今天遇到个生产平台的网卡降速问题，由1000M降速到10M。这个一般的原因是？目前准备已经协调了机房明天更换下网线看下，但是除了网线一般还有什么原因，网卡是自适应的双工貌似，下面贴下指标。网卡本身经过测试应该是没有问题的。
[linux]$ dmesg | grep -i eth0
igb 0000:02:00.0: eth0: (PCIe:5.0Gb/s:Width x4) 10:1b:54:43:c1:8d
igb 0000:02:00.0: eth0: PBA No: 106300-000
bonding: bond0: Adding slave eth0.
**igb: eth0 NIC Link is Up 10 Mbps Full Duplex, Flow Control: RX**
8021q: adding VLAN 0 to HW filter on device eth0
bonding: bond0: enslaving eth0 as an active interface with an up link.
**device eth0 entered promiscuous mode**
type=1700 audit(1398768126.654:3): dev=eth0 prom=256 old_prom=0 auid=4294967295 ses=4294967295
device eth0 left promiscuous mode
type=1700 audit(1398768185.647:4): dev=eth0 prom=0 old_prom=256 auid=4294967295 ses=4294967295
看到标粗的部分，已经变成了混杂模式了，也降速到10M，正常的如下：
[linux]$ dmesg | grep -i eth0
igb 0000:02:00.0: eth0: (PCIe:5.0Gb/s:Width x4) 48:46:fb:01:46:bd
igb 0000:02:00.0: eth0: PBA No: 106300-000
bonding: bond0: Adding slave eth0.
igb: eth0 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: RX
8021q: adding VLAN 0 to HW filter on device eth0
bonding: bond0: enslaving eth0 as an active interface with an up link.
另外用mii-tool 、iftop、ifconfig以及ethool都看了，没什么异常
mii-tool和ethool的指标如下：
[linux]$ sudo /sbin/mii-tool -v
eth0: negotiated 100baseTx-FD, link ok
product info: vendor 00:55:00, model 59 rev 1
basic mode: autonegotiation enabled
basic status: autonegotiation complete, link ok
capabilities: 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD
advertising: 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD flow-control
link partner: 100baseTx-FD 10baseT-FD
eth1: negotiated 100baseTx-FD, link ok
product info: vendor 00:55:00, model 59 rev 1
basic mode: autonegotiation enabled
basic status: autonegotiation complete, link ok
capabilities: 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD
advertising: 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD flow-control
link partner: 100baseTx-FD 10baseT-FD
[linux]$ sudo /sbin/ethtool eth0
Settings for eth0:
Supported ports: [ TP ]
Supported link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Full
Supports auto-negotiation: Yes
Advertised link modes: 10baseT/Half 10baseT/Full
100baseT/Half 100baseT/Full
1000baseT/Full
Advertised auto-negotiation: Yes
Speed: 10Mb/s
Duplex: Full
Port: Twisted Pair
PHYAD: 1
Transceiver: internal
Auto-negotiation: on
Supports Wake-on: pumbg
Wake-on: g
Current message level: 0x00000003 (3)
Link detected: yes
另外用了speedtest_cli测试了下速度，上传下载达到了10多M了，所以很奇怪，下面是测试后的指标：
[linux]$ sudo python speedtest_cli.py
Retrieving speedtest.net configuration...
Retrieving speedtest.net server list...
Testing from China Telecom Guangdong (14.17.85.2)...
Selecting best server based on ping...
Hosted by Unicom-GZ (Guangzhou) [2.51 km]: 23.206 ms
Testing download speed........................................
Download: 18.76 Mbits/s
Testing upload speed..................................................
Upload: 16.45 Mbits/s
该问题已经解决，是由于网线松动导致的。把网线从新插拔下就好了。