The vL3 DNS doesn't support PTR requests about sdk

[fr-Pursuit]

@glazychev-art Hi! PTR requests seem to be handled correctly now. ping doesn't freeze at all :)

However, I now need to explicitly use IPv4 in order for the ping to work...

/ # ping -c 4 alpine2.my-interdomain-vl3-network
ping: bad address 'alpine2.my-interdomain-vl3-network'

/ # ping -c 4 alpine2.my-interdomain-vl3-network -4
PING alpine2.my-interdomain-vl3-network (172.16.0.2): 56 data bytes
64 bytes from 172.16.0.2: seq=0 ttl=59 time=65.076 ms
64 bytes from 172.16.0.2: seq=1 ttl=59 time=2.696 ms
64 bytes from 172.16.0.2: seq=2 ttl=59 time=12.237 ms
64 bytes from 172.16.0.2: seq=3 ttl=59 time=60.345 ms

When the ping fails, this error appears in the NSE's logs:

Mar 26 21:04:34.885 [TRAC] [id:22041] [type:dnsServer] (1) ⎆ sdk/pkg/tools/dnsutils/dnsconfigs/dnsConfigsHandler.ServeDNS()
Mar 26 21:04:34.885 [TRAC] [id:22041] [type:dnsServer] (1.1)   message-request={"Id":22041,"Response":false,"Opcode":0,"Authoritative":false,"Truncated":false,"RecursionDesired":false,"RecursionAvailable":false,"Zero":false,"AuthenticatedData":false,"CheckingDisabled":false,"Rcode":0,"Question":[{"Name":"alpine2.my-interdomain-vl3-network.","Qtype":28,"Qclass":1}],"Answer":null,"Ns":null,"Extra":null}
Mar 26 21:04:34.885 [DEBU] [id:22041] [type:dnsServer] (1.2)   passed clientURLs: [{udp   172.16.0.1   false   } {udp   172.16.0.1   false   }]
Mar 26 21:04:34.885 [DEBU] [id:22041] [type:dnsServer] (1.3)   passed SearchDomains: []
Mar 26 21:04:34.885 [TRAC] [id:22041] [type:dnsServer] (2)  ⎆ sdk/pkg/tools/dnsutils/noloop/noloopDNSHandler.ServeDNS()
Mar 26 21:04:34.886 [TRAC] [id:22041] [type:dnsServer] (3)   ⎆ sdk/pkg/tools/dnsutils/norecursion/norecursionDNSHandler.ServeDNS()
Mar 26 21:04:34.886 [TRAC] [id:22041] [type:dnsServer] (1) ⎆ sdk/pkg/tools/dnsutils/dnsconfigs/dnsConfigsHandler.ServeDNS()
Mar 26 21:04:34.887 [TRAC] [id:22041] [type:dnsServer] (4)    ⎆ sdk/pkg/tools/dnsutils/memory/memoryHandler.ServeDNS()
Mar 26 21:04:34.887 [TRAC] [id:22041] [type:dnsServer] (1.1)   message-request={"Id":22041,"Response":false,"Opcode":0,"Authoritative":false,"Truncated":false,"RecursionDesired":false,"RecursionAvailable":false,"Zero":false,"AuthenticatedData":false,"CheckingDisabled":false,"Rcode":0,"Question":[{"Name":"alpine2.my-interdomain-vl3-network.","Qtype":28,"Qclass":1}],"Answer":null,"Ns":null,"Extra":null}
Mar 26 21:04:34.887 [DEBU] [id:22041] [type:dnsServer] (1.2)   passed clientURLs: [{udp   172.16.0.1   false   } {udp   172.16.0.1   false   }]
Mar 26 21:04:34.887 [DEBU] [id:22041] [type:dnsServer] (1.3)   passed SearchDomains: []
Mar 26 21:04:34.887 [TRAC] [id:22041] [type:dnsServer] (2)  ⎆ sdk/pkg/tools/dnsutils/noloop/noloopDNSHandler.ServeDNS()
Mar 26 21:04:34.887 [ERRO] [id:22041] [noloopDNSHandler:ServeDNS] [type:dnsServer] (2.1)    loop is not allowed: query: ;; opcode: QUERY, status: NOERROR, id: 22041;   ;; flags:; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0;    ;      ;; QUESTION SECTION:;    ;alpine2.my-interdomain-vl3-network.    IN       AAAA;  ;
Mar 26 21:04:34.887 [TRAC] [id:22041] [type:dnsServer] (2.2)    message-response={"Id":22041,"Response":true,"Opcode":0,"Authoritative":false,"Truncated":false,"RecursionDesired":false,"RecursionAvailable":false,"Zero":false,"AuthenticatedData":false,"CheckingDisabled":false,"Rcode":2,"Question":[{"Name":"alpine2.my-interdomain-vl3-network.","Qtype":28,"Qclass":1}],"Answer":[],"Ns":[],"Extra":[]}
Mar 26 21:04:34.888 [TRAC] [id:22041] [type:dnsServer] (5)     ⎆ sdk/pkg/tools/dnsutils/fanout/fanoutHandler.ServeDNS()
Mar 26 21:04:34.915 [TRAC] [id:22041] [type:dnsServer] (5.1)       message-response={"Id":22041,"Response":true,"Opcode":0,"Authoritative":false,"Truncated":false,"RecursionDesired":false,"RecursionAvailable":false,"Zero":false,"AuthenticatedData":false,"CheckingDisabled":false,"Rcode":2,"Question":[{"Name":"alpine2.my-interdomain-vl3-network.","Qtype":28,"Qclass":1}],"Answer":[],"Ns":[],"Extra":[]}

It seems the AAAA request fails in a way that makes ping fail before it even attempts to make a A request. I don't remember seeing that before. Is it be caused by a change in NSM or somewhere else?

[denis-tingaikin]

@glazychev-art Could you please add a test into deployments-k8s?

[glazychev-art]

@fr-Pursuit
Could you check PTR requests on the latest main branch if you get a chance?

[glazychev-art]

@fr-Pursuit
No, there were no changes in NSM in this direction. And this behavior was before, you can check versions v1.8.0 or v1.7.1 :)
ping utility is the reason for this. Depending on the system settings, it prefers IPv6 over IPv4.

As far as I can see, in some linux versions this is solved by changing /etc/gai.conf. But not for alpine. Perhaps this will help you.

[denis-tingaikin]

@glazychev-art I feel we might need to verify it.

@NikitaSkrynnik Could you please compare behaviour with NSM v1.5.0 (with coredns) and current main version?

[NikitaSkrynnik]

@fr-Pursuit Hello, I've fixed the problem with ping and explicit IPv4. Could you please check it?

[fr-Pursuit]

@NikitaSkrynnik Hi! Sorry for the late reply.

It's all fixed, thanks!

/ # ping -c 4 alpine2.my-interdomain-vl3-network
PING alpine2.my-interdomain-vl3-network (172.16.1.2): 56 data bytes
64 bytes from 172.16.1.2: seq=0 ttl=56 time=1.426 ms
64 bytes from 172.16.1.2: seq=1 ttl=56 time=1.503 ms
64 bytes from 172.16.1.2: seq=2 ttl=56 time=1.652 ms
64 bytes from 172.16.1.2: seq=3 ttl=56 time=4.073 ms

--- alpine2.my-interdomain-vl3-network ping statistics ---
4 packets transmitted, 4 packets received, 0% packet loss
round-trip min/avg/max = 1.426/2.163/4.073 ms

[glazychev-art]

@fr-Pursuit
Thanks for checking!
Can you close the issue?