PTR request ( Reverse lan scan requests)

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mail2rst
Posts: 110
Joined: Fri Apr 13, 2018 4:53 pm

PTR request ( Reverse lan scan requests)

Post by mail2rst »

I have observed one weired thing. In my home LAN network there are two dietpi machines (one nuc and one raspberryPi). In raspberrypi I have installed bitwarden, homeassisttant & mqtt brocker via dietpi software. On nuc only docker & docker compose via dietpi-software (through docker compose plex,adguard, unbound & wireguard) both machines are running happily. But I observed both machines send PTR request to adguard (XX.1.168.192.in-addr.arpa). raspberry send PTR request to whole lan (192.168.1.1 to 192.168.1.254) every hour and in nuc side these request are coming after each 10 minute interval (only active lan devicies & docker internal network). So my question, is there any way to remove this reverse lan scan lookup thing as it unnecessary send request to dns resolver. Each day these are creating about 6K PTR request to my unbound system. In pihole or adguard forum it shown it is default patron but why reaspberry pi also sending these type of requests.
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Joulinar
Posts: 4783
Joined: Sat Nov 16, 2019 12:49 am

Re: PTR request ( Reverse lan scan requests)

Post by Joulinar »

Hi,

not sure if this is something special. I see similar request created by my Windows laptop

Code: Select all

00:02:38.375799 IP 192.168.0.54.49748 > 192.168.0.11.53: 50476+ PTR? 11.0.168.192.in-addr.arpa. (43)
00:02:38.375808 IP 192.168.0.54.53397 > 192.168.0.11.53: 41315+ PTR? 9.0.168.192.in-addr.arpa. (42)
00:02:38.376140 IP 192.168.0.11.53 > 192.168.0.54.49748: 50476* 1/0/0 PTR wpad.lan. (65)
00:02:38.376343 IP 192.168.0.11.53 > 192.168.0.54.53397: 41315* 1/0/0 PTR GS1900.lan. (66)

Code: Select all

nslookup 192.168.0.54
54.0.168.192.in-addr.arpa       name = Surface.lan.
Pls let us know if a solution is working. This could help others if they hit by similar situation. Your DietPi Team
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trendy
Posts: 306
Joined: Tue Feb 25, 2020 2:54 pm

Re: PTR request ( Reverse lan scan requests)

Post by trendy »

You could try to raise the TTL of the PTR records. I suppose they are set to an hour, you could then make it a day.
mail2rst
Posts: 110
Joined: Fri Apr 13, 2018 4:53 pm

Re: PTR request ( Reverse lan scan requests)

Post by mail2rst »

what is the procedure to raise the TTL of the PTR records? i will very happy to raise it for one day if it is not breaking anything. as most of my devises are fixed by router DHCP reservation.
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trendy
Posts: 306
Joined: Tue Feb 25, 2020 2:54 pm

Re: PTR request ( Reverse lan scan requests)

Post by trendy »

It depends on the nameserver running the zone with the PTR records.
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