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Sun Bear
Asked: 2024-10-30 21:29:40 +0800 CST

How to verify that all resolved domain IPs are from an external DNS resolver when Unbound is configured to forward domain queries?

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I have configured Unbound to:

  1. listen for domain queries on all interfaces in a LAN,
  2. forward these domain queries to an external DNS resolver via TLS,
  3. receive the resolved domain IPs from the external DNS resolver and return them to the corresponding clients.

How do I verify that such a configuration is functioning? Especially, how do I verify that:

  1. Unbound has forwarded the domain queries to the desired external DNS resolver over TLS?
  2. The resolved domain IPS are from the external DNS resolver and are not resolved by Unbound?

Below are two results from digging google.com. How can i use these results to do the above mentioned verifications?

root@DNS:/etc/unbound# dig google.com A @192.168.1.50 -p 3000

; <<>> DiG 9.18.28-0ubuntu0.24.04.1-Ubuntu <<>> google.com A @192.168.1.50 -p 3000
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 22452
;; flags: qr rd ra; QUERY: 1, ANSWER: 6, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1232
;; QUESTION SECTION:
;google.com.            IN  A

;; ANSWER SECTION:
google.com.     300 IN  A   142.251.175.138
google.com.     300 IN  A   142.251.175.100
google.com.     300 IN  A   142.251.175.113
google.com.     300 IN  A   142.251.175.101
google.com.     300 IN  A   142.251.175.139
google.com.     300 IN  A   142.251.175.102

;; Query time: 12 msec
;; SERVER: 192.168.1.50#3000(192.168.1.50) (UDP)
;; WHEN: Wed Oct 30 14:04:16 UTC 2024
;; MSG SIZE  rcvd: 135

root@DNS:/etc/unbound# dig google.com A @192.168.1.50 -p 3000

; <<>> DiG 9.18.28-0ubuntu0.24.04.1-Ubuntu <<>> google.com A @192.168.1.50 -p 3000
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 39764
;; flags: qr rd ra; QUERY: 1, ANSWER: 6, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1232
;; QUESTION SECTION:
;google.com.            IN  A

;; ANSWER SECTION:
google.com.     300 IN  A   142.251.175.139
google.com.     300 IN  A   142.251.175.113
google.com.     300 IN  A   142.251.175.100
google.com.     300 IN  A   142.251.175.101
google.com.     300 IN  A   142.251.175.138
google.com.     300 IN  A   142.251.175.102

;; Query time: 184 msec
;; SERVER: 192.168.1.50#3000(192.168.1.50) (UDP)
;; WHEN: Wed Oct 30 14:05:30 UTC 2024
;; MSG SIZE  rcvd: 135

Below are logs in unbound.log with verbosity: 3 after restarting the unbound.service and running the above dig command twice. I can see that the external DNS resolver is mentioned but I can't understand which line shows that it has resolved the domain and return the results to unbound.

[1730296502] unbound[6506:0] info: service stopped (unbound 1.19.2).
[1730296502] unbound[6506:0] info: server stats for thread 0: 0 queries, 0 answers from cache, 0 recursions, 0 prefetch, 0 rejected by ip ratelimiting
[1730296502] unbound[6506:0] info: server stats for thread 0: requestlist max 0 avg 0 exceeded 0 jostled 0
[1730296502] unbound[6506:0] info: server stats for thread 1: 0 queries, 0 answers from cache, 0 recursions, 0 prefetch, 0 rejected by ip ratelimiting
[1730296502] unbound[6506:0] info: server stats for thread 1: requestlist max 0 avg 0 exceeded 0 jostled 0
[1730296502] unbound[6506:0] info: server stats for thread 2: 0 queries, 0 answers from cache, 0 recursions, 0 prefetch, 0 rejected by ip ratelimiting
[1730296502] unbound[6506:0] info: server stats for thread 2: requestlist max 0 avg 0 exceeded 0 jostled 0
[1730296502] unbound[6506:0] info: server stats for thread 3: 0 queries, 0 answers from cache, 0 recursions, 0 prefetch, 0 rejected by ip ratelimiting
[1730296502] unbound[6506:0] info: server stats for thread 3: requestlist max 0 avg 0 exceeded 0 jostled 0
[1730296503] unbound[6658:0] debug: module config: "subnetcache validator iterator"
[1730296503] unbound[6658:0] notice: init module 0: subnetcache
[1730296503] unbound[6658:0] warning: subnetcache: serve-expired is set but not working for data originating from the subnet module cache.
[1730296503] unbound[6658:0] warning: subnetcache: prefetch is set but not working for data originating from the subnet module cache.
[1730296503] unbound[6658:0] debug: subnetcache: option registered (8)
[1730296503] unbound[6658:0] notice: init module 1: validator
[1730296503] unbound[6658:0] notice: init module 2: iterator
[1730296503] unbound[6658:0] debug: target fetch policy for level 0 is 3
[1730296503] unbound[6658:0] debug: target fetch policy for level 1 is 2
[1730296503] unbound[6658:0] debug: target fetch policy for level 2 is 1
[1730296503] unbound[6658:0] debug: target fetch policy for level 3 is 0
[1730296503] unbound[6658:0] debug: target fetch policy for level 4 is 0
[1730296503] unbound[6658:0] debug: Forward zone server list:
[1730296503] unbound[6658:0] info: DelegationPoint<dns.quad9.net.>: 0 names (0 missing), 4 addrs (0 result, 4 avail) parentNS
[1730296503] unbound[6658:2] debug: Forward zone server list:
[1730296503] unbound[6658:2] info: DelegationPoint<dns.quad9.net.>: 0 names (0 missing), 4 addrs (0 result, 4 avail) parentNS
[1730296503] unbound[6658:0] debug: cache memory msg=66104 rrset=66104 infra=7952 val=66400 subnet=74536
[1730296503] unbound[6658:1] debug: Forward zone server list:
[1730296503] unbound[6658:1] info: DelegationPoint<dns.quad9.net.>: 0 names (0 missing), 4 addrs (0 result, 4 avail) parentNS
[1730296503] unbound[6658:0] info: start of service (unbound 1.19.2).
[1730296503] unbound[6658:2] debug: cache memory msg=66104 rrset=66104 infra=7952 val=66400 subnet=74536
[1730296503] unbound[6658:3] debug: Forward zone server list:
[1730296503] unbound[6658:3] info: DelegationPoint<dns.quad9.net.>: 0 names (0 missing), 4 addrs (0 result, 4 avail) parentNS
[1730296503] unbound[6658:1] debug: cache memory msg=66104 rrset=66104 infra=7952 val=66400 subnet=74536
[1730296503] unbound[6658:3] debug: cache memory msg=66104 rrset=66104 infra=7952 val=66400 subnet=74536
[1730297056] unbound[5388:0] debug: subnetcache[module 0] operate: extstate:module_state_initial event:module_event_new
[1730297056] unbound[5388:0] info: subnetcache operate: query google.com. A IN
[1730297056] unbound[5388:0] debug: validator[module 1] operate: extstate:module_state_initial event:module_event_pass
[1730297056] unbound[5388:0] info: validator operate: query google.com. A IN
[1730297056] unbound[5388:0] debug: iterator[module 2] operate: extstate:module_state_initial event:module_event_pass
[1730297056] unbound[5388:0] info: resolving google.com. A IN
[1730297056] unbound[5388:0] info: resolving (init part 2):  google.com. A IN
[1730297056] unbound[5388:0] info: resolving (init part 3):  google.com. A IN
[1730297056] unbound[5388:0] info: processQueryTargets: google.com. A IN
[1730297056] unbound[5388:0] info: sending query: google.com. A IN
[1730297056] unbound[5388:0] debug: sending to target: <google.com.> 216.239.38.10#53
[1730297056] unbound[5388:0] debug: cache memory msg=70045 rrset=100203 infra=29147 val=67208 subnet=74536
[1730297056] unbound[5388:0] debug: iterator[module 2] operate: extstate:module_wait_reply event:module_event_reply
[1730297056] unbound[5388:0] info: iterator operate: query google.com. A IN
[1730297056] unbound[5388:0] info: response for google.com. A IN
[1730297056] unbound[5388:0] info: reply from <google.com.> 216.239.38.10#53
[1730297056] unbound[5388:0] info: query response was ANSWER
[1730297056] unbound[5388:0] info: finishing processing for google.com. A IN
[1730297056] unbound[5388:0] debug: validator[module 1] operate: extstate:module_wait_module event:module_event_moddone
[1730297056] unbound[5388:0] info: validator operate: query google.com. A IN
[1730297056] unbound[5388:0] debug: subnetcache[module 0] operate: extstate:module_wait_module event:module_event_moddone
[1730297056] unbound[5388:0] info: subnetcache operate: query google.com. A IN
[1730297056] unbound[5388:0] debug: cache memory msg=70045 rrset=100203 infra=29147 val=67208 subnet=74536
[1730297130] unbound[5379:0] debug: subnetcache[module 0] operate: extstate:module_state_initial event:module_event_new
[1730297130] unbound[5379:0] info: subnetcache operate: query google.com. A IN
[1730297130] unbound[5379:0] debug: validator[module 1] operate: extstate:module_state_initial event:module_event_pass
[1730297130] unbound[5379:0] info: validator operate: query google.com. A IN
[1730297130] unbound[5379:0] debug: iterator[module 2] operate: extstate:module_state_initial event:module_event_pass
[1730297130] unbound[5379:0] info: resolving google.com. A IN
[1730297130] unbound[5379:0] info: resolving (init part 2):  google.com. A IN
[1730297130] unbound[5379:0] info: resolving (init part 3):  google.com. A IN
[1730297130] unbound[5379:0] info: processQueryTargets: google.com. A IN
[1730297130] unbound[5379:0] info: sending query: google.com. A IN
[1730297130] unbound[5379:0] debug: sending to target: <com.> 2001:503:83eb::30#53
[1730297130] unbound[5379:0] debug: cache memory msg=78073 rrset=130165 infra=41184 val=69264 subnet=74536
[1730297130] unbound[5379:0] debug: iterator[module 2] operate: extstate:module_wait_reply event:module_event_noreply
[1730297130] unbound[5379:0] info: iterator operate: query google.com. A IN
[1730297130] unbound[5379:0] info: processQueryTargets: google.com. A IN
[1730297130] unbound[5379:0] info: sending query: google.com. A IN
[1730297130] unbound[5379:0] debug: sending to target: <com.> 192.41.162.30#53
[1730297130] unbound[5379:0] debug: cache memory msg=78073 rrset=130165 infra=41184 val=69264 subnet=74536
[1730297130] unbound[5379:0] debug: iterator[module 2] operate: extstate:module_wait_reply event:module_event_reply
[1730297130] unbound[5379:0] info: iterator operate: query google.com. A IN
[1730297130] unbound[5379:0] info: response for google.com. A IN
[1730297130] unbound[5379:0] info: reply from <com.> 192.41.162.30#53
[1730297130] unbound[5379:0] info: query response was REFERRAL
[1730297130] unbound[5379:0] info: processQueryTargets: google.com. A IN
[1730297130] unbound[5379:0] info: sending query: google.com. A IN
[1730297130] unbound[5379:0] debug: sending to target: <google.com.> 216.239.32.10#53
[1730297130] unbound[5379:0] debug: cache memory msg=78073 rrset=132972 infra=41184 val=69414 subnet=74536
[1730297130] unbound[5379:0] debug: iterator[module 2] operate: extstate:module_wait_reply event:module_event_reply
[1730297130] unbound[5379:0] info: iterator operate: query google.com. A IN
[1730297130] unbound[5379:0] info: response for google.com. A IN
[1730297130] unbound[5379:0] info: reply from <google.com.> 216.239.32.10#53
[1730297130] unbound[5379:0] info: query response was ANSWER
[1730297130] unbound[5379:0] info: finishing processing for google.com. A IN
[1730297130] unbound[5379:0] debug: validator[module 1] operate: extstate:module_wait_module event:module_event_moddone
[1730297130] unbound[5379:0] info: validator operate: query google.com. A IN
[1730297130] unbound[5379:0] debug: subnetcache[module 0] operate: extstate:module_wait_module event:module_event_moddone
[1730297130] unbound[5379:0] info: subnetcache operate: query google.com. A IN
[1730297130] unbound[5379:0] debug: cache memory msg=78333 rrset=133364 infra=41492 val=69414 subnet=74536
networking

2 Answers

  1. You can leave tshark running on the server while resolving names from a client using dig:

    sudo tshark -i eth0 -Y'ip.src == 192.168.1.50 and dns.qry.type == 1'

    on the server (replacing eth0 with the interface used by Unbound to communicate with the external resolver) and, e.g.

    dig @192.168.1.50 -p3000 askubuntu.com A

    on the client.

    • -Y'ip.src == 192.168.1.50 and dns.qry.type == 1': sets up a filter to display only type 1 (A) DNS requests coming from IP 192.168.1.50 (the server)

    By setting tshark up this way, any type 1 (A) DNS request coming from IP 192.168.1.50 (the server) passing through interface eth0 on the server will be displayed, easily allowing you to understand if a request was forwarded or resolved by Unbound itself because Unbound itself was authoritative for the name / the name was cached.

    For example, if I leave sudo tshark -i wlo1 -Y'ip.src == 192.168.1.93 and dns.qry.type == 1' running on a terminal and run dig askubuntu.com A on another terminal, this shows up (my machine is on 192.168.1.93 and is set up to resolve names by querying 192.168.1.254):

    % sudo resolvectl flush-caches && sudo tshark -i wlo1 -Y'ip.src == 192.168.1.93 and dns.qry.type == 1'
Running as user "root" and group "root". This could be dangerous.
Capturing on 'wlo1'
    4 2.092316755 192.168.1.93 → 192.168.1.254 DNS 84 Standard query 0xa9f9 A askubuntu.com OPT
1 packet captured
    • 2
  2. Best Answer

    I discovered a way to check this via checking /etc/unbound/unbound.log. The file /etc/unbound/unbound.conf must declare these attributes.

    server:
    # For debugging
    verbosity: 4   # default is 1
    log-time-ascii:     yes
    log-queries:        yes
    log-replies:        yes
    log-tag-queryreply: yes
    #log-destaddr:       yes  # not working
    log-local-actions:  yes
    log-servfail:       yes

    unbound.log would contain logs stating that :

    1. The query is forwarded to external DNS over TLS.

      info: sending query: cnn.com. A IN
debug: sending to target: <.> 9.9.9.9#853
...
debug: the query is using TLS encryption, for dns.quad9.net
...
debug: SSL connection to dns.quad9.net authenticated ip4 9.9.9.9 port 853 (len 16)

    2. The external DNS replying:

        debug: process_response: new external response event
  ...
  info: response for cnn.com. A IN
  info: reply from <.> 9.9.9.9#853

    3. The ip address of the queried domain:

        ;; ANSWER SECTION:
  cnn.com.   43  IN  A   151.101.195.5
  cnn.com.   43  IN  A   151.101.67.5
  cnn.com.   43  IN  A   151.101.131.5
  cnn.com.   43  IN  A   151.101.3.5

    The logs shown in my question did not contain these lines as they were not generated using these attributes.

    • 2