[master]

+- Add support for a simple check that the server id in a request message
+  to a failover peer matches the server id of the server.  This support
+  is enabled by editing the file includes/site.h and uncommenting the
+  definition for SERVER_ID_CHECK.  The option has several restrictions
+  and issues - please read the comment in the site.h file before
+  enabling it.
+  [ISC-Bugs #31463]

1 files changed, 27 insertions, 0 deletions

diff --git a/includes/site.h b/includes/site.h
index f424129d..76be056c 100644
--- a/includes/site.h
+++ b/includes/site.h
@@ -248,3 +248,30 @@
    computed for a NAK may not match that computed for an ACK. */
 
 #define SERVER_ID_FOR_NAK
+
+/* When processing a request do a simple check to compare the
+   server id the client sent with the one the server would send.
+   In order to minimize the complexity of the code the server
+   only checks for a server id option in the global and subnet
+   scopes.  Complicated configurations may result in differnet
+   server ids for this check and when the server id for a reply
+   packet is determined, which would prohibit the server from
+   responding.
+
+   The primary use for this option is when a client broadcasts
+   a request but requires the response to come from one of the
+   failover peers.  An example of this would be when a client
+   reboots while its lease is still active - in this case both
+   servers will normally respond.  Most of the time the client
+   won't check the server id and can use either of the responses.
+   However if the client does check the server id it may reject
+   the response if it came from the wrong peer.  If the timing
+   is such that the "wrong" peer responds first most of the time
+   the client may not get an address for some time.
+
+   Currently this option is only available when failover is in
+   use.
+
+   Care should be taken before enabling this option. */
+
+/* #define SERVER_ID_CHECK */