Point to Point Ethernet

William Herrin herrin-nanog at dirtside.com
Wed Jul 8 09:30:00 CDT 2009


On Wed, Jul 8, 2009 at 6:01 AM, Andre Oppermann<nanog-list at nrg4u.com> wrote:
> Do you think this is useful?

Andre,

Some thoughts on this:

1. What's the point of increasing the max MTU from 9000 to 9012? If we
want a higher MTU, why not just ask for one in the next standard?

2. Why do we need to save 12 bytes per packet by eliminating the MAC
address? Why not just get the next larger ethernet size?

3. Could we be better served by using RFC1918 addresses that we define
as link-local and asking the router vendors to support a "link local"
config option that causes it to use the address from loopback0 for any
communications it initiates over that interface instead of using the
interface IP address? In other words, if your loop0 is 199.33.224.1
and your g0/0 is 10.3.2.1/30 the link-local option would cause the
router to send any host-unreachable messages out g0/0 from
199.33.225.1 instead of 10.3.2.1. Likewise, pings and snmp traps would
originate from 199.33.224.1. Only packets to 10.3.2.2 would originate
from 10.3.2.1.

Such a software-only change would be less expensive to implement than
custom ethernet hardware and it would be applicable on all interface
types, not just ethernet. And of course we already have tools to
prevent such link-local addresses from entering the routing protocol.

At a software level, we could also declare a specific remote address
as the point-to-point destination so that we could use the interface
name as shorthand elsewhere in the config if that proves desirable.

4. L3->L2 lookup is a pretty negligible cost. It's cached for a good
long while. And you already have tools to hardcode it if so desired.
With Ciscos at least, you can even hardcode addresses to
ffff.ffff.ffff though this causes some unexpected behavior.

Regards,
Bill

-- 
William D. Herrin ................ herrin at dirtside.com  bill at herrin.us
3005 Crane Dr. ...................... Web: <http://bill.herrin.us/>
Falls Church, VA 22042-3004




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