tcpdump: snaplen set to 0 but still get "Packet size limited during capture"?
Due to this problem, I'm going to sniff some packets on the MySQL server backend to see what happens:
# tcpdump -vv -s0 -c 100 -i bond0 tcp port 3306 and host 192.168.3.87 -w /home/quanta/3.87_aborted.pcap
As you can see, I set snaplen to 0, but still get the message "Packet size limited during capture":
MySQL Protocol
Packet Length: 579
Packet Number: 96
text: 336
text: 1004352
text: 147619
text: 336
[Packet size limited during capture: MySQL truncated]
The offload settings on my interface:
# 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
Reply to @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
Reply to @Doon:
bond0 UP BROADCAST RUNNING MASTER MULTICAST MTU:1500 Metric:1
Sniffing with -s 1500
also shows:
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]
Here it is in answer form, with correct wording :) I would try this with segmentation offload disabled. With it enabled, it's very possible that tcpdump isn't able to get what it is expecting.
--Matt
Something about TCP offloading I fully comply with: http://www.linuxfoundation.org/collaborate/workgroups/networking/toe