Date: Sun, 24 Sep 2000 22:18:41 -0700 (PDT) From: Tom Samplonius <tom@sdf.com> To: sthaug@nethelp.no Cc: abcjr@southwind.net, freebsd-isp@FreeBSD.ORG Subject: RE: Using 'private net' IPs for WAN Addresses Message-ID: <Pine.BSF.4.05.10009242208260.3189-100000@misery.sdf.com> In-Reply-To: <98411.969859778@verdi.nethelp.no>
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On Mon, 25 Sep 2000 sthaug@nethelp.no wrote: > > > Here is a great description on why one should not use RFC 1918 addresses > > > for inter-router links: > > > > > > http://www.worldgate.com/~marcs/mtu/ > > > > Wow... MTU path detection. Most routers use the same MTU on all > > interfaces, so it isn't a factor. > > Sorry, that's wrong. There are plenty of routers with 1500 byte Ethernet > MTUs, and considerably higher MTUs on serial/ATM/SDH interfaces. Then it is factor. Many networks have hundreds routers and not one with anything other than 1500. Besides an interior network lines link with >1500 MTU isn't going to lead to fragmentation if everything else is 1500. Serial, ATM, SDH, etc. aren't really an issue, because so few devices that originate traffic (ie. servers) live on them. However, gig ethernet is a major problem. > > Next, if you assign a /30 for every p2p interface, you can only achieve > > 50% utilization of the address space (2 used out of 4). That isn't enough > > to meet the threshold to get more address space. I know a a network > > provider that is numbering hundreds of p2p links just to free up address > > space because they don't meet the density requirements. > > So you have only 50% utilization of the address space for your p-p links. > Unless you are very different from other providers, this is going to be a > very small fraction of your total address space. It amounts to several /24s for a mid-size network. ARIN only allocates small blocks at a time now. That 50% drags the entire average down. You need at least at 80% density these days. If you are network provider, your IPs are either used on routers or for customer allocations. Trying to get customers to use their IPs properly is like herding cats. > Not using RFC 1918 addresses for p-p links on the Internet is still good > advice. Just not practical in todays IPv4 space starved Internet. > Steinar Haug, Nethelp consulting, sthaug@nethelp.no Tom To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-isp" in the body of the message
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