Enclosure Bay IP Addressing (EBIPA) issue

[chuckk281]

Dave had a question about EBIPA and how to calculate subnet addresses and what is reserved for what:

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Have a customer using a subnet mask of 255.255.252.0 and filled in the first bay with address 172.16.230.249 and select autofill.  Bay 7 gets the address of 172.16.230.255 and bay 8 gets the address 172.16.231.0.  I know EBIPA is doing what its designed to do, and the customer hasn’t complained that they cannot reach the iLO in bay 8 but I thought IP address “xxx.xxx.xxx.0” was reserved for lack of a better term.  Is this a potential issue for this customer?

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Cullen and Monty chimed in:

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Cullen:  

There are two “reserved” addresses used for broadcast in a network:  host bits all 0, and host bits all 1.

The network portion of 172.16.231.0/22 (255.255.252.0) is 172.16.228.0 and the host portion is 3.0 (or binary 1100000000) which is neither all 0 nor all 1.

Monty: 

IP Subnet Calculator is your friend J

http://www.subnet-calculator.com/subnet.php?net_class=B

If you select Class B and 22 Mask Bits and plug in 172.16.230.251

The calculator indicates the Host Address Range is 172.16.228.1 – 172.16.231.254.

Both 172.16.230.255 and 172.16.231.0 are allowed host IP addresses.

Only two IP addresses are reserved in all subnets – the first .0 and the last .255.  The ones in between for subnets larger than 255 are allowed.

Cullen:

Real men figure out subnet masks in their head.

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Good discussion and good info with the calculator. Any other good tools you use?