大家好，我遇到了个头疼的网络问题，想请各位帮忙分析下。我的内部网络一直都是千兆配置（工作站、服务器、交换机全是千兆规格），但最近在OpenSuSE Leap 15.5工作站的syslog里，发现网卡频繁掉线还自动降速，日志内容如下：

[  145.886888] r8169 0000:07:00.0 eth0: Link is Down

[  149.670266] r8169 0000:07:00.0 eth0: Link is Up - 1Gbps/Full - flow control rx/tx

[  171.555271] r8169 0000:07:00.0 eth0: Link is Down

[  185.386620] Generic FE-GE Realtek PHY r8169-0-700:00: Downshift occurred from negotiated speed 1Gbps to actual speed 100Mbps, check cabling!

[  185.386635] r8169 0000:07:00.0 eth0: Link is Up - 100Mbps/Full (downshifted) - flow control rx/tx

我用几个网络调试工具查了系统和网卡的详细信息：

系统内核版本 #

╭─jacek@epica ~
╰─➤  uname -a
Linux epica 5.14.21-150500.55.36-default #1 SMP PREEMPT_DYNAMIC Tue Oct 31 08:37:43 UTC 2023 (e7a2e23) x86_64 x86_64 x86_64 GNU/Linux

网卡链路状态 #

╭─jacek@epica ~
╰─➤  ip link
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000
link/ether b4:2e:99:c6:e9:9f brd ff:ff:ff:ff:ff:ff
altname enp7s0

网卡详细参数 #

╭─jacek@epica ~
╰─➤  sudo ethtool eth0
Settings for eth0:
Supported ports: [ TP    MII ]
Supported link modes:   10baseT/Half 10baseT/Full
                        100baseT/Half 100baseT/Full
                        1000baseT/Full
Supported pause frame use: Symmetric Receive-only
Supports auto-negotiation: Yes
Supported FEC modes: Not reported
Advertised link modes:  10baseT/Half 10baseT/Full
                        100baseT/Half 100baseT/Full
                        1000baseT/Full
Advertised pause frame use: Symmetric Receive-only
Advertised auto-negotiation: Yes
Advertised FEC modes: Not reported
Link partner advertised link modes:  10baseT/Half 10baseT/Full
                                     100baseT/Half 100baseT/Full
                                     1000baseT/Full
Link partner advertised pause frame use: Symmetric
Link partner advertised auto-negotiation: Yes
Link partner advertised FEC modes: Not reported
Speed: 100Mb/s
Duplex: Full
Auto-negotiation: on
master-slave cfg: preferred slave
master-slave status: slave
Port: Twisted Pair
PHYAD: 0
Transceiver: external
MDI-X: Unknown
Supports Wake-on: pumbg
Wake-on: d
Link detected: yes

YaST的硬件信息里显示我的网卡是：RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller

我在Linux Mint论坛看到有人建议重新加载网卡驱动，于是试了这个命令：

╭─jacek@epica ~
╰─➤  sudo modprobe -r r8169 && sudo modprobe r8169

但完全没用！网卡确实会先以1Gbps的速度启动，但没过多久就自动降到100Mbps了，对应的系统日志如下：

[ 6470.039948] r8169 0000:07:00.0 eth0: Link is Down
[ 6470.341900] libphy: r8169: probed
[ 6470.342189] r8169 0000:07:00.0 eth0: RTL8168g/8111g, b4:2e:99:c6:e9:9f, XID 4c0, IRQ 81
[ 6470.342196] r8169 0000:07:00.0 eth0: jumbo features [frames: 9194 bytes, tx checksumming: ko]
[ 6470.402643] Generic FE-GE Realtek PHY r8169-0-700:00: attached PHY driver (mii_bus:phy_addr=r8169-0-700:00, irq=MAC)
[ 6470.603188] r8169 0000:07:00.0 eth0: Link is Down
[ 6477.014457] r8169 0000:07:00.0 eth0: Link is Up - 1Gbps/Full - flow control rx/tx
[ 6478.210793] r8169 0000:07:00.0 eth0: Link is Down
[ 6481.311902] r8169 0000:07:00.0 eth0: Link is Up - 1Gbps/Full - flow control rx/tx
[ 6482.077305] r8169 0000:07:00.0 eth0: Link is Down
[ 6496.122480] Generic FE-GE Realtek PHY r8169-0-700:00: Downshift occurred from negotiated speed 1Gbps to actual speed 100Mbps, check cabling!
[ 6496.122492] r8169 0000:07:00.0 eth0: Link is Up - 100Mbps/Full (downshifted) - flow control rx/tx

我的网线、插座、配线架都是Cat5e规格的，跳线也是现成的成品线，这套硬件已经稳定运行好几年了，完全搞不懂为什么突然会出现降速的情况。

想请教下各位，到底哪里出问题了？会不会是几个月前从Leap 15.4升级到15.5导致的？还是说我应该先换根网线试试？

备注：内容来源于stack exchange，提问作者Neppomuk