第九章ICMP协议.ppt

Chapter 9
Control Message Protocol
ICMP
IP
Lack of error control
Lack of assistance mechanism
ICMP
panion to the IP
Provide error reporting for IP
Provide assistance mechanism for other layers(TCP/UDP and application)
Error Reporting & Error Correction
IP传输过程中出现差错是不可避免的
IP分组传输出现差错时,会产生相应的ICMP报文
通过ICMP报文提供差错报告
ICMP差错报告只能送给IP分组的源站,协议只提供了差错处理建议
出错点可能不是当前的路由器
反向传输路径可能与原路径不同
源站可能无法确定差错源,
需要与网络管理员一起协作处理
Control Message Protocol
RFC792: Control Message Protocol, 1981
RFC1256: ICMP Router Discovery Messages, 1991
IP
LANs
MANs
WANs
ICMP
IGMP
ARP
RARP
Network
Layer
Network
Access
Layer
Transport Layer
Application Layer
Message delivery and Encapsulation
ICMP在IP之上实现,逻辑上与IP同在网络层
munication
直接送达目的站点,沿途的转发路由器不能获知ICMP报文内容
Encapsulation
ICMP message
IP header
IP data
Frame data
Trailer (if any)
Frame header
ICMP message
IP header
IP data
Protocol = 1
Types of Messages
ICMP messages
Error-reporting
差错报告
Query
测试查询
To report problems that a router or a destination host may encounter when it processes an IP packet
To help a host or work manager get specific information from a router or another host
Types
Category
Type
Message
Reason
Error-reporting messages
3
Destination unreachable
Unreachable
4
Source quench
Congestion
11
Time exceeded
Too long route
12
Parameter problem
Format error
5
Redirection
Route changed
Query messages
8 or 0
Echo request or reply
Reachability
13 or 14
Timestamp request or reply
Synchronization
17 or 18
Address mask request or reply
Mask maintenance
10 or 9
Router solicitation or advertisement
Coincidence between routers
过时:
15 Information request
16 Information response
Message Format
Code
Checksum
Data section
Type
8 bits
8 bits
16 bits
差错报文:引起差错的原始分组的一部分(首部+ 数据部分的前8个字节)
查询报文:基于查询类型的额外信息
Error Reporting
ICMP just simply report errors
ICMP always reports error messages to the original source
ICMP error message will NOT be generated for:
A datagram carrying an I