在我们的应用程序中，我们使用的是运行于8081的apache tomcat webserver。
我们观察到一种行为，其中来自客户端的HTTP POST请求正在碎片化，而HTTP响应“200 OK”未得到碎片化。我们通过收集iptraces来观察。
我们的ETH MTU值为1500字节。
===( 331 bytes received on interface en0 )==== 13:50:01.040393849
ETHERNET packet : [ 00:26:cb:eb:df:7f -> 00:1a:64:47:3c:02 ] type 800 (IP)
IP header breakdown:
< SRC = 172.30.17.142 >
< DST = 10.16.0.72 > (un51sv01_if0)
ip_v=4, ip_hl=20, ip_tos=0, ip_len=317, ip_id=57225, ip_off=0 DF
ip_ttl=62, ip_sum=942d, ip_p = 6 (TCP)
TCP header breakdown:
<source port=43795, destination port=8081 >
th_seq=2849969884, th_ack=3790782429
th_off=5, flags<PUSH | ACK>
th_win=49680, th_sum=ba63, th_urp=0
00000000 504f5354 202f6973 61736f61 702f656e |POST /isasoap/en|
00000010 64706f69 6e742f49 6e766f6b 65417070 |dpoint/InvokeApp|
00000020 53657276 69636549 46204854 54502f31 |ServiceIF HTTP/1|
00000030 2e310d0a 436f6e74 656e742d 54797065 |.1..Content-Type|
00000040 3a207465 78742f78 6d6c3b20 63686172 |: text/xml; char|
00000050 7365743d 7574662d 380d0a41 63636570 |set=utf-8..Accep|
00000060 743a2074 6578742f 786d6c2c 20746578 |t: text/xml, tex|
00000070 742f6874 6d6c2c20 696d6167 652f6769 |t/html, image/gi|
00000080 662c2069 6d616765 2f6a7065 672c202a |f, image/jpeg, *|
00000090 3b20713d 2e322c20 2a2f2a3b 20713d2e |; q=.2, */*; q=.|
000000a0 320d0a53 4f415041 6374696f 6e3a2022 |2..SOAPAction: "|
000000b0 220d0a55 7365722d 4167656e 743a204a |"..User-Agent: J|
000000c0 6176612f 312e362e 305f3831 0d0a486f |ava/1.6.0_81..Ho|
000000d0 73743a20 31302e31 362e302e 37323a38 |st: 10.16.0.72:8|
000000e0 3038310d 0a436f6e 6e656374 696f6e3a |081..Connection:|
000000f0 206b6565 702d616c 6976650d 0a436f6e | keep-alive..Con|
00000100 74656e74 2d4c656e 6774683a 20333634 |tent-Length: 364|
00000110 390d0a0d 0a |9.... |
====( 1434 bytes received on interface en0 )==== 13:50:01.040697474
ETHERNET packet : [ 00:26:cb:eb:df:7f -> 00:1a:64:47:3c:02 ] type 800 (IP)
IP header breakdown:
< SRC = 172.30.17.142 >
< DST = 10.16.0.72 > (un51sv01_if0)
ip_v=4, ip_hl=20, ip_tos=0, ip_len=1420, ip_id=57227, ip_off=0 DF
ip_ttl=62, ip_sum=8fdc, ip_p = 6 (TCP)
TCP header breakdown:
<source port=43795, destination port=8081 >
th_seq=2849970161, th_ack=3790782429
th_off=5, flags<ACK>
th_win=49680, th_sum=f8e9, th_urp=0
00000000 3c3f786d 6c207665 7273696f 6e3d2231 |<?xml version="1|
00000010 2e302220 656e636f 64696e67 3d225554 |.0" encoding="UT|
00000020 462d3822 3f3e0a3c 656e763a 456e7665 |F-8"?>.<env:Enve|
00000030 6c6f7065 20786d6c 6e733a65 6e763d22 |lope xmlns:env="|
00000040 68747470 3a2f2f73 6368656d 61732e78 |http://schemas.x|
00000050 6d6c736f 61702e6f 72672f73 6f61702f |mlsoap.org/soap/|
00000060 656e7665 6c6f7065 2f222078 6d6c6e73 |envelope/" xmlns|
00000070 3a787364 3d226874 74703a2f 2f777777 |:xsd="http://www|
00000080 2e77332e 6f72672f 32303031 2f584d4c |.w3.org/2001/XML|
00000090 53636865 6d612220 786d6c6e 733a7873 |Schema" xmlns:xs|
与上面类似，还有另一个数据包。
====( 943 bytes received on interface en0 )==== 13:50:01.040713619
ETHERNET packet : [ 00:26:cb:eb:df:7f -> 00:1a:64:47:3c:02 ] type 800 (IP)
IP header breakdown:
< SRC = 172.30.17.142 >
< DST = 10.16.0.72 > (un51sv01_if0)
ip_v=4, ip_hl=20, ip_tos=0, ip_len=929, ip_id=57229, ip_off=0 DF
ip_ttl=62, ip_sum=91c5, ip_p = 6 (TCP)
TCP header breakdown:
<source port=43795, destination port=8081 >
th_seq=2849972921, th_ack=3790782429
th_off=5, flags<PUSH | ACK>
th_win=49680, th_sum=32ac, th_urp=0
00000000 74612069 643d2249 44313122 20787369 |ta id="ID11" xsi|
00000010 3a747970 653d226e 73313a49 6e766f6b |:type="ns1:Invok|
00000020 65417070 44617461 223e3c64 61746154 |eAppData"><dataT|
.....
经过我们的应用程序的一些内部处理后，我们发送200 OK和HTTP Response。
====( 3209 bytes transmitted on interface en0 )==== 13:50:01.041804849
ETHERNET packet : [ 00:1a:64:47:3c:02 -> 00:00:0c:07:ac:32 ] type 800 (IP)
IP header breakdown:
< SRC = 10.16.0.72 > (un51sv01_if0)
< DST = 172.30.17.142 >
ip_v=4, ip_hl=20, ip_tos=0, ip_len=3195, ip_id=60324, ip_off=0
ip_ttl=60, ip_sum=ffff, ip_p = 6 (TCP)
TCP header breakdown:
<source port=8081, destination port=43574 >
th_seq=3486085705, th_ack=3771812741
th_off=5, flags<PUSH | ACK>
th_win=65535, th_sum=564, th_urp=0
00000000 48545450 2f312e31 20323030 204f4b0d |HTTP/1.1 200 OK.|
00000010 0a416363 6570743a 20746578 742f786d |.Accept: text/xm|
00000020 6c2c2074 6578742f 68746d6c 2c20696d |l, text/html, im|
00000030 6167652f 6769662c 20696d61 67652f6a |age/gif, image/j|
00000040 7065672c 202a3b20 713d2e32 2c202a2f |peg, *; q=.2, */|
00000050 2a3b2071 3d2e320d 0a436f6e 74656e74 |*; q=.2..Content|
从上面请注意，对于200 OK HTTP响应，en0上收到的数据包长度为“3209”，实际上是整个响应。但它超过了以太网的MTU ......
我们的MTU值是默认值 - 1500字节
un51sv01# lsattr -El en0 |grep mtu
mtu 1500 Maximum IP Packet Size for This Device True
有人可以说明为什么会这样发生吗？
Change / Show Characteristics of an Ethernet Adapter
Type or select values in entry fields.
Press Enter AFTER making all desired changes.
[Entry Fields]
Ethernet Adapter ent0
Description Logical Host Ethernet Port (lp-hea)
Status Available
Location
Request Transmit and Receive Jumbo Frames no +
Enable hardware Transmit TCP segmentation yes +
Enable receive TCP segment aggregation yes +
Enable hardware Transmit checksum yes +
Enable hardware Receive checksum yes +
Requested media speed Auto_Negotiation +
Enable ALTERNATE ETHERNET address no +
ALTERNATE ETHERNET address [0x000000000000] +
Apply change to DATABASE only no +
以上表示未启用巨型帧。
谢谢， Sashi