Issues of EDNS buffer size
Although the edns buffer size
is set to 1232 for a query, Knot Resolver still receives a response with a size larger than 1232, even than 4096.
As suggested here https://www.dnsflagday.net/2020/:
It is important for DNS software vendors to comply with DNS standards,
and to use a default EDNS buffer size (1232 bytes) that will not cause
fragmentation on typical network links.
We recommend following current practices by only accepting responses less than 1,232 by default, which are implemented by PowerDNS Recursor.
We also wonder why Knot Resolver does this.