Redundancy in DHCP & DNS
SLaw
Some questions about server redundancy in DHCP-DNS.
DHCP: Am I right in thinking that you can't have two Netware DHCP servers
up simultaneously servicing the same subnets, but you can have a second DHCP
server is reserve which can be activated by loading DHCPSRVR when the first
(primary) one goes down.
DNS: However you can have two servers simultaneously running DNS and
servicing the same zone/domain - right?
Do both servers provide exactly the same functionality? I am thinking of
having two servers permanently running DNS, the second server running DNS
but not DHCP (unless the DHCP server goes down). In normal operation will
the second DNS server (not running DHCP) be aware of Dynamic DNS entries
created by the other server (running DHCP)?
Hope these questions aren't too vague,
Steve Law
Joerg Schiffer
>Hi,
>
>Some questions about server redundancy in DHCP-DNS.
>
>DHCP: Am I right in thinking that you can't have two Netware DHCP servers
>up simultaneously servicing the same subnets, but you can have a second DHCP
>server is reserve which can be activated by loading DHCPSRVR when the first
>(primary) one goes down.
You can have a second server not running the dhcpsrvr.nlm. If the
first server fails, just change the server assignments in the subnet
objects and load the dhcpsrvr.nlm on the second server.
If you want two servers running simultaneously, do the following.
Create two SAR´2 per subnet. Define them as "Dynamic DHCP" not
"Dynamic BOOTP and DHCP". Then you can assign different servers to
each SAR.
Joerg
SLaw
Are you saying that I can create two identical SAR's within each subnet
object - i.e. both SAR's covering the same range - and assign each one to a
different DHCP server?
Will they be aware of the address assignments granted by the other?
Thanks,
Steve Law
"Joerg Schiffer" <Joerg.S...@FernUni-Hagen.de> wrote in message
news:m80f10plo2aa03hb4...@4ax.com...
Brad Doster
> However you can have two servers simultaneously running DNS and
> servicing the same zone/domain - right?
>
they should both be Authoritative for each zone they service.
> Do both servers provide exactly the same functionality?
>
Yes, but which is used actually depends on the workstation configs -- the
1st one listed at each workstation will ALWAYS be used, unless it is down,
in which case the workstations will fall to the 2nd server listed, etc.
> In normal operation will
> the second DNS server (not running DHCP) be aware of Dynamic DNS entries
> created by the other server (running DHCP)?
>
Only one DNS server can be assigned as the one to receive DDNS updates
(Designated Primary) at a time. So as long as both servers are up, yes
the 2nd will be aware, but only in as much as the 1st (assuming it's the
DP) has updated NDS with the DDNS info. If the DP goes down, the 2nd
server will have no knowledge of DHCP changes -- they will be queued until
the DP is back online, at which time they will be implemented.
bd
NSC Volunteer SysOp
www.InsightNetSolutions.net
Brad Doster
> Are you saying that I can create two identical SAR's within each subnet
> object - i.e. both SAR's covering the same range - and assign each one to a
> different DHCP server?
>
assigned to a different DHCP server. Each server will have NO KNOWLEDGE of
what the other has handed out. The benefit here is that, if you have plenty
of addresses, and one server goes down, you still have DHCP functionality
without requiring human intervention. Of course the "real" answer to this
kind of redundancy is to use clustering.
SLaw
> > the second DNS server (not running DHCP) be aware of Dynamic DNS entries
> > created by the other server (running DHCP)?
Brad wrote:
> Only one DNS server can be assigned as the one to receive DDNS updates
> (Designated Primary) at a time. So as long as both servers are up, yes
> the 2nd will be aware, but only in as much as the 1st (assuming it's the
> DP) has updated NDS with the DDNS info. If the DP goes down, the 2nd
> server will have no knowledge of DHCP changes -- they will be queued until
> the DP is back online, at which time they will be implemented.
Right, thanks Brad. I'm looking at a setup where we have two servers, the
first running DHCP and DNS, the second running DNS and ready to run DHCP if
the first goes down for any reason.
I interpet what you've said to mean that if the first server's DHCP is up
but DNS is down, then the second server's DNS will not be aware of any
Dynamic DNS entries created by workstations being assigned IP addresses by
the first servers DHCP. This would be because the first server is the
designated primary and so only it's own DNS service can register DDNS
entries. Is that correct?
What about in the case where the first server's DHCP is down too, and both
DHCP and DNS are loaded on the second server. Does this change anything?
Will the DDNS entries created by workstations getting IP addresses from the
second servers DHCP still not be read by the second servers DNS? And again
will the reason be because there can only be one designated primary DNS
server?
In the case where the first server was going to be down for several days, is
there a relatively quick and easy way to set the second server temporarily
as designated primary?
Thanks for you help! This really is invaluable info.
Steve Law
Joerg Schiffer
thought it is a zone you define. So the dns-entry might be created
directly in the NDS and both DNS-servers can read the info!
Joerg
Brad Doster
> This would be because the first server is the
> designated primary and so only it's own DNS service can register DDNS
> entries. Is that correct?
>
> What about in the case where the first server's DHCP is down too, and both
> DHCP and DNS are loaded on the second server.
>
If ANY Novell DHCP server creates a new IP address in a subnet assigned to a
zone for DDNS updates, it will try to communicate the update to the Designated
Primary server for the zone. If the DP is up, DDNS gets updated. If not, the
update is queued until the DP is online and accepting updates again. The key
here is that DHCP Subnets are assigned to zones to be updated, so it doesn't
matter which DHCP server is servicing the Subnet. OTOH, there can only be one
DP for each zone, so that's why the DNS server up time is more restricting for
DDNS.
> In the case where the first server was going to be down for several days, is
> there a relatively quick and easy way to set the second server temporarily
> as designated primary?
>
Sure, just change the setting for the zone, then restart NAMED on the
remaining DNS server.
Brad Doster
Designated Primary server. In older DNSDHCP MC's this was called "DNS
Server for Dynamic Updates" or something equally obvious. The point
being that only one DNS server per zone can be configured to accept
DDNS updates. And failure to set this on the DNS side of things is a
frequent cause of new DDNS configs not working.
So, yes, you set the DHCP Subnet to update a zone, but at the same
time, if a the zone has no DP assigned, the updates won't work.
Joerg Schiffer
Joerg
Brad Doster
SLaw
"Brad Doster" <b...@NSCSysOps.net> wrote in message
news:VA.000024f...@nscsysops.net...