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author | peter <peter@FreeBSD.org> | 1998-05-02 11:04:44 +0000 |
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committer | peter <peter@FreeBSD.org> | 1998-05-02 11:04:44 +0000 |
commit | 58ca52f41726d17758909ddafba7b6b6766c789c (patch) | |
tree | bf60fe39ce5fbbf445ea2ef5462024ee99d3613b /contrib/bind/doc/misc | |
parent | 47492cc08d0e2630b8140cc5b25e635606858ad8 (diff) | |
download | FreeBSD-src-58ca52f41726d17758909ddafba7b6b6766c789c.zip FreeBSD-src-58ca52f41726d17758909ddafba7b6b6766c789c.tar.gz |
Import ISC bind v4.9.7-T1B as a reference. We may need this if we update
-stable to 4.9.7 instead of 8.1.2 for whatever reason.
Diffstat (limited to 'contrib/bind/doc/misc')
-rw-r--r-- | contrib/bind/doc/misc/DynamicUpdate | 286 |
1 files changed, 286 insertions, 0 deletions
diff --git a/contrib/bind/doc/misc/DynamicUpdate b/contrib/bind/doc/misc/DynamicUpdate new file mode 100644 index 0000000..4cd43a1 --- /dev/null +++ b/contrib/bind/doc/misc/DynamicUpdate @@ -0,0 +1,286 @@ +[ Deprecated, unsupported, nonfunctional, but not yet completely excised. ] + + + + 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). + |