I support the adoption of this document. Was there a discussion of any actual downsides besides "I'd like to know if it's stale" and monitoring?
On Mon, Sep 11, 2017 at 11:11 AM, Bob Harold <rharo...@umich.edu> wrote: > > On Thu, Sep 7, 2017 at 10:07 PM, Mark Andrews <ma...@isc.org> wrote: >> >> >> Part of the problem is that we have one TTL value for both freshness >> and don't use beyond. >> >> This is fixable. It is possible to specify two timer values. It >> does require adding signaling between recursive servers and >> authoritative servers, on zone transfers and update requests. >> >> You basically add a additional timer field to every record immediately >> after the TTL field. This is only returned if the client has >> signalled support for the extended field, I suggest using the last >> DNS header bit for this as you can determine how you will parse the >> response base on whether the bit is set in the response or not. >> This field is used to expire records from the cache and its value >> is set to the TTL field if the server has learnt the record from >> server that doesn't support the extension. >> >> The existing TTL field is used for freshness checking. When a query >> comes in after that value has expired a freshness check is performed >> similar to the existing prefetches that happen today. A TTL of 1 >> is returned unless the original TTL was 0 in which case 0 is returned. >> >> New client - new recursive server - new authservers >> >> example.com. 300 86400 IN A 1.2.3.4 >> >> +300 seconds >> >> example.com. 1 86100 IN A 1.2.3.4 >> (background query is in process) >> >> Old client - new recursive server - new authservers >> >> example.com. 300 IN A 1.2.3.4 >> >> +300 seconds >> >> example.com. 1 IN A 1.2.3.4 >> (background query is in process) >> >> New client - new recusive server - old auth servers >> >> example.com. 300 300 IN A 1.2.3.4 >> >> +300 seconds >> (record has expired from cache, >> new query is performed) >> >> example.com. 300 300 IN A 1.2.3.4 >> >> For UPDATE a replacement opcode would be cleanest way to signal the >> new format is being used. NOTIMP should be returned by servers >> that don't support the new opcode. >> >> There will be a few broken servers that just echo back the new >> header bit. >> >> This way the authoritative servers still control how long records >> are stored for. Dead servers will get a little bit of traffic until >> the the refresh completes. If the authorative servers are under >> attack the clients still see a answer. >> >> The alternative is to perform the refresh query and if it fails to >> complete within X milliseconds return the cached data rather than >> returning the cached data and doing the refresh in the background. >> >> Mark >> >> -- >> Mark Andrews, ISC >> 1 Seymour St., Dundas Valley, NSW 2117, Australia >> PHONE: +61 2 9871 4742 INTERNET: ma...@isc.org > > > While I like the idea of a "don't use beyond" timer, I think it will be a > very long time before it is widely deployed (and actually configured by zone > owners), and therefore won't solve our immediate need. It would be great if > clients could opt-in, but again I don't see that happening anytime soon. So > I would start with resolver-operators deciding what seems best for their > clients (which is hat is happening whether we like it or not). Adding > client opt-out/opt-in would be good. Signalling to say that a response is > stale would be good. Adding the second timer (both per-RR and as a zone > default value, like TTL is handled) would be good. > > On a related note - the SOA "expire" timer tells a slave how long to keep > serving "stale" zone data when the master cannot be reached. Would that be > a reasonable default value for how long a resolver should serve "stale" data > when the authoritative servers cannot be reached? (Currently I think most > people set a very high value compared to the TTL.) > > -- > Bob Harold > > > > _______________________________________________ > DNSOP mailing list > DNSOP@ietf.org > https://www.ietf.org/mailman/listinfo/dnsop > _______________________________________________ DNSOP mailing list DNSOP@ietf.org https://www.ietf.org/mailman/listinfo/dnsop
