Using /31 for router links

Michael Sokolov msokolov at ivan.Harhan.ORG
Sat Jan 23 20:20:03 UTC 2010

Stephen Sprunk <stephen at> wrote:

> Ah, but who's to say that all PTP links are WANs?  Are you really going
> to run an OC-48 from one router to another _in the same building_ when
> you need 1Gb/s between them?

Can't say - I have never needed that much bandwidth. :)  I still live in
an alternate Universe where 10 Mbps coaxial Ethernet for LANs is near-
infinity and 2 Mbps or so makes for a *very* sweet WAN.  The facility
housing the mail server from which I am sending this message is
connected to the outside Inet via a 384 kbps SDSL pipe which I am using
basically as ARPANET replacement - I miss the ARPANET.

If I wanted a PTP link between two routers in the same building that
runs at the same speed as my Ethernet (10 Mbps), I would use EIA-422
(which is rated up to 10 Mbps) and run something HDLC-based over it.

> Even for MANs or WANs, the price of a pipe (plus equipment at each end)
> will still often be significantly lower for Ethernet than for "real"
> circuits

Wait a moment here.  With a MAN/WAN involving wires/fiber running over
public property, what one is paying for is the right to use those wires
for your data, right?  The wires themselves do NOT run Ethernet at the
electrical level, so if you have some "MAN/WAN Ethernet" service, there
is a black box of some kind that converts the native electrical signal
format to Ethernet.  Why not take that black box out of service, use it
for baseball practice (Office Space style), and use the exact same
wires/fiber (rented at exactly the same monthly recurring price) in its
native non-Ethernet form?

IOW, if you are renting dry copper / dark fiber, you have a choice to
use it either through a stinky "black box" Ethernet converter or in the
native non-Ethernet form directly, but the monthly recurring cost
remains exactly the same.

> Well, it'd certainly be nice if someone would make something even
> cheaper than Ethernet for that purpose (which would squeeze out a few
> more bits of payload), but so far nobody has.  It's hard to beat
> Ethernet on volume, and that's the main determinant of cost/price...

But that's non-recurring equipment cost only, and at least in my case
the little investment in V.35 etc hardware is a much lower cost than the
price of pain and suffering with Ethernet for a purist like me.


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