316:
Network
Working Group of the IETF, December 2001, RFC 3225: Indicating Resolver Support of DNSSEC, page 3, The mechanism chosen for the explicit notification of the ability of the client to accept (if not understand) DNSSEC security RRs is using the most significant bit of the Z field on the
142:, because older DNS responders ignore any RR of the unknown OPT type in a request and a newer DNS responder never includes an OPT in a response unless there was one in the request. The presence of the OPT in the request signifies a newer requester that knows what to do with an OPT in the response.
149:
and the version number (at present 0) are contained in the OPT record. A variable length data field allows further information to be registered in future versions of the protocol. The original DNS protocol provided two label types, which are defined by the first two bits in the length octet of a
199:
There are standards for using EDNS to set how much padding should be around a DNS message. Padding is essential when encrypting DNS, because without padding it may be possible to determine the queried domain name from the encrypted size of the query.
84:
The restrictions in the size of several flags fields, return codes and label types available in the basic DNS protocol prevented the support of some desirable features. Moreover, DNS messages carried by
109:
proposed extending DNS to allow for new flags and response codes and to provide support for longer responses in a framework that is backwards compatible with previous implementations.
307:
Network
Working Group of the IETF, August 1999, RFC 2671: Extension Mechanisms for DNS (EDNS0), page 3, Full conformance with this specification is indicated by version "0."
81:
was first developed in the early 1980s. Since then, it has been progressively enhanced with new features, while maintaining compatibility with earlier versions of the protocol.
228:
In practice, difficulties can arise when using EDNS traversing firewalls, since some firewalls assume a maximum DNS message length of 512 bytes and block longer DNS packets.
462:
41:
engineering community deemed too limited for increasing functionality of the protocol. The first set of extensions was published in 1999 by the
472:
216:
EDNS is also used for sending general information from resolvers to name servers about clients' geographic location in the form of the
236:
174:
The result of "EDNS: version: 0" indicates full conformance with EDNS0. The result "flags: do" indicates that "DNSSEC OK" is set.
145:
The OPT pseudo-record provides space for up to 16 flags and it extends the space for the response code. The overall size of the
42:
135:
As pseudo-RRs, OPT type RRs never appear in any zone file; they exist only in messages, fabricated by the DNS participants.
125:
included in the "additional data" section of a DNS message. Note that this section exists in both requests and responses.
102:
467:
20:
105:(TCP), would greatly increase overhead. This presented a major obstacle to adding new features to DNS. In 1999,
232:
117:
Since no new flags could be added in the DNS header, EDNS adds information to DNS messages in the form of
86:
150:
label (RFC 1035): 00 (standard label) and 11 (compressed label). EDNS introduces the label type 01 as
239:, since EDNS facilitates very large response packets compared to relatively small request packets.
139:
442:
217:
120:
78:
34:
90:
274:
254:
58:
46:
98:
94:
154:. The lower 6 bits of the first byte may be used to define up to 63 new extended labels.
456:
164:
317:
EDNS0 OPT header in the query. This bit is referred to as the "DNSSEC OK" (DO) bit.
366:
341:
278:
258:
62:
50:
146:
106:
208:
EDNS is used for indicating how long a TCP connection should be kept alive.
38:
33:) is a specification for expanding the size of several parameters of the
367:"RFC 8467: Padding Policies for Extension Mechanisms for DNS (EDNS(0))"
416:
391:
188:
187:
EDNS is essential for the implementation of DNS Security
Extensions (
330:, R. Arends, Telematica Instituut, 2005. Section 4.1 EDNS Support
447:
171:;; OPT PSEUDOSECTION: ; EDNS: version: 0, flags: do; udp: 4096
19:"EDNS" redirects here. For the alternative root system, see
162:
An example of an OPT pseudo-record, as displayed by the
328:
37:(DNS) protocol which had size restrictions that the
89:were restricted to 512 bytes, not considering the
392:"RFC 7828: The edns-tcp-keepalive EDNS0 Option"
296:Domain Names - Implementation and Specification
265:, P. Vixie, The Internet Society (August 1999)
8:
285:, J. Damas, M. Graff, P. Vixie, (April 2013)
231:The introduction of EDNS made feasible the
65:in 2013 changing abbreviation slightly to
128:EDNS introduces a single pseudo-RR type:
417:"RFC 7871: Client Subnet in DNS Queries"
463:Internet properties established in 1999
247:
342:"RFC 7830: The EDNS(0) Padding Option"
283:Extension Mechanisms for DNS (EDNS(0))
365:Mayrhofer, Alexander (October 2018).
7:
263:Extension Mechanisms for DNS (EDNS0)
16:Specification for Domain Name System
237:reflected denial-of-service attack
14:
340:Mayrhofer, Alexander (May 2016).
298:, P. Mockapetris (November 1987)
43:Internet Engineering Task Force
415:Contavalli, Carlo (May 2016).
1:
473:Domain name system extensions
103:Transmission Control Protocol
390:Wouters, Paul (April 2016).
27:Extension Mechanisms for DNS
21:eDNS (alternative DNS root)
489:
18:
233:DNS amplification attack
212:EDNS Client Subnet (ECS)
97:headers. Resorting to a
101:transport, using the
57:which was updated by
140:backward compatible
468:Domain Name System
443:EDNS Client Subnet
218:EDNS Client Subnet
79:Domain Name System
35:Domain Name System
448:DNS Flag Day 2019
138:The mechanism is
91:Internet Protocol
480:
431:
430:
428:
427:
412:
406:
405:
403:
402:
387:
381:
380:
378:
377:
362:
356:
355:
353:
352:
337:
331:
324:
318:
314:
308:
305:
299:
292:
286:
272:
266:
252:
131:
121:Resource Records
53:, also known as
488:
487:
483:
482:
481:
479:
478:
477:
453:
452:
439:
434:
425:
423:
414:
413:
409:
400:
398:
389:
388:
384:
375:
373:
364:
363:
359:
350:
348:
339:
338:
334:
325:
321:
315:
311:
306:
302:
293:
289:
273:
269:
253:
249:
245:
226:
214:
206:
197:
185:
180:
172:
160:
129:
115:
99:virtual circuit
95:transport layer
75:
24:
17:
12:
11:
5:
486:
484:
476:
475:
470:
465:
455:
454:
451:
450:
445:
438:
435:
433:
432:
421:tools.ietf.org
407:
396:tools.ietf.org
382:
371:tools.ietf.org
357:
346:tools.ietf.org
332:
319:
309:
300:
287:
267:
246:
244:
241:
225:
222:
220:(ECS) option.
213:
210:
205:
204:EDNS Keepalive
202:
196:
193:
184:
181:
179:
176:
170:
159:
156:
152:extended label
123:("pseudo-RR"s)
114:
111:
74:
71:
15:
13:
10:
9:
6:
4:
3:
2:
485:
474:
471:
469:
466:
464:
461:
460:
458:
449:
446:
444:
441:
440:
436:
422:
418:
411:
408:
397:
393:
386:
383:
372:
368:
361:
358:
347:
343:
336:
333:
329:
323:
320:
313:
310:
304:
301:
297:
291:
288:
284:
280:
276:
271:
268:
264:
260:
256:
251:
248:
242:
240:
238:
234:
229:
223:
221:
219:
211:
209:
203:
201:
194:
192:
190:
182:
177:
175:
169:
167:
166:
157:
155:
153:
148:
143:
141:
136:
133:
126:
124:
122:
112:
110:
108:
104:
100:
96:
92:
88:
82:
80:
72:
70:
68:
64:
60:
56:
52:
48:
44:
40:
36:
32:
28:
22:
424:. Retrieved
420:
410:
399:. Retrieved
395:
385:
374:. Retrieved
370:
360:
349:. Retrieved
345:
335:
327:
322:
312:
303:
295:
290:
282:
270:
262:
250:
235:, a type of
230:
227:
215:
207:
198:
195:EDNS Padding
186:
178:Applications
173:
163:
161:
151:
144:
137:
134:
127:
118:
116:
83:
76:
66:
54:
30:
26:
25:
165:dig command
457:Categories
426:2018-02-02
401:2018-02-02
376:2018-10-01
351:2018-02-02
326:RFC 4035,
294:RFC 1035,
243:References
147:UDP packet
107:Paul Vixie
73:Motivation
113:Mechanism
93:(IP) and
437:See also
39:Internet
158:Example
119:pseudo-
67:EDNS(0)
277:
257:
224:Issues
189:DNSSEC
183:DNSSEC
61:
49:
55:EDNS0
279:6891
259:2671
77:The
63:6891
51:2671
31:EDNS
275:RFC
255:RFC
191:).
130:OPT
87:UDP
59:RFC
47:RFC
45:as
459::
419:.
394:.
369:.
344:.
281:,
261:,
168::
132:.
69:.
429:.
404:.
379:.
354:.
29:(
23:.
Text is available under the Creative Commons Attribution-ShareAlike License. Additional terms may apply.