Latency observed with Stubby when TLS connections Failed

[amitguptakiitian]

Hi, I am using the OpenWrt platform and my stubby configurations are as below. root@OpenWrt:~# uci show stubby stubby.global=stubby stubby.global.manual='0' stubby.global.trigger='wan' stubby.global.tls_query_padding_blocksize='128' stubby.global.appdata_dir='/var/lib/stubby' stubby.global.edns_client_subnet_private='1' stubby.global.listen_address='127.0.0.1@5453' '0::1@5453' stubby.global.log_level='7' stubby.global.round_robin_upstreams='0' stubby.global.idle_timeout='5000' stubby.global.tls_authentication='GETDNS_AUTHENTICATION_NONE' stubby.global.dns_transport='GETDNS_TRANSPORT_TLS' 'GETDNS_TRANSPORT_UDP' 'GETDNS_TRANSPORT_TCP' stubby.@resolver[0]=resolver stubby.@resolver[0].address='1.1.1.1' stubby.@resolver[0].tls_auth_name='one.one.one.one' stubby.@resolver[1]=resolver stubby.@resolver[1].address='8.8.8.8' stubby.@resolver[1].tls_auth_name='dns.google' stubby.@resolver[2]=resolver stubby.@resolver[2].address='192.168.1.1' stubby.@resolver[2].tls_auth_name='dummy.domaindoesnotexists.com'

the third resolver is the ISP DNS Server IP address (here I am using a cascaded router, the upstream points to the first router, that accepts the DNS request in clear ).

I wanted to use 192.168.1.1 (or ISP DNS Server) IP as a fallback server(which supports TCP and UDP only) when the other two fail to resolve the DNS requests. 1.1.1.1 and 8.8.8.8 I have taken as an example here that would be replaced in my project with some third-party custom DNS servers.

I have observed the latency when my thrid party DNS servers were down. Stubby takes more time to resolve or sometimes failed to resolve the DNS request when only 192.168.1.1 is working.

I tested the above use case by configuring the wrong IPs for first two TLS Servers. I changed 1.1.1.1 to 1.1.1.111 and 8.8.8.8 changed to 8.8.8.111 such that first two TLS fail and stubby can use the fallback. with this case, I have observed the latency.

can any confirm if the above configurations hold good? if yes, then is the latency expected or is there some defect in Stubby?

Thanks!