Using /31 for router links

Mark Smith nanog at
Sat Jan 23 06:04:46 UTC 2010

On Sat, 23 Jan 2010 04:22:50 GMT
msokolov at ivan.Harhan.ORG (Michael Sokolov) wrote:

> 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.
> <soapbox>
> 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.
> </soapbox>

That's not a soapbox, that's a soap factory!

What about NAT, ATM cell tax, unnecessary addressing fields in PTP
protocols (including your beloved HDLC), SSAP, DSAP fields not being big
enough in 802.2 necessitating SNAP, IPX directly over 802.3, AAL1
through AAL4, PPPoE "dumbell" MTUs and MSS hacks? Some of those are far
worse sins in my opinion.

More information about the NANOG mailing list