Re: Setting up a static IP behind a router
- From: buzzbomb <buzzbombattheusualntlworld.comaddress@xxxxxxxxxxxxxxx>
- Date: Mon, 29 May 2006 16:05:38 GMT
Paul F. Johnson wrote:
Hi,
When I run neat (or system-config-network - whatever FC call it this week),
it needs me to enter a default gateway address and subnet mask. Is the
subnet mask what the router expects or what my ISP expects (255.255.248.0
for the ISP) and what is my default gateway address (the router is giving
the value 82.42.48.1)?
I've been reliably told by some Windows people that if I set my router to
accept values between 192.168.2.100 and 179 and set my machines at values
above 179 that it will be way more reliable in terms of dropping faster
than a whores knickers!
TTFN
Paul
The netmask is used by the TCP/IP to determine if another machine is on the same subnet as itself. Essentially machines on the same subnet are one that can communicate without going through a router. The way its works is that the netmask and the machine address are AND'ed bitwise togther and if the answer is the same for two addresses they should be on the same subnet - e.g.
192.168.1.100 AND 255.255.255.0 = 192.168.1.0
192.168.1.123 AND 255.255.255.0 = 192.168.1.0
192.168.8.100 AND 255.255.255.0 = 192.168.8.0
Thus the first two addresses are on the same subnet. The third is on a different subnet and therefore can only be reached through a router.
The default gateway is the address a machine will send its traffic to if it destined for a machine on another subnet and it otherwise has no idea how to reach it. The default gateway address will typically be an address on the same subnet as the machine you are configuring.
Its quite possible to have multiple routers on a subnet. In this case there would be sepcific routes defined for specific subnets and a default gateway as a catchall.
I'm not sure what the windows people are trying to say... it doesn't seem to make much sense. What they may be driving at is the use of *private* subnets. These are sets of addresses that can not legitimately appear on the public Internet. An ISPs routers will be set to drop any addresses from one of these ranges on the basis they can only come from a misconfigured network. The private ranges are
Class A 10.0.0.0 - 10.255.255.255
Class B 172.16.0.0 - 172.31.255.255
Class C 192.168.0.0 - 192.168.255.255
It is good practice to use one of these ranges for your private network That way if you misconfigure anything and your traffic leaks onto the Internet it will be quietly dropped and therefore not screw anyone else up (as might happen if you choose public IP addresses for use on your private network).
B.
.
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- From: Paul F. Johnson
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