Using /31 for router links

Michael Sokolov msokolov at ivan.Harhan.ORG
Sat Jan 23 04:22:50 UTC 2010

Nathan Ward <nanog at> wrote:

> ARP is still required on ethernet links, so that the MAC address can be =
> discovered for use in the ethernet frame header. /31 does not change the =
> behavior of ARP at all.


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.

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.



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