蒂姆,我谨恳请您不要对更改MTU存有疑问。您的问题已经写满了MTU问题,并且我已经成为专业的网络工程师超过15年了。
为了证明MTU是否有帮助,请使用ping和DF
IP标头中设置的位在Linux机器上进行测试...
ping -M do -s 1232 <some pingable internet ip address>
我-s
假设您的PPPoE IP MTU为1300字节,计算出该参数。如果ping成功,则使用-s 1472
并观察会发生什么...如果ping现在失败,则有确凿的证据表明存在MTU问题(假设您尚未将以太网链路MTU设置得较低)。仅供参考,-s 1472
将发送1500字节的以太网有效载荷echo-request;-M do -s 1472
发送与IP头中设置的DF位相同的1500字节有效负载。
还请记住,必须在链接的两边都设置MTU ...因此您也需要在调制解调器上进行此设置。
编辑
蒂姆,您仍然没有运行我要求您执行的命令。让我给你举一个例子,说明你做错了什么(我需要将目标主机修改为stackexchange.com,这是因为在通往8.8.8.8的路径中进行了IP分片的防火墙保护)
负面示例(使用ping标志)
[mpenning@Bucksnort ~]$ ping -c 1 -s 65507 64.34.119.12
PING 64.34.119.12 (64.34.119.12) 65507(65535) bytes of data.
65515 bytes from 64.34.119.12: icmp_seq=1 ttl=51 time=53.2 ms
--- 64.34.119.12 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 53.246/53.246/53.246/0.000 ms
[mpenning@Bucksnort ~]$
修辞性问题:64KB ping数据包如何通过1500字节的以太网段获得?(请参阅尾注A)除非您发布我要的信息,否则我将无济于事。这是同一个例子ping -M do
正面的例子
[mpenning@Bucksnort ~]$ ping -M do -c 1 -s 65507 64.34.119.12
PING 64.34.119.12 (64.34.119.12) 65507(65535) bytes of data.
From 24.102.60.3 icmp_seq=1 Frag needed and DF set (mtu = 1500)
--- 64.34.119.12 ping statistics ---
0 packets transmitted, 0 received, +1 errors
[mpenning@Bucksnort ~]$
ping -M do
提供有关沿路径的最大MTU的信息(在这种情况下,我们知道第一跳以太网段IP MTU
的1500字节)。
结束语:
答:您的ping可以作为一系列IP片段来完成,因为默认情况下ping
允许IP片段化。如果您尝试查找将通过链接的最大数据包大小,则必须修改IP报头(我用进行了说明-M do
),以确保最后不会得到一堆零碎的响应。使用ping -c 1 -s 65507 64.34.119.12
:
[mpenning@Bucksnort ~]$ sudo tshark -n -i eth0 icmp
1 0.000000 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=0)
2 0.000058 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=1480)
3 0.000071 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=2960)
4 0.000081 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=4440)
5 0.000094 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=5920)
6 0.000105 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=7400)
7 0.000116 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=8880)
8 0.000124 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=10360)
9 0.000133 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=11840)
10 0.000143 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=13320)
11 0.000152 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=14800)
12 0.000162 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=16280)
13 0.000172 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=17760)
14 0.000181 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=19240)
15 0.000191 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=20720)
16 0.000201 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=22200)
17 0.000211 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=23680)
18 0.000221 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=25160)
19 0.000230 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=26640)
20 0.000240 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=28120)
21 0.000250 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=29600)
22 0.000259 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=31080)
23 0.000269 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=32560)
24 0.000278 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=34040)
25 0.000288 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=35520)
26 0.000298 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=37000)
27 0.000308 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=38480)
28 0.000318 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=39960)
29 0.000327 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=41440)
30 0.000337 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=42920)
31 0.000352 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=44400)
32 0.000361 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=45880)
33 0.000372 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=47360)
34 0.000384 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=48840)
35 0.000394 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=50320)
36 0.000403 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=51800)
37 0.000411 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=53280)
38 0.000419 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=54760)
39 0.000428 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=56240)
40 0.000437 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=57720)
41 0.000446 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=59200)
42 0.000455 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=60680)
43 0.000466 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=62160)
44 0.000477 24.102.60.3 -> 64.34.119.12 IP Fragmented IP protocol (proto=ICMP 0x01, off=63640)
45 0.000486 24.102.60.3 -> 64.34.119.12 ICMP Echo (ping) request
46 0.044402 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=0)
47 0.044439 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=1480)
48 0.044899 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=2960)
49 0.044910 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=4440)
50 0.044916 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=5920)
51 0.045149 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=7400)
52 0.045399 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=8880)
53 0.045409 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=10360)
54 0.045415 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=11840)
55 0.045649 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=13320)
56 0.045899 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=14800)
57 0.045908 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=16280)
58 0.045915 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=17760)
59 0.046148 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=19240)
60 0.046163 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=20720)
61 0.046402 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=22200)
62 0.046421 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=23680)
63 0.046650 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=25160)
64 0.046668 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=26640)
65 0.046901 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=28120)
66 0.046918 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=29600)
67 0.047151 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=31080)
68 0.047171 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=32560)
69 0.047399 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=34040)
70 0.047418 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=35520)
71 0.047424 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=37000)
72 0.047650 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=38480)
73 0.047900 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=39960)
74 0.048149 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=41440)
75 0.048165 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=42920)
76 0.048172 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=44400)
77 0.048178 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=45880)
78 0.048398 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=47360)
79 0.048650 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=48840)
80 0.048667 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=50320)
81 0.048674 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=51800)
82 0.048900 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=53280)
83 0.048922 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=54760)
84 0.049150 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=56240)
85 0.049174 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=57720)
86 0.049398 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=59200)
87 0.049649 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=60680)
88 0.049671 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=62160)
89 0.049677 64.34.119.12 -> 24.102.60.3 IP Fragmented IP protocol (proto=ICMP 0x01, off=63640)
90 0.049683 64.34.119.12 -> 24.102.60.3 ICMP Echo (ping) reply