tcpdump：snaplen 設置為 0，但仍然得到“擷取期間數據包大小受限”？

由於這個問題，我將在 MySQL 伺服器後端嗅探一些數據包，看看會發生什麼：

# tcpdump -vv -s0 -c 100 -i bond0 tcp port 3306 and host 192.168.3.87 -w /home/quanta/3.87_aborted.pcap

如您所見，我將 snaplen 設置為 0，但仍然收到消息*“擷取期間數據包大小受限”*：

MySQL Protocol
   Packet Length: 579
   Packet Number: 96
   text: 336
   text: 1004352
   text: 147619
   text: 336
[Packet size limited during capture: MySQL truncated]

我界面上的解除安裝設置：

# ethtool -k bond0
Offload parameters for bond0:
Cannot get device rx csum settings: Operation not supported
rx-checksumming: off
tx-checksumming: on
scatter-gather: on
tcp segmentation offload: on
udp fragmentation offload: off
generic segmentation offload: off
generic-receive-offload: off

---

/proc/net/bonding/bond0:

Ethernet Channel Bonding Driver: v3.4.0-1 (October 7, 2008)

Bonding Mode: adaptive load balancing
Primary Slave: None
Currently Active Slave: eth1
MII Status: up
MII Polling Interval (ms): 100
Up Delay (ms): 0
Down Delay (ms): 0

Slave Interface: eth1
MII Status: up
Speed: 1000 Mbps
Duplex: full
Link Failure Count: 0
Permanent HW addr: 00:30:48:c3:20:be

---

回复@HeatfanJohn：

# ethtool -k eth1
Offload parameters for eth1:
Cannot get device udp large send offload settings: Operation not supported
rx-checksumming: on
tx-checksumming: on
scatter-gather: on
tcp segmentation offload: on
udp fragmentation offload: off
generic segmentation offload: off
generic-receive-offload: on

---

回复@Doon：

bond0     UP BROADCAST RUNNING MASTER MULTICAST  MTU:1500  Metric:1

嗅探-s 1500也顯示：

41  11.371783  192.168.6.7 -> 192.168.3.87 MySQL Response OK
42  11.371974 192.168.3.87 -> 192.168.6.7  MySQL Request Ping
43  11.371996  192.168.6.7 -> 192.168.3.87 MySQL Response OK
44  11.378562 192.168.3.87 -> 192.168.6.7  MySQL Request Query
45  11.379604  192.168.6.7 -> 192.168.3.87 MySQL Response
46  11.402431 192.168.3.87 -> 192.168.6.7  MySQL Request Query
47  11.402992  192.168.6.7 -> 192.168.3.87 MySQL Response[Packet size limited during capture]

這是答案形式，措辭正確:)我會在禁用分段解除安裝的情況下嘗試這個。啟用它後，tcpdump 很可能無法得到它所期望的。

——馬特

關於 TCP 解除安裝的一些事情我完全遵守： http ://www.linuxfoundation.org/collaborate/workgroups/networking/toe

引用自：https://serverfault.com/questions/413481