How to check why ssh is not working?

Question

SSH

Good afternoon.
There is a router "ASUS Wireless Router RT-AC68U".
Today suddenly stopped letting ssh into the server. Didn't change anything, just stopped working.
The firmware is the latest, I turned on the ssh daemon and went via ssh to the router and from there also does not let me go to other servers via SSH. Everything else works and ping and wget. There are no restrictions, no port forwarding. everything is set to default.
How can I check why ssh is not working?
I'm not very friendly with iptables.

[email protected](none):/tmp# iptables -L
Chain INPUT (policy ACCEPT)
target     prot opt source               destination         

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination         
TCPMSS     tcp  --  anywhere             anywhere             tcpflags: SYN,RST/SYN TCPMSS clamp to PMTU
ACCEPT     all  --  anywhere             anywhere             state RELATED,ESTABLISHED
DROP       all  --  anywhere             anywhere            
DROP       all  --  anywhere             anywhere            
DROP       all  --  anywhere             anywhere             state INVALID
ACCEPT     all  --  anywhere             anywhere            
ACCEPT     all  --  anywhere             anywhere             ctstate DNAT

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination         

Chain FUPNP (0 references)
target     prot opt source               destination         

Chain PControls (0 references)
target     prot opt source               destination         
ACCEPT     all  --  anywhere             anywhere            

Chain SECURITY (0 references)
target     prot opt source               destination         
RETURN     tcp  --  anywhere             anywhere             tcpflags: FIN,SYN,RST,ACK/SYN limit: avg 1/sec burst 5
DROP       tcp  --  anywhere             anywhere             tcpflags: FIN,SYN,RST,ACK/SYN
RETURN     tcp  --  anywhere             anywhere             tcpflags: FIN,SYN,RST,ACK/RST limit: avg 1/sec burst 5
DROP       tcp  --  anywhere             anywhere             tcpflags: FIN,SYN,RST,ACK/RST
RETURN     icmp --  anywhere             anywhere             icmp echo-request limit: avg 1/sec burst 5
DROP       icmp --  anywhere             anywhere             icmp echo-request
RETURN     all  --  anywhere             anywhere            

Chain logaccept (0 references)
target     prot opt source               destination         
LOG        all  --  anywhere             anywhere             state NEW LOG level warning tcp-sequence tcp-options ip-options prefix "ACCEPT "
ACCEPT     all  --  anywhere             anywhere            

Chain logdrop (0 references)
target     prot opt source               destination         
LOG        all  --  anywhere             anywhere             state NEW LOG level warning tcp-sequence tcp-options ip-options prefix "DROP "
DROP       all  --  anywhere             anywhere

Answer 1

$ ssh -vvvv site.ru

Answer 2

Check /etc/ssh/sshd_config for
PermitRootLogin Port