WAN Technologies - Cable/DSL /32?

I'm studying WAN technologies today. Fascinating topic! How do ISPs not waste public addresses to their many customers? I've learned that a /30 is commonly used from router to router, but the subnet mask on my DSL router is 255.255.255.255. Clearly something is going on here that I don't understand! I get that they would need a way to not waste 2 addresses per customer by using a /30 with 5000 different home users, the question is how is this done?

Thanks for your wisdom

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Comments

gosh1976

I don't think it's uncommon for pppoe or dial-up connections. It indicates a single host rather than a subnet.

Of course with dial-up you aren't going from router to router you are going from modem to modem and with DSL you are going from modem to DSLAM.

I don't know the answer as to how or why that subnet mask can work on a point-to-point connection but I know it can!

ehnde

I don't think it's uncommon for pppoe or dial-up connections. It indicates a single host rather than a subnet.

I thought that 255.255.255.255 was just for broadcasts, obviously I have ALOT to learn!

Of course with dial-up you aren't going from router to router you are going from modem to modem and with DSL you are going from modem to DSLAM.

I'm grateful that I'm completely able to understand this statement. It's a good feeling! Sounds like we're talking about a distinction from IP and layer 2 technologies. Does that sound about right? What you said makes sense.

I don't know the answer as to how or why that subnet mask can work on a point-to-point connection but I know it can!

But you've provided some clarification. Thank you! You've cleared up some of the question...now I'm just fuzzy on how this /32 can be used like that

dead_p00l

ehnde wrote: »

I thought that 255.255.255.255 was just for broadcasts, obviously I have ALOT to learn!

I'm grateful that I'm completely able to understand this statement. It's a good feeling! Sounds like we're talking about a distinction from IP and layer 2 technologies. Does that sound about right? What you said makes sense.

But you've provided some clarification. Thank you! You've cleared up some of the question...now I'm just fuzzy on how this /32 can be used like that

A /32 is quite commonly used for point-to-point or link addresses between 2 routers. This is done to conserve IP space. You can use 2 ip's in a /32 for each side of a link instead of wasting 2 ip's by using 2 for each side of a link and wasting 2 for network and broadcast. Hopefully this makes sense.

ehnde

I understand what you're saying, but at the same time I'm amazed that I didn't already know this. Haven't ran across this bit of information in either CBT Nuggets CCENT videos, or Wendell Odom's book. I thought you had to use a /30 for router to router connections before this conversation.....but my home DSL connection is not router to router, so that probably doesn't apply

Maybe I should stop professing my ignorance on the interwebs!