VPP, after configuring the CGNAT, the host does not respond to SSH and cannot initiate a DNS request
To reproduce:
```
set interfaces ethernet eth0 address '192.168.122.14/24'
set interfaces ethernet eth0 description 'WAN'
set interfaces ethernet eth1 address '100.64.0.1/24'
set interfaces ethernet eth1 description 'LAN'
set vpp settings interface eth0 driver 'dpdk'
set vpp settings interface eth1 driver 'dpdk'
set vpp settings unix poll-sleep-usec '222'
set vpp nat cgnat interface inside 'eth1'
set vpp nat cgnat interface outside 'eth0'
set vpp nat cgnat rule 100 inside-prefix '100.64.0.0/24'
set vpp nat cgnat rule 100 outside-prefix '192.168.122.111/32'
set vpp nat cgnat timeout icmp '30'
set vpp nat cgnat timeout tcp-established '600'
set vpp nat cgnat timeout tcp-transitory '120'
set vpp nat cgnat timeout udp '150'
```
1. After this configuration, the SSH connection to the VyOS host `192.168.122.14` is broken, logs from the client (192.168.122.1):
```
sever@sever:~$ ssh -v vyos@192.168.122.14
OpenSSH_9.6p1 Ubuntu-3ubuntu13.11, OpenSSL 3.0.13 30 Jan 2024
debug1: Reading configuration data /home/sever/.ssh/config
debug1: /home/sever/.ssh/config line 1: Applying options for 192.168.122.14
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: include /etc/ssh/ssh_config.d/*.conf matched no files
debug1: /etc/ssh/ssh_config line 21: Applying options for *
debug1: /etc/ssh/ssh_config line 55: Applying options for 192.168.122.*
debug1: Connecting to 192.168.122.14 [192.168.122.14] port 22.
debug1: connect to address 192.168.122.14 port 22: Connection timed out
ssh: connect to host 192.168.122.14 port 22: Connection timed out
```
The client (192.168.122.1) can only ping the VPP server:
```
sever@sever:~$ ping 192.168.122.14
PING 192.168.122.14 (192.168.122.14) 56(84) bytes of data.
64 bytes from 192.168.122.14: icmp_seq=1 ttl=64 time=0.681 ms
^C
--- 192.168.122.14 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.681/0.681/0.681/0.000 ms
```
2. The server with VPP configuration cannot initiate a DNS request
```
vyos@r14# sudo nslookup
> set debug
> github.com
;; communications error to 1.1.1.1#53: timed out
;; communications error to 1.1.1.1#53: timed out
;; communications error to 1.1.1.1#53: timed out
;; no servers could be reached
>
```
The client under NAT (100.64.0.10) has the Internet connection but cannot ping the VPP host `192.168.122.14`
```
$ ping 1.1.1.1 count 1
PING 1.1.1.1 (1.1.1.1) 56(84) bytes of data.
64 bytes from 1.1.1.1: icmp_seq=1 ttl=57 time=11.1 ms
--- 1.1.1.1 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 11.064/11.064/11.064/0.000 ms
vyos@r15:~$
vyos@r15:~$
vyos@r15:~$ ping 192.168.122.14 count 1
PING 192.168.122.14 (192.168.122.14) 56(84) bytes of data.
--- 192.168.122.14 ping statistics ---
1 packets transmitted, 0 received, 100% packet loss, time 0ms
```