[Dnsmasq-discuss] dnsmasq 2.90 reply truncated

[Adam Pribyl]

In this case the query is from Windows 10 machine->dnsmasq server on 
Fedora 38 forwards to -> bind on debian.

The result on Windows nslookup

Server: UnKnown
Address: 192.168.34.1

*** UnKnown can't find login.microsoftonline.com: Unspecified error

In dnsmasq there is this "reply is truncated" for this forwarded query.

I do not think the problem is the Windows client, because from the time I 
downgraded the dnsmasq on Fedora to 2.89, I did not get any "reply is 
truncated" dnsmasq log message anymore.

I can not judge if client should do anything else in this case thou..

Adam Pribyl


On Tue, 12 Mar 2024, Petr Menšík wrote:

> The response seems correct and acceptable in size. It should not 
> truncate, at least what I see. It should also retry with TCP when 
> truncated reply arrives. I have verified even last release works with 
> dig. Dnsmasq does not do tcp query by itself, it expects client to do 
> TCP query. What client do you use?
>
> $ dig login.microsoftonline.com a
>
> ; <<>> DiG 9.18.24 <<>> login.microsoftonline.com a
> ;; global options: +cmd
> ;; Got answer:
> ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 20188
> ;; flags: qr rd ra; QUERY: 1, ANSWER: 11, AUTHORITY: 0, ADDITIONAL: 1
>
> ;; OPT PSEUDOSECTION:
> ; EDNS: version: 0, flags:; udp: 1232
> ; EDE: 3 (Stale Answer)
> ;; QUESTION SECTION:
> ;login.microsoftonline.com.    IN    A
>
> ;; ANSWER SECTION:
> login.microsoftonline.com. 10360 IN    CNAME login.mso.msidentity.com.
> login.mso.msidentity.com. 30    IN    CNAME ak.privatelink.msidentity.com.
> ak.privatelink.msidentity.com. 30 IN    CNAME 
> www.tm.ak.prd.aadg.trafficmanager.net.
> www.tm.ak.prd.aadg.trafficmanager.net. 30 IN A    40.126.31.71
> www.tm.ak.prd.aadg.trafficmanager.net. 30 IN A    20.190.159.0
> www.tm.ak.prd.aadg.trafficmanager.net. 30 IN A    20.190.159.68
> www.tm.ak.prd.aadg.trafficmanager.net. 30 IN A    20.190.159.71
> www.tm.ak.prd.aadg.trafficmanager.net. 30 IN A    20.190.159.73
> www.tm.ak.prd.aadg.trafficmanager.net. 30 IN A    20.190.159.75
> www.tm.ak.prd.aadg.trafficmanager.net. 30 IN A    40.126.31.67
> www.tm.ak.prd.aadg.trafficmanager.net. 30 IN A    40.126.31.69
>
> ;; Query time: 0 msec
> ;; SERVER: 127.0.0.1#53(127.0.0.1) (UDP)
> ;; WHEN: Tue Mar 12 10:07:36 CET 2024
> ;; MSG SIZE  rcvd: 303
>
> I have tried dig +ignore +noedns -t txt on google.com or cisco.com. If 
> client does not retry, it gets no response. If it does, it does. It 
> seems to work as intended.
>
> If might help querying your bind server by dig @10.101.255.253 txt ch 
> version.bind. But I suspect the problem is in client incorrectly 
> omitting TCP query retry. Is it glibc program? Can you tell us more 
> about client program making those queries?
>
> Cheers,
> Petr
>
> On 3/11/24 09:27, Adam Pribyl wrote:
>> After upgrade of dnsmasq 2.89 to dnsmasq-2.90-1.fc38.x86_64 I started 
>> to notice, that some queries won't resolve when asked thru dnsmasq, 
>> but work asked directly to upstream nameserver.
>>
>> I found that certain queries forwarded to anycast bind nameservers 
>> return only a "reply is truncated" message and no record.
>>
>> Mar 11 07:30:05 server dnsmasq[4054056]: query[A] 
>> login.microsoftonline.com from 192.168.34.194
>> Mar 11 07:30:05 server dnsmasq[4054056]: forwarded 
>> login.microsoftonline.com to 10.101.255.253
>> Mar 11 07:30:05 server dnsmasq[4054056]: reply is truncated
>>
>> Downgrading to dnsmasq-2.89-1.fc38.x86_64 seems to solve the problem.
>>
>> The response for login.microsoftonline.com is a long one.
>>
>> In the dnsmasq changelog I found, there were some changes with edns 
>> max size, but I can not find the commit to find out what was there 
>> before, to set the --edns-packet-max.
>>
>> The general question would be - what is the correct DNS setup then? I 
>> probably need to change the bind config, as I do not want to fix every 
>> dnsmasq "client" in the network.
>>
>> Thanks
>>
>> Adam Pribyl
>>
>>
>>
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>>
> -- 
> Petr Menšík
> Software Engineer, RHEL
> Red Hat, https://www.redhat.com/
> PGP: DFCF908DB7C87E8E529925BC4931CA5B6C9FC5CB
>
>
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