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diff --git a/contrib/bind/doc/misc/DynamicUpdate b/contrib/bind/doc/misc/DynamicUpdate deleted file mode 100644 index fb4152c..0000000 --- a/contrib/bind/doc/misc/DynamicUpdate +++ /dev/null @@ -1,284 +0,0 @@ - - - Description of Dynamic Update and T_UNSPEC Code - - - - - Added by Mike Schwartz - University of Washington Computer Science Department - 11/86 - schwartz@cs.washington.edu - - - - -I have incorporated 2 new features into BIND: - 1. Code to allow (unauthenticated) dynamic updates: surrounded by - #ifdef ALLOW_UPDATES - 2. Code to allow data of unspecified type: surrounded by - #ifdef ALLOW_T_UNSPEC - -Note that you can have one or the other or both (or neither) of these -modifications running, by appropriately modifying the makefiles. Also, -the external interface isn't changed (other than being extended), i.e., -a BIND server that allows dynamic updates and/or T_UNSPEC data can -still talk to a 'vanilla' server using the 'vanilla' operations. - -The description that follows is broken into 3 parts: a functional -description of the dynamic update facility, a functional description of -the T_UNSPEC facility, and a discussion of the implementation of -dynamic updates. The implementation description is mostly intended for -those who want to make future enhancements (especially the addition of -a good authentication mechanism). If you make enhancements, I would be -interested in hearing about them. - - - - - - 1. Dynamic Update Facility - -I added this code in conjunction with my research into naming in large -heterogeneous systems. For the purposes of this research, I ignored -security issues. In other words, no authentication/authorization -mechanism exists to control updates. Authentication will hopefully be -addressed at some future point (although probably not by me). In the -mean time, BIND Internet name servers (as opposed to "private" name -server networks operating with their own port numbers, as I use in my -research) should be compiled *without* -DALLOW_UPDATES, so that the -integrity of the Internet name database won't be compromised by this -code. - - -There are 5 different dynamic update interfaces: - UPDATEA - add a resource record - UPDATED - delete a specific resource record - UPDATEDA - delete all named resource records - UPDATEM - modify a specific resource record - UPDATEMA - modify all named resource records - -These all work through the normal resolver interface, i.e., these -interfaces are opcodes, and the data in the buffers passed to -res_mkquery must conform to what is expected for the particular -operation (see the #ifdef ALLOW_UPDATES extensions to nstest.c for -example usage). - -UPDATEM is logically equivalent to an UPDATED followed by an UPDATEA, -except that the updates occur atomically at the primary server (as -usual with Domain servers, secondaries may become temporarily -inconsistent). The difference between UPDATED and UPDATEDA is that the -latter allows you to delete all RRs associated with a name; similarly -for UPDATEM and UPDATEMA. The reason for the UPDATE{D,M}A interfaces -is two-fold: - - 1. Sometimes you want to delete/modify some data, but you know you'll - only have a single RR for that data; in such a case, it's more - convenient to delete/modify the RR by just giving the name; - otherwise, you would have to first look it up, and then - delete/modify it. - - 2. It is sometimes useful to be able to delete/modify multiple RRs - this way, since one can then perform the operation atomically. - Otherwise, one would have to delete/modify the RRs one-by-one. - -One additional point to note about UPDATEMA is that it will return a -success status if there were *zero* or more RRs associated with the given -name (and the RR add succeeds), whereas UPDATEM, UPDATED, and UPDATEDA -will return a success status if there were *one* or more RRs associated -with the given name. The reason for the difference is to handle the -(probably common) case where what you want to do is set a particular -name to contain a single RR, irrespective of whether or not it was -already set. - - - - - 2. T_UNSPEC Facility - -Type T_UNSPEC allows you to store data whose layout BIND doesn't -understand. Data of this type is not marshalled (i.e., converted -between host and network representation, as is done, for example, with -Internet addresses) by BIND, so it is up to the client to make sure -things work out ok w.r.t. heterogeneous data representations. The way -I use this type is to have the client marshal data, store it, retrieve -it, and demarshal it. This way I can store arbitrary data in BIND -without having to add new code for each specific type. - -T_UNSPEC data is dumped in an ASCII-encoded, checksummed format so -that, although it's not human-readable, it at least doesn't fill the -dump file with unprintable characters. - -Type T_UNSPEC is important for my research environment, where -potentially lots of people want to store data in the name service, and -each person's data looks different. Instead of having BIND understand -the format of each of their data types, the clients define marshaling -routines and pass buffers of marshalled data to BIND; BIND never tries -to demarshal the data...it just holds on to it, and gives it back to -the client when the client requests it, and the client must then -demarshal it. - -The Xerox Network System's name service (the Clearinghouse) works this -way. The reason 'vanilla' BIND understands the format of all the data -it holds is probably that BIND is tailored for a very specific -application, and wants to make sure the data it holds makes sense (and, -for some types, BIND needs to take additional action depending on the -data's semantics). For more general purpose name services (like the -Clearinghouse and my usage of BIND), this approach is less tractable. - -See the #ifdef ALLOW_T_UNSPEC extensions to nstest.c for example usage of -this type. - - - - - - - 3. Dynamic Update Implementation Description - -This section is divided into 3 subsections: General Discussion, -Miscellaneous Points, and Known Defects. - - - - - 3.1 General Discussion - -The basic scheme is this: When an update message arrives, a call is -made to InitDynUpdate, which first looks up the SOA record for the zone -the update affects. If this is the primary server for that zone, we do -the update and then update the zone serial number (so that secondaries -will refresh later). If this is a secondary server, we forward the -update to the primary, and if that's successful, we update our copy -afterwards. If it's neither, we refuse the update. (One might think -to try to propagate the update to an authoritative server; I figured -that updates will probably be most likely within an administrative -domain anyway; this could be changed if someone has strong feelings -about it). - -Note that this mechanism disallows updates when the primary is -down, preserving the Domain scheme's consistency requirements, -but making the primary a critical point for updates. This seemed -reasonable to me because - 1. Alternative schemes must deal with potentially complex - situations involving merging of inconsistent secondary - updates - 2. Updates are presumed to be rare relative to read accesses, - so this increased restrictiveness for updates over reads is - probably not critical - -I have placed comments through out the code, so it shouldn't be -too hard to see what I did. The majority of the processing is in -doupdate() and InitDynUpdate(). Also, I added a field to the zone -struct, to keep track of when zones get updated, so that only changed -zones get checkpointed. - - - - - - 3.2 Miscellaneous Points - -I use ns_maint to call zonedump() if the database changes, to -provide a checkpointing mechanism. I use the zone refresh times to -set up ns_maint interrupts if there are either secondaries or -primaries. Hence, if there is a secondary, this interrupt can cause -zoneref (as before), and if there is a primary, this interrupt can -cause doadump. I also checkpoint if needed before shutting down. - -You can force a server to checkpoint any changed zones by sending the -maint signal (SIGALRM) to the process. Otherwise it just checkpoints -during maint. interrupts, or when being shutdown (with SIGTERM). -Sending it the dump signal causes the database to be dumped into the -(single) dump file, but doesn't checkpoint (i.e., update the boot -files). Note that the boot files will be overwritten with checkpoint -files, so if you want to preserve the comments, you should keep copies -of the original boot files separate from the versions that are actually -used. - -I disallow T_SOA updates, for several reasons: - - T_SOA deletes at the primary wont be discovered by the secondaries - until they try to request them at maint time, which will cause - a failure - - the corresponding NS record would have to be deleted at the same - time (atomically) to avoid various problems - - T_SOA updates would have to be done in the right order, or else - the primary and secondaries will be out-of-sync for that zone. -My feeling is that changing the zone topology is a weighty enough thing -to do that it should involve changing the load file and reloading all -affected servers. - -There are alot of places where bind exits due to catastrophic failures -(mainly malloc failures). I don't try to dump the database in these -places because it's probably inconsistent anyway. It's probably better -to depend on the most recent dump. - - - - - - 3.2 Known Defects - -1. I put the following comment in nlookup (db_lookup.c): - - Note: at this point, if np->n_data is NULL, we could be in one - of two situations: Either we have come across a name for which - all the RRs have been (dynamically) deleted, or else we have - come across a name which has no RRs associated with it because - it is just a place holder (e.g., EDU). In the former case, we - would like to delete the namebuf, since it is no longer of use, - but in the latter case we need to hold on to it, so future - lookups that depend on it don't fail. The only way I can see - of doing this is to always leave the namebufs around (although - then the memory usage continues to grow whenever names are - added, and can never shrink back down completely when all their - associated RRs are deleted). - - Thus, there is a problem that the memory usage will keep growing for - the situation described. You might just choose to ignore this - problem (since I don't see any good way out), since things probably - wont grow fast anyway (how many names are created and then deleted - during a single server incarnation, after all?) - - The problem is that one can't delete old namebufs because one would - want to do it from db_update, but db_update calls nlookup to do the - actual work, and can't do it there, since we need to maintain place - holders. One could make db_update not call nlookup, so we know it's - ok to delete the namebuf (since we know the call is part of a delete - call); but then there is code with alot of overlapping functionality - in the 2 routines. - - This also causes another problem: If you create a name and then do - UPDATEDA, all it's RRs get deleted, but the name remains; then, if you - do a lookup on that name later, the name is found in the hash table, - but no RRs are found for it. It then forwards the query to itself (for - some reason), and then somehow decides there is no such domain, and then - returns (with the correct answer, but after going through extra work). - But the name remains, and each time it is looked up, we go through - these same steps. This should be fixed, but I don't have time right - now (and the right answer seems to come back anyway, so it's good - enough for now). - -2. There are 2 problems that crop up when you store data (other than - T_SOA and T_NS records) in the root: - a. Can't get primary to doaxfr RRs other than SOA and NS to - secondary. - b. Upon checkpoint (zonedump), this data sometimes comes out after other - data in the root, so that (since the SOA and NS records have null - names), they will get interpreted as being records under the - other names upon the next boot up. For example, if you have a - T_A record called ABC, the checkpoint may look like: - $ORIGIN . - ABC IN A 128.95.1.3 - 99999999 IN NS UW-BORNEO. - IN SOA UW-BORNEO. SCHWARTZ.CS.WASHINGTON.EDU. - ( 50 3600 300 3600000 3600 ) - Then when booting up the next time, the SOA and NS records get - interpreted as being called "ABC" rather than the null root - name. - -3. The secondary server caches the T_A RR for the primary, and hence when - it tries to ns_forw an update, it won't find the address of the primary - using nslookup unless that T_A RR is *also* stored in the main hashtable - (by putting it in a named.db file as well as the named.ca file). - |
