大家好，我遇到了一个非常奇怪的网络问题，折腾了很久都没头绪，想请各位帮忙分析下：

环境说明 #

• 服务器：ServerA（Debian Bookworm）
• 客户端：PI1、PI2、PI3（均为Raspbian Bookworm）
• 所有设备处于同一子网，连接同一WiFi接入点，防火墙配置完全一致，跨设备的用户UID和GID也完全相同

NFS共享异常情况 #

我在ServerA上配置了NFS共享，导出项如下：

/mnt/NAS 192.168.1.0/255.255.255.0(no_root_squash,async,insecure,no_subtree_check,nohide,rw,fsid=0,crossmnt)

• PI1和PI2都能正常访问这个共享，读写操作完全没问题
• PI3看起来成功挂载了共享，执行mount命令能看到如下信息：

  192.168.1.2:/mnt/NAS on /mnt/NAS type nfs (rw,relatime,vers=3,rsize=1048576,wsize=1048576,namlen=255,soft,proto=tcp,timeo=600,retrans=2,sec=sys,mountaddr=192.168.1.2,mountvers=3,mountport=56271,mountproto=tcp,local_lock=none,addr=192.168.1.2)
  

• ServerA的日志也显示PI3的挂载请求已经通过认证：

  Dec 30 16:26:39 thindebian daemon.notice rpc.mountd[2099]: authenticated mount request from 192.168.1.104:1006 for /mnt/NAS (/mnt/NAS)
  

• 但当我在PI3上执行ls /mnt/NAS时，命令会无限挂起，既没有报错也没有权限提示，只能按CTRL+C强制终止

SSH连接异常情况 #

更奇怪的是，ServerA和PI3之间的SSH连接双向都失败，但其他设备之间的连接一切正常：

• PI3无法SSH到ServerA，ServerA也无法SSH到PI3
• PI3可以正常SSH到PI1、PI2；PI1、PI2也能正常SSH到PI3；我的笔记本可以正常SSH到PI3；PI1、PI2也能正常SSH到ServerA

SSH连接失败的具体现象 #

1. 从PI3连接到ServerA：

   • 执行命令：ssh root@192.168.1.2
   • PI3端会提示：Connection closed by 192.168.1.2 port 22
   • ServerA的日志记录：

     Dec 30 18:02:49 thindebian auth.info sshd[81994]: Connection from 192.168.1.104 port 41742 on 192.168.1.2 port 22 rdomain ""
     Dec 30 18:03:54 thindebian auth.crit sshd[81843]: fatal: Timeout before authentication for 192.168.1.104 port 52798
     

2. 从ServerA连接到PI3（带-v调试参数）：
   调试输出卡在了expecting SSH2_MSG_KEX_ECDH_REPLY这一步，完整的调试信息如下：

   debug1: Connecting to 192.168.1.104 [192.168.1.104] port 22.
   debug1: Connection established.
   debug1: identity file /home/john/.ssh/id_rsa type 0
   debug1: identity file /home/john/.ssh/id_rsa-cert type -1
   debug1: identity file /home/john/.ssh/id_ecdsa type -1
   debug1: identity file /home/john/.ssh/id_ecdsa-cert type -1
   debug1: identity file /home/john/.ssh/id_ecdsa_sk type -1
   debug1: identity file /home/john/.ssh/id_ecdsa_sk-cert type -1
   debug1: identity file /home/john/.ssh/id_ed25519 type -1
   debug1: identity file /home/john/.ssh/id_ed25519-cert type -1
   debug1: identity file /home/john/.ssh/id_ed25519_sk type -1
   debug1: identity file /home/john/.ssh/id_ed25519_sk-cert type -1
   debug1: identity file /home/john/.ssh/id_xmss type -1
   debug1: identity file /home/john/.ssh/id_xmss-cert type -1
   debug1: identity file /home/john/.ssh/id_dsa type -1
   debug1: identity file /home/john/.ssh/id_dsa-cert type -1
   debug1: Local version string SSH-2.0-OpenSSH_9.2p1 Debian-2+deb12u2
   debug1: Remote protocol version 2.0, remote software version OpenSSH_9.2p1 -2+deb12u1
   debug1: compat_banner: match: OpenSSH_9.2p1 -2+deb12u1 pat OpenSSH* compat 0x04000000
   debug1: Authenticating to 192.168.1.104:22 as 'john'
   debug1: load_hostkeys: fopen /etc/ssh/ssh_known_hosts: No such file or directory
   debug1: load_hostkeys: fopen /etc/ssh/ssh_known_hosts2: No such file or directory
   debug1: SSH2_MSG_KEXINIT sent
   debug1: SSH2_MSG_KEXINIT received
   debug1: kex: algorithm: sntrup761x25519-sha512@openssh.com
   debug1: kex: host key algorithm: ssh-ed25519
   debug1: kex: server->client cipher: aes128-ctr MAC: umac-64-etm@openssh.com compression: none
   debug1: kex: client->server cipher: aes128-ctr MAC: umac-64-etm@openssh.com compression: none
   debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
   

   • 反过来从PI3连接到ServerA的调试输出，同样卡在了这个阶段

已尝试但无效的解决方案 #

• 将所有设备的MTU值统一调整为1500
• 手动指定MAC算法连接：ssh -o MACs=hmac-sha2-256 <HOST>

现在完全搞不懂为什么只有ServerA和PI3之间的连接有问题，其他设备间都正常，希望各位能给点思路！

备注：内容来源于stack exchange，提问作者John Tetreault