The reason I ask is that I was perusing RFC 3330 and noted that it
specifically stated that the basis for the reservation of
223.255.255.0/24 no longer applied and that the block was subject to
future allocation to a RIR. Yet there was an argument about it.
The argument was because it wasn't clear what the original basis was for
the reservation nor was it clear how things had changed.
Imagine you have a device that uses lots of addresses but considers them
to be sequential numbers rather than bit patterns. For instance, this
device could be configured with a starting number and then dole out
sequential numbers to connections based on that starting number. This is
how a lot of terminal servers work.
Imagine that you give the terminal server a number like 223.255.255.200 as
the starting number to assign to dialup connections and that terminal
server has a 32 port card installed. Then one day an engineer installs a
second 32 port card. The terminal server continues to function just fine
until one day when it tries to assign 223.255.255.255 to an incoming call
followed by assigning 224.0.0.0 to the next call. Suddenly you have all
kinds of wierdness breaking out with mysterious broadcast traffic and
multicast traffic coming from the device. But it only happens for short
bursts during the busiest times of the day. What the heck is going on!?
Could you debug that? Would you want to debug that?
Maybe that's why 223.255.255/24 should be forever reserved.
--Michael Dillon
Imagine you have a device that uses lots of addresses but considers them
to be sequential numbers rather than bit patterns. For instance, this
device could be configured with a starting number and then dole out
sequential numbers to connections based on that starting number. This is
how a lot of terminal servers work.
Have you configured any terminal/access servers recently?
Imagine that you give the terminal server a number like 223.255.255.200 as
the starting number to assign to dialup connections and that terminal
server has a 32 port card installed. Then one day an engineer installs a
second 32 port card. The terminal server continues to function just fine
until one day when it tries to assign 223.255.255.255 to an incoming call
followed by assigning 224.0.0.0 to the next call. Suddenly you have all
kinds of wierdness breaking out with mysterious broadcast traffic and
multicast traffic coming from the device. But it only happens for short
bursts during the busiest times of the day. What the heck is going on!?
I'd call that incompetence. A starting number of 200 + 64 ports = too
small an IP pool. The cisco gear I use is a bit smarter and when
configuring IP pools, both the starting address and ending address are
specified (and you can specify multiple non-contiguous ranges). I
generally omit /24 network/broadcast addresses from IP pools because too
much software assumes everything's a /24 and if you assign someone a /24
broadcast IP, they're going to receive some (maybe alot of) junk traffic
depending on what's in the other subnets of the /24 they're in.
Maybe that's why 223.255.255/24 should be forever reserved.
That's way too stupid a reason. That better not be it.