another nsupdate question

[Barry Margolin]

In article <9ht8qq$m6q at pub3.rc.vix.com>,
Charles Bodley <Bodley at tflogic.com> wrote:
>     The examples below show how nsupdate could be used to insert and delete
>     resource records from the example.com zone.  Notice that the input in
>     each example contains a trailing blank line so that a group of commands
>     are sent as one dynamic update request to the master name server for
>     example.com.
>
>           # nsupdate
>           > update delete oldhost.example.com A
>           > update add newhost.example.com 86400 A 172.16.1.1
>           >
>Is there anyway to just update not remove then re-add? According to the man

No, there's no way to do a direct update.  If you read RFC 2136, which
defines the dynamic update protocol, the only operations are:

      (1) Add RRs to an RRset.
      (2) Delete an RRset.
      (3) Delete all RRsets from a name.
      (4) Delete an RR from an RRset.

>page it's sent as one request does this mean that if it fails nothing
>happens or can it fail in such away that there in no record left?

The RFC never comes out and says that the server must implement "all or
nothing" semantics, although it mentions that all the operations in a
request must be implemented atomically with respect to other requests.  But
it's strongly implied by the detailed explanation of how you can use the
prerequisite feature to implement idempotency and safe read-modify-write
cycles.  It also says:

   3.4.2.1. If any system failure (such as an out of memory condition,
   or a hardware error in persistent storage) occurs during the
   processing of this section, signal SERVFAIL to the requestor and undo
   all updates applied to the zone during this transaction.

-- 
Barry Margolin, barmar at genuity.net
Genuity, Burlington, MA
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