[techtalk] Netstat weirdness

C. M. Martin caitlyn at netferrets.net
Wed Aug 16 15:31:32 EST 2000


Hi, Malcolm,
> 
> Notice the field labelled "Mask:" in the second row? This means that you
> have been assigned a group of eight IP addresses where the top 29 bits
> of the address are set (248 is 11111000 in binary). So, in other words,
> you are on a subnet and the individual IPs of the machines on that
> subnet will come from altering the last three bits of the IP address
> (I'll explain how below).

I actually do understand subnet masking :)

> I assume the company you are setting this up 
> for has purchased a block of external IP addresses and due to the
> shortage of addresses, service providers are handing them out in very
> small blocks.

Precisely.
> 
> Now, in reality, you can only use six of those addresses because you
> have the "network address" and the "broadcast address" as well. To work
> out which are the network and broadcast IPs, look at the 63.251.67.58
> address. Since we know the top three bytes of this address are fixed, it
> will at least look like 63.251.67.x. To work out the last byte, write 58
> in binary -- 00111010 -- and remember that the bottom three bits are
> "yours". The network address for a subnet is when all the bits that
> represent the machines on that subnet are zero. In other words, the
> subnet address is 111000 in binary, or 56 in decimal!

That last part is what I didn't get rigt, or understand in the routing table. 
Thank you for clarifying this for me.
 > 
> In this case, looking at the "Mask:", we see that you get to choose the
> lower 8 bits of the IP address on this subnet (and the top three bytes
> are 192.168.0 for this subnet). So the network address will be
> 192.168.0.0 and the broadcast address will be 192.168.0.255 and you can
> put 254 other machines on this network. Clear as mud?

No, actually, it's quite clear :)

> And the last line is saying to get to anything
> else (the default route), go to the specific machine 64.251.67.57 (but I
> think it was only the first two lines that were giving you grief?).

Correct.  The third address is the router, and that address is correct.
> 
> It doesn't need to be fixed. It's saying the right thing. If the network
> is not working, it's for some other reason.

Actually, it is working :)

Thanks,
Caity






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