[네트워크] OSPF DB Description 패킷 구조

• Interface MTU is the size, in octets, of the largest IP packet that can be sent out the originator's interface without fragmentation. This field is set to 0x0000 when the packet is sent over virtual links.

• Options field is included in the Database Description packet so that a router may choose not to forward certain LSAs to a neighbor that doesn't support the necessary capabilities.

• The first five bits of the next octet are unused and are always set to 00000b.

• I-bit, or Initial bit, is set to 1 when the packet is the initial packet in series of DD packets. Subsequent DD packets have I-bit = 0.

• M-bit, or More bit, is set to 1 to indicate that the packet is not the last in a series of DD packets. The last DD packet has M-bit = 0.

• MS-bit, or Master/Slave bit, is set to 1 to indicate that the originator is the master (that is, is in control of the polling process) during a database synchronization. The slave has MS-bit = 0.

• DD Sequence Number ensures that the full sequence of DD packets is received in the database synchronization process. The sequence number is set by the master to some unique value in the first DD packet, and the sequence is incremented in subsequent packets.

• LSA Headers list some or all of the headers of the LSAs in the originator's link-state database. See the section "Link State Header," for a full description of the LSA header; the header contains enough information to uniquely identify the LSA and the particular instance of the LSA.