Arista Routing Solutions

Thu Apr 28 13:13:13 UTC 2016

Laszln,

Thu, Apr 28, 2016 at 12:47:45PM +0000, Laszlo Hanyecz wrote:

> On 2016-04-28 11:06, Alain Hebert wrote:
> >
> >      Well,
> >
> >      Once you eliminate the ~160k superfluous prefixes (last time I
> > checked)...  This is a none issue.
> >
> >      Some work on some sort summary function would keep those devices
> > alive...  but we all know there is more money to be made the faster the
> > device become obsolete :(
> >
> >
> 
> Can you explain how this works?  How can a router determine which prefix 
> is superfluous?  How does it cope when a suppressed prefix is withdrawn 
> or a more specific prefix is added? Is this just one of those 'it works 
> some of the time' solutions or is this something that can be done safely 
> with an appropriate algorithm?

A fair chunk of the routing table is aggregable.  If multiple
aggregable prefixes share the same nexthop, the HW entries can be 
summarised accordingly, reducing the HW resource footprint.

Should one of the smaller prefixes be withdrawn or best path
change to another nexthop, the control plane needs to be smart 
enough to adapt and reprogram the HW accordingly.   It is a fairly
logical and reasonable algorithm to construct

-- 
Patrick Cole <z at wwwires.com>
Senior Network Specialist
World Without Wires
PO Box 869. Palm Beach, QLD, 4221
Ph:  0410 626 630