Question about 223/8

Tue Apr 29 12:06:16 UTC 2003

On Tue, 29 Apr 2003 Michael.Dillon at radianz.com wrote:

> 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.

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