Subnetting
O.K.
Lets say I have an IP of xxx.xxx.074.002
and a subnet of 255.255.255.248
My Net ID is xxx.xxx.074.000 right?
Well if my studies serve me correctly, with that subnet, my Net ID should start at xxx.xxx.074.008. But I'm pulling an xxx.xxx.074.000 w/ my Default Gateway of .001 and IP at .002. What gives?
Lets say I have an IP of xxx.xxx.074.002
and a subnet of 255.255.255.248
My Net ID is xxx.xxx.074.000 right?
Well if my studies serve me correctly, with that subnet, my Net ID should start at xxx.xxx.074.008. But I'm pulling an xxx.xxx.074.000 w/ my Default Gateway of .001 and IP at .002. What gives?
Comments
Maybe I should have posted this in the CCNA forum.
The reason I'm asking is because this is contrary to what Meyers' Net+ book teaches.
Now if I assume your network is a class C network with a subnet mask of /29, your first subnet ID would be:
256-248 = 8 and you're first host ID would be 9. You can't use the 0 subnet ID. So that means you can't use host ID's 1-7. The broadcast address for your "8" subnet would be 15. This is becuase the broadcast address is the number right before the next subnet ID.
Thus, the IP address 192.168.74.9's network ID would be 192.168.74.8
Hope that helps.
2lbs.
Magnanimous as the ocean, persistent as time.
However, My default gateway is .1 and my IP is .2, even w/ my subnet at /29. My Net ID isn't .8 like it should be. However, I read that theoretically this is OK, as long as my Host ID is not .8, .16, etc. It even says this in the Meyer's book in the note on p320.
By the way, my ISP set this up, not me. I'm sure I could telnet into my router and fix it if I was real **** about it. This is just the first time I've seen the "rules" broken. Thanks again.
So your configuration would also depend on whether you're using a Class B, or class A network.
But with what I've learned, you shouldn't use subnet 0 in a class C address while you're around "Cisco".
2lbs.
Magnanimous as the ocean, persistent as time.
I'm curious where you've learned not to use the first subnet available? In this case, the block from x.x.x.0 - x.x.x.7 ? Does it really say not to do so in the Lammle book? If so, where?
If your IP address is x.x.x.2 with subnet of 255.255.255.248 then your subnet MUST be x.x.x.0 - x.x.x.7 with network address of x.x.x.0 and broadcast address of x.x.x.7 and usable range of .1 (gateway IP) to .6.
-Mike
Net ID: 192.168.074.000
Sub Mask:255.255.255.248
.248 = 11111000 (Add 5 Net ID bits)
2^5=32-2=30 subnets
Subnets:
========
00000 = n/a
00001 = .8 <
...
11111 = n/a
It is not that it won't work, but it is unneccessary to subnet.
I could get a .1 w/ a standard class C subnet.
I don't know if this helps, but to get the "block size" I just subtract the 248 from 256 which gives 8.
So, knowing the block size of eight, starting with zero - gives you the first block of .0 to .7 with .0 being the network address and .7 being the broadcast (both non-usable).
Yes, you could use the same IP without subnetting, by using a class C for example. But, that doesn't make subnetting unnecessary - since you can still divide up IPs into subnets this way and make multiple networks.
-Mike