59 lines
1.8 KiB
Markdown
59 lines
1.8 KiB
Markdown
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# teaching DNS
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Welcome to tdns, the teaching authoritative server, implementing all of
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basic DNS in 1000 lines of code.
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The goals of tdns are:
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* Protocol correctness
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* Suitable for educational purposes
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* Display best practices
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Non-goals are:
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* Performance
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* Implementing more features
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# Current status
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Features are complete:
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* A, AAAA, NS, MX, CNAME, TXT, SOA
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* UDP & TCP
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* AXFR
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* Wildcards
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* Delegations
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* Glue records
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Missing:
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* Truncation
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* Compression (may not fit in the 1000 lines!)
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* EDNS (not 'basic' DNS by our definition, but ok)
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Known broken:
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* Embedded 0s in DNS labels don't yet work
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* Case-insensitive comparison isn't 100% correct
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* RCode after one CNAME chase
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* On output (to screen) we do not escape DNS names correctly
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The code is not yet in a teachable state, and the layout is somewhat
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confusing: some stuff is in the wrong files.
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# Layout
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Key to a good DNS implementation is having a faithful DNS storage model.
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Over the decades, many many nameservers have started out with an incorrect
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storage model, leading to pain later on with empty non-terminals, setting
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the 'AA' bit on glue (or not) and eventually DNSSEC ordering problems.
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When storing DNS as a tree, as described in RFC 1034, a lot of things go
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right "automatically".
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The core or `tdns` therefore is the tree of nodes as intended in 1034. This
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is implemented in `dns-storage.cc` and `dns-storage.hh`.
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This lookup mechanism will tell you if a name is fully present in a zone, or
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if it was matched by an NS record. It will also perform wildcard matching,
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but not CNAME chasing.
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# Best practices
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The code does not do any form of DNS escaping. Instead, DNS names are stored
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and manipulated as a sequence of DNS labels. So instead of messing with
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"www.powerdns.org", we use {"www", "powerdns", "org"}.
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