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Point to point and DHCP

Posted on 2006-10-31
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Last Modified: 2010-04-10
I recently made connection between two sites. We set up a point to point with cisco routers naturally. Our main server is 10.0.0.x and our new site is at 10.0.1.x. Our remote site we can connect to everything using a static IP address but we can not use DHCP to obtain an IP from the other site. What do I need to add to the server in order for it to hand out IPs to the other adress?
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Question by:selhs
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marine7275 earned 500 total points
ID: 17844779
You should only need to setup another dhcp scope. I prefer to do dhcp locally though.
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by:Freya28
ID: 17845314
as long as the 2 sites can communicate with each other then there shouldnt be a problem as long as your dhcp server has a new scope for the 10.0.1.x network and make sure that the router option ont he dhcp server has the address of the remote sites router (or default-gateway for the workstations)
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by:Steve Knight
ID: 17845458
Agreed.  On your main site dhcp server you should have two scopes. one for each site . make sure the subnet mask is 255.255.255.0 if you use the ranges you had.  Then on the cisco router at the remote site you need to configure an iphelper (other kit calls this dhcp relay or dhcp helper) to forward the dhcp broadcast requests to the IP of your dhcp server at the other site.

I presume you can ping the dhcp server from the other site.  If not we might have to some route changes, especially if there are multiple routers at main office for internet aswell as your other sitr for instance.
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by:knightrider2k2
ID: 17845490
If the cisco router supports BOOTP forwarding then you do not need to configure dhcp relay agent. Just enable bootp forwarding and configure the dhcp server with another scope.
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by:Freya28
ID: 17846216
yes ip-helper on the interface that connects the remote router to the host,
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by:Steve Knight
ID: 17846298
Personally I'd also put a local dhcp server in, even if it is just the router doing it.  Is there any resources at the remote site they will come to rely on such as network printing, local server etc.  If so give them a local dhcp and split the scope across that server and yours.  While you are at it do the same in reverse and set an iphelper on your router to point at their server.  Now you have redundant offsite  dhcp for two sites...  This works because the local server will always answer a dhcp broadcast first and the other answer will be ignored.  If the local server fails the other will be there ready.
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by:selhs
ID: 17849388
It's been years since i've even used any cisco. Can you refresh my memory if i'm doing this correctly when i get into the routre. I want to view the DHCP service in the router. Then plug in my DNS server at the main site, plus in the WINS server, then specify that router to be the default router for DHCP? This will obtain an IP from the server at our main site if i'm do this correctly?

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by:Steve Knight
ID: 17849424
As far as I know it is a single line of config called iphelper that you define the ip address of your main dhcp server.  You shouldn;t have to specify anything else unless you want the router to act as a dhcp server itself.

Steve
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by:Steve Knight
ID: 17849430
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by:selhs
ID: 17850335
Ok, I have the provider setting up the router. Since technically they own it, they won't allow anyone but them to program it. I did check their running config of the router and there was no IP helper-address so i'm assuming that is causing the problem with obtaining an IP address from our site. On our end we created a Superscope broken down into a tree one being 10.0.1.x the other being 10.0.0.x. I have setup the point to point router IPs in the router options of of DHCP, and I also put it in under Server Options. That is all we've done to the server, is there anything else i could possibly be missing on our end?
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by:Steve Knight
ID: 17850873
Don't use a superscope, just two individual scopes IMHO.  For options you need the default gateway and DNS servers and domain  name normally -- 003,006,015 I think from memory :-)

It won;t work unless you can get the router down there to do the iphelper unless you can run a dhcp relay agent on a MS server for instance.  In which case you might aswell run up a seperate DHCP server really.

Just ask the ISP to amend it to include iphelper I would say BTW.
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by:selhs
ID: 17851176
I'm curious as to why not to use the Superscope? I just want to know for future referrence. I have the ISP adding the iphelper, but they seem to be taking their merry old time.
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by:Freya28
ID: 17852384
here is the definition of superscopes.  they are definitely not needed in your situation

What is Superscope?

A superscope is a collection of individual scopes that can be
managed as a single administrative unit. That's what the book
says, so it must make sense, right? Well if that doesn't make
much sense to you, join the club. Let's see if we can shed some
light on what superscopes are and what they can be used for.

A superscope is actually a collection of individual scopes. When
you group different scopes together into a single superscope, you
can do the following:




Place DHCP clients from multiple network IDs on the same
physical segment

Allow remote DCHP clients from multiple network IDs to
obtain an address from a DHCP Server

Place multiple DHCP Servers on the same physical segment,
with each DCHP Server being responsible for a different
scope.



The superscope will allow the DHCP Server to answer requests from
DHCP clients from different network IDs. Now, you might ask,
can't you just create multiple scopes on a DHCP Server and then
everything will be cool? Let's see what happens.
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by:Steve Knight
ID: 17853519
Thanks Freya28, was away for a while there but thats pretty well what I was thinking :-)

In 99.999% of cases you just create a single scope per subnet... In a 100,000 user network I am currently dealing with there are maybe 4 superscopes and 6000+ normal ones... and you have two subnets = two scopes.

For a small installation with server only at one place you can set the server options for dns server and domain name and set a scope option for each scope for the default gateway.  If you want to balance dns server usage to a local server then you put that as a scope option too and point the clients at their local server first then the remote one.


Steve
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