[Pdns-users] No response from pdns-recursor for some clients

[Robby Pedrica]

Hi pdns community

I've got an odd issue where some clients do not get a response from 
either of my 2 recursors. Both are v5.1.4 deployed via docker with 
fairly std configs. Generally the logs will indicate if something is not 
in the allowed-from list but these clients don't show there. For all 
intents and purposes, the recursors work normally and well for all my 
other clients.

Design:

client ---> firewall --- ipsec vpn --- firewall ---> recursor ---> internet

Troubleshooting:

- check for blocks due to allow_from (nothing listed for these clients)
- check local firewall rules (nothing special or different for specific 
clients)
- tcpdump on the recursor hosts show queries hitting those hosts
- pcaps on both firewalls show good traffic
- the start of the logs show the ACL for allow_from is correct

PDNS-rec Config:
------------------------

//
/######### SECTION incoming #########
incoming:
   listen:
   - 0.0.0.0
   - '::'
   allow_from:
   - x.x.x.x/y
   - etc.

   port: 53
   proxy_protocol_from: [a.a.a.a/b]
   use_incoming_edns_subnet: true
   max_tcp_clients: 128/
//


PDNS-rec docker config:
---------------------------------

//
/---
version: '2.0'
services:
   recursor:
     image: powerdns/pdns-recursor-51:latest
     restart: always
     ports:
       - "53:53"
       - "53:53/udp"
       - "8082:8082"
     logging:
       driver: "syslog"
     volumes:
       - ./recursor.yml:/etc/powerdns/recursor.yml
       - ./named.root.txt:/etc/named.root.txt
       - ./proxy-map.lua:/etc/proxy-map.lua/
//

PDNS-rec logs:
---------------------

recursor_1  | Apr 29 13:53:49 PowerDNS Recursor 5.1.4 (C) PowerDNS.COM BV
recursor_1  | Apr 29 13:53:49 Using 64-bits mode. Built using gcc 10.2.1 
20210110 on Apr  8 2025 10:17:24 by root at localhost.
recursor_1  | Apr 29 13:53:49 PowerDNS comes with ABSOLUTELY NO 
WARRANTY. This is free software, and you are welcome to redistribute it 
according to the terms of the GPL version 2.
recursor_1  | Apr 29 13:53:49 msg="Processing main YAML settings" 
subsystem="config" level="0" prio="Notice" tid="0" ts="1745934829.121" 
path="/etc/powerdns/recursor.yml"
recursor_1  | Apr 29 13:53:49 msg="YAML config found and processed" 
subsystem="config" level="0" prio="Notice" tid="0" ts="1745934829.121" 
configname="/etc/powerdns/recursor.yml"
recursor_1  | Apr 29 13:53:49 msg="Enabling IPv4 transport for outgoing 
queries" subsystem="config" level="0" prio="Notice" tid="0" 
ts="1745934829.123"
recursor_1  | Apr 29 13:53:49 msg="Setting access control" 
subsystem="config" level="0" prio="Info" tid="0" ts="1745934829.125" 
acl="allow-from" addresses="x.x.x.x/y a.a.a.a/b etc."
recursor_1  | Apr 29 13:53:49 msg="Will not send queries to" 
subsystem="config" level="0" prio="Notice" tid="0" ts="1745934829.132" 
addresses="127.0.0.0/8 10.0.0.0/8 100.64.0.0/10 169.254.0.0/16 
192.168.0.0/16 172.16.0.0/12 ::1/128 fc00::/7 fe80::/10 0.0.0.0/8 
192.0.0.0/24 192.0.2.0/24 198.51.100.0/24 203.0.113.0/24 240.0.0.0/4 
::/96 ::ffff:0:0/96 100::/64 2001:db8::/32 0.0.0.0 ::"

PDNS-rec host pcap:
------------------------------

tcpdump -i any -v 'host <client-ip>'
tcpdump: listening on any, link-type LINUX_SLL (Linux cooked), capture 
size 262144 bytes
14:01:49.419703 IP (tos 0x0, ttl 124, id 45946, offset 0, flags [none], 
proto UDP (17), length 83)
     <client-hostname>.65424 > <recursor-hostname>.domain: 16579+ [1au] 
A? canary.officeapps.live.com. (55)
14:01:49.419758 IP (tos 0x0, ttl 123, id 45946, offset 0, flags [none], 
proto UDP (17), length 83)
     <client-hostname>.65424 > 172.24.0.2.domain: 16579+ [1au] A? 
canary.officeapps.live.com. (55)
14:01:49.419766 IP (tos 0x0, ttl 123, id 45946, offset 0, flags [none], 
proto UDP (17), length 83)
     <client-hostname>.65424 > 172.24.0.2.domain: 16579+ [1au] A? 
canary.officeapps.live.com. (55)

Any ideas on what could be wrong or what I'm missing here is appreciated.

Regards

Robby







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