PIM Assert报文格式
在共享网段上，如果PIM路由器从（S，G）或（*，G）表项的下游接口收到（S，G）报文，则表示该网段存在其他的转发者。路由器从该下游接口发出Assert消息，参与竞选。竞选落败者停止下游接口的转发。Assert消息同时在PIM-DM和PIM-SM中使用。
一、PIM Assert报文消息格式
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
+-------+-------+---------------+-------------------------------+
|PIM Ver| Type | Reserved | Checksum |
+-------+-------+---------------+-------------------------------+
| Group Address (Encoded-Group format) |
+---------------------------------------------------------------+
| Source Address (Encoded-Unicast format) |
+-+-------------------------------------------------------------+
|R| Metric Preference |
+-+-------------------------------------------------------------+
| Metric |
+---------------------------------------------------------------+
二、PIM Assert报文消息格式示例
| 字段 | 长度 | 说明 |
|---|---|---|
| PIM Ver | 4比特 | PIM版本，值为2。 |
| Type | 4比特 | 消息类型，值为5。 |
| Reserved | 8比特 | 保留。发送者将其设置为0，接收者忽略此字段。 |
| Checksum | 16比特 | 校验和。 |
| Group Address | 32比特 | 组播组地址。 |
| Source address | 32比特 | 如果竞选（S，G）表项的唯一转发者，则为组播源地址。如果竞选（*，G）表项的唯一转发者，则为RP地址。 |
| R | 1比特 | RPT位。如果竞选（S，G）表项的唯一转发者，该位为0；如果竞选（*，G）表项的唯一转发者，该位为1。 |
| Metric Preference | 31比特 | 到Source address的单播路径的优先级。 |
| Metric | 32比特 | 到Source address的单播路由的开销。 |
三、PIM Assert报文消息示例
Frame 2: 68 bytes on wire (544 bits), 68 bytes captured (544 bits)
Encapsulation type: Ethernet (1)
Arrival Time: Jan 1, 1970 08:00:00.009385000
[Time shift for this packet: 0.000000000 seconds]
Epoch Time: 0.009385000 seconds
[Time delta from previous captured frame: -0.032072000 seconds]
[Time delta from previous displayed frame: -0.032072000 seconds]
[Time since reference or first frame: -0.032072000 seconds]
Frame Number: 2
Frame Length: 68 bytes (544 bits)
Capture Length: 68 bytes (544 bits)
[Frame is marked: False]
[Frame is ignored: False]
[Protocols in frame: eth:ethertype:vlan:ethertype:ip:pim]
[Coloring Rule Name: Broadcast]
[Coloring Rule String: eth[0] & 1]
Ethernet II, Src: 00:ee:44:44:44:44 (00:ee:44:44:44:44), Dst: IPv4mcast_0d (01:00:5e:00:00:0d)
Destination: IPv4mcast_0d (01:00:5e:00:00:0d)
Address: IPv4mcast_0d (01:00:5e:00:00:0d)
.... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
.... ...1 .... .... .... .... = IG bit: Group address (multicast/broadcast)
Source: 00:ee:44:44:44:44 (00:ee:44:44:44:44)
Address: 00:ee:44:44:44:44 (00:ee:44:44:44:44)
.... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
.... ...0 .... .... .... .... = IG bit: Individual address (unicast)
Type: 802.1Q Virtual LAN (0x8100)
802.1Q Virtual LAN, PRI: 6, CFI: 0, ID: 1300
110. .... .... .... = Priority: Voice, < 10ms latency and jitter (6)
...0 .... .... .... = CFI: Canonical (0)
.... 0101 0001 0100 = ID: 1300
Type: IP (0x0800)
Trailer: 6e23a3b7
Internet Protocol Version 4, Src: 10.130.130.2 (10.130.130.2), Dst: 224.0.0.13 (224.0.0.13)
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: 46
Identification: 0x6b85 (27525)
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
Protocol: PIM (103)
Header checksum: 0x6892 [validation disabled]
[Good: False]
[Bad: False]
Source: 10.130.130.2 (10.130.130.2)
Destination: 224.0.0.13 (224.0.0.13)
[Source GeoIP: Unknown]
[Destination GeoIP: Unknown]
Protocol Independent Multicast
0010 .... = Version: 2
.... 0101 = Type: Assert (5)
Reserved byte(s): 00
Checksum: 0xe10d [correct]
PIM options
Group: 227.0.7.8 (227.0.7.8)/32
Source: 10.1.0.200 (10.1.0.200)
0... .... = RP Tree: False
.000 0000 0000 0000 0000 0000 0000 0000 = Metric Preference: 0
Metric: 0
发表评论