Modem connectivity question

RadicalCookie

RadicalCookie

RadicalCookie

Associate
Joined
4 Jan 2012
Posts
114
Hey, I'm a bit of a noob when it comes to networking but I was wondering, will a problem occur when loads of devices are using one modem? In my case, we're using BT Infinty (if that helps), and we have quite a few devices connected using the modem BT provided us.

We have a family computer and my rig connected via ethernet and my sister's laptop via wifi and my ps3 connected wifi. These are usually the devices that will constantly connect to the internet for quite long periods of time.

We also have smaller devices; an iPod touch, iPad 2 and 2 samsung Galaxy Aces'. I'm not exactly sure whether to be worried about this, I've heard something about IP allocation but my understanding in networking is very little :( One thing to note is that although all the devices uses one modem, they're not all on at the same time, usually about 3 (max) will probably use the modem at once.

Also, when should I invest in a router?
 
Last edited:
You already have a router, if not - you would only have 1 device connected at a time or 1 device connected and everything else connecting through that.

Your router will be able to allocate 253 internal addresses. 254 are usable in a C class network such as 192.168.0.0/24. One address will be assigned to your router (Typically .1 or .254) 0 and 255 are not usable.

Typically the DHCP server on the router will have a pool of ~100 addresses such as 192.168.0.100 to 192.168.0.200.

You are not going to 'run out'.
 
.255 and .0 are unusable addresses leaving 1 to 254

You can have more to play with if you want by using a B class, but you will never need that many IP addresses.
 
Alright, I guess whle this thread is active, I might as well ask a few more questions (if you don't mind)

Firstly, when a router/modem (whichever device it is) assigns an ip address to a device, is. That ip permanently fixed to that device? If so, is there a way to reset that? I understand that there is a way for using the devices MAC address whilst using one IP address, but I'm assuming that is for NAT?

Last question, how would you get class B?
 
You can probably change the DHCP scope in the routers configuration pages to use a different subnet mask, you could set this to 255.255.0.0 to give you a class B, although why would you want to?

When your router assigns an IP address to a device it will use DHCP. Each time the device connects to the network it will ask the DHCP server for an IP address. Depending on how frequently the server refreshes its IP address leases it will probably assign the same address to a device each time it sees it.

If you're playing around with these things you may want to give a device a static IP address which is outside the DHCP scope.

NAT is the process whereby your router will have an internet facing IP address and all the devices connected to the device will have an internal address. The traffic from all your devices will appear to all originate from the same IP address to the outside world.
 
Devices will have a preferential address in DHCP but this is not a reservation.

A device will contact the DHCP server more frequently the closer the address expiry is and say "Hey, my lease is expiring in X amount of time, please renew it" at which point the server might issue a new address or simply leave as is and extend the lease.

To fix an IP address permanently you need to assign a reservation for that IP against the devices MAC address.
 
To do a private class B properly you are supposed to change to IP range to 172.16.0.0 with a subnet mask of 255.255.0.0 but doesn't really matter these days - 192.168.0.0 /23 is fine.

Not sure why you'd need a /23 outside of an large enterprise environment but each to their own.
 
You must log in or register to reply here.
Back
Top Bottom