DHCP on router or server

[Pabs]

Hi, typically the SBS server would be handing out DHCP addresses.
However I'm wondering if the router should be the one handing out DHCP
addresses. For example, a colleague of mine had their SBS 2003 server
go down due to a hardware issue. Now no one in the office can access
the Internet. If the router was the DHCP server, I believe they'd
have Internet access right now from their workstations. Any thoughts
or experiences on this? Thanks.

[Larry Struckmeyer[SBS-MVP]]

Regardless of single or dual nic SBS setups, leave the SBS as the DHCP server.
If the SBS is off line for more that a short while, you can initiate the
DHCP on any capable device until you restore the SBS.

SBS DHCP passes out more than the gateway and the IP for the LAN.
-
Larry
Please post the resolution to your
issue so others may benefit
-
Get Your SBS Health Check at
www.sbsbpa.com

[Joe]

No, they wouldn't. Your workstations *must* be using *only* the SBS
server for DNS, so if the SBS is down, so is the Internet. DHCP is
irrelevant, as IP addresses don't disappear the moment the DHCP server
goes down. Have a look at the lease expiry times in the Server
Management console.

There is no cheap, practical way of arranging failover. The absolute
minimum requirement is a second server also holding the SBS Active
Directory database and providing a secondary DNS service. No DNS server
which does not link to the AD information is suitable to provide DNS to
workstations.

The short answer is to do your very best to avoid the SBS going down. If
the business will suffer badly from a short loss of access to the
Internet, then they need to spend a significant amount of money ensuring
that it will not happen, starting with a second, completely independent
wide-bandwidth Internet connection and a good quality dual-WAN router.
In the real world, the most vulnerable part of the Internet connection
is the router, followed by the ISP. The server comes well down the list.

--
Joe

[Cliff Galiher]

Pabs:

Even if you move DHCP to the router, you'll discover that you have a problem
with DNS lookups. Since DNS is an integral part of Active Directory, your
clients should only be using internal DNS servers that have the various AD
SRV records. So in a single-server environment, when SBS goes down, so does
DNS, and if the clients are configured properly, so does their ability to do
name resolution...even if DHCP was moved. Adding non-AD DNS servers
introduces other problems where clients can't find AD services.

First, I need to say that in a well designed system, SBS shouldn't be going
down often enough for this to even be an issue. With dual-power supplies,
RAID SAS systems, etc, you can schedule maintenance during non-business
hours, and almost every other "common" hardware failure has redundancies. So
if you are having problems with this regularly, my *first* recommendation is
to look at *why* SBS is down in the first place. It may be time to adjust
some hardware purchasing practices or maintenance (patch management, etc)
practices.

With that said, sometimes things really do happen. A mainboard fails and
isn't redundant, and a business wants to plan for that. There are two
common solutions to this.

1) Install a second windows server (SBS premium is good for this) and make
it a DC. It'll offer redundant DNS and login at this point and the SBS
cal's already cover it. You can even configure it to offer DHCP as well if
you want, doing split-zone DHCP configuration is trivial. Although in most
configurations I'd consider it unnecessary.

2) For companies that don't have the budget for a windows server, I have in
rare instances set up a linux machine running BIND and configured it as a
slave of the SBS server. SBS supports standard zone notificatoins so the AD
stuff is kept intact on the BIND slave. In general though, for small
businesses where SBS is found, they don't have a person with the skillset to
maintain such a box on their own. So cost of out-sourced maintenance
(usually me) quickly outpaces the cost of just installing a second windows
server...so as I said before...RARE instances...but it is always an option.

-Cliff

"Pabs" <pb...@yahoo.com> wrote in message
news:40d748cc-9680-41b2...@j19g2000yqk.googlegroups.com...

[James Hurrell]

The other replies all make very valid points and you should definitely
use the SBS DHCP server. However, as you suggest, when SBS is down, no
body can access the internet at all due to the fact that when using the
SBS DHCP server, it will hand out itself as the DNS server (as it
rightly should). Thus, no DNS server, no internet. This is my real-world
experience when I had a main board fail on me.

In that situation, I temporarily enabled our edge router's DHCP server
configured to hand out the OpenDNS DNS server IP addresses and internet
was back on (after a workstation reboot to get new IP address and
lease). I also temporarily set up a NAS drive to hold the various shared
data (from the SBS backup) so that at least some work could be done
while the server was repaired.

[Leythos]

In article <40d748cc-9680-41b2-a552-ee9f91c09c06
@j19g2000yqk.googlegroups.com>, pb...@yahoo.com says...

If the router does the DHCP you will have tons of problems unless the
router points to the server for DNS, and if it does you're still in the
same boat.

--
You can't trust your best friends, your five senses, only the little
voice inside you that most civilians don't even hear -- Listen to that.
Trust yourself.
spam9...@rrohio.com (remove 999 for proper email address)

[Ab]

SBS should run DHCP as the norm. You can get redundancy if you enable
DHCP on the router only when the server is down so clients will be able
to get to the Internet - it would be a manual switch over and back when
the server is back on.

The alternate is to include your external DNS as a secondary DNS setting
the the DHCP settings. Most wet themselves when this is mentioned and
*assume* the Windows clients will have terrible issues as the 2nd DNS
will be used on occasion and cause client errors etc etc - except it
doesn't ever happen due to the redundancy of DNS lookups.

Another alternate is to install DNS on a second server in the domain.

[Joe]

Ab wrote:
>
> The alternate is to include your external DNS as a secondary DNS setting
> the the DHCP settings. Most wet themselves when this is mentioned and
> *assume* the Windows clients will have terrible issues as the 2nd DNS
> will be used on occasion and cause client errors etc etc - except it
> doesn't ever happen due to the redundancy of DNS lookups.
>

Yes, it does, I've seen it happen. And we get quite a few people with
problems here with secondary DNS servers on the clients, who don't come
back and say that doing it right didn't fix the trouble.

--
Joe

[Cliff Galiher]

Actually I wouldn't say most "wet themselves" but we also don't "assume"
anything. There are plenty of real instances of problems that many have
seen, and have even been posted here, that have been caused by having non-AD
DNS servers on a windows client. You also state "it never happens due to
the redundancy of DNS lookups" which is also false. Redundancy, in this
case, implies that if the DNS client doesn't find an answer on one server,
it'll ask another. There is a difference between getting an answer of
"record not found" and not getting an answer at all (a DNS server being
down, timeout exceeded, etc.) If a server replies that a record does not
exist, the DNS client will *not* query other servers. Also keep in mind
that the windows DNS client uses a fairly complex algorithm to decide
whether to talk to a preferred or alternate DNS server. This means that if
there is only one DNS server listed then the windows client will wait the
full time-out period. If, however, there are multiple servers listed, the
DNS client can, in some instances, decide that it would get a faster
response from an alternate DNS server based on previous response times from
the preferred DNS server.

In the real world, this means that if your internal DNS server is
temporarily under load and doesn't reply quickly enough (not completely
uncommon in an SBS environment where SBS is running DNS, AD, Exchange, and
Sharepoint) then the windows client will fire off a request to an alternate
DNS server. If the request is for an AD resource then the secondary server
will reply with a record not found and the client will believe the DNS
server is accurate (as it should, otherwise why list it as a DNS server) and
proceed as if the resource is unavailable. This is obviously inaccurate and
will cause client issues.

-Cliff

"Ab" <A...@abnet2.com> wrote in message
news:#XktMejf...@TK2MSFTNGP05.phx.gbl...