HP 6125G HP 6125G & 6125G/XG Blade Switches Layer 3 - IP Routing Confi - Page 66

OSPF packet formats OSPF packets are directly encapsulated into IP packets. OSPF uses the IP protocol number 89. The format of an OSPF LSU packet is shown in Figure 20. Figure 20 OSPF packet format OSPF packet header OSPF packets are classified into five types that have the same packet header. Figure 21 OSPF packet header Major fields of the OSPF packet header are as follows: • Version-OSPF version number, which is 2 for OSPFv2. • Type-OSPF packet type from 1 to 5, corresponding to hello, DD, LSR, LSU, and LSAck, respectively. • Packet length-Total length of the OSPF packet in bytes, including the header. • Router ID-ID of the advertising router. • Area ID-ID of the area where the advertising router resides. • Checksum-Checksum of the message. • AuType-Authentication type, ranging from 0 to 2, corresponding to non-authentication, simple (plaintext) authentication, and MD5 authentication, respectively. • Authentication-Information determined by authentication type. It is not defined for authentication type 0. It is defined as password information for authentication type 1, and defined as Key ID, MD5 authentication data length, and sequence number for authentication type 2. NOTE: MD5 authentication data is added following an OSPF packet rather than contained in the Authentication field. Hello packet A router sends hello packets periodically to find and maintain neighbor relationships, and to elect the DR or BDR, including information about values of timers, DR, BDR, and neighbors that are already known. 56