OSPF DD 报文
OSPF DD（Database Description）报文描述了本地LSDB的摘要信息，用于两台路由器进行数据库同步。
一、OSPF DD报文格式
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+-------------------------------+
| Version = 2 | 2 | Packet length |
+---------------+---------------+-------------------------------+
| Router ID |
+---------------------------------------------------------------+
| Area ID |
+-------------------------------+-------------------------------+
| Checksum | AuType |
+-------------------------------+-------------------------------+
| Authentication |
+---------------------------------------------------------------+
| Authentication |
+-------------------------------+---------------+-+-+-+-+-+-+-+-+
| Interface MTU | Options |0|0|0|0|0|I|M|MS
+-------------------------------+---------------+-+-+-+-+-+-+-+-+
| DD sequence number |
+---------------------------------------------------------------+
| |
+- -+
| |
+- An LSA Header -+
| |
+- -+
| |
+- -+
| |
+---------------------------------------------------------------+
| ... |
二、OSPF DD报文解释
| 字段 | 长度 | 含义 |
|---|---|---|
| Version | 1字节 | 版本，OSPF的版本号。对于OSPFv2来说，其值为2。 |
| Packet length | 2字节 | OSPF报文的总长度，包括报文头在内，单位为字节。 |
| Router ID | 4字节 | 发送该报文的路由器标识。 |
| Area ID | 4字节 | 发送该报文的所属区域。 |
| Checksum | 2字节 | 校验和，包含除了认证字段的整个报文的校验和。 |
| AuType | 2字节 | 验证类型，值有如下几种表示， 0：不验证；1：简单认证；2：MD5认证。 |
| Authentication | 8字节 |
鉴定字段，其数值根据验证类型而定。当验证类型为0时未作定义；类型为1时此字段为密码信息；类型为2时此字段包括Key ID、MD5验证数据长度和序列号的信息。 MD5验证数据添加在OSPF报文后面，不包含在Authenticaiton字段中。 |
| Interface MTU | 16比特 | 在不分片的情况下，此接口最大可发出的IP报文长度。 |
| Options | 8比特 | 可选项：
|
| I | 1比特 | 当发送连续多个DD报文时，如果这是第一个DD报文，则置为1，否则置为0。 |
| M (More) | 1比特 | 当发送连续多个DD报文时，如果这是最后一个DD报文，则置为0。否则置为1，表示后面还有其他的DD报文。 |
| MS (Master/Slave) | 1比特 | 当两台OSPF路由器交换DD报文时，首先需要确定双方的主从关系，Router ID大的一方会成为Master。当值为1时表示发送方为Master。 |
| DD sequence number | 32比特 | DD报文序列号。主从双方利用序列号来保证DD报文传输的可靠性和完整性。 |
| An LSA Header | 每个20字节 | 该DD报文中所包含的LSA的头部信息。 |
三、OSPF DD报文示例
Frame 15754: 106 bytes on wire (848 bits), 106 bytes captured (848 bits)
Encapsulation type: Ethernet (1)
Arrival Time: Jun 8, 2014 01:51:15.281786000
[Time shift for this packet: 0.000000000 seconds]
Epoch Time: 1402163475.281786000 seconds
[Time delta from previous captured frame: 0.000012000 seconds]
[Time delta from previous displayed frame: 0.000012000 seconds]
[Time since reference or first frame: 27894.654445000 seconds]
Frame Number: 15754
Frame Length: 106 bytes (848 bits)
Capture Length: 106 bytes (848 bits)
[Frame is marked: False]
[Frame is ignored: False]
[Protocols in frame: eth:ethertype:ip:ospf]
[Coloring Rule Name: OSPF State Change]
[Coloring Rule String: ospf.msg != 1]
Ethernet II, Src: Novell_40:64:00 (1b:00:00:40:64:00), Dst: 00:0d:05:00:ff:ff (00:0d:05:00:ff:ff)
Destination: 00:0d:05:00:ff:ff (00:0d:05:00:ff:ff)
Address: 00:0d:05:00:ff:ff (00:0d:05:00:ff:ff)
.... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
.... ...0 .... .... .... .... = IG bit: Individual address (unicast)
Source: Novell_40:64:00 (1b:00:00:40:64:00)
[Expert Info (Warn/Protocol): Source MAC must not be a group address: IEEE 802.3-2002, Section 3.2.3(b)]
[Source MAC must not be a group address: IEEE 802.3-2002, Section 3.2.3(b)]
[Severity level: Warn]
[Group: Protocol]
Address: Novell_40:64:00 (1b:00:00:40:64:00)
.... ..1. .... .... .... .... = LG bit: Locally administered address (this is NOT the factory default)
.... ...1 .... .... .... .... = IG bit: Group address (multicast/broadcast)
Type: IP (0x0800)
Internet Protocol Version 4, Src: 10.93.0.37 (10.93.0.37), Dst: 10.93.0.1 (10.93.0.1)
Version: 4
Header Length: 20 bytes
Differentiated Services Field: 0xc0 (DSCP 0x30: Class Selector 6; ECN: 0x00: Not-ECT (Not ECN-Capable Transport))
1100 00.. = Differentiated Services Codepoint: Class Selector 6 (0x30)
.... ..00 = Explicit Congestion Notification: Not-ECT (Not ECN-Capable Transport) (0x00)
Total Length: 92
Identification: 0x3ac3 (15043)
Flags: 0x00
0... .... = Reserved bit: Not set
.0.. .... = Don't fragment: Not set
..0. .... = More fragments: Not set
Fragment offset: 0
Time to live: 1
[Expert Info (Note/Sequence): "Time To Live" only 1]
["Time To Live" only 1]
[Severity level: Note]
[Group: Sequence]
Protocol: OSPF IGP (89)
Header checksum: 0x3ae6 [validation disabled]
[Good: False]
[Bad: False]
Source: 10.93.0.37 (10.93.0.37)
Destination: 10.93.0.1 (10.93.0.1)
[Source GeoIP: Unknown]
[Destination GeoIP: Unknown]
Open Shortest Path First
OSPF Header
Version: 2
Message Type: DB Description (2)
Packet Length: 72
Source OSPF Router: 10.26.26.1 (10.26.26.1)
Area ID: 10.2.2.2 (10.2.2.2)
Checksum: 0x8542 [correct]
Auth Type: Null (0)
Auth Data (none): 0000000000000000
OSPF DB Description
Interface MTU: 0
Options: 0x02 (E)
0... .... = DN: Not set
.0.. .... = O: Not set
..0. .... = DC: Demand Circuits are NOT supported
...0 .... = L: The packet does NOT contain LLS data block
.... 0... = NP: NSSA is NOT supported
.... .0.. = MC: NOT Multicast Capable
.... ..1. = E: External Routing Capability
.... ...0 = MT: NO Multi-Topology Routing
DB Description: 0x00
.... 0... = R: OOBResync bit is NOT set
.... .0.. = I: Init bit is NOT set
.... ..0. = M: More bit is NOT set
.... ...0 = MS: Master/Slave bit is NOT set
DD Sequence: 14857710
LSA Header
.000 0000 0000 0101 = LS Age (seconds): 5
0... .... .... .... = Do Not Age Flag: 0
Options: 0x02 (E)
0... .... = DN: Not set
.0.. .... = O: Not set
..0. .... = DC: Demand Circuits are NOT supported
...0 .... = L: The packet does NOT contain LLS data block
.... 0... = NP: NSSA is NOT supported
.... .0.. = MC: NOT Multicast Capable
.... ..1. = E: External Routing Capability
.... ...0 = MT: NO Multi-Topology Routing
LS Type: Router-LSA (1)
Link State ID: 10.26.26.1 (10.26.26.1)
Advertising Router: 10.26.26.1 (10.26.26.1)
Sequence Number: 0x80000009
Checksum: 0xadb2
Length: 36
LSA Header
.000 0000 0000 1100 = LS Age (seconds): 12
0... .... .... .... = Do Not Age Flag: 0
Options: 0x02 (E)
0... .... = DN: Not set
.0.. .... = O: Not set
..0. .... = DC: Demand Circuits are NOT supported
...0 .... = L: The packet does NOT contain LLS data block
.... 0... = NP: NSSA is NOT supported
.... .0.. = MC: NOT Multicast Capable
.... ..1. = E: External Routing Capability
.... ...0 = MT: NO Multi-Topology Routing
LS Type: Router-LSA (1)
Link State ID: 10.80.0.1 (10.80.0.1)
Advertising Router: 10.80.0.1 (10.80.0.1)
Sequence Number: 0x80000004
Checksum: 0x1e8e
Length: 36
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