DNS/DNSSEC loose ends
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1 DNS/DNSSEC loose ends Karst Koymans & Niels Sijm Informatics Institute University of Amsterdam Friday, September 21, 2012 Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
2 1 Encoding of domain names 2 Wildcards in DNS 3 Denial of existence Ignoring wildcards Including wildcard processing Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
3 Encoding of domain names Outline 1 Encoding of domain names 2 Wildcards in DNS 3 Denial of existence Ignoring wildcards Including wildcard processing Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
4 Encoding of domain names Composition of domain names Domain name is a sequence of labels Start at leaf 1 www 2 os3 3 nl Start at root 1 nl 2 os3 3 www DNS starts at leaf (least signicant label) Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
5 Encoding of domain names Encoding of domain names 1 Use a delimiter to seperate labels <label> <delimiter> <label> www. os3. nl. 2 Specify length of labels in label encoding <label> <label> {3,www} {3,os3} {2,nl} {0,} 3 DNS uses latter way of encoding Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
6 Encoding of domain names Normal label length encoding First byte used for length First 2 bits are ags 00 means normal label length Remaining 6 specify label length Hence the maximum label length of = 63 octets Remaining bytes contain the label itself Number of remaining bytes is encoded in rst byte of label Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
7 Encoding of domain names Normal label length encoding Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
8 Encoding of domain names Normal label length encoding Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
9 Encoding of domain names Compressed encoding Domain name with compressed encoding has xed length of 2 bytes First 2 bits are ags 11 means compressed label Remaining 6 bits + 8 subsequent bits are used as pointer Points to label at other position in packet Value is oset from beginning of packet Saves space when a domain name is used more than once Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
10 Encoding of domain names Compressed encoding Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
11 Encoding of domain names Compressed encoding Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
12 Encoding of domain names Reading domain names Read rst 2 bits of domain name eld: If values is 00 (normal label length): 1 If label length is 0 (empty label, thus root): Return sequence of noted labels as domain name 2 Read 6 subsequent bits and determine length of label 3 Read rst 2 bits of next byte and iterate If value is 11 (compressed encoding): 1 Read 14 subsequent bits and determine position of domain name 2 Jump to position and decode domain name Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
13 Encoding of domain names One more type: extended First byte value: First two bits are 01 Denes the use of EDSN0 Can be used for binary labels IPv6 PTR resource records Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
14 Wildcards in DNS Outline 1 Encoding of domain names 2 Wildcards in DNS 3 Denial of existence Ignoring wildcards Including wildcard processing Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
15 Wildcards in DNS Wildcards according to RFC 1034 From RFC 1034, section The contents of the wildcard RRs follows the usual rules and formats for RRs. The wildcards in the zone have an owner name that controls the query names they will match. The owner name of the wildcard RRs is of the form "*.<anydomain>", where <anydomain> is any domain name. <anydomain> should not contain other * labels, and should be in the authoritative data of the zone. The wildcards potentially apply to descendants of <anydomain>, but not to <anydomain> itself. Another way to look at this is that the "*" label always matches at least one whole label and sometimes more, but always whole labels. Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
16 Wildcards in DNS Wildcards according to RFC 1034 From RFC 1034, section Wildcard RRs do not apply: When the query is in another zone. That is, delegation cancels the wildcard defaults. When the query name or a name between the wildcard domain and the query name is known to exist. For example, if a wildcard RR has an owner name of "*.X", and the zone also contains RRs attached to B.X, the wildcards would apply to queries for name Z.X (presuming there is no explicit information for Z.X), but not to B.X, A.B.X, or X. Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
17 Wildcards in DNS Problems with wildcards in RFC 1034 Notions are intuitive, not well-dened When does a domain name exist? How does matching work exactly? What about empty non-terminals? RFC 4592 tries to clarify all of this Denes existence of a domain name Denes asterisk label and wildcard domain name Denes source of synthesis and closest encloser Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
18 Wildcards in DNS Wildcard supporting denitions Denitions A domain name exists if itself or any of its descendants has at least one RR In particular empty non-terminals exist An asterisk label is a label of length 1 containing as only octet the ASCII equivalent of * A wildcard domain name is a domain name with an asterisk label as its leftmost label The closest encloser of a query name is the longest matching ancestor that exists The source of synthesis of a query name is the domain name *.<closest encloser> (if it exists) Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
19 Wildcards in DNS RFC 4592 example $ORIGIN example. example IN SOA <SOA RDATA> example NS ns.example.com. example NS ns.example.net. *.example TXT "this is a wildcard" *.example MX 10 host1.example. sub.*.example TXT "... not a wildcard" host1.example A _ssh..host1.example SRV <SRV RDATA> _ssh..host2.example SRV <SRV RDATA> subdel.example NS ns.example.com. subdel.example NS ns.example.net. Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
20 Wildcards in DNS RFC 4592 example tree example SOA, NS * TXT, MX host1 A host2 subdel NS sub TXT Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
21 Wildcards in DNS RFC 4592 example queries QNAME QTYPE synthesized? result host3.example. MX example SOA, NS * TXT, MX host1 A host2 subdel NS sub TXT Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
22 Wildcards in DNS RFC 4592 example queries QNAME QTYPE synthesized? result host3.example. MX yes non-empty example SOA, NS * TXT, MX host1 A host2 subdel NS sub TXT Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
23 Wildcards in DNS RFC 4592 example queries QNAME QTYPE synthesized? result foo.bar.example. TXT example SOA, NS * TXT, MX host1 A host2 subdel NS sub TXT Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
24 Wildcards in DNS RFC 4592 example queries QNAME QTYPE synthesized? result foo.bar.example. TXT yes non-empty example SOA, NS * TXT, MX host1 A host2 subdel NS sub TXT Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
25 Wildcards in DNS RFC 4592 example queries QNAME QTYPE synthesized? result host1.example. MX example SOA, NS * TXT, MX host1 A host2 subdel NS sub TXT Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
26 Wildcards in DNS RFC 4592 example queries QNAME QTYPE synthesized? result host1.example. MX no empty example SOA, NS * TXT, MX host1 A host2 subdel NS sub TXT Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
27 Wildcards in DNS RFC 4592 example queries QNAME QTYPE synthesized? result host3.example. A example SOA, NS * TXT, MX host1 A host2 subdel NS sub TXT Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
28 Wildcards in DNS RFC 4592 example queries QNAME QTYPE synthesized? result host3.example. A yes empty example SOA, NS * TXT, MX host1 A host2 subdel NS sub TXT Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
29 Wildcards in DNS RFC 4592 example queries QNAME QTYPE synthesized? result sub.*.example. MX example SOA, NS * TXT, MX host1 A host2 subdel NS sub TXT Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
30 Wildcards in DNS RFC 4592 example queries QNAME QTYPE synthesized? result sub.*.example. MX no empty example SOA, NS * TXT, MX host1 A host2 subdel NS sub TXT Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
31 Wildcards in DNS RFC 4592 example queries QNAME QTYPE synthesized? result _telnet..host1.example. SRV example SOA, NS * TXT, MX host1 A host2 subdel NS sub TXT Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
32 Wildcards in DNS RFC 4592 example queries QNAME QTYPE synthesized? result _telnet..host1.example. SRV no no such domain example SOA, NS * TXT, MX host1 A host2 subdel NS sub TXT Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
33 Wildcards in DNS RFC 4592 example queries QNAME QTYPE synthesized? result host.subdel.example. A example SOA, NS * TXT, MX host1 A host2 subdel NS sub TXT Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
34 Wildcards in DNS RFC 4592 example queries QNAME QTYPE synthesized? result host.subdel.example. A no referral example SOA, NS * TXT, MX host1 A host2 subdel NS sub TXT Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
35 Wildcards in DNS RFC 4592 example queries QNAME QTYPE synthesized? result ghost.*.example. MX example SOA, NS * TXT, MX host1 A host2 subdel NS sub TXT Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
36 Wildcards in DNS RFC 4592 example queries QNAME QTYPE synthesized? result ghost.*.example. MX no no such domain example SOA, NS * TXT, MX host1 A host2 subdel NS sub TXT Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
37 Wildcards in DNS RFC 4592 example queries QNAME QTYPE synthesized? result host3.example. MX yes non-empty host3.example. A yes empty foo.bar.example. TXT yes non-empty host1.example. MX no empty sub.*.example. MX no empty _telnet..host1.example. SRV no no such domain host.subdel.example. A no referral ghost.*.example. MX no no such domain Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
38 Denial of existence Outline 1 Encoding of domain names 2 Wildcards in DNS 3 Denial of existence Ignoring wildcards Including wildcard processing Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
39 Denial of existence Ignoring wildcards Outline 1 Encoding of domain names 2 Wildcards in DNS 3 Denial of existence Ignoring wildcards Including wildcard processing Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
40 Denial of existence Ignoring wildcards Example zone 0 apex SOA, NS 1 data empty TXT nxdomain 4 wildcard TXT * 3 data TXT 5 * the TXT 2 leaf TXT matches Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
41 Denial of existence Ignoring wildcards Proving Nodata with matching NSEC record Nodata means No Error, but also no data So some QTYPE's have data, but the queried QTYPE has not The NSEC record at the owner contains a bitmap for existing types Given the query data.apex A Consider the NSEC record data.apex NSEC leaf.*.empty.apex TXT Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
42 Denial of existence Ignoring wildcards Proving Nodata for empty non-terminals An empty non-terminal implies No Error, but also no data But now no QTYPE's at all have data There is no NSEC record for the empty non-terminal The empty non-terminal is covered (skipped) by some NSEC record Given the query empty.apex A Consider the NSEC record data.apex NSEC leaf.*.empty.apex TXT Server should include this NSEC record in the answer Client should verify this NSEC record is the right one Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
43 Denial of existence Ignoring wildcards Proving NXDOMAIN (Name Error or No such domain) There is no NSEC record for the non-existing domain name The non-existing domain name is covered by some NSEC record Given the query nxdomain.apex A Consider the NSEC record data.empty.apex NSEC wildcard.apex TXT Server should include this NSEC record in the answer Client should verify this NSEC record is the right one What is the dierence with the previous case? Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
44 Denial of existence Including wildcard processing Outline 1 Encoding of domain names 2 Wildcards in DNS 3 Denial of existence Ignoring wildcards Including wildcard processing Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
45 Denial of existence Including wildcard processing NSEC records in the (positive) answer case If a domain name is synthesized from a wildcard record we also need proof that this has been done correctly The next closer is the last (non-existing) domain name on the path to the closest encloser The next closer domain name is covered by some NSEC record Given the query matches.the.wildcard.apex TXT Consider the NSEC record *.wildcard.apex NSEC apex TXT Server should include this NSEC record in the answer Client should verify this NSEC record is the right one Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
46 Denial of existence Including wildcard processing Proving Nodata for wildcard expansions This is a combination of previous cases Use the NSEC type bitmap to prove queried QTYPE is not available Use a covering NSEC RR for the next closer domain name Given the query matches.the.wildcard.apex A Consider the NSEC record *.wildcard.apex NSEC apex TXT This sole NSEC record works for both requirements above Server includes and client veries this NSEC record What if the wildcard happens to be an empty non-terminal? Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
47 Denial of existence Including wildcard processing Proving NXDOMAIN revisited Find the NSEC record that covers the next closer domain name Moreover nd the NSEC record that covers the (non-existing) source of synthesis Given the query nxdomain.apex A Consider the NSEC record data.empty.apex NSEC wildcard.apex TXT And also the NSEC record apex NSEC data.apex SOA NS Server includes and client veries these NSEC records Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
48 Denial of existence Including wildcard processing NSEC3 records NSEC3 also creates a (circular) chain, but uses hashes of the original domain names as labels for the owner domain names of the NSEC3 records also hashes empty non-terminals orders the hashes instead of the original domain names uses the NSEC3PARAM type to specify hashing parameters and indicate the use of NSEC3 instead of NSEC denes the Opt-Out ag to exclude insecure delegations from the chain Karst Koymans & Niels Sijm (UvA) DNS/DNSSEC loose ends Friday, September 21, / 48
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