Ip addresses

[syco83]

Why cannot be all "1"s or all "0"s in the network portion of the IP address?
This is in binary numbers.
I really need to know a good explanation of why you can not

 

[n0cmonkey]

You can't have all 1's or 0's at the beginning or end of an IP address. 255 (what all 1's adds up to) is a broadcast address. A 0 (what all 0's adds up to) can also be a broadcast address (old school, probably not recognized anymore by modern IP stacks).
192.168.0.1 is fine, but 192.168.0.0 would be a network address, usually followed by a /24.

 

[syco83]

that wasn't the right answer

 

[SpunkyJones]

All 0's in the network portion would be a network with a first octet of 0, which is invalid. First valid network is 1.0.0.0, or 00000001

All 1's in the network portion would be a network starting with 255 for the first octet, which is a class E network, which is an invalid network for ip addressing. It is used for experimental purposes.

 

[Goosemaster]

Originally posted by: syco83
that wasn't the right answer

yes it was.

 

[Goosemaster]

Originally posted by: SpunkyJones
All 0's in the network portion would be a network with a first octet of 0, which is invalid. First valid network is 1.0.0.0, or 00000001

All 1's in the network portion would be a network starting with 255 for the first octet, which is a class E network, which is an invalid network for ip addressing. It is used for experimental purposes.

as is this answer.

 

[n0cmonkey]

Originally posted by: syco83
that wasn't the right answer

I'm not the one taking the class.

My answer was definitely rough, but unless I REALLY misunderstood your poorly worded homework question, I got it just about right.

 

[syco83]

spunky jones got it right

 

[n0cmonkey]

Originally posted by: syco83
spunky jones got it right

Did you get an A?

 

[n0cmonkey]

Not sure what's wrong with my statement. The 0 thing only becomes a problem really at the beginning or end of the ip address, and 255 is definitely a broadcast address...

 

[SpunkyJones]

Originally posted by: n0cmonkey

Originally posted by: syco83
spunky jones got it right

Did you get an A?

Sweet, wait till I tell me mum!

 

[gcbrowni]

Now explain how /31's work and why the lower /64 of an IPv6 address can't be all 0's.

 

[Goosemaster]

Originally posted by: gcbrowni
Now explain how /31's work and why the lower /64 of an IPv6 address can't be all 0's.

31's will give you 0 hosts.....!!??!?

 

[spidey07]

Originally posted by: Goosemaster

Originally posted by: gcbrowni
Now explain how /31's work and why the lower /64 of an IPv6 address can't be all 0's.

31's will give you 0 hosts.....!!??!?

you can use them for WAN circuits where there are only two hosts. In this case there is no need for a subnet broadcast.

-ps- hey NOC, he said "network" portion of a IPv4 address, not host.

 

[n0cmonkey]

Originally posted by: spidey07

Originally posted by: Goosemaster

Originally posted by: gcbrowni
Now explain how /31's work and why the lower /64 of an IPv6 address can't be all 0's.

31's will give you 0 hosts.....!!??!?

you can use them for WAN circuits where there are only two hosts. In this case there is no need for a subnet broadcast.

-ps- hey NOC, he said "network" portion of a IPv4 address, not host.

Yeah, I got it. Not enough sleep I guess.

 

[rfb]

Originally posted by: gcbrowni
Now explain how /31's work and why the lower /64 of an IPv6 address can't be all 0's.

An IPv6 address can be all 0's in the lower 64 bits. A subnet-router anycast address is an IPv6 address that has the interface ID set to all 0's. For all IPv6 addresses that start with a value other than b'000', the interface ID is 64 bits in length. So, for all IPv6 addresses that start with anything other than b'000', an address with the lower 64 bits set to 0's is a subnet-router anycast address.

Roy