[GH-ISSUE #323] shortcut localhost TLD in resolver #149

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opened 2026-03-07 22:28:30 +03:00 by kerem · 3 comments

kerem commented

2026-03-07 22:28:30 +03:00

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Originally created by @briansmith on GitHub (Jan 2, 2018).
Original GitHub issue: https://github.com/hickory-dns/hickory-dns/issues/323

The following logic from https://tools.ietf.org/html/rfc6761#section-6.3 should be implemented:

The domain "localhost." and any names falling within ".localhost."
are special in the following ways: [...]

Application software MAY recognize localhost names as special, or
MAY pass them to name resolution APIs as they would for other
domain names.

Name resolution APIs and libraries SHOULD recognize localhost
names as special and SHOULD always return the IP loopback address
for address queries and negative responses for all other query
types. Name resolution APIs SHOULD NOT send queries for
localhost names to their configured caching DNS server(s).

Caching DNS servers SHOULD recognize localhost names as special
and SHOULD NOT attempt to look up NS records for them, or
otherwise query authoritative DNS servers in an attempt to
resolve localhost names. Instead, caching DNS servers SHOULD,
for all such address queries, generate an immediate positive
response giving the IP loopback address, and for all other query
types, generate an immediate negative response. This is to avoid
unnecessary load on the root name servers and other name servers.

Further, if the application attempts to configure localhost to refer to anything other than the loopback interface, the configuration should be rejected, or the localhost configuration should be silently ignored w/ a warning.

Originally created by @briansmith on GitHub (Jan 2, 2018). Original GitHub issue: https://github.com/hickory-dns/hickory-dns/issues/323 The following logic from https://tools.ietf.org/html/rfc6761#section-6.3 should be implemented: > The domain "localhost." and any names falling within ".localhost." are special in the following ways: [...] > > 2. Application software MAY recognize localhost names as special, or MAY pass them to name resolution APIs as they would for other domain names. > > 3. Name resolution APIs and libraries SHOULD recognize localhost names as special and SHOULD always return the IP loopback address for address queries and negative responses for all other query types. Name resolution APIs SHOULD NOT send queries for localhost names to their configured caching DNS server(s). > > 4. Caching DNS servers SHOULD recognize localhost names as special and SHOULD NOT attempt to look up NS records for them, or otherwise query authoritative DNS servers in an attempt to resolve localhost names. Instead, caching DNS servers SHOULD, for all such address queries, generate an immediate positive response giving the IP loopback address, and for all other query types, generate an immediate negative response. This is to avoid unnecessary load on the root name servers and other name servers. Further, if the application attempts to configure `localhost` to refer to anything other than the loopback interface, the configuration should be rejected, or the localhost configuration should be silently ignored w/ a warning.

kerem

2026-03-07 22:28:30 +03:00

closed this issue
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kerem commented

2026-03-07 22:28:46 +03:00

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@briansmith commented on GitHub (Jan 2, 2018):

Actually, my "Further" comment is addressed on the next page of the RFC:

Authoritative DNS servers SHOULD recognize localhost names as
special and handle them as described above for caching DNS
servers.

DNS server operators SHOULD be aware that the effective RDATA for
localhost names is defined by protocol specification and cannot
be modified by local configuration.

@briansmith commented on GitHub (Jan 2, 2018): Actually, my "Further" comment is addressed on the next page of the RFC: > 5. Authoritative DNS servers SHOULD recognize localhost names as special and handle them as described above for caching DNS servers. > > 6. DNS server operators SHOULD be aware that the effective RDATA for localhost names is defined by protocol specification and cannot be modified by local configuration.

kerem commented

2026-03-07 22:28:51 +03:00

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@bluejekyll commented on GitHub (Jan 2, 2018):

and cannot be modified by local configuration.

currently the zone configuration with the trust-dns authoritative server is to allow this to be managed through zone configuration. This implies that it should be hard-coded in the authority, and not allow admins to adjust it.

@bluejekyll commented on GitHub (Jan 2, 2018): > and cannot be modified by local configuration. currently the zone configuration with the trust-dns authoritative server is to allow this to be managed through zone configuration. This implies that it should be hard-coded in the authority, and not allow admins to adjust it.

kerem commented

2026-03-07 22:28:56 +03:00

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@briansmith commented on GitHub (Jan 4, 2018):

This implies that it should be hard-coded in the authority, and not allow admins to adjust it.

Exactly. I think any explicit configuration for localhost or *.localhost should be rejected.

@briansmith commented on GitHub (Jan 4, 2018): > This implies that it should be hard-coded in the authority, and not allow admins to adjust it. Exactly. I think any explicit configuration for localhost or *.localhost should be rejected.

kerem referenced this issue

2026-03-16 01:57:16 +03:00

[PR #149] [MERGED] bump chrono to 0.3.1 #1270