研究MPLS MTU的问题

实验目的：研究MPLS MTU的问题。

Step 1:
R1#show mpl interfaces s2/2 detail //查看默认情况下接口的MPLS MTU
Interface Serial2/2:
        IP labeling enabled (tdp)
        LSP Tunnel labeling not enabled
        BGP tagging not enabled
        Tagging operational
        Fast Switching Vectors:
          IP to MPLS Fast Switching Vector
          MPLS Turbo Vector
          MTU = 1500

Step 2:使用扩展ping，不分片，可以通信。
R1#ping
Protocol [ip]: 
Target IP address: 4.4.4.4
Repeat count [5]: 10     
Datagram size [100]: 
Timeout in seconds [2]: 
Extended commands [n]: y
Source address or interface: 1.1.1.1
Type of service [0]: 
Set DF bit in IP header? [no]: yes
Validate reply data? [no]: 
Data pattern [0xABCD]: 
Loose, Strict, Record, Timestamp, Verbose[none]: 
Sweep range of sizes [n]: 
Type escape sequence to abort.
Sending 10, 100-byte ICMP Echos to 4.4.4.4, timeout is 2 seconds:
Packet sent with a source address of 1.1.1.1 
Packet sent with the DF bit set
!!!!!!!!!!
Success rate is 100 percent (10/10), round-trip min/avg/max = 32/68/128 ms

Step 3:当不分片，MTU设置为1504，无法通信。
R1#ping
Protocol [ip]: 
Target IP address: 4.4.4.4
Repeat count [5]: 
Datagram size [100]: 1504
Timeout in seconds [2]: 
Extended commands [n]: y
Source address or interface: 1.1.1.1
Type of service [0]: 
Set DF bit in IP header? [no]: yes
Validate reply data? [no]: 
Data pattern [0xABCD]: 
Loose, Strict, Record, Timestamp, Verbose[none]: 
Sweep range of sizes [n]: 
Type escape sequence to abort.
Sending 5, 1504-byte ICMP Echos to 4.4.4.4, timeout is 2 seconds:
Packet sent with a source address of 1.1.1.1 
Packet sent with the DF bit set
.....
Success rate is 0 percent (0/5)
R1#ping
Protocol [ip]: 
Target IP address: 4.4.4.4
Repeat count [5]: 
Datagram size [100]: 1500
Timeout in seconds [2]: 
Extended commands [n]: y
Source address or interface: 1.1.1.1
Type of service [0]: 
Set DF bit in IP header? [no]: yes
Validate reply data? [no]: 
Data pattern [0xABCD]: 
Loose, Strict, Record, Timestamp, Verbose[none]: 
Sweep range of sizes [n]: 
Type escape sequence to abort.
Sending 5, 1500-byte ICMP Echos to 4.4.4.4, timeout is 2 seconds:
Packet sent with a source address of 1.1.1.1 
Packet sent with the DF bit set
.....

Success rate is 0 percent (0/5)
R1#ping
Protocol [ip]: 
Target IP address: 4.4.4.4
Repeat count [5]: 10
Datagram size [100]: 1490
Timeout in seconds [2]: 
Extended commands [n]: y
Source address or interface: 1.1.1.1
Type of service [0]: 
Set DF bit in IP header? [no]: yes
Validate reply data? [no]: 
Data pattern [0xABCD]: 
Loose, Strict, Record, Timestamp, Verbose[none]: 
Sweep range of sizes [n]: 
Type escape sequence to abort.
Sending 10, 1490-byte ICMP Echos to 4.4.4.4, timeout is 2 seconds:
Packet sent with a source address of 1.1.1.1 
Packet sent with the DF bit set
!!!!!!!!!!
Success rate is 100 percent (10/10), round-trip min/avg/max = 28/60/88 ms
R1#ping
Protocol [ip]: 
Target IP address: 4.4.4.4
Repeat count [5]: 
Datagram size [100]: 1499
Timeout in seconds [2]: 
Extended commands [n]: y
Source address or interface: 1.1.1.1
Type of service [0]: 
Set DF bit in IP header? [no]: yes
Validate reply data? [no]: 
Data pattern [0xABCD]: 
Loose, Strict, Record, Timestamp, Verbose[none]: 
Sweep range of sizes [n]: 
Type escape sequence to abort.
Sending 5, 1499-byte ICMP Echos to 4.4.4.4, timeout is 2 seconds:
Packet sent with a source address of 1.1.1.1 
Packet sent with the DF bit set
.....
Success rate is 0 percent (0/5)
R1#ping
Protocol [ip]: 
Target IP address: 4.4.4.4
Repeat count [5]: 
Datagram size [100]: 
Timeout in seconds [2]:  
Extended commands [n]: 
Sweep range of sizes [n]: 
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 4.4.4.4, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 36/54/104 ms
R1#

R1#
R1#ping
Protocol [ip]: 
Target IP address: 4.4.4.4
Repeat count [5]: 
Datagram size [100]: 1498
Timeout in seconds [2]: 
Extended commands [n]: y
Source address or interface: 1.1.1.1
Type of service [0]: 
Set DF bit in IP header? [no]: yes
Validate reply data? [no]: 
Data pattern [0xABCD]: 
Loose, Strict, Record, Timestamp, Verbose[none]: 
Sweep range of sizes [n]: 
Type escape sequence to abort.
Sending 5, 1498-byte ICMP Echos to 4.4.4.4, timeout is 2 seconds:
Packet sent with a source address of 1.1.1.1 
Packet sent with the DF bit set
...
Success rate is 0 percent (0/3)
R1#
R1#ping
Protocol [ip]: 
Target IP address: 4.4.4.4
Repeat count [5]: 
Datagram size [100]: 1497
Timeout in seconds [2]: 
Extended commands [n]: y
Source address or interface: 1.1.1.1
Type of service [0]: 
Set DF bit in IP header? [no]: yes
Validate reply data? [no]: 
Data pattern [0xABCD]: 
Loose, Strict, Record, Timestamp, Verbose[none]: 
Sweep range of sizes [n]: 
Type escape sequence to abort.
Sending 5, 1497-byte ICMP Echos to 4.4.4.4, timeout is 2 seconds:
Packet sent with a source address of 1.1.1.1 
Packet sent with the DF bit set
...
Success rate is 0 percent (0/3)
R1#
R1#ping
Protocol [ip]: 
Target IP address: 4.4.4.4
Repeat count [5]:   
Datagram size [100]: 1496
Timeout in seconds [2]: 
Extended commands [n]: y
Source address or interface: 1.1.1.1
Type of service [0]: 
Set DF bit in IP header? [no]: yes
Validate reply data? [no]: 
Data pattern [0xABCD]: 
Loose, Strict, Record, Timestamp, Verbose[none]: 
Sweep range of sizes [n]: 
Type escape sequence to abort.
Sending 5, 1496-byte ICMP Echos to 4.4.4.4, timeout is 2 seconds:
Packet sent with a source address of 1.1.1.1 
Packet sent with the DF bit set
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 12/47/76 ms
R1#
R1#ping
Protocol [ip]: 
Target IP address: 4.4.4.4
Repeat count [5]: 
Datagram size [100]: 1500
Timeout in seconds [2]: 
Extended commands [n]: y
Source address or interface: 1.1.1.1
Type of service [0]: 
Set DF bit in IP header? [no]: 
Validate reply data? [no]: 
Data pattern [0xABCD]: 
Loose, Strict, Record, Timestamp, Verbose[none]: 
Sweep range of sizes [n]: 
Type escape sequence to abort.
Sending 5, 1500-byte ICMP Echos to 4.4.4.4, timeout is 2 seconds:
Packet sent with a source address of 1.1.1.1 
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 60/100/140 ms

从测试中发现，如果在默认情况下，不分片，1496才可正常通信，这是因为标签占用了4byte。

Step 4 :尝试把接口MPLS MTU设置为1504，再测试，不分片，1500。

int s2/2
mpl mtu 1504

R1#sh mpls interfaces s2/2 detail 
Interface Serial2/2:
        IP labeling enabled (tdp)
        LSP Tunnel labeling not enabled
        BGP tagging not enabled
        Tagging operational
        Fast Switching Vectors:
          IP to MPLS Fast Switching Vector
          MPLS Turbo Vector
        MTU = 1504
R1#
R1#
R1#ping
Protocol [ip]: 
Target IP address: 4.4.4.4
Repeat count [5]: 
Datagram size [100]: 1500
Timeout in seconds [2]: 
Extended commands [n]: y
Source address or interface: 1.1.1.1
Type of service [0]: 
Set DF bit in IP header? [no]: yes
Validate reply data? [no]: 
Data pattern [0xABCD]: 
Loose, Strict, Record, Timestamp, Verbose[none]: 
Sweep range of sizes [n]: 
Type escape sequence to abort.
Sending 5, 1500-byte ICMP Echos to 4.4.4.4, timeout is 2 seconds:
Packet sent with a source address of 1.1.1.1 
Packet sent with the DF bit set
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 40/59/88 ms