Destination Host Unreachable to host on LAN after some time

I have internal network with the following setup: * router - 192.168.1.1 - that is running dd-wrt * rasberrypi - 192.168.1.190 (rp1.local) - that is running Rasberry Pi OS * notebook - 192.168.1.185 - that is running Ubuntu * some phones Everything is working as expected - I am able to connect to rp1.local or 192.168.1.190 - but there is some strange behavior, that I am not able to figure out: 1) everything was working 2) 2023-12-27 22:00 - it's not possible to connect to rp1.local from the notebook, because the host name cannot be resolved, it's still possible to connect to the IP address 192.168.1.190 3) 2023-12-28 01:00 - it's still possible to connect to 192.168.1.190 4) 2023-12-28 11:00 - notebook is not able to connect (ping/http) to the rasberry pi IP address 192.168.1.190 (ERR_ADDRESS_UNREACHABLE / Destination Host Unreachable), some phones are still able to connect to that IP address 5) 2023-12-28 15:00 - none of the phones is able to connect to that IP address During all that I can still connect to the router - 192.168.1.1 and from that router I can access 192.168.1.190 (or just rp1). This has happened to me several times, but in the past it has resolved in few hours. ## Other information: ### On the notebook:

ip addr
1: lo:  mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: enp3s0:  mtu 1500 qdisc mq state DOWN group default qlen 1000
    link/ether 74:d0:2b:0a:04:2c brd ff:ff:ff:ff:ff:ff
3: wlp2s0:  mtu 1500 qdisc noqueue state UP group default qlen 1000
    link/ether 6c:71:d9:9c:82:4d brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.185/24 brd 192.168.1.255 scope global dynamic noprefixroute wlp2s0
       valid_lft 3925466sec preferred_lft 3925466sec
    inet6 fe80::352b:2ef9:850:124e/64 scope link noprefixroute 
       valid_lft forever preferred_lft forever

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resolvectl
Global
       Protocols: -LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
resolv.conf mode: stub

Link 2 (enp3s0)
Current Scopes: none
     Protocols: -DefaultRoute +LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported

Link 3 (wlp2s0)
    Current Scopes: DNS
         Protocols: +DefaultRoute +LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
Current DNS Server: 192.168.1.1
       DNS Servers: 192.168.1.1

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grep hosts /etc/nsswitch.conf
hosts:          files mdns4_minimal [NOTFOUND=return] dns myhostname

### Rasberry PI

ip addr
1: lo:  mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host noprefixroute 
       valid_lft forever preferred_lft forever
2: eth0:  mtu 1500 qdisc mq state DOWN group default qlen 1000
    link/ether d8:3a:dd:34:c7:01 brd ff:ff:ff:ff:ff:ff
3: wlan0:  mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether d8:3a:dd:34:c7:02 brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.190/24 brd 192.168.1.255 scope global dynamic noprefixroute wlan0
       valid_lft 3927658sec preferred_lft 3927658sec
    inet6 fe80::a22e:9352:19e5:9fab/64 scope link noprefixroute 
       valid_lft forever preferred_lft forever

-----

resolvectl
Failed to get global data: Failed to activate service 'org.freedesktop.resolve1': timed out (service_start_timeout=25000ms)

# but it wasn't there, so I had installed sudo apt-get install systemd-resolved

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grep hosts /etc/nsswitch.conf
hosts:          files mdns4_minimal [NOTFOUND=return] resolve [!UNAVAIL=return] dns myhostname

### On the router

ip addr
1: lo:  mtu 65536 qdisc noqueue state UNKNOWN 
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 brd 127.255.255.255 scope host lo
       valid_lft forever preferred_lft forever
2: eth0:  mtu 1500 qdisc sfq state UP qlen 1000
    link/ether 70:4f:57:8f:19:e6 brd ff:ff:ff:ff:ff:ff
3: vlan1@eth0:  mtu 1500 qdisc noqueue master br0 state UP 
    link/ether 70:4f:57:8f:19:e6 brd ff:ff:ff:ff:ff:ff
4: vlan2@eth0:  mtu 1500 qdisc noqueue state UP 
    link/ether 70:4f:57:8f:19:e6 brd ff:ff:ff:ff:ff:ff
    inet 10.2.236.203/24 brd 10.2.236.255 scope global vlan2
       valid_lft forever preferred_lft forever
7: br0:  mtu 1500 qdisc noqueue state UP 
    link/ether 70:4f:57:8f:19:e6 brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.1/24 brd 192.168.1.255 scope global br0
       valid_lft forever preferred_lft forever
12: wlan1:  mtu 1500 qdisc mq master br0 state UP qlen 1000
    link/ether 70:4f:57:8f:19:e8 brd ff:ff:ff:ff:ff:ff
13: wlan0:  mtu 1500 qdisc noqueue master br0 state UP 
    link/ether 70:4f:57:8f:19:e5 brd ff:ff:ff:ff:ff:ff

On the router I was also manually adding some rules to open some ports, but from the IP tables output it's hard to say, which ones it could be. Furthermore, they would most likely not cause this type of behaviour. Do you have any idea?