How are you doing DHCPv6 ?

Jimmy Hess mysidia at gmail.com
Sat Jan 21 16:52:39 CST 2012


On Sat, Jan 21, 2012 at 1:05 PM, Randy Carpenter <rcarpen at network1.net>wrote:

> Several people have mentioned clustering software. Does any one have any
> examples of such a thing that supports v4 and v6?
>
> Linux-HA, RSF-1, Oracle Solaris Cluster,  Veritas cluster, are a few
examples of clustering software.

ocf_heartbeat_anything + ocf_heartbeat_IPv6addr
http://linux-ha.org/doc/man-pages/man-pages.html

Obviously, building a DHCPD failover cluster involves some scripting and
significant design considerations,  but as far as clusters go, DNS and
DHCPD failover clusters are very simple.


And don't require special application support to achieve redundancy,
unlike, say Firewalls, SQL, FTP, SMTP or HTTPD clusters,  where a
requirement may exist not to drop a single TCP connection,  or fail a
single query, in case of server failure.

DHCPD doesn't even use TCP connections;  and some amount of automatic retry
by the client is a  feature of the protocol.


Database servers, HTTP,  Firewalls, etc, are  "stateful services",  because
there is an "in-flight" status  which is not recorded in a database,  and
must be preserved by the application itself for graceful failover.

If the  Firewall connection table is not synchronized online,  the failover
between clustered firewalls would cause a disruption in the form of lost
TCP connections, and online users will experience an immediate temporary
issue at the moment of failover.

The same for HTTP...  a TCP connection dropping is a  "permanent" error.
The in-flight transactions would result in the user seeing an error page.

Those are the types of applications that actually require special support
or coordination from the application itself.

Graceful DHCPD failover  to deal with server issues  can be achieved by
using one of the open source or commercial clustering packages, plus a
little bit of scripting.

--
-JH


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