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2704n router does not answer DNS queries that need TCP rather than UDP

seebee
Aspiring Pro
Posts: 107
Thanks: 80
Fixes: 9
Registered: ‎08-07-2017

2704n router does not answer DNS queries that need TCP rather than UDP

I have a PlusNet 2704n router (Hub Zero), on the latest firmware I believe:

Firmware version: 7.275.17_F2704N_Plusnet

I have just noticed that it does not appear to use TCP when DNS answers are too large for UDP.

For example, using BBC as an example of a domain with a "large" TXT record

Ask a DNS server directly


$ dig @212.159.13.50 bbc.co.uk. TXT

; <<>> DiG 9.11.5-P4-5.1+deb10u7-Raspbian <<>> @212.159.13.50 bbc.co.uk. TXT
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 38795
;; flags: qr rd ra; QUERY: 1, ANSWER: 18, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;bbc.co.uk. IN TXT

;; ANSWER SECTION:
bbc.co.uk. 180 IN TXT "_globalsign-domain-verification=WgTu2FOy64Yx8z8cOweOeyZ_YpUaQOmSTD9uyMwKbd"
bbc.co.uk. 180 IN TXT "miro-verification=1a94b0fef7a6d5136a272d5cb425e8dc034e8cfc"
bbc.co.uk. 180 IN TXT "v=spf1 a ip4:212.58.224.0/19 ip4:132.185.0.0/16 ip4:78.136.53.80/28 ip4:78.136.14.192/27 ip4:78.136.19.8/29 ip4:89.234.
10.72/29 ip4:89.234.53.236 ip4:212.111.33.181 ip4:78.137.117.8 ip4:46.37.176.74 ip4:185.184.237.181" " ip4:185.119.233.144/30 ip4:185.119.232.158 +include:sf.sis.bbc.co
.uk +include:spf.messagelabs.com ~all"
bbc.co.uk. 180 IN TXT "docusign=50f10407-e3e4-4f6a-aae4-712d4eb31329"
bbc.co.uk. 180 IN TXT "docusign=a10ad7b6-cf7e-472d-8157-23061f5b5116"
bbc.co.uk. 180 IN TXT "2RLXso9TrRPyhWOEhYggL0U/r1D+g8H7z9RqDBOmcJjSbj88TobGKimtkCrXZNBkDXQDj89lS4mDskNOJyWLdg=="
bbc.co.uk. 180 IN TXT "voUGv5zARbEV516E/S8Ugsy9/FOgDGg4n/rpmKZQRROVOj0+2tgzKw3Tk9+Ks6qVbNKU18KTrR5khxTQutDvBg=="
bbc.co.uk. 180 IN TXT "google-site-verification=ITX3CwHXxGVfkCmhF4eSwdfo8h2ZGLAZ3zRpYvZi5XA"
bbc.co.uk. 180 IN TXT "MS=ms10378910"
bbc.co.uk. 180 IN TXT "dropbox-domain-verification=l5djk65wpy3z"
bbc.co.uk. 180 IN TXT "adobe-idp-site-verification=9b850a4a56e3fac19aea1e0ac5db302e5cefab444cd73519dce1c72ccd4db058"
bbc.co.uk. 180 IN TXT "google-site-verification=RaiMXJBIiFvqXHd43kv_ekzmXT2l8ibq5Xy0mulndvU"
bbc.co.uk. 180 IN TXT "atlassian-domain-verification=SQsgJ5h/FqwMTXuSG/G4Nd1Gx6uX2keREOsZSa22D5XT46EsEuyaic8Aej4cR4Tr"
bbc.co.uk. 180 IN TXT "Huddle"
bbc.co.uk. 180 IN TXT "J0kgGm0XqA3/6pLD4DHeC5x/dAduzT809P1Iwx/PRCYvVS32rv75RIHKC2aVz47dJxKhPlxGf3h3KXiL6+dyXw=="
bbc.co.uk. 180 IN TXT "apple-domain-verification=jFFO0rdS9IrxgWUR"
bbc.co.uk. 180 IN TXT "msfpkey=69eew9c10ryb9cn8msgg2d4vg"
bbc.co.uk. 180 IN TXT "_globalsign-domain-verification=zgnCaep7wCvKr1E33tAk2yr9-kXVnCP93bMFk7WYQD"

;; Query time: 16 msec
;; SERVER: 212.159.13.50#53(212.159.13.50)
;; WHEN: Wed Aug 03 10:51:33 BST 2022
;; MSG SIZE rcvd: 1610

 

Ask the 2740n directly

$ dig @192.168.1.254 bbc.co.uk. TXT
;; Truncated, retrying in TCP mode.
;; Connection to 192.168.1.254#53(192.168.1.254) for bbc.co.uk. failed: connection refused.


It's not a problem with TXT records per se, eg ask for a smaller answer is fine

$ dig @192.168.1.254 nowtv.com. TXT

; <<>> DiG 9.11.5-P4-5.1+deb10u7-Raspbian <<>> @192.168.1.254 nowtv.com. TXT
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 29149
;; flags: qr rd ra; QUERY: 1, ANSWER: 4, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;nowtv.com. IN TXT

;; ANSWER SECTION:
nowtv.com. 60 IN TXT "facebook-domain-verification=2m7fhef3fynuzdzzu2kptvlppcdg8o"
nowtv.com. 60 IN TXT "MS=ms30766871"
nowtv.com. 60 IN TXT "v=msv1 t=938F2527-A2D5-41B6-BC9C-44FD5E3E8F6D"
nowtv.com. 60 IN TXT "v=spf1 include:spf.protection.outlook.com include:_spf.salesforce.com include:spf.messagelabs.com -all"

;; Query time: 25 msec
;; SERVER: 192.168.1.254#53(192.168.1.254)
;; WHEN: Wed Aug 03 10:52:16 BST 2022
;; MSG SIZE rcvd: 309

 

(Same in windows if you prefer, commands like "nslookup -type=TXT bbc.com. 192.168.1.254" fail and "nslookup -type=TXT bbc.com. 1.1.1.1" work etc)


It's not causing me any actual problems as far as I am aware, and I wouldn't know if it's related to firmware version as I don't recall seeing (or looking for) it in the past.
Does anyone else see the same?

1 REPLY 1
bobpullen
Community Gaffer
Community Gaffer
Posts: 16,930
Thanks: 5,016
Fixes: 317
Registered: ‎04-04-2007

Re: 2704n router does not answer DNS queries that need TCP rather than UDP

This wouldn't surprise me.

I've seen other hub DNS forwarders behave the same.

Bob Pullen
Plusnet Product Team
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