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Checking references for intended status: Best Current Practice ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 5966 (Obsoleted by RFC 7766) ** Obsolete normative reference: RFC 6195 (Obsoleted by RFC 6895) Summary: 2 errors (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group M. Andrews 3 Internet-Draft ISC 4 Intended status: Best Current Practice November 28, 2015 5 Expires: May 31, 2016 7 A Common Operational Problem in DNS Servers - Failure To Respond. 8 draft-ietf-dnsop-no-response-issue-00 10 Abstract 12 The DNS is a query / response protocol. Failure to respond or to 13 respond correctly to queries causes both immediate operational 14 problems and long term problems with protocol development. 16 This document identifies a number of common classes of queries to 17 which some servers either fail to respond or else respond 18 incorrectly. This document also suggests procedures for TLD and 19 other similar zone operators to apply to help reduce / eliminate the 20 problem. 22 The document does not look at the DNS data itself, just the structure 23 of the responses. 25 Status of This Memo 27 This Internet-Draft is submitted in full conformance with the 28 provisions of BCP 78 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering 31 Task Force (IETF). Note that other groups may also distribute 32 working documents as Internet-Drafts. The list of current Internet- 33 Drafts is at http://datatracker.ietf.org/drafts/current/. 35 Internet-Drafts are draft documents valid for a maximum of six months 36 and may be updated, replaced, or obsoleted by other documents at any 37 time. It is inappropriate to use Internet-Drafts as reference 38 material or to cite them other than as "work in progress." 40 This Internet-Draft will expire on May 31, 2016. 42 Copyright Notice 44 Copyright (c) 2015 IETF Trust and the persons identified as the 45 document authors. All rights reserved. 47 This document is subject to BCP 78 and the IETF Trust's Legal 48 Provisions Relating to IETF Documents 49 (http://trustee.ietf.org/license-info) in effect on the date of 50 publication of this document. Please review these documents 51 carefully, as they describe your rights and restrictions with respect 52 to this document. Code Components extracted from this document must 53 include Simplified BSD License text as described in Section 4.e of 54 the Trust Legal Provisions and are provided without warranty as 55 described in the Simplified BSD License. 57 Table of Contents 59 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 60 2. Common queries class that result in non responses. . . . . . 3 61 2.1. EDNS Queries - Version Independent . . . . . . . . . . . 4 62 2.2. EDNS Queries - Version Specific . . . . . . . . . . . . . 4 63 2.3. EDNS Options . . . . . . . . . . . . . . . . . . . . . . 4 64 2.4. EDNS Flags . . . . . . . . . . . . . . . . . . . . . . . 4 65 2.5. DNS Flags . . . . . . . . . . . . . . . . . . . . . . . . 5 66 2.6. Unknown / Unsupported Type Queries . . . . . . . . . . . 5 67 2.7. Unknown DNS opcodes . . . . . . . . . . . . . . . . . . . 5 68 2.8. TCP Queries . . . . . . . . . . . . . . . . . . . . . . . 5 69 3. Remediating . . . . . . . . . . . . . . . . . . . . . . . . . 6 70 4. Firewalls and Load Balancers . . . . . . . . . . . . . . . . 7 71 5. Scrubbing Services . . . . . . . . . . . . . . . . . . . . . 8 72 6. Whole Answer Caches . . . . . . . . . . . . . . . . . . . . . 9 73 7. Response Code Selection . . . . . . . . . . . . . . . . . . . 9 74 8. Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 75 8.1. Testing - Basic DNS . . . . . . . . . . . . . . . . . . . 10 76 8.2. Testing - Extended DNS . . . . . . . . . . . . . . . . . 12 77 9. Security Considerations . . . . . . . . . . . . . . . . . . . 15 78 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 79 11. Normative References . . . . . . . . . . . . . . . . . . . . 15 80 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 16 82 1. Introduction 84 The DNS [RFC1034], [RFC1035] is a query / response protocol. Failure 85 to respond to queries or to respond incorrectly causes both immediate 86 operational problems and long term problems with protocol 87 development. 89 Failure to respond to a query is indistinguishable from a packet loss 90 without doing a analysis of query response patterns and results in 91 unnecessary additional queries being made by DNS clients and 92 unnecessary delays being introduced to the resolution process. 94 Due to the inability to distinguish between packet loss and 95 nameservers dropping EDNS [RFC6891] queries, packet loss is sometimes 96 misclassified as lack of EDNS support which can lead to DNSSEC 97 validation failures. 99 Allowing servers which fail to respond to queries to remain results 100 in developers being afraid to deploy implementations of recent 101 standards. Such servers need to be identified and corrected / 102 replaced. 104 The DNS has response codes that cover almost any conceivable query 105 response. A nameserver should be able to respond to any conceivable 106 query using them. 108 Unless a nameserver is under attack, it should respond to all queries 109 directed to it as a result of following delegations. Additionally 110 code should not assume that there isn't a delegation to the server 111 even if it is not configured to serve the zone. Broken delegations 112 are a common occurrence in the DNS and receiving queries for zones 113 that you are not configured for is not a necessarily a indication 114 that you are under attack. Parent zone operators are supposed to 115 regularly check that the delegating NS records are consistent with 116 those of the delegated zone and to correct them when they are not 117 [RFC1034]. If this was being done regularly, the instances of broken 118 delegations would be much lower. 120 When a nameserver is under attack it may wish to drop packets. A 121 common attack is to use a nameserver as a amplifier by sending 122 spoofed packets. This is done because response packets are bigger 123 than the queries and big amplification factors are available 124 especially if EDNS is supported. Limiting the rate of responses is 125 reasonable when this is occurring and the client should retry. This 126 however only works if legitimate clients are not being forced to 127 guess whether EDNS queries are accept or not. While there is still a 128 pool of servers that don't respond to EDNS requests, clients have no 129 way to know if the lack of response is due to packet loss, EDNS 130 packets not being supported or rate limiting due to the server being 131 under attack. Mis-classifications of server characteristics are 132 unavoidable when rate limiting is done. 134 2. Common queries class that result in non responses. 136 There are three common query classes that result in non responses 137 today. These are EDNS queries, queries for unknown (unallocated) or 138 unsupported types, and filtering of TCP queries. 140 2.1. EDNS Queries - Version Independent 142 Identifying servers that fail to respond to EDNS queries can be done 143 by first identifying that the server responds to regular DNS queries, 144 followed by a series of otherwise identical responses using EDNS, 145 then making the original query again. A series of EDNS queries is 146 needed as at least one DNS implementation responds to the first EDNS 147 query with FORMERR but fails to respond to subsequent queries from 148 the same address for a period until a regular DNS query is made. The 149 EDNS query should specify a UDP buffer size of 512 bytes to avoid 150 false classification of not supporting EDNS due to response packet 151 size. 153 If the server responds to the first and last queries but fails to 154 respond to most or all of the EDNS queries, it is probably faulty. 155 The test should be repeated a number of times to eliminate the 156 likelihood of a false positive due to packet loss. 158 Firewalls may also block larger EDNS responses but there is no easy 159 way to check authoritative servers to see if the firewall is 160 misconfigured. 162 2.2. EDNS Queries - Version Specific 164 Some servers respond correctly to EDNS version 0 queries but fail to 165 respond to EDNS queries with version numbers that are higher than 166 zero. Servers should respond with BADVERS to EDNS queries with 167 version numbers that they do not support. 169 Some servers respond correctly to EDNS version 0 queries but fail to 170 set QR=1 when responding to EDNS versions they do not support. Such 171 answers are discarded or treated as requests. 173 2.3. EDNS Options 175 Some servers fail to respond to EDNS queries with EDNS options set. 176 Unknown EDNS options are supposed to be ignored by the server 177 [RFC6891]. 179 2.4. EDNS Flags 181 Some servers fail to respond to EDNS queries with EDNS flags set. 182 Server should ignore EDNS flags there do not understand and should 183 not add them to the response [RFC6891]. 185 2.5. DNS Flags 187 Some servers fail to respond to DNS queries with various DNS flags 188 set, regardless of whether they are defined or still reserved. At 189 the time of writing there are servers that fail to respond to queries 190 with the AD bit set to 1 and servers that fail to respond to queries 191 with the last reserved flag bit set. 193 2.6. Unknown / Unsupported Type Queries 195 Identifying servers that fail to respond to unknown or unsupported 196 types can be done by making an initial DNS query for an A record, 197 making a number of queries for an unallocated type, them making a 198 query for an A record again. IANA maintains a registry of allocated 199 types. 201 If the server responds to the first and last queries but fails to 202 respond to the queries for the unallocated type, it is probably 203 faulty. The test should be repeated a number of times to eliminate 204 the likelihood of a false positive due to packet loss. 206 2.7. Unknown DNS opcodes 208 The use of previously undefined opcodes is to be expected. Since the 209 DNS was first defined two new opcodes have been added, UPDATE and 210 NOTIFY. 212 NOTIMP is the expected rcode to an unknown / unimplemented opcode. 214 Note: while new opcodes will most probably use the current layout 215 structure for the rest of the message there is no requirement than 216 anything other than the DNS header match. 218 2.8. TCP Queries 220 All DNS servers are supposed to respond to queries over TCP 221 [RFC5966]. Firewalls that drop TCP connection attempts rather that 222 resetting the connect attempt or send a ICMP/ICMPv6 administratively 223 prohibited message introduce excessive delays to the resolution 224 process. 226 Whether a server accepts TCP connections can be tested by first 227 checking that it responds to UDP queries to confirm that it is up and 228 operating, then attempting the same query over TCP. An additional 229 query should be made over UDP if the TCP connection attempt fails to 230 confirm that the server under test is still operating. 232 3. Remediating 234 While the first step in remediating this problem is to get the 235 offending nameserver code corrected, there is a very long tail 236 problem with DNS servers in that it can often take over a decade 237 between the code being corrected and a nameserver being upgraded with 238 corrected code. With that in mind it is requested that TLD, and 239 other similar zone operators, take steps to identify and inform their 240 customers, directly or indirectly through registrars, that they are 241 running such servers and that the customers need to correct the 242 problem. 244 TLD operators are being asked to do this as they, due to the nature 245 of running a TLD and the hierarchical nature of the DNS, have access 246 to a large numbers of nameserver names as well as contact details for 247 the registrants of those nameservers. One can construct lists of 248 nameservers from other sources and that has been done to survey the 249 state of the Internet, but that doesn't give you the contact details 250 necessary to inform the operators. The SOA RNAME is often invalid 251 and whois data is obscured and / or not available which makes it 252 infeasible for others to do this. 254 TLD operators should construct a list of servers child zones are 255 delegated to along with a delegated zone name. This name shall be 256 the query name used to test the server as it is supposed to exist. 258 For each server the TLD operator shall make an SOA query of the 259 delegated zone name. This should result in the SOA record being 260 returned in the answer section. If the SOA record is not returned 261 but some other response is returned, this is a indication of a bad 262 delegation and the TLD operator should take whatever steps it 263 normally takes to rectify a bad delegation. If more that one zone is 264 delegated to the server, it should choose another zone until it finds 265 a zone which responds correctly or it exhausts the list of zones 266 delegated to the server. 268 If the server fails to get a response to a SOA query, the TLD 269 operator should make an A query as some nameservers fail to respond 270 to SOA queries but respond to A queries. If it gets no response to 271 the A query, another delegated zone should be queried for as some 272 nameservers fail to respond to zones they are not configured for. If 273 subsequent queries find a responding zone, all delegation to this 274 server need to be checked and rectified using the TLD's normal 275 procedures. 277 Having identified a working tuple the TLD 278 operator should now check that the server responds to EDNS, Unknown 279 Query Type and TCP tests as described above. If the TLD operator 280 finds that server fails any of the tests, the TLD operator shall take 281 steps to inform the operator of the server that they are running a 282 faulty nameserver and that they need to take steps to correct the 283 matter. The TLD operator shall also record the 284 for follow-up testing. 286 If repeated attempts to inform and get the customer to correct / 287 replace the faulty server are unsuccessful the TLD operator shall 288 remove all delegations to said server from the zone. 290 It will also be necessary for TLD operators to repeat the scans 291 periodically. It is recommended that this be performed monthly 292 backing off to bi-annually once the numbers of faulty servers found 293 drops off to less than 1 in 100000 servers tested. Follow-up tests 294 for faulty servers still need to be performed monthly. 296 Some operators claim that they can't perform checks at registration 297 time. If a check is not performed at registration time, it needs to 298 be performed within a week of registration in order to detect faulty 299 servers swiftly. 301 Checking of delegations by TLD operators should be nothing new as 302 they have been required from the very beginnings of DNS to do this 303 [RFC1034]. Checking for compliance of nameserver operations should 304 just be a extension of such testing. 306 It is recommended that TLD operators setup a test web page which 307 performs the tests the TLD operator performs as part of their regular 308 audits to allow nameserver operators to test that they have correctly 309 fixed their servers. Such tests should be rate limited to avoid 310 these pages being a denial of service vector. 312 4. Firewalls and Load Balancers 314 Firewalls and load balancers can affect the externally visible 315 behaviour of a nameserver. Tests for conformance need to be done 316 from outside of any firewall so that the system as a whole is tested. 318 Firewalls and load balancers should not drop DNS packets that they 319 don't understand. They should either pass through the packets or 320 generate an appropriate error response. 322 Requests for unknown query types are not attacks and should not be 323 treated as such. 325 Requests with unassigned flags set (DNS or EDNS) are not attacks and 326 should not be treated as such. The behaviour for unassigned is to 327 ignore them in the request and to not set them in the response. All 328 dropping DNS / EDNS packets with unassigned flags does is make it 329 harder to deploy extensions that make use of them due to the need to 330 reconfigure / update firewalls. 332 Requests with unknown EDNS options are not an attack and should not 333 be treated as such. The correct behaviour for unknown EDNS options 334 is to ignore them. 336 Requests with unknown EDNS versions are not a attack and should not 337 be treated as such. The correct behaviour for unknown EDNS versions 338 is to return BADVERS along with the highest EDNS version the server 339 supports. All dropping EDNS packets does is break EDNS version 340 negotiation. 342 Firewalls should not assume that there will only be a single response 343 message to a requests. There have been proposals to use EDNS to 344 signal that multiple DNS messages be returned rather than a single 345 UDP message that is fragmented at the IP layer. 347 5. Scrubbing Services 349 Scrubbing services, like firewalls, can affect the externally visible 350 behaviour of a nameserver. If you use a scrubbing service, you 351 should check that legitimate queries are not being blocked. 353 Scrubbing services, unlike firewalls, are also turned on and off in 354 response to denial of service attacks. One needs to take care when 355 choosing a scrubbing service and ask questions like: 357 Do they pass unknown DNS query types? 359 Do they pass unknown EDNS versions? 361 Do they pass unknown EDNS options? 363 Do they pass unknown EDNS flags? 365 Do they pass requests with unknown DNS opcodes? 367 Do they pass requests with the remaining reserved DNS header flag 368 bit set? 370 All of these are not attack vectors but some scrubbing services treat 371 them as such. 373 6. Whole Answer Caches 375 Whole answer caches can return the wrong response to a query if they 376 do not take all of the query into account. This has implications 377 when testing and with overall protocol compliance. 379 e.g. There are whole answer caches that ignore the EDNS version 380 field which results in incorrect answers to non EDNS version 0 381 queries being returned if they were proceeded by a EDNS version 0 382 query for the same name and type. 384 7. Response Code Selection 386 Choosing the correct response code when fixing a nameserver is 387 important. Just because a type is not implemented does not mean that 388 NOTIMP is the correct response code to return. Response codes need 389 to be chosen considering how clients will handle them. 391 For unimplemented opcodes NOTIMP is the expected response code. 392 Additionally a new opcode could change the message format by 393 extending the header or changing the structure of the records etc. 394 This may result in FORMERR being returned though NOTIMP would be more 395 correct. 397 In general, for unimplemented type codes Name Error (NXDOMAIN) and 398 NOERROR (no data) are the expected response codes. A server is not 399 supposed to serve a zone which contains unsupported types ([RFC1034]) 400 so the only thing left is return if the QNAME exists or not. NOTIMP 401 and REFUSED are not useful responses as they force the clients to try 402 all the authoritative servers for a zone looking for a server which 403 will answer the query. 405 Meta queries type may be the exception but these need to be thought 406 about on a case by case basis. 408 If you support EDNS and get a query with an unsupported EDNS version, 409 the correct response is BADVERS [RFC6891]. 411 If you do not support EDNS at all, FORMERR and NOTIMP are the 412 expected error codes. That said a minimal EDNS server implementation 413 just requires parsing the OPT records and responding with an empty 414 OPT record. There is no need to interpret any EDNS options present 415 in the request as unsupported options are expected to be ignored 416 [RFC6891]. 418 8. Testing 420 Testing is broken into two sections. Basic DNS which all servers 421 should meet and Extended DNS which should be met by all servers that 422 support EDNS. 424 It is advisable to run all the below tests in parallel so as to 425 minimise the delays due to multiple timeouts when the servers do not 426 respond. 428 The below tests use dig from BIND 9.11.0 which is still in 429 development. 431 8.1. Testing - Basic DNS 433 This first set of tests cover basic DNS server behaviour and all 434 servers should pass these tests. 436 Verify the server is configured for the zone: 438 dig +noedns +noad +norec soa $zone @$server 440 expect: status: NOERROR 441 expect: SOA record 442 expect: flag: aa to be present 444 Check that TCP queries work: 446 dig +noedns +noad +norec +tcp soa $zone @$server 448 expect: status: NOERROR 449 expect: SOA record 450 expect: flag: aa to be present 452 The requirement that TCP be supported is defined in [RFC5966]. 454 Check that queries for an unknown type work: 456 dig +noedns +noad +norec type1000 $zone @$server 458 expect: status: NOERROR 459 expect: an empty answer section. 460 expect: flag: aa to be present 462 That new types are to be expected is specified in Section 3.6, 463 [RFC1035]. Servers that don't support a new type are expected to 464 reject a zone that contains a unsupported type as per Section 5.2, 465 [RFC1035]. This means that a server that does load a zone can answer 466 questions for unknown types with NOERROR or NXDOMAIN as per 467 Section 4.3.2, [RFC1034]. [RFC6195] later reserved distinct ranges 468 for meta and data types which allows servers to be definitive about 469 whether a query should be answerable from zone content or not. 471 Check that queries with CD=1 work: 473 dig +noedns +noad +norec +cd soa $zone @$server 475 expect: status: NOERROR 476 expect: SOA record to be present 477 expect: flag: aa to be present 479 CD use in queries is defined in [RFC4035]. 481 Check that queries with AD=1 work: 483 dig +noedns +norec +ad soa $zone @$server 485 expect: status: NOERROR 486 expect: SOA record to be present 487 expect: flag: aa to be present 489 AD use in queries is defined in [RFC6840]. 491 Check that queries with the last unassigned DNS header flag work and 492 that the flag bit is not copied to the response: 494 dig +noedns +noad +norec +zflag soa $zone @$server 496 expect: status: NOERROR 497 expect: SOA record to be present 498 expect: MBZ to not be in the response 499 expect: flag: aa to be present 501 MBZ (Must Be Zero) presence indicates the flag bit has been 502 incorrectly copied. See Section 4.1.1, [RFC1035] "Z Reserved for 503 future use. Must be zero in all queries and responses." 505 Check that new opcodes are handled: 507 dig +noedns +noad +opcode=15 +norec +header-only @$server 509 expect: status: NOTIMP 510 expect: SOA record to not be present 511 expect: flag: aa to NOT be present 512 As unknown opcodes have no definition, including packet format other 513 than there must be a DNS header present, there is only one possible 514 rcode that make sense to return to a request with a unknown opcode 515 and that is NOTIMP. 517 8.2. Testing - Extended DNS 519 The next set of test cover various aspects of EDNS behaviour. If any 520 of these tests succeed, then all of them should succeed. There are 521 servers that support EDNS but fail to handle plain EDNS queries 522 correctly so a plain EDNS query is not a good indicator of lack of 523 EDNS support. 525 Check that plain EDNS queries work: 527 dig +nocookie +edns=0 +noad +norec soa $zone @$server 529 expect: status: NOERROR 530 expect: SOA record to be present 531 expect: OPT record to be present 532 expect: EDNS Version 0 in response 533 expect: flag: aa to be present 535 +nocookie disables sending a EDNS COOKIE option in which is on by 536 default. 538 Check that EDNS version 1 queries work (EDNS supported): 540 dig +nocookie +edns=1 +noednsneg +noad +norec soa $zone @$server 542 expect: status: BADVERS 543 expect: SOA record to not be present 544 expect: OPT record to be present 545 expect: EDNS Version 0 in response 546 expect: flag: aa to NOT be present 548 Only EDNS Version 0 is currently defined so the response should 549 always be a 0 version. This will change when EDNS version 1 is 550 defined. BADVERS is the expected rcode if EDNS is supported as per 551 Section 6.1.3, [RFC6891]. 553 Check that EDNS queries with an unknown option work (EDNS supported): 555 dig +nocookie +edns=0 +noad +norec +ednsopt=100 soa $zone @$server 557 expect: status: NOERROR 558 expect: SOA record to be present 559 expect: OPT record to be present 560 expect: OPT=100 to not be present 561 expect: EDNS Version 0 in response 562 expect: flag: aa to be present 564 Unknown EDNS options are supposed to be ignored, Section 6.1.2, 565 [RFC6891]. 567 Check that EDNS queries with unknown flags work (EDNS supported): 569 dig +nocookie +edns=0 +noad +norec +ednsflags=0x40 soa $zone @$server 571 expect: status: NOERROR 572 expect: SOA record to be present 573 expect: OPT record to be present 574 expect: MBZ not to be present 575 expect: EDNS Version 0 in response 576 expect: flag: aa to be present 578 MBZ (Must Be Zero) presence indicates the flag bit has been 579 incorrectly copied as per Section 6.1.4, [RFC6891]. 581 Check that EDNS version 1 queries with unknown flags work (EDNS 582 supported): 584 dig +nocookie +edns=1 +noednsneg +noad +norec +ednsflags=0x40 soa \ 585 $zone @$server 587 expect: status: BADVERS 588 expect: SOA record to NOT be present 589 expect: OPT record to be present 590 expect: MBZ not to be present 591 expect: EDNS Version 0 in response 592 expect: flag: aa to NOT be present 594 +noednsneg disables EDNS version negotiation in DiG; MBZ (Must Be 595 Zero) presence indicates the flag bit has been incorrectly copied. 597 Check that EDNS version 1 queries with unknown options work (EDNS 598 supported): 600 dig +nocookie +edns=1 +noednsneg +noad +norec +ednsopt=100 soa \ 601 $zone @$server 603 expect: status: BADVERS 604 expect: SOA record to NOT be present 605 expect: OPT record to be present 606 expect: OPT=100 to NOT be present 607 expect: EDNS Version 0 in response 608 expect: flag: aa to be present 610 +noednsneg disables EDNS version negotiation in DiG. 612 Check that a DNSSEC queries work (EDNS supported): 614 dig +nocookie +edns=0 +noad +norec +dnssec soa $zone @$server 616 expect: status: NOERROR 617 expect: SOA record to be present 618 expect: OPT record to be present 619 expect: DO=1 to be present if a RRSIG is in the response 620 expect: EDNS Version 0 in response 621 expect: flag: aa to be present 623 DO=1 should be present if RRSIGs are returned as they indicate that 624 the server supports DNSSEC. Servers that support DNSSEC are supposed 625 to copy the DO bit from the request to the response as per [RFC3225]. 627 Check that EDNS version 1 DNSSEC queries work (EDNS supported): 629 dig +nocookie +edns=1 +noednsneg +noad +norec +dnssec soa \ 630 $zone @$server 632 expect: status: BADVERS 633 expect: SOA record to not be present 634 expect: OPT record to be present 635 expect: DO=1 to be present if the EDNS version 0 DNSSEC query test 636 returned DO=1 637 expect: EDNS Version 0 in response 638 expect: flag: aa to NOT be present 640 +noednsneg disables EDNS version negotiation in DiG. 642 Check that EDNS queries with multiple defined EDNS options work. 644 dig +edns=0 +noad +norec +cookie +nsid +expire +subnet=0.0.0.0/0 \ 645 soa $zone @$server 647 expect: status: NOERROR 648 expect: SOA record to be present 649 expect: OPT record to be present 650 expect: EDNS Version 0 in response 651 expect: flag: aa to be present 653 If EDNS is not supported by the nameserver, we expect a response to 654 all the above queries. That response may be a FORMERR or NOTIMP 655 error response or the OPT record may just be ignored. 657 9. Security Considerations 659 Testing protocol compliance can potentially result in false reports 660 of attempts to break services from Intrusion Detection Services and 661 firewalls. None of the tests listed above should break nominally 662 EDNS compliant servers. None of the tests above should break non 663 EDNS servers. All the tests above are well formed, though not 664 necessarily common, DNS queries. 666 Relaxing firewall settings to ensure EDNS compliance could 667 potentially expose a critical implementation flaw in the nameserver. 668 Nameservers should be tested for conformance before relaxing firewall 669 settings. 671 10. IANA Considerations 673 IANA / ICANN needs to consider what tests, if any, from above that it 674 should add to the zone maintenance procedures for zones under its 675 control including pre-delegation checks. Otherwise this document has 676 no actions for IANA. 678 11. Normative References 680 [RFC1034] Mockapetris, P., "Domain names - concepts and facilities", 681 STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987, 682 . 684 [RFC1035] Mockapetris, P., "Domain names - implementation and 685 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 686 November 1987, . 688 [RFC3225] Conrad, D., "Indicating Resolver Support of DNSSEC", 689 RFC 3225, DOI 10.17487/RFC3225, December 2001, 690 . 692 [RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S. 693 Rose, "Protocol Modifications for the DNS Security 694 Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005, 695 . 697 [RFC5966] Bellis, R., "DNS Transport over TCP - Implementation 698 Requirements", RFC 5966, DOI 10.17487/RFC5966, August 699 2010, . 701 [RFC6195] Eastlake 3rd, D., "Domain Name System (DNS) IANA 702 Considerations", RFC 6195, DOI 10.17487/RFC6195, March 703 2011, . 705 [RFC6840] Weiler, S., Ed. and D. Blacka, Ed., "Clarifications and 706 Implementation Notes for DNS Security (DNSSEC)", RFC 6840, 707 DOI 10.17487/RFC6840, February 2013, 708 . 710 [RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms 711 for DNS (EDNS(0))", STD 75, RFC 6891, 712 DOI 10.17487/RFC6891, April 2013, 713 . 715 Author's Address 717 M. Andrews 718 Internet Systems Consortium 719 950 Charter Street 720 Redwood City, CA 94063 721 US 723 Email: marka@isc.org