我的 SSH 服务器在大学防火墙后面工作。
我连接到我的大学 VPN，并且一直能够通过 SSH 进入它。最近我使用 VSCode 通过 SSH 对其进行远程工作。连接断开了几次，我无法再登录。甚至 ping 也没有返回任何内容。
奇怪的是：如果我通过 VPN 接入，然后通过 SSH 进入我工作时的第二个工作站，然后从该工作站 SSH 进入原始工作站，它就可以正常工作。
因此，看起来我的 IP 被工作站阻止了。但我检查了一下：
sudo iptables -L INPUT -v -n | less
它显示：
Chain INPUT (policy ACCEPT 401K packets, 599M bytes)
pkts bytes target prot opt in out source destination
(END)
所以这不是我的工作站？发生了什么事？我还能检查什么吗？
更新
ssh -vvv 的输出：
>>ssh -vvv [email protected]
OpenSSH_9.3p2, LibreSSL 3.3.6
debug1: Reading configuration data /Users/me/.ssh/config
debug1: /Users/me/.ssh/config line 1: Applying options for 172.18.2.28
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 21: include /etc/ssh/ssh_config.d/* matched no files
debug1: /etc/ssh/ssh_config line 54: Applying options for *
debug2: resolve_canonicalize: hostname 172.18.2.28 is address
debug3: expanded UserKnownHostsFile '~/.ssh/known_hosts' -> '/Users/me/.ssh/known_hosts'
debug3: expanded UserKnownHostsFile '~/.ssh/known_hosts2' -> '/Users/me/.ssh/known_hosts2'
debug1: Authenticator provider $SSH_SK_PROVIDER did not resolve; disabling
debug3: ssh_connect_direct: entering
debug1: Connecting to 172.18.2.28 [172.18.2.28] port 22.
debug3: set_sock_tos: set socket 3 IP_TOS 0x48
debug1: connect to address 172.18.2.28 port 22: Operation timed out
ssh: connect to host 172.18.2.28 port 22: Operation timed out
更新 2
检查sudo vi +26 /etc/ssh/sshd_config。唯一未注释的行是：
Include /etc/ssh/sshd_config.d/*.conf
Port 22
ChallengeResponseAuthentication no
usePAM yes
X11Forwarding yes
PrintMotd no
AcceptEnv LANG LC_*
Subsystem sftp /usr/lib/openssh/sftp-server
文件夹/etc/ssh/sshd_config.d是空的。
检查tail /var/log/auth.log：
Nov 14 15:16:15 COMP sshd[113124]: pam_unix(sshd:session): session opened for user dorien by (uid=0)
Nov 14 15:16:15 COMP systemd-logind[756]: New session 191 of user dorien.
Nov 14 15:16:28 COMP sudo: dorien : TTY=pts/1 ; PWD=/home/dorien ; USER=root ; COMMAND=/usr/bin/vi +26 /etc/ssh/sshd_config
Nov 14 15:16:28 COMP sudo: pam_unix(sudo:session): session opened for user root by dorien(uid=0)
Nov 14 15:17:01 COMP CRON[113225]: pam_unix(cron:session): session opened for user root by (uid=0)
Nov 14 15:17:01 COMP CRON[113225]: pam_unix(cron:session): session closed for user root
Nov 14 15:18:27 COMP sudo: pam_unix(sudo:session): session closed for user root
Nov 14 15:19:23 COMP sudo: dorien : TTY=pts/1 ; PWD=/etc/ssh/sshd_config.d ; USER=root ; COMMAND=/usr/bin/ls
Nov 14 15:19:23 COMP sudo: pam_unix(sudo:session): session opened for user root by dorien(uid=0)
Nov 14 15:19:23 COMP sudo: pam_unix(sudo:session): session closed for user root
这并没有记录我在 15:21 进行的超时 ssh 登录尝试。
更新 3
ssh -vvv -o IPQoS=none [email protected]
输出超时：
OpenSSH_9.3p2, LibreSSL 3.3.6
debug1: Reading configuration data /Users/dorien_herremans/.ssh/config
debug1: /Users/dorien_herremans/.ssh/config line 1: Applying options for 172.18.2.28
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 21: include /etc/ssh/ssh_config.d/* matched no files
debug1: /etc/ssh/ssh_config line 54: Applying options for *
debug2: resolve_canonicalize: hostname 172.18.2.28 is address
debug3: expanded UserKnownHostsFile '~/.ssh/known_hosts' -> '/Users/dorien_herremans/.ssh/known_hosts'
debug3: expanded UserKnownHostsFile '~/.ssh/known_hosts2' -> '/Users/dorien_herremans/.ssh/known_hosts2'
debug1: Authenticator provider $SSH_SK_PROVIDER did not resolve; disabling
debug3: ssh_connect_direct: entering
debug1: Connecting to 172.18.2.28 [172.18.2.28] port 22.
debug1: connect to address 172.18.2.28 port 22: Operation timed out
ssh: connect to host 172.18.2.28 port 22: Operation timed out
答案1
虽然我没有直接遇到过这个问题，但在线搜索发现这个问题与 QoS（服务质量）有关。
- 看这个服务器故障答案。
- 还有这个GitHub 上的问题报告。
查看ssh -vvv输出中的此行：
debug3: set_sock_tos set socket 3 IP_TOS 0x48
因此，解决方案是使用以下命令运行 SSH 命令-o IPQoS=none：
ssh -o IPQoS=none [email protected]
看看禁用 QoS 是否可以解决问题。
如果可行，请考虑添加此配置以~/.ssh/config使所有主机的设置更加永久：
Host *
IPQoS=none
或者将其具体到您遇到问题的服务器：
Host 172.18.2.28
IPQoS=none