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IP Packet Format

IP Packets Product Documentation contains the main data transmission protocol used in a variety of packet formats, packet example. By IP Packets Product Documentation, be able to enhance understanding of various protocol packets.

IP Packets Product Documentation contains the main data transmission protocol used in a variety of packet formats, packet example. By IP Packets Product Documentation, be able to enhance understanding of various protocol packets.

PIM Hello

PIM Hello

PIM routers exchange Hello messages to discover PIM neighbors and maintain neighbor relationships. This type of message is used in both PIM-DM and PIM-SM. PIM-DM and PIM-SM cannot be distinguished through Hello messages.

Packet Format

Figure 3-142 Hello message format 
    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            |
   +-------+-------+---------------+-------------------------------+
   |          OptionType           |         OptionLength          |
   +-------------------------------+-------------------------------+
   |                          OptionValue                          |
   |                              ...                              |
   +---------------------------------------------------------------+
   |                               .                               |
   |                               .                               |
   |                               .                               |
   +-------------------------------+-------------------------------+
   |          OptionType           |         OptionLength          |
   +-------------------------------+-------------------------------+
   |                          OptionValue                          |
   |                              ...                              |
   +---------------------------------------------------------------+
Field Length Description
PIM Ver 4 bits PIM version. The value is 2.
Type 4 bits Message type. The value is 0.
Reserved 8 bits Reserved. The field is set to 0 when the message is sent and is ignored when the message is received.
Checksum 16 bits Checksum.
OptionType 2 bytes Type of the option parameter.

The options are as follows:

  • 1: Holdtime. Timeout period during which a neighbor remains in the reachable state. If no Hello message is received within this period, the neighbor is considered unreachable.

  • 2: LAN Prune Delay, which consists of three parts:

         +-+-------------------+-------------------+
     |T| Propagation_Delay | Override_Interval |
     +-+-------------------+-------------------+
    • T: 1 bit. It indicates the Join message suppression capability.
    • Propagation_Delay: 15 bits. It indicates the delay in transmitting Prune messages on a shared network segment.
    • Override_Interval: 16 bits. It indicates the interval for overriding a prune action on a shared network segment.
  • 3-16: reserved for future use.
  • 18: Reserved.
  • 19: DR_Priority. Indicates the priority used by a router interface for designated router (DR) election. The higher the priority, the higher the possibility that the interface becomes the DR.
  • 20: Generation ID. Indicates the current neighbor status and is a random number carried in the Hello message. If the neighbor status changes, the random number is updated. When a router detects that the Hello messages received from an upstream device contain different Generation IDs, the router considers the upstream neighbor down or the status of the upstream neighbor has changed.
  • 21: State Refresh Capable. It is the interval for refreshing neighbor status.
  • 24: Address List. It is the secondary address list of PIM interfaces.
OptionLength 2 bytes Length of the OptionValue field, in bytes.
OptionValue Variable Fields in the Option parameter.

Packet Example

Figure 3-143 PIM Hello messages (IPv4) 
Frame 1: 68 bytes on wire (544 bits), 68 bytes captured (544 bits)
    Encapsulation type: Ethernet (1)
    Arrival Time: Jul 16, 2009 00:04:01.029410000
    [Time shift for this packet: 0.000000000 seconds]
    Epoch Time: 1247673841.029410000 seconds
    [Time delta from previous captured frame: 0.000000000 seconds]
    [Time delta from previous displayed frame: 0.000000000 seconds]
    [Time since reference or first frame: 0.000000000 seconds]
    Frame Number: 1
    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:ip:pim]
    [Coloring Rule Name: Broadcast]
    [Coloring Rule String: eth[0] & 1]
Ethernet II, Src: 00:16:9c:6e:7a:40 (00:16:9c:6e:7a:40), 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: 00:16:9c:6e:7a:40 (00:16:9c:6e:7a:40)
        Address: 00:16:9c:6e:7a:40 (00:16:9c:6e:7a:40)
        .... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
        .... ...0 .... .... .... .... = IG bit: Individual address (unicast)
    Type: IP (0x0800)
Internet Protocol Version 4, Src: 10.20.7.54 (10.20.7.54), 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: 54
    Identification: 0xb636 (46646)
    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: 0x6f13 [validation disabled]
        [Good: False]
        [Bad: False]
    Source: 10.20.7.54 (10.20.7.54)
    Destination: 224.0.0.13 (224.0.0.13)
    [Source GeoIP: Unknown]
    [Destination GeoIP: Unknown]
Protocol Independent Multicast
    0010 .... = Version: 2
    .... 0000 = Type: Hello (0)
    Reserved byte(s): 00
    Checksum: 0xd026 [correct]
    PIM options: 4
        Option 1: Hold Time: 105s 
            Type: 1
            Length: 2
            Holdtime: 105s 
        Option 20: Generation ID: 3620
            Type: 20
            Length: 4
            Generation ID: 3620
        Option 19: DR Priority: 1
            Type: 19
            Length: 4
            DR Priority: 1
        Option 21: State Refresh Capable: Version = 1, Interval = 0s
            Type: 21
            Length: 4
            Version: 1
            Interval: 0
            Reserved: 0
Figure 3-144 PIM Hello messages (IPv6) 
Frame 1: 118 bytes on wire (944 bits), 118 bytes captured (944 bits)
    Encapsulation type: Ethernet (1)
    Arrival Time: Apr  7, 2010 11:55:07.000000000
    [Time shift for this packet: 0.000000000 seconds]
    Epoch Time: 1270612507.000000000 seconds
    [Time delta from previous captured frame: 0.000000000 seconds]
    [Time delta from previous displayed frame: 0.000000000 seconds]
    [Time since reference or first frame: 0.000000000 seconds]
    Frame Number: 1
    Frame Length: 118 bytes (944 bits)
    Capture Length: 118 bytes (944 bits)
    [Frame is marked: False]
    [Frame is ignored: False]
    [Protocols in frame: eth:ethertype:vlan:ethertype:ipv6:ipv6.nxt:pim]
    [Coloring Rule Name: Broadcast]
    [Coloring Rule String: eth[0] & 1]
Ethernet II, Src: 00:e0:fc:00:29:d8 (00:e0:fc:00:29:d8), Dst: IPv6mcast_0d (33:33:00:00:00:0d)
    Destination: IPv6mcast_0d (33:33:00:00:00:0d)
        Address: IPv6mcast_0d (33:33:00:00:00:0d)
        .... ..1. .... .... .... .... = LG bit: Locally administered address (this is NOT the factory default)
        .... ...1 .... .... .... .... = IG bit: Group address (multicast/broadcast)
    Source: 00:e0:fc:00:29:d8 (00:e0:fc:00:29:d8)
        Address: 00:e0:fc:00:29:d8 (00:e0:fc:00:29:d8)
        .... ..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: 8
    110. .... .... .... = Priority: Voice, < 10ms latency and jitter (6)
    ...0 .... .... .... = CFI: Canonical (0)
    .... 0000 0000 1000 = ID: 8
    Type: IPv6 (0x86dd)
    Trailer: acf6471a
Internet Protocol Version 6, Src: fe80::2e0:fcff:fe00:29d8 (fe80::2e0:fcff:fe00:29d8), Dst: ff02::d (ff02::d)
    0110 .... = Version: 6
        [0110 .... = This field makes the filter "ip.version == 6" possible: 6]
    .... 0000 0000 .... .... .... .... .... = Traffic class: 0x00000000
        .... 0000 00.. .... .... .... .... .... = Differentiated Services Field: Default (0x00000000)
        .... .... ..0. .... .... .... .... .... = ECN-Capable Transport (ECT): Not set
        .... .... ...0 .... .... .... .... .... = ECN-CE: Not set
    .... .... .... 0000 0000 0000 0000 0000 = Flowlabel: 0x00000000
    Payload length: 56
    Next header: PIM (103)
    Hop limit: 1
    Source: fe80::2e0:fcff:fe00:29d8 (fe80::2e0:fcff:fe00:29d8)
    [Source SA MAC: 00:e0:fc:00:29:d8 (00:e0:fc:00:29:d8)]
    Destination: ff02::d (ff02::d)
    [Source GeoIP: Unknown]
    [Destination GeoIP: Unknown]
Protocol Independent Multicast
    0010 .... = Version: 2
    .... 0000 = Type: Hello (0)
    Reserved byte(s): 00
    Checksum: 0x45a1 [correct]
    PIM options: 5
        Option 1: Hold Time: 105s 
            Type: 1
            Length: 2
            Holdtime: 105s 
        Option 19: DR Priority: 1
            Type: 19
            Length: 4
            DR Priority: 1
        Option 20: Generation ID: 461646429
            Type: 20
            Length: 4
            Generation ID: 461646429
        Option 2: LAN Prune Delay: T = 0, Propagation Delay = 500ms, Override Interval = 2500ms
            Type: 2
            Length: 4
            0... .... = T: False
            .000 0001 1111 0100 = Propagation Delay: 500
            Override Interval: 2500
        Option 24: Address List
            Type: 24
            Length: 18
            Address List (24)
                Address: 2000::10 (2000::10)

References

Standard Description
RFC 4601 Protocol Independent Multicast - Sparse Mode (PIM-SM):Protocol Specification (Revised)
RFC 3973 Protocol Independent Multicast - Dense Mode (PIM-DM): Protocol Specification (Revised)
RFC 4607 Source-Specific Multicast for IP

Protocol Stack Structure

A PIM Hello message is encapsulated in an IP packet.

Figure 3-145 Encapsulation format of a PIM Hello message 
+------------------+----------------+
|     IP Header    |    PIM Hello   |
| (Protocol = 103) |     Message    |
+------------------+----------------+
  • In the header of an IP packet that contains a PIM message, the Protocol field is set to 103.
  • In an IP packet that carries a Hello message, the source address is a local interface's address, the destination address is 224.0.0.13, and the TTL value is 1.
  • The IP packet is transmitted in multicast mode.
Translation
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Update Date：2025-08-12
Document ID：EDOC1100174721
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