Router advice needed

On Mon, 18 Jun 2007 15:40:48 +0100, "S W" wrote for the entire planet to see:

Why not just expand your local subnet, like to 192.168.8.0/21? Leave the default gateway at 192.168.10.1 and change your DHCP server to hand out new addresses, or at least revised subnet mask. Then change the static-assigned subnet masks on your old machines at your leisure. Router not required, just a decent L2 switch.

- Eric

Hi Eric,

Thanks for your input. Sorry but you've lost me on a couple of points, could you explain in laymans terms why I'd have to hand out new addresses on the dhcp server OR a revised subnet mask (You mean 255.255.0.0 instead of 255.255.255.0?) And what would I do with the decent L2 switch? Sorry again, but I'm obvioulsy no network expert!!!

Steve

Hi Eric,

I did some reading about what you said, this website was useful

Thanks, Steve

Because a broadcast domain of 2000 machines can represent a lot of traffic for processing. If you are only putting a few hundred machines, you should be fine, but if you have any goal of turning up all the addresses in that VLAN, you may be asking for trouble with lower class hardware. You just want to make sure your switch can support as many ports as you have machines/nodes, but also is prepared for the type of network you are placing it in. Generally speaking, I have run fairly full /22 networks (1022 addresses give or take), but on enterprise class hardware (Cisco 6500s). What you don't want to do is have daisy chained switches to support this many nodes, etc, as broadcast traffic will kill smaller trunks and tax your switch processors. Hopefully this makes sense.

Hi,

I will have approx 300 devices on the network for the time being. If 2000 plus addresses are available, then that should take care of future growth for a while. I am using basic unmanaged 10/100 switches with a fibre backbone. Most traffic passes through two switches (from client to server), some passes through three. It could be better, I know.

What do you mean about switches supporting as many ports as you have machines/nodes? Are the Cisco 6500s rated in that way? So I will need a switch at the server end that will support 300 machines?

Thanks, Steve

On Tue, 19 Jun 2007 08:54:17 +0100, "S W" wrote for the entire planet to see:

Almost any switch will do. Usually medium size, lost cost lans have one switch at or near the core that gets the concentrated traffic. If it had some GB/fiber links to the edge switches that will do fine. Even trunked 100s will often suffice.

I think most lans seqments have only a few percent average utilization anyway. You could measure yours and see if you have any switch capacity issues. Your traffic isn't really changing, only the potential size of your lan. Just for architectural reasons it's good to have some extra room in your IP scheme for growth/segmentation. If the lan grows substantially, then your L2 backbone will have to grow with it.

OK, we do indeed have a switch near the core that gets all the traffic. This has a gigabit uplink, and I intend to move the servers onto this switch same time as I change their subnet masks. I noticed a "blink" in communications when I changed one earlier, so its probably better if I warn the users in advance, and do them all at the same time. Thanks for your advice,

Best Regards, Steve

On Tue, 19 Jun 2007 16:53:38 +0100, "S W" wrote for the entire planet to see:

Just one last thing. The first and most important step when expanding your LAN subnet is to change the subnet mask on the router interface that has your default gateway IP defined. This means that the router knows about the larger subnet right away, and any host with an inconsistent subnet mask that incorrectly sends LAN-bound traffic to the gateway router will still have their packet delivered, just detoured in and out of the router's LAN interface. Then all the subnets on each of the hosts and DHCP servers can be changed without gyrating the whole LAN.

I'd also recommend that you keep a few /24s of your new range unallocated. Probably just start using 192.168.11.xxx and leave the other 6 /24s for the future.

Hi, yes I did do the router/default gateway first. I went live this morning, with all the DHCP devices in the 192.168.8.xxx range, leaving everything static as is on 192.168.10.xxx No real issues, apart from an application that went belly-up. The third-party suppliers took about two hours to uninstall/reinstall, I don't think I'll ever know if it was because of the subnet mask change or just a coincidence! I've now got lots of IP addresses free for the future.

Best Regards, Steve