What is the difference in using a .254 vs .255 mask. I know simply that the /32 is for a single host, but have used /31 for the same application.
What would a /31 be specifically used for?
- posted
14 years ago
/31 vs /32 sm
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- posted
14 years ago
Since the /31 is only defined for a point-to-point connection type..
The most typical example would be a WAN link like a T1. Its useful to have both serial ports numbered, (ie. to do troubleshooting, conditional routing, etc, etc), but you only need two IPs for the connection.
In the good old days, we used /30's, but that wasted half the block for low and high broadcasts that weren't used ever. Using a /31 on a PtP T1 link lets you use all the IP addresses, without features you don't need (ie. unicast broadcast).
Its not so useful on Ethernet, as other devices won't necessarily take a /31 (ie. a firewall), even if you are essentially using a router port as a point to point ethernet.
So, the biggest use area still remains the WAN PtP Connections.