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qbakies🇺🇸

New subnet on router

I have a Cisco 2811 router that I use as a gateway for a local /24 LAN. We are shutting down another office and moving the assets and functionality to this office so we are going to need more space than the /24. I am going to just take the second Fe interface on that router and create another /24 subnet on it. We will have all servers and printers on the first LAN (192.168.100.0/24) and the all the users and their IP phones on the second LAN (192.168.101.0/24).

I know that since they are on the same router it will automatically see and create the route between the two networks but I would like some confirmation. Will the computers on the user LAN automatically be able to hit the domain controllers on the server LAN for logging into the domain and DNS? I don't really need any kind of filtering between the two subnets right now so I wasn't going to do an access-list unless necessary.

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Ernie Beek🇳🇱

If there are no access lists in between and the machines have the right default gateway, you should be ok.

mrklaxon

As long as the 2811 is your default gateway for all devices/servers then all packets will go to it and get dumped to the correct interface.

You could also expand your subnet, may create some work re-addressing but would reduce dependency on the router when accessing resources.

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Otto_N🇿🇦

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qbakies🇺🇸

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The 2811 is set as the default gateway through DHCP. But the DHCP server is in the server subnet. So DHCP requests will not be sent from the user subnet to the server subnet automatically?

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Ernie Beek🇳🇱

Nope, a router doesn't forward broadcasts.
You could use the 'ip helper' command though.

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Ernie Beek🇳🇱

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qbakies🇺🇸

ASKER

That is exactly what I wanted to know. I know switches break up collision domains and routers breakup broadcast domains but I'm not sure of all the relevant network traffic that is broadcast. So is there anything else that is broadcast but needed?

Ernie Beek🇳🇱

Nothing comes to mind right now.......

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Otto_N🇿🇦

Just make sure that the DHCP Server have a scope for the user subnet, and that it permits BOOTP. I know this is counter-intuitive, but the relay-action is classified as part of the BOOTP protocol, and is not recognised as DHCP packets, even though the relayed packets contains DHCP information.

qbakies🇺🇸

ASKER

"Just make sure that the DHCP Server have a scope for the user subnet, and that it permits BOOTP"

Is this a setting in the DHCP scope or the server?

mrklaxon

Server is where the scope is so yes?
Read:
http://technet.microsoft.com/en-us/library/dd759168.aspx
It talks about setting up a Super Scope to handle multiple subnets.
You might want to look at a backup DHCP on the second subnet as well.

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Otto_N🇿🇦

I'ts been a while since I created a new scope on a Windows DHCP Server, but as far as I recall, you need a scope for each subnet you wish to administer. You don't really need a superscope.

When you set-up a scope (in Windows), one of the steps ask you to choose the protocol allowed for the scope: "DHCP", "BOOTP" or "Both". Choose either "BOOTP" or "Both" to allow packets redirected by the router. But as I said, it's been a while, and perhaps this isn't an issue anymore...

qbakies🇺🇸

ASKER

Thank you.

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A router is a networking device that forwards data packets between computer networks. Routers perform the "traffic directing" functions on the Internet. The most familiar type of routers are home and small office cable or DSL routers that simply pass data, such as web pages, email, IM, and videos between computers and the Internet. More sophisticated routers, such as enterprise routers, connect large business or ISP networks up to the powerful core routers that forward data at high speed along the optical fiber lines of the Internet backbone. Though routers are typically dedicated hardware devices, use of software-based routers has grown increasingly common.