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What is IGMP? What is the difference between IGMP and ICMP?

2022-06-29 23:53:00 【InfoQ】

Hello , This is the network technology alliance station .

A few days ago, I brought you ICMP The article ：

What is? ICMP ？ping and ICMP What's the relationship between ？

It is popular on many platforms , Have friends and want to see IGMP The article , At first glance, there is a letter missing between the two technologies , But the two are completely different technologies , So today, Rego will arrange ！

Let's go straight to ！

What is? IGMP？

English full name ：
Internet Group Management Protocol

Chinese name ：
Internet Group Management Protocol

The first 3 Layer protocol

IP Agreement No ：
2

IPv4 The key component of multicast

IGMP Yes 3 A version ：IGMPv1、IGMPv2 and IGMPv3

IGMP Allow the host to announce its multicast membership to adjacent switches and routers , The host sends... To its local multicast router IGMP Message to identify group membership , stay IGMP Next , Router listening IGMP Message and periodically send queries to find which groups on a particular subnet are active or inactive .

Flow type

There are three types of flow ：

unicast

Unicast English name

Unicast

, It's point-to-point transmission , Unicast requires a sender and a receiver to send packets using session based protocols , for example TCP and UDP.

TCP Examples of common transport modes for are
http
、
telnet
、
smtp
.

UDP Examples of common transport modes for are
VoIP
、
Videoconferencing
、
Streaming media
、
Real time services
.

radio broadcast

The English name of the broadcast is

Broadcast

, A single device sends communications to all other devices on the network .

LAN Common examples of broadcast traffic on include queries LAN Of all computers on the

ARP

news .

Broadcast traffic is not routable traffic .

null

Multicast

Multicast English name

Multicast

, Also called

multicast

, Supports a single copy of data transfer from one node to multiple recipients , The sending device will send UDP Packet forwarding to multicast IP Address and port , So that all destinations that want to receive the stream can receive the transmission , This saves bandwidth and network overhead .

Multicast traffic is

Routable

Of traffic , But you need IGMP and PIM To control the flooding of the entire network 、 Saturate the uplink and may cause network paralysis .

Multicast version

In the introduction of multicast , We introduced that multicast has 3 A version ：

Let's take a closer look at .

IGMPv1

IGMPv1 yes TCP The first development and release version of the communication protocol used in the network , For this version , The group address is defined

0.0.0.0

, And defined

224.0.0.1

As the target address of general query .

The standard time for these routers to generate requests is

second , And allow the computer to join the corresponding multicast group .

And then , Send a membership request to the corresponding multicast address .

IGMPv1 Computers are not allowed to leave the group by themselves beyond the time limit , This removes the computer from the group it accesses .

IGMP The total length of the head is 64 position , front 8 Bits indicate protocol version and message type .

lGMPv1 The message header is as follows ：

IGMPv2

IGMPv2 After the first release , On 1997 In RFC 2236 In the definition of , stay lGMPv2 in ,group(0.0.0.0) and destination(224.0.0.1) The address hasn't changed , But the interval increases to

125

second .

The main innovation of the second version is to speed up the process by replacing the logout time limit , The first version of the logout process is initiated by the device .

Another innovation is that the receiving status of a specific multicast address is determined by group specific messages .

In this version , Address

224.0.0.2

Is defined as the destination address ,IGMPv2 Easy to use IP Packet sending message ,

IP The agreement number is 2

stay IGMPv2 In the version , The subnet has the lowest IP Address routers are used for

Multicast query

lGMPv2 Baotou is as follows ：

IGMPv3

IGMPv3 Version in RFC 3376 and RFC 4604 stay 2002 In the definition of , In this version ,

0.0.0.0

and

224.0.0.1

An address is considered a group and a destination address , Interval and version 2 identical .

The new feature is that it can

Select a multicast stream specially

, This greatly reduces the demand for the network , And because unknown or random sources are not used in the transmission process , Therefore, it also provides higher security .

The first two 32 Bit sequence and lGMPv2 Head type 、 Maximum response time 、 The checksum and group address are the same .

IGMPv3 Baotou is as follows ：

IGMP How to work ？

We already know that multicast is sending a message to a group of hosts , The multicast router is responsible for copying and forwarding messages to each host of the multicast group , Each host of the multicast group will receive a message , Unless a filter is applied to the receiving host .

IGMP The core of the protocol is to manage the membership of the host in the multicast group , When managing the membership of hosts or routers in a multicast group , The protocol must deal with the following process ：

ICMP news

Not yet IGMP Version of , Generally speaking , In a big way ,IGMP There are six types of messages ：

Membership Report Member report messages

The client sends this message when it wants to receive the multicast group , The member report is essentially a piece of information , Indicate interest in listening to a particular group .

Leave Leave the news

The client sends this message when it wants to leave the Group .

General Query General query messages

The querier sends general query messages to all clients , Whether the query is currently sending multicast to the client or not , To find out which group they are listening to , The response to the general query ensures that the group member information of the inquirer is kept up to date .

The group address field of general query is set to

0.0.0.0

, They are sent to the destination address 224.0.0.1, By default ,Allied Telesis Routers and switches per

125

Seconds to send .

Specific Query Specific query messages

The querier sends the specific query message to the group address , To check if the client is still listening to the Group , After the client sends a leave message for the group , The querier sends a specific query , Specific queries enable the querier to confirm when all downstream clients leave the Group , So that the querier can stop sending multicast streams .

Membership Query Member query messages

This is a general term for specific queries and general queries .

IGMP Advantages and disadvantages

advantage

IGMP Promote the effective utilization of bandwidth

More flexible , You can immediately leave one group and join another

There is no large amount of garbage , Improved performance

shortcoming

The lack of TCP, Network congestion may occur

Low security , Vulnerable to attack

IGMP Listen

IGMP In the 3 Layer operation , therefore , The switch cannot understand IGMP news , in addition , It is also impossible for a switch to multicast MAC Add the address to the forwarding table , This is because multicast MAC The address is never used as the source address , This will cause multicast traffic to be flooded to all hosts in the broadcast domain .

IGMP Listening is on the 2 A feature enabled on a layer switch , Used to check the connection between the host and the router IGMP transmission , Through this inspection , Set up a mapping , It contains specific VLAN Which hosts in the need to receive multicast transmission , then , The switch uses this information to forward the multicast traffic of a given multicast group only to a given VLAN Receiver in .

ICMP and IGMP The difference between

The beginning of the article also said , There is only one letter difference between the two agreements , But the difference in the agreement itself is huge , Let's get to know ：

1、 Definition

ICMP representative Internet Control message protocol

IGMP representative Internet Group message protocol

2、 Typical features

ICMP：ping

IGMP： Multicast

3、 Work agreement layer

ICMP： The first 3 Layer protocol

IGMP： The first 3 Layer protocol

4、 purpose

ICMP： Used to test the accessibility of host or network

IGMP： be used for DTS Service and other component data transmission

summary

IGMP representative Internet Multicast management protocol , yes IPv4 A communication protocol used by hosts and neighboring routers on a network to establish multicast group membership , When a multicast host wants to join a specific multicast group and start receiving group traffic ,IGMP Messages are mainly used to send signals to their local multicast routers ,IGMP There are three versions ： edition 1、 edition 2、 edition 3, Of which version 2 It's the default version .

This paper mainly introduces ：