"Computer Network" chapter fourth Network layer (4)

Six. ICMP

1. Internet Control Message Protocol ICMP

(1) function: Support the host or router to do error (or abnormal) report, Network inquiry

(2) Two types of ICMP packets

• Error Reporting messages (5 ): Destination Unreachable, source suppression, timeout / Extended, parameter issues, redirection

• Network Inquiry messages (2 groups): Echo (echo) Request and Response (Reply) message, timestamp request and Response message

2. exceptions (do not send ICMP)

(1) Error Reporting messages are no longer sent to ICMP error reporting messages

(2) No ICMP Error Reporting messages are sent for all subsequent shards except the first IP Shard

(3) No ICMP Error Reporting messages are sent for all multicast IP datagrams

(4) do not send ICMP to IP datagrams with special addresses (such as 127.0.0.0 or 0.0.0.0) Error Reporting Messages

(5) Several non-use ICMP messages: Information request and reply message, subnet mask request and reply message, Router inquiry and notification message

3. format

(1) ICMP packet encapsulation to IP datagram type transmission

(2) ICMP Error Reporting packet data Encapsulation

4. Application Example:Traceroute

Seven. IPv6 Introduction

1. Motivation

(1) Initial motive: the IPv4 address space has been allocated

(2) Other motives: Improve the first format, so that it can quickly process / forward datagrams, support QoS

2. IPV6 Datagram Format

(1) fixed length of the Basic header, can be extended by the option header

(2) Composition: basic header + payload, no shards allowed

• Priority: Identifies the priority of the datagram

• Flow Tags: Identify the same-class datagrams

• Next Header: Identifies the next option header or upper-level protocol header (e.g. TCP header)

• Skip step limit: Similar to TTL

3. IPv6 vs IPv4

(1) Complete checksum removal, reducing each processing time

(2) Allow the option to move out from the base header, define multiple option headers, and indicate through the next header field

(3) new ICMP: Additional message types (such as packet over large messages), multicast group management function

4. IPv6 Address representation ( kilobits)

(1) general form: Colon split hex, e.g. 1080:0:ff:0:8:800:200c:417a

(2) compression form: The continuous 0 compression : :, such as ff01:0:0:0:0:0:0:43-ff01::43

(3) ipv4- embedded form: The first 80 bits fixed is 0, the next 16 bits is 1, the remaining Three Bit write as IPv4 form

(4) address prefix:2002:43c:476b::/48, do not use subnet masks

(5) URLs:http://[3ffe::1:800:200c:417a]:8000

5. IPV6 Base Address type

(1) Unicast address: one-to-one communication

(2) Multicast address: one-to-many communication

(3) Anycast address: One pair of one group (usually the most recent) communication

6. IPv4 transition to IPv6

(1) It is not possible to replace all IPv6 agreements at some point

(2) tunneling technology:IPv6 datagram is encapsulated as a payload of the IPv4 datagram, traversing the IPv4 Network

"Computer Network" chapter fourth Network layer (4)