Appendix A Constants and Limits

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The articles cited are authoritative; this appendix collects their values in one place.

A.1 Limits and timers #

BoundValueDescribed in
Native request size ceiling (payload)65 536 bytes§5.1
Maximum buffered native frame65 540 bytes§5.1
Native connection read chunk4 096 bytes§5.1
Native request delivery bound5 s§5.1
Native connections still sending a request256§5.1
Queued native replies256§2.5
Queued stub TCP replies256§2.5
Native reply write deadline1 s total§5.1
Stub TCP connections still sending a query256§6.1
Stub TCP query delivery bound10 s§6.1
Stub TCP message buffer65 537 bytes§6.1
Stub TCP read chunk4 096 bytes§6.1
Stub UDP read buffer4 096 bytes§6.1
Stub TCP reply write deadline1 s total§6.2
Classic UDP reply limit, no OPT512 bytes§6.2
EDNS0 payload size advertised, upstream and stub1 232 bytes§4.7, §6.2
Transaction timeout2 s§4.6
Attempts per question (all candidates and transports)3§4.6
Demotion period30 s§4.6
Service descriptor limit16 384§2.1
Listener retry delay after accept error250 ms§2.5, §9.1
Upstream transactions in flight4 096§4.6
Upstream UDP read buffer4 096 bytes§4.7
Cache entries8 192§4.5
Positive lifetime cap86 400 s§4.5
Negative lifetime cap300 s§4.5
CNAME chase depth in lookup16§4.9
netd reconnect backoff0.5 s doubling to 10 s§3.2
netd channel write timeout2 s§3.1
netd frame ceiling65 536 bytes§3.1
netd channel read chunk8 192 bytes§3.1
Registry watch event buffer16 384 bytes§2.3
Kernel hostname read buffer256 bytes§3.3
Unknown-value nesting depth, native requests32§5.1
NSS shim read and write timeout10 s§7.1
DNS label63 bytes§4.1
DNS name on the wire255 bytes§4.1

A.2 Rights #

RightValueDescribed in
RESOLVER_QUERY0x00000001§5.2
RESOLVER_CONTROL0x00000002§5.2
RESOLVER_ALL_ACCESS0x000F0003§5.2

A.3 Paths, addresses and identities #

ItemValueDescribed in
Daemon/usr/sbin/resolvd§2.1
Operator command/usr/bin/resolv§8.1
NSS shim/usr/lib/x86_64-linux-peios/libnss_peios_net.so.2§7.1
Runtime directory/run/resolvd, mode 0755§2.4
Native socket/run/resolvd/resolv.sock, mode 0666§2.4
Stub listener127.0.0.53:53, UDP and TCP§2.4
netd control socket/run/netd/control.sock§3.1
Upstream port53§4.7
Constant resolver configuration/usr/etc/resolv.conf§2.1
Service definition seed/usr/share/regim/resolvd-service.reg§2.1
Port reservation seed/usr/share/regim/resolvd-port.reg§2.1
Registry reference/usr/share/regman/resolvd.regman§2.1
Service SIDS-1-5-80-3864064249-1823296737-2008945602-1354971773-2894779966§2.1
Fallback scope keyfallback§4.4

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