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diff --git a/contrib/bind9/doc/draft/draft-ietf-dnsop-respsize-02.txt b/contrib/bind9/doc/draft/draft-ietf-dnsop-respsize-02.txt deleted file mode 100644 index 63fe2de..0000000 --- a/contrib/bind9/doc/draft/draft-ietf-dnsop-respsize-02.txt +++ /dev/null @@ -1,480 +0,0 @@ - - - - - - - DNSOP Working Group Paul Vixie, ISC - INTERNET-DRAFT Akira Kato, WIDE - <draft-ietf-dnsop-respsize-02.txt> July 2005 - - DNS Response Size Issues - - Status of this Memo - By submitting this Internet-Draft, each author represents that any - applicable patent or other IPR claims of which he or she is aware - have been or will be disclosed, and any of which he or she becomes - aware will be disclosed, in accordance with Section 6 of BCP 79. - - Internet-Drafts are working documents of the Internet Engineering - Task Force (IETF), its areas, and its working groups. Note that - other groups may also distribute working documents as Internet- - Drafts. - - Internet-Drafts are draft documents valid for a maximum of six months - and may be updated, replaced, or obsoleted by other documents at any - time. It is inappropriate to use Internet-Drafts as reference - material or to cite them other than as "work in progress." - - The list of current Internet-Drafts can be accessed at - http://www.ietf.org/ietf/1id-abstracts.txt - - The list of Internet-Draft Shadow Directories can be accessed at - http://www.ietf.org/shadow.html. - - Copyright Notice - - Copyright (C) The Internet Society (2005). All Rights Reserved. - - - - - Abstract - - With a mandated default minimum maximum message size of 512 octets, - the DNS protocol presents some special problems for zones wishing to - expose a moderate or high number of authority servers (NS RRs). This - document explains the operational issues caused by, or related to - this response size limit. - - - - - - - Expires December 2005 [Page 1] - - INTERNET-DRAFT July 2005 RESPSIZE - - - 1 - Introduction and Overview - - 1.1. The DNS standard (see [RFC1035 4.2.1]) limits message size to 512 - octets. Even though this limitation was due to the required minimum UDP - reassembly limit for IPv4, it is a hard DNS protocol limit and is not - implicitly relaxed by changes in transport, for example to IPv6. - - 1.2. The EDNS0 standard (see [RFC2671 2.3, 4.5]) permits larger - responses by mutual agreement of the requestor and responder. However, - deployment of EDNS0 cannot be expected to reach every Internet resolver - in the short or medium term. The 512 octet message size limit remains - in practical effect at this time. - - 1.3. Since DNS responses include a copy of the request, the space - available for response data is somewhat less than the full 512 octets. - For negative responses, there is rarely a space constraint. For - positive and delegation responses, though, every octet must be carefully - and sparingly allocated. This document specifically addresses - delegation response sizes. - - 2 - Delegation Details - - 2.1. A delegation response will include the following elements: - - Header Section: fixed length (12 octets) - Question Section: original query (name, class, type) - Answer Section: (empty) - Authority Section: NS RRset (nameserver names) - Additional Section: A and AAAA RRsets (nameserver addresses) - - 2.2. If the total response size would exceed 512 octets, and if the data - that would not fit belonged in the question, answer, or authority - section, then the TC bit will be set (indicating truncation) which may - cause the requestor to retry using TCP, depending on what information - was desired and what information was omitted. If a retry using TCP is - needed, the total cost of the transaction is much higher. (See [RFC1123 - 6.1.3.2] for details on the protocol requirement that UDP be attempted - before falling back to TCP.) - - 2.3. RRsets are never sent partially unless truncation occurs, in which - case the final apparent RRset in the final nonempty section must be - considered "possibly damaged". With or without truncation, the glue - present in the additional data section should be considered "possibly - incomplete", and requestors should be prepared to re-query for any - damaged or missing RRsets. For multi-transport name or mail services, - - - - Expires December 2005 [Page 2] - - INTERNET-DRAFT July 2005 RESPSIZE - - - this can mean querying for an IPv6 (AAAA) RRset even when an IPv4 (A) - RRset is present. - - 2.4. DNS label compression allows a domain name to be instantiated only - once per DNS message, and then referenced with a two-octet "pointer" - from other locations in that same DNS message. If all nameserver names - in a message are similar (for example, all ending in ".ROOT- - SERVERS.NET"), then more space will be available for uncompressable data - (such as nameserver addresses). - - 2.5. The query name can be as long as 255 characters of presentation - data, which can be up to 256 octets of network data. In this worst case - scenario, the question section will be 260 octets in size, which would - leave only 240 octets for the authority and additional sections (after - deducting 12 octets for the fixed length header.) - - 2.6. Average and maximum question section sizes can be predicted by the - zone owner, since they will know what names actually exist, and can - measure which ones are queried for most often. For cost and performance - reasons, the majority of requests should be satisfied without truncation - or TCP retry. - - 2.7. Requestors who deliberately send large queries to force truncation - are only increasing their own costs, and cannot effectively attack the - resources of an authority server since the requestor would have to retry - using TCP to complete the attack. An attack that always used TCP would - have a lower cost. - - 2.8. The minimum useful number of address records is two, since with - only one address, the probability that it would refer to an unreachable - server is too high. Truncation which occurs after two address records - have been added to the additional data section is therefore less - operationally significant than truncation which occurs earlier. - - 2.9. The best case is no truncation. This is because many requestors - will retry using TCP by reflex, or will automatically re-query for - RRsets that are "possibly truncated", without considering whether the - omitted data was actually necessary. - - 2.10. Each added NS RR for a zone will add a minimum of between 16 and - 44 octets to every untruncated referral or negative response from the - zone's authority servers (16 octets for an NS RR, 16 octets for an A RR, - and 28 octets for an AAAA RR), in addition to whatever space is taken by - the nameserver name (NS NSDNAME and A/AAAA owner name). - - - - - Expires December 2005 [Page 3] - - INTERNET-DRAFT July 2005 RESPSIZE - - - 3 - Analysis - - 3.1. An instrumented protocol trace of a best case delegation response - follows. Note that 13 servers are named, and 13 addresses are given. - This query was artificially designed to exactly reach the 512 octet - limit. - - ;; flags: qr rd; QUERY: 1, ANS: 0, AUTH: 13, ADDIT: 13 - ;; QUERY SECTION: - ;; [23456789.123456789.123456789.\ - 123456789.123456789.123456789.com A IN] ;; @80 - - ;; AUTHORITY SECTION: - com. 86400 NS E.GTLD-SERVERS.NET. ;; @112 - com. 86400 NS F.GTLD-SERVERS.NET. ;; @128 - com. 86400 NS G.GTLD-SERVERS.NET. ;; @144 - com. 86400 NS H.GTLD-SERVERS.NET. ;; @160 - com. 86400 NS I.GTLD-SERVERS.NET. ;; @176 - com. 86400 NS J.GTLD-SERVERS.NET. ;; @192 - com. 86400 NS K.GTLD-SERVERS.NET. ;; @208 - com. 86400 NS L.GTLD-SERVERS.NET. ;; @224 - com. 86400 NS M.GTLD-SERVERS.NET. ;; @240 - com. 86400 NS A.GTLD-SERVERS.NET. ;; @256 - com. 86400 NS B.GTLD-SERVERS.NET. ;; @272 - com. 86400 NS C.GTLD-SERVERS.NET. ;; @288 - com. 86400 NS D.GTLD-SERVERS.NET. ;; @304 - - ;; ADDITIONAL SECTION: - A.GTLD-SERVERS.NET. 86400 A 192.5.6.30 ;; @320 - B.GTLD-SERVERS.NET. 86400 A 192.33.14.30 ;; @336 - C.GTLD-SERVERS.NET. 86400 A 192.26.92.30 ;; @352 - D.GTLD-SERVERS.NET. 86400 A 192.31.80.30 ;; @368 - E.GTLD-SERVERS.NET. 86400 A 192.12.94.30 ;; @384 - F.GTLD-SERVERS.NET. 86400 A 192.35.51.30 ;; @400 - G.GTLD-SERVERS.NET. 86400 A 192.42.93.30 ;; @416 - H.GTLD-SERVERS.NET. 86400 A 192.54.112.30 ;; @432 - I.GTLD-SERVERS.NET. 86400 A 192.43.172.30 ;; @448 - J.GTLD-SERVERS.NET. 86400 A 192.48.79.30 ;; @464 - K.GTLD-SERVERS.NET. 86400 A 192.52.178.30 ;; @480 - L.GTLD-SERVERS.NET. 86400 A 192.41.162.30 ;; @496 - M.GTLD-SERVERS.NET. 86400 A 192.55.83.30 ;; @512 - - ;; MSG SIZE sent: 80 rcvd: 512 - - - - - - Expires December 2005 [Page 4] - - INTERNET-DRAFT July 2005 RESPSIZE - - - 3.2. For longer query names, the number of address records supplied will - be lower. Furthermore, it is only by using a common parent name (which - is GTLD-SERVERS.NET in this example) that all 13 addresses are able to - fit. The following output from a response simulator demonstrates these - properties: - - % perl respsize.pl a.dns.br b.dns.br c.dns.br d.dns.br - a.dns.br requires 10 bytes - b.dns.br requires 4 bytes - c.dns.br requires 4 bytes - d.dns.br requires 4 bytes - # of NS: 4 - For maximum size query (255 byte): - if only A is considered: # of A is 4 (green) - if A and AAAA are condered: # of A+AAAA is 3 (yellow) - if prefer_glue A is assumed: # of A is 4, # of AAAA is 3 (yellow) - For average size query (64 byte): - if only A is considered: # of A is 4 (green) - if A and AAAA are condered: # of A+AAAA is 4 (green) - if prefer_glue A is assumed: # of A is 4, # of AAAA is 4 (green) - - % perl respsize.pl ns-ext.isc.org ns.psg.com ns.ripe.net ns.eu.int - ns-ext.isc.org requires 16 bytes - ns.psg.com requires 12 bytes - ns.ripe.net requires 13 bytes - ns.eu.int requires 11 bytes - # of NS: 4 - For maximum size query (255 byte): - if only A is considered: # of A is 4 (green) - if A and AAAA are condered: # of A+AAAA is 3 (yellow) - if prefer_glue A is assumed: # of A is 4, # of AAAA is 2 (yellow) - For average size query (64 byte): - if only A is considered: # of A is 4 (green) - if A and AAAA are condered: # of A+AAAA is 4 (green) - if prefer_glue A is assumed: # of A is 4, # of AAAA is 4 (green) - - (Note: The response simulator program is shown in Section 5.) - - Here we use the term "green" if all address records could fit, or - "orange" if two or more could fit, or "red" if fewer than two could fit. - It's clear that without a common parent for nameserver names, much space - would be lost. For these examples we use an average/common name size of - 15 octets, befitting our assumption of GTLD-SERVERS.NET as our common - parent name. - - - - - Expires December 2005 [Page 5] - - INTERNET-DRAFT July 2005 RESPSIZE - - - We're assuming an average query name size of 64 since that is the - typical average maximum size seen in trace data at the time of this - writing. If Internationalized Domain Name (IDN) or any other technology - which results in larger query names be deployed significantly in advance - of EDNS, then new measurements and new estimates will have to be made. - - 4 - Conclusions - - 4.1. The current practice of giving all nameserver names a common parent - (such as GTLD-SERVERS.NET or ROOT-SERVERS.NET) saves space in DNS - responses and allows for more nameservers to be enumerated than would - otherwise be possible. (Note that in this case it is wise to serve the - common parent domain's zone from the same servers that are named within - it, in order to limit external dependencies when all your eggs are in a - single basket.) - - 4.2. Thirteen (13) seems to be the effective maximum number of - nameserver names usable traditional (non-extended) DNS, assuming a - common parent domain name, and given that response truncation is - undesirable as an average case, and assuming mostly IPv4-only - reachability (only A RRs exist, not AAAA RRs). - - 4.3. Adding two to five IPv6 nameserver address records (AAAA RRs) to a - prototypical delegation that currently contains thirteen (13) IPv4 - nameserver addresses (A RRs) for thirteen (13) nameserver names under a - common parent, would not have a significant negative operational impact - on the domain name system. - - 5 - Source Code - - #!/usr/bin/perl - # - # SYNOPSIS - # repsize.pl [ -z zone ] fqdn_ns1 fqdn_ns2 ... - # if all queries are assumed to have zone suffux, such as "jp" in - # JP TLD servers, specify it in -z option - # - use strict; - use Getopt::Std; - my ($sz_msg) = (512); - my ($sz_header, $sz_ptr, $sz_rr_a, $sz_rr_aaaa) = (12, 2, 16, 28); - my ($sz_type, $sz_class, $sz_ttl, $sz_rdlen) = (2, 2, 4, 2); - my (%namedb, $name, $nssect, %opts, $optz); - my $n_ns = 0; - - - - - Expires December 2005 [Page 6] - - INTERNET-DRAFT July 2005 RESPSIZE - - - getopt('z', opts); - if (defined($opts{'z'})) { - server_name_len($opts{'z'}); # just register it - } - - foreach $name (@ARGV) { - my $len; - $n_ns++; - $len = server_name_len($name); - print "$name requires $len bytes\n"; - $nssect += $sz_ptr + $sz_type + $sz_class + $sz_ttl + $sz_rdlen + $len; - } - print "# of NS: $n_ns\n"; - arsect(255, $nssect, $n_ns, "maximum"); - arsect(64, $nssect, $n_ns, "average"); - - sub server_name_len { - my ($name) = @_; - my (@labels, $len, $n, $suffix); - - $name =~ tr/A-Z/a-z/; - @labels = split(/./, $name); - $len = length(join('.', @labels)) + 2; - for ($n = 0; $#labels >= 0; $n++, shift @labels) { - $suffix = join('.', @labels); - return length($name) - length($suffix) + $sz_ptr - if (defined($namedb{$suffix})); - $namedb{$suffix} = 1; - } - return $len; - } - - sub arsect { - my ($sz_query, $nssect, $n_ns, $cond) = @_; - my ($space, $n_a, $n_a_aaaa, $n_p_aaaa, $ansect); - $ansect = $sz_query + 1 + $sz_type + $sz_class; - $space = $sz_msg - $sz_header - $ansect - $nssect; - $n_a = atmost(int($space / $sz_rr_a), $n_ns); - $n_a_aaaa = atmost(int($space / ($sz_rr_a + $sz_rr_aaaa)), $n_ns); - $n_p_aaaa = atmost(int(($space - $sz_rr_a * $n_ns) / $sz_rr_aaaa), $n_ns); - printf "For %s size query (%d byte):\n", $cond, $sz_query; - printf "if only A is considered: "; - printf "# of A is %d (%s)\n", $n_a, &judge($n_a, $n_ns); - printf "if A and AAAA are condered: "; - printf "# of A+AAAA is %d (%s)\n", $n_a_aaaa, &judge($n_a_aaaa, $n_ns); - - - - Expires December 2005 [Page 7] - - INTERNET-DRAFT July 2005 RESPSIZE - - - printf "if prefer_glue A is assumed: "; - printf "# of A is %d, # of AAAA is %d (%s)\n", - $n_a, $n_p_aaaa, &judge($n_p_aaaa, $n_ns); - } - - sub judge { - my ($n, $n_ns) = @_; - return "green" if ($n >= $n_ns); - return "yellow" if ($n >= 2); - return "orange" if ($n == 1); - return "red"; - } - - sub atmost { - my ($a, $b) = @_; - return 0 if ($a < 0); - return $b if ($a > $b); - return $a; - } - - Security Considerations - - The recommendations contained in this document have no known security - implications. - - IANA Considerations - - This document does not call for changes or additions to any IANA - registry. - - IPR Statement - - Copyright (C) The Internet Society (2005). This document is subject to - the rights, licenses and restrictions contained in BCP 78, and except as - set forth therein, the authors retain all their rights. - - This document and the information contained herein are provided on an - "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR - IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET - ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, - INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE - INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED - WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. - - - - - - Expires December 2005 [Page 8] - - INTERNET-DRAFT July 2005 RESPSIZE - - - Authors' Addresses - - Paul Vixie - 950 Charter Street - Redwood City, CA 94063 - +1 650 423 1301 - vixie@isc.org - - Akira Kato - University of Tokyo, Information Technology Center - 2-11-16 Yayoi Bunkyo - Tokyo 113-8658, JAPAN - +81 3 5841 2750 - kato@wide.ad.jp - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Expires December 2005 [Page 9] -
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