET GROUP MANAGEMENT PROTOCOL - IGMP ..................   84
5.3  SPECIFIC ISSUES ..............................................   84
5.3.1  Time to Live (TTL) .........................................   84
5.3.2  Type of Service (TOS) ......................................   85
5.3.3  IP Precedence ..............................................   87
5.3.3.1  Precedence-Ordered Queue Service .........................   88
5.3.3.2  Lower Layer Precedence Mappings ..........................   88
5.3.3.3  Precedence Handling For All Routers ......................   89
5.3.4  Forwarding of Link Layer Broadcasts ........................   92
5.3.5  Forwarding of Internet Layer Broadcasts ....................   92
5.3.5.1  Limited Broadcasts .......................................   94
5.3.5.2  Net-directed Broadcasts ..................................   94
5.3.5.3  All-subnets-directed Broadcasts ..........................   95
5.3.5.4  Subnet-directed Broadcasts ...............................   97
5.3.6  Congestion Control .........................................   97
5.3.7  Martian Address Filtering ..................................   99
5.3.8  Source Address Validation ..................................   99
5.3.9  Packet Filtering and Access Lists ..........................  100
5.3.10  Multicast Routing .........................................  101
5.3.11  Controls on Forwarding ....................................  101
5.3.12  State Changes .............................................  101
5.3.12.1  When a Router Ceases Forwarding .........................  102
5.3.12.2  When a Router Starts Forwarding .........................  102
5.3.12.3  When an Interface Fails or is Disabled ..................  103
5.3.12.4  When an Interface is Enabled ............................  103
5.3.13  IP Options ................................................  103
5.3.13.1  Unrecognized Options ....................................  103
5.3.13.2  Security Option .........................................  104
5.3.13.3  Stream Identifier Option ................................  104
5.3.13.4  Source Route Options ....................................  104
5.3.13.5  Record Route Option .....................................  104
5.3.13.6  Timestamp Option ........................................  105


Almquist & Kastenholz                                          [Page iv]

RFC 1716          Towards Requirements for IP Routers      November 1994


6.  TRANSPORT LAYER ...............................................  106
6.1  USER DATAGRAM PROTOCOL - UDP .................................  106
6.2  TRANSMISSION CONTROL PROTOCOL - TCP ..........................  106
7.  APPLICATION LAYER - ROUTING PROTOCOLS .........................  109
7.1  INTRODUCTION .................................................  109
7.1.1  Routing Security Considerations ............................  109
7.1.2  Precedence .................................................  110
7.2  INTERIOR GATEWAY PROTOCOLS ...................................  110
7.2.1  INTRODUCTION ...............................................  110
7.2.2  OPEN SHORTEST PATH FIRST - OSPF ............................  111
7.2.2.1  Introduction .............................................  111
7.2.2.2  Specific Issues ..........................................  111
7.2.2.3  New Version of OSPF ......................................  112
7.2.3  INTERMEDIATE SYSTEM TO INTERMEDIATE SYSTEM -  DUAL  IS-IS
     ..............................................................  112
7.2.4  ROUTING INFORMATION PROTOCOL - RIP .........................  113
7.2.4.1  Introduction .............................................  113
7.2.4.2  Protocol Walk-Through ....................................  113
7.2.4.3  Specific Issues ..........................................  118
7.2.5  GATEWAY TO GATEWAY PROTOCOL - GGP ..........................  119
7.3  EXTERIOR GATEWAY PROTOCOLS ...................................  119
7.3.1  INTRODUCTION ...............................................  119
7.3.2  BORDER GATEWAY PROTOCOL - BGP ..............................  120
7.3.2.1  Introduction .............................................  120
7.3.2.2  Protocol Walk-through ....................................  120
7.3.3  EXTERIOR GATEWAY PROTOCOL - EGP ............................  121
7.3.3.1  Introduction .............................................  121
7.3.3.2  Protocol Walk-through ....................................  122
7.3.4  INTER-AS ROUTING WITHOUT AN EXTERIOR PROTOCOL ..............  124
7.4  STATIC ROUTING ...............................................  125
7.5  FILTERING OF ROUTING INFORMATION .............................  127
7.5.1  Route Validation ...........................................  127
7.5.2  Basic Route Filtering ......................................  127
7.5.3  Advanced Route Filtering ...................................  128
7.6  INTER-ROUTING-PROTOCOL INFORMATION EXCHANGE ..................  129
8.  APPLICATION LAYER - NETWORK MANAGEMENT PROTOCOLS ..............  131
8.1  The Simple Network Management Protocol - SNMP ................  131
8.1.1  SNMP Protocol Elements .....................................  131
8.2  Community Table ..............................................  132
8.3  Standard MIBS ................................................  133
8.4  Vendor Specific MIBS .........................................  134
8.5  Saving Changes ...............................................  135
9.  APPLICATION LAYER - MISCELLANEOUS PROTOCOLS ...................  137
9.1  BOOTP ........................................................  137
9.1.1  Introduction ...............................................  137
9.1.2  BOOTP Relay Agents .........................................  137
10.  OPERATIONS AND MAINTENANCE ...................................  139


Almquist & Kastenholz                                           [Page v]

RFC 1716          Towards Requirements for IP Routers      November 1994


10.1  Introduction ................................................  139
10.2  Router Initialization .......................................  140
10.2.1  Minimum Router Configuration ..............................  140
10.2.2  Address and Address Mask Initialization ...................  141
10.2.3  Network Booting using BOOTP and TFTP ......................  142
10.3  Operation and Maintenance ...................................  143
10.3.1  Introduction ..............................................  143