SSH Connection closed after a short time centos 7

Question

When I trying to connect centos 7 server via ssh it connects asks for username password, I enter then login. But after a while, the connection is closed and doesn't response. Then I go to server console, i send a ping to anywhere on internet (sometimes restart network needed) it succeeds. After that i try again ssh connection from client it reconnects, but again after a short time closes the connection again.

When I checked my network status with systemctl status network:

network.service - LSB: Bring up/down networking
   Loaded: loaded (/etc/rc.d/init.d/network; bad; vendor preset: disabled)
   Active: active (exited) since Thu 2022-02-17 10:28:03 +03; 43min ago
     Docs: man:systemd-sysv-generator(8)
  Process: 4314 ExecStop=/etc/rc.d/init.d/network stop (code=exited, status=0/SUCCESS)
  Process: 4551 ExecStart=/etc/rc.d/init.d/network start (code=exited, status=0/SUCCESS)
    Tasks: 0

Why it's set exited? also there is preset:disabled can cause problem? Here is the ethernet connection config:

DEVICE=ens18
TYPE=Ethernet
ONBOOT=yes
NM_CONTROLLED=yes
BOOTPROTO=none
HWADDR=<hw mac address hidden>
IPADDR=<server ip hidden>
NETMASK=255.255.255.192
GATEWAY=<gateway ip hidden>
DNS1=<dns ip hidden>
DNS2=<dns ip hidden>
DEFROUTE=yes
IPV4_FAILURE_FATAL=yes
IPV6INIT=no
NAME=ens18

SSH Client Logs:

$ ssh root@<server ip> -v
OpenSSH_7.7p1, OpenSSL 1.0.2p  14 Aug 2018
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Connecting to <server ip> [<server ip>] port 22.
debug1: Connection established.
debug1: key_load_public: No such file or directory
debug1: identity file /c/Users/serhat/.ssh/id_rsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /c/Users/serhat/.ssh/id_rsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /c/Users/serhat/.ssh/id_dsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /c/Users/serhat/.ssh/id_dsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /c/Users/serhat/.ssh/id_ecdsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /c/Users/serhat/.ssh/id_ecdsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /c/Users/serhat/.ssh/id_ed25519 type -1
debug1: key_load_public: No such file or directory
debug1: identity file /c/Users/serhat/.ssh/id_ed25519-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /c/Users/serhat/.ssh/id_xmss type -1
debug1: key_load_public: No such file or directory
debug1: identity file /c/Users/serhat/.ssh/id_xmss-cert type -1
debug1: Local version string SSH-2.0-OpenSSH_7.7
debug1: Remote protocol version 2.0, remote software version OpenSSH_7.4
debug1: match: OpenSSH_7.4 pat OpenSSH* compat 0x04000000
debug1: Authenticating to <server ip>:22 as 'root'
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: algorithm: curve25519-sha256
debug1: kex: host key algorithm: ecdsa-sha2-nistp256
debug1: kex: server->client cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none
debug1: kex: client->server cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: Server host key: ecdsa-sha2-nistp256 SHA256:MiFljnjU0tNBZzpOa2tl5oean+77W4wZ1/cy8f2ULeU
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that a host key has just been changed.
The fingerprint for the ECDSA key sent by the remote host is
SHA256:MiFljnjU0tNBZzpOa2tl5oean+77W4wZ1/cy8f2ULeU.
Please contact your system administrator.
Add correct host key in /c/Users/serhat/.ssh/known_hosts to get rid of this message.
Offending ECDSA key in /c/Users/serhat/.ssh/known_hosts:3
ECDSA host key for <server ip> has changed and you have requested strict checking.
Host key verification failed.

Answer 1

On SSH the server may close a connection after a certain period of inactivity (no communication between client and server). You can approach this behaviour via a client setting or a server setting.

On the client side edit the file ~/.ssh/config (create it if it doesn't exist):

Host *
    ServerAliveInterval 240

ServerAliveInterval specifies the client to send a signal to the server after an amount of seconds.

If you have access to the server you can modify the file /etc/ssh/sshd_config:

ClientAliveInterval 300
ClientAliveCountMax 10

This will cause the server to send a signal to the client every 5 minutes of inactivity. It does it 10 times before it closes the connection.