windows与IOS中的ping与MTU

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orzzz 2012-01-03 12:19:59 博主文章分类：网络技术 ©著作权

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windows的ping中-l（length）是指ICMP的净荷，不包括IP包头（一般20字节）和ICMP头（8字节），所以默认情况下MTU为1500字节，windows中：

ping 1.1.1.1 -f -l 1472 是通的，

ping 1.1.1.1 -f -l 1473 是不通的。

IOS的ping中Datagram size和sweep size都是指MTU，即

R1#ping
Protocol [ip]:
Target IP address: 1.1.1.1
Repeat count [5]: 1
Datagram size [100]: 1600 (在扩展ping中此选项好像失效，没起作用)
Timeout in seconds [2]:
Extended commands [n]: y
Source address or interface:
Type of service [0]:
Set DF bit in IP header? [no]: y
Validate reply data? [no]:
Data pattern [0xABCD]:
Loose, Strict, Record, Timestamp, Verbose[none]:
Sweep range of sizes [n]: y
Sweep min size [36]: 1500
Sweep max size [18024]: 1501
Sweep interval [1]:
Type escape sequence to abort.
Sending 2, [1500..1501]-byte ICMP Echos to 34.1.1.4, timeout is 1 seconds:
Packet sent with the DF bit set
!.
Success rate is 50 percent (1/2), round-trip min/avg/max = 212/212/212 ms

如图，所有路由器均为3620路由器，将R2的s0/0口MTU设为1480,

R1#ping
Protocol [ip]:
Target IP address: 34.1.1.4
Repeat count [5]: 1
Datagram size [100]:
Timeout in seconds [2]:
Extended commands [n]: y
Source address or interface:
Type of service [0]:
Set DF bit in IP header? [no]: y
Validate reply data? [no]:
Data pattern [0xABCD]:
Loose, Strict, Record, Timestamp, Verbose[none]:
Sweep range of sizes [n]: y
Sweep min size [36]: 1475
Sweep max size [18024]: 1485
Sweep interval [1]:
Type escape sequence to abort.
Sending 11, [1475..1485]-byte ICMP Echos to 34.1.1.4, timeout is 2 seconds:
Packet sent with the DF bit set
!!!!!!.....
Success rate is 54 percent (6/11), round-trip min/avg/max = 100/127/200 ms