Re: [gentoo-user] Linksys router BEFSR41 loosing internet

[Stroller]

On 19/12/2010, at 8:35pm, Dale wrote:
> ...
> Ohhhh.  Light bulb moment here, I think.  The modem has a network, even tho it only has one device connected to it.  The router has its own network but can have 4 devices connected to it.  So, if the modem has 192.168.1.1 >255 then the router needs 192.168.2.1 >255 which is two separate networks.
>
> So, if that is true, set the modem to 192.168.1.1 for its IP.  Then set the router to to 192.168.2.1 for it's network.  That would give my puter a IP and the second puter another IP and they can talk to each other since they are on the same network.  Is my light bulb OK so far?

Sounds like you're getting it.

A computer (this includes routers) cannot have two interfaces on the same subnet. They can have multiple network interfaces, as long as they're all on different subnets. A router is a computer with multiple network interfaces, acting to gateway data  between those subnets. 

Whether the machines are on the same subnet is determined by the "subnet mask". If the subnet mask is 255.255.0.0 then only the first two bytes of the IP address need to be the same for the computers to be on the same subnet. I.E. 192.168.1.1 and 192.168.2.3 would be on the same subnet if they had the mask of 255.255.0.0.

But a subnet mask of 255.255.255.0 means that the first 3 bytes need to be the same for them to be on the same subnet - so 192.168.1.1 would be on the same subnet as 192.168.1.2, but not on the same subnet as 192.168.2.3, 192.168.2.4, 192.168.3.3, or 192.168.44.8.

IP addresses and subnet masks can be written more succinctly using the "/" notation. "/16" means "255.255.0.0", "/24" means "255.255.255.0". So 192.168.2.3/16 means "IP address 192.168.2.3, subnet mask 255.255.0.0" whereas 192.168.2.3/24 means "IP address 192.168.2.3, subnet mask 255.255.255.0". Ranges are sometimes written 192.168.1.100-200, but don't do that when you're talking about a whole subnet (1-255) because it just looks odd. Use the slash notation instead, or just say "192.168.1.x and 192.168.2.y". So this email is to say that I don't know what you're doing writing with a ">". :P

On these networks the final .255 address (eg. 192.168.1.255) is reserved for broadcast use, and you cannot allocate it to your PCs. Addresses ending in a .1 (e.g. 192.168.0.1) tend generally to be used for the subnet's gateway (the router).

When a computer wants to send a packet to a computer on a different subnet it send it to the router instead (set in its configuration as the "gateway" to the network, typically the default gateway) with the instructions "hi, please forward this to ...".

Stroller.