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.
IGMPv1 Message
IGMP has several versions, and IGMPv1 is defined by RFC 1112. IGMPv1, like IGMPv2, manages multicast groups based on the query and response mechanism (the exchange of IGMP Query messages and IGMP Report messages). However, there are differences between IGMPv1 and IGMPv2. For example, when using IGMPv1: a host does not send an IGMP Leave message when leaving a multicast group; a host does reply to an IGMP Report message when receiving an IGMP Query message; an IGMP router deletes the record of a multicast group when the timer for maintaining members in the multicast group expires.
Packet Format
Figure 3-43 IGMPv1 packet format
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| Type | Unused | Checksum | +--------------------------------------------------------------- | Group Address | +---------------------------------------------------------------
| Field | Length | Description |
|---|---|---|
| Version | 4 bit | 0x1 for IGMPv1. Version 0 is specified in RFC-988 and is now obsolete. |
| Type | 4 bit | There are two types of IGMP message of concern to hosts:
|
| Unused | 8 bit | Unused field, zeroed when sent, ignored when received. |
| Checksum | 16 bit | Indicates the checksum of the IGMP message. The value of this field is set to 0 when the checksum is calculated. Before an IGMP message is sent, the checksum character must be calculated and the calculated result must be filled in the field. When an IGMP message is received, the checksum character must be checked before the message is processed. |
| Group Address | 32 bit | In a Host Membership Query message, the group address field is zeroed when sent, ignored when received. In a Host Membership Report message, the group address field holds the IP host group address of the group being reported. |
Packet Example
Figure 3-44 IGMPv1 Membership Report
Frame 1: 42 bytes on wire (336 bits), 42 bytes captured (336 bits)
Arrival Time: Jan 29, 2016 10:19:17.088956000
Epoch Time: 1454033957.088956000 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: 42 bytes (336 bits)
Capture Length: 42 bytes (336 bits)
[Frame is marked: False]
[Frame is ignored: False]
[Protocols in frame: eth:ip:igmp]
[Coloring Rule Name: Routing]
[Coloring Rule String: hsrp || eigrp || ospf || bgp || cdp || vrrp || gvrp || igmp || ismp]
Ethernet II, Src: HuaweiTe_26:e9:bf (00:e0:fc:26:e9:bf), Dst: IPv4mcast_00:00:00 (01:00:5e:00:00:00)
Destination: IPv4mcast_00:00:00 (01:00:5e:00:00:00)
Address: IPv4mcast_00:00:00 (01:00:5e:00:00:00)
.... ...1 .... .... .... .... = IG bit: Group address (multicast/broadcast)
.... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
Source: HuaweiTe_26:e9:bf (00:e0:fc:26:e9:bf)
Address: HuaweiTe_26:e9:bf (00:e0:fc:26:e9:bf)
.... ...0 .... .... .... .... = IG bit: Individual address (unicast)
.... ..0. .... .... .... .... = LG bit: Globally unique address (factory default)
Type: IP (0x0800)
Internet Protocol Version 4, Src: 10.0.3.100 (10.0.3.100), Dst: 225.0.0.0 (225.0.0.0)
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: 28
Identification: 0x0000 (0)
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: IGMP (2)
Header checksum: 0xc0bc [correct]
[Good: True]
[Bad: False]
Source: 10.0.3.100 (10.0.3.100)
Destination: 225.0.0.0 (225.0.0.0)
Internet Group Management Protocol [IGMP Version: 1] Type: Membership Report (0x12) Header checksum: 0x0cff [correct] Multicast Address: 225.0.0.0 (225.0.0.0)
Reference
| Standard | Description |
|---|---|
| RFC 1112 | Host extensions for IP multicasting |
Protocol Stack
The IGMPv1 Message is encapsulated in IP, and the value of the protocol type field in the IP header is 0x02, indicating that the IGMP message is encapsulated in the data part. The destination address field in the IP header identifies the destination address of the IGMP message. The time to live (TTL) value in the IP header is 1, indicating that the IGMP message is transmitted only in the local network segment.
Figure 3-45 IGMPv1 Encapsulation
+-------------------------------+ | IGMPv1 | +-------------------------------+ | IP (Protocol = 0x02) | +-------------------------------+ | L2 | +-------------------------------+ | L1 | +-------------------------------+
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