Maximum number of bytes packet size to advertise via EDNS.
Set to "none" to disable EDNS large packet support.
For legacy reasons DNS UDP replies will default to 512 bytes which
is too small for many responses. EDNS provides a means for Squid to
negotiate receiving larger responses back immediately without having
to failover with repeat requests. Responses larger than this limit
will retain the old behaviour of failover to TCP DNS.
Squid has no real fixed limit internally, but allowing packet sizes
over 1500 bytes requires network jumbogram support and is usually not
necessary.
WARNING: The RFC also indicates that some older resolvers will reply
with failure of the whole request if the extension is added. Some
resolvers have already been identified which will reply with mangled
EDNS response on occasion. Usually in response to many-KB jumbogram
sizes being advertised by Squid.
Squid will currently treat these both as an unable-to-resolve domain
even if it would be resolvable without EDNS.