North American Network Operators Group

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RE: 240/4

  • From: michael.dillon
  • Date: Thu Oct 18 18:25:53 2007

> I think Michael's point is that it can be allocated as 
> "unique space for internal use".  i.e. kind of like 1918 
> space, but you know your slice of
> 240/4 is only used on your network[1].  For that purpose, 
> it's fine, as long as you determine that all your gear allows it.

Not quite. I don't want to see 240/4 space considered to be like RFC
1918 space in any way shape or form. I just want it available for use
between consenting partners which is why I suggest that the RIRs only
give it to people who ask for it. 

Eventually I expect that some ISPs will support this due to customer
demand and because it isn't that hard to install the patches required in
routers. Anyone who doesn't want to support it need not do anything
because the packets will fall on the floor as soon as they hit a router
that doesn't support 240/4 addresses. 

Depending on how the IPv6 transition pans out, there might be a day when
240/4 addressing is widely supported on the Internet. Or there might
not. I would just like to see the "reserved" status removed for 240/4
because it is no longer appropriate or necessary.

> If anyone really thinks it can be announced into the global 
> routing table and expected to function, I'm afraid they've 
> swallowed the crack pipe so far down that this thread is 
> pointless for them.  Too many devices will never (can 
> never[2]) be upgraded and are unlikely to go away in the 
> forseeable future.

Agreed. Routing between consenting networks is not the same as universal
routing (if that even exists anymore). Unfortunately, many people do not
understand that Internet connectivity is not an all-or-nothing
proposition. There are many extranets that function using only a small
group of certified ISPs, for instance. 

> I could see bits of 240/4 perhaps being of use to large cable 
> companies for whom there just isn't enough 1918 space to 
> address all their CPE gear...and/or they really want unique 
> addressing so that if/when networks merge IP conflicts are avoided.

I think that RFC 1918 exhaustion is a separate issue and can only be
solved by setting aside another /8 for RFC 1918 space. Either take 125/8
or else see if Softbank Japan is willing to allow 126/8 to be set aside
for that purpose.

> 1) As much as this can ever be can't stop random 
> IP squatters from picking random IP space out of their hats 
> for use as "private" 
> networks behind NAT.  Eventually, they realize some bit of 
> the internet is unreachable...because it's their LAN. 

Not necessarily. In many cases they only want to reach a subnet of the
Internet so they never see the unreachability problem. Or they don't
route packets into or out of the public Internet and use split-horizon

> 2) Anyone care to guess how much network gear is deployed 
> that either won't or can't be upgraded?  i.e. Old cisco gear 
> without the RAM and/or flash to handle a newer code 
> train...the old one in use long since unsupported, or gear 
> from vendors that no longer exist?  As long as this stuff 
> generally works, nobody's likely to replace it.

That's why we will see IPv4 in widespread use for at least the next 20

--Michael Dillon