RFC 2178 (rfc2178) - Page 3 of 211

OSPF Version 2

RFC 2178                     OSPF Version 2                    July 1997


    11       The Routing Table Structure ........................... 93
    11.1     Routing table lookup .................................. 96
    11.2     Sample routing table, without areas ................... 97
    11.3     Sample routing table, with areas ...................... 97
    12       Link State Advertisements (LSAs) ......................100
    12.1     The LSA Header ........................................100
    12.1.1   LS age ............................................... 101
    12.1.2   Options .............................................. 101
    12.1.3   LS type .............................................. 102
    12.1.4   Link State ID ........................................ 102
    12.1.5   Advertising Router ................................... 104
    12.1.6   LS sequence number ................................... 104
    12.1.7   LS checksum .......................................... 105
    12.2     The link state database .............................. 105
    12.3     Representation of TOS ................................ 106
    12.4     Originating LSAs ..................................... 107
    12.4.1   Router-LSAs .......................................... 110
    12.4.1.1 Describing point-to-point interfaces ................. 112
    12.4.1.2 Describing broadcast and NBMA interfaces ............. 113
    12.4.1.3 Describing virtual links ............................. 113
    12.4.1.4 Describing Point-to-MultiPoint interfaces ............ 114
    12.4.1.5 Examples of router-LSAs .............................. 114
    12.4.2   Network-LSAs ......................................... 116
    12.4.2.1 Examples of network-LSAs ............................. 116
    12.4.3   Summary-LSAs ......................................... 117
    12.4.3.1 Originating summary-LSAs into stub areas ............. 119
    12.4.3.2 Examples of summary-LSAs ............................. 119
    12.4.4   AS-external-LSAs ..................................... 120
    12.4.4.1 Examples of AS-external-LSAs ......................... 121
    13       The Flooding Procedure ............................... 122
    13.1     Determining which LSA is newer ....................... 126
    13.2     Installing LSAs in the database ...................... 127
    13.3     Next step in the flooding procedure .................. 128
    13.4     Receiving self-originated LSAs ....................... 130
    13.5     Sending Link State Acknowledgment packets ............ 131
    13.6     Retransmitting LSAs .................................. 133
    13.7     Receiving link state acknowledgments ................. 134
    14       Aging The Link State Database ........................ 134
    14.1     Premature aging of LSAs .............................. 135
    15       Virtual Links ........................................ 135
    16       Calculation of the routing table ..................... 137
    16.1     Calculating the shortest-path tree for an area ....... 138
    16.1.1   The next hop calculation ............................. 144
    16.2     Calculating the inter-area routes .................... 145
    16.3     Examining transit areas' summary-LSAs ................ 146
    16.4     Calculating AS external routes ....................... 149
    16.4.1   External path preferences ............................ 151
    16.5     Incremental updates -- summary-LSAs .................. 151



Moy                         Standards Track