----- Original Message ---- > From: Mark Andrews > To: Fr34k > Cc: Bindlist > Sent: Wed, March 23, 2011 9:04:00 PM > Subject: Re: Q on clients-per-query, max-clients-per-query > > > In message <>, Fr34k writes: > > Hello, > > > > # The ARM says: # > > clients-per-query, max-clients-per-query > > These set the initial value (minimum) and maximum number of recursive > > simultaneous clients for any given query (<qname,qtype,qclass>) that the >serv > > er > > will accept before dropping additional clients. named will attempt to self >tu > > ne > > this value and changes will be logged. The default values are 10 and 100. > > If clients-per-query is set to zero, then there is no limit on the number > > of > > > clients per query and no queries will be dropped. If > > max-clients-per-query >i > > s > > set to zero, then there is no upper bound other than imposed by > > recursive-clients. > > > > > > # Consider that I have: # > > clients-per-query 10 ; max-clients-per-query 20 ; > > > > > > # What I think this means in hypothetical situations: # > > 1. If I have 100 customer Windows machines requesting A record(s) for > > non-responsive-domain.com, then my caching server will only recurs the > > first > > > 20 > > of such requests and drop the other 80. Is this correct, or what is the >like > > ly > > process? > > > > 2. If I have 100 customer Windows machines requesting A record(s) for > > very-slow-to-respond.com, then my caching server will only recurs the > > first > > > 20 > > of such requests and drop the other 80. Is this correct, or what is the >like > > ly > > process? > > > > Let's say the name servers authoritative for this domain finally respond, >the > > n > > my bind server will respond to the 20 queries. > > Is this correct, or what is the likely process? > > > > Now that I have the A record for www.very-slow-to-respond.com in cache > > (say >T > > TL > > is 24h) and it is likely that the 80 unsatisfied customer Windows machines >wi > > ll > > make another query attempt and, because I have this cached, finally get a > > response. > > Is this correct, or what is the likely process? > > > > It won't hurt my feeling if someone rather provide a better example that > > may > > > demonstrate how these settings work. > > You have a empty cache. You get a query for google.com. You send > a query to the root servers for google.com. Another query for > google.com comes in. You add it to the existing query for google.com. > You get the answer back from the root servers. You ask the com > servers for google.com. You get another 3 query for google.com, > you add these to the original query. You get a response from the > com servers. You ask the google.com servers for google.com. You > get more queries for google.com. You get a answer back from the > google.com servers and you send the answers back to all the clients > that asked you for google.com. Future queries for google.com will > be answered from the cache until the record expires. > > Now if more than 10 clients ask you for google.com while this is > happening you will just drop the new clients (they should retry). > Named will remember that it dropped clients and as it got a answer > it will increase the number of clients that it serve for the next > query. It's a little more complicted than this but this will do > for this explaination. This lets named adjust to the normal query > rate and how far it is from the usual nameservers it talks to round > trip wise. This normally take less than a second. > > Now lets say the servers for a zone are unreachable. Named will > only queue up 10 clients before it starts dropping them. This stops > the recursive client slots all being taken on queries talking to > these servers. > > Similar a flash crowd of queries for the same name will be mostly > dropped until the answer is received.
So, does BIND behave the same whether it is a single PC making 100 queries for the same record compared to 555 PCs making queries for the same record? That is, how does BIND treat "clients-per-query, max-clients-per-query" differently based upon the query requesters' IP address(es)? (I want to assume I know the answer, but I have an interesting network event and I want to be able to understand/communicate the snoop logs we captured) I'm using 9.7.2-P2, if version is significant. Thank you. > Mark > > > Thank you. > > > > _______________________________________________ > > bind-users mailing list > > bind-users@lists.isc.org > > https://lists.isc.org/mailman/listinfo/bind-users > -- > Mark Andrews, ISC > 1 Seymour St., Dundas Valley, NSW 2117, Australia > PHONE: +61 2 9871 4742 INTERNET: > _______________________________________________ bind-users mailing list bind-users@lists.isc.org https://lists.isc.org/mailman/listinfo/bind-users
