Using /31 for router links

Stephen Sprunk stephen at
Sat Jan 23 19:52:54 UTC 2010

Michael Sokolov wrote:
> That is why I hate Ethernet with a passion.  Ethernet should be for LANs
> only; using Ethernet for WANs and PTP links is the vilest invention in
> the entire history of data networking in my opinion.

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?  Have you looked at how much more that
would cost?  Ethernet interfaces, particularly copper, are dirt cheap.

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--especially if you don't plan on using all the bandwidth all of
the time.

> My medium of choice for PTP links (WAN) is HDLC over a synchronous
> serial bit stream, with a V.35 or EIA-530 interface between the router
> and the modem/DSU.  Over HDLC I then run either RFC 1490 routed mode or
> straight PPP (RFC 1662); in the past I used Cisco HDLC (0F 00 08 00 IP
> header follows...).  My 4.3BSD router (or I should better say gateway as
> that's the proper 80s/90s term) then sees a PTP interface which has no
> netmask at all, hence the near and far end IP addresses don't have to
> have any numerical relationship between them at all.  No netmask, no MAC
> addresses, no ARP, none of that crap, just a PTP IP link.

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...


Stephen Sprunk         "God does not play dice."  --Albert Einstein
CCIE #3723         "God is an inveterate gambler, and He throws the
K5SSS        dice at every possible opportunity." --Stephen Hawking

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