Re: [v6ops] Routers are hosts too!

[t.petch <[e-mail]>]

----- Original Message -----
From: "Joe Touch" <[e-mail]>
To: "Alexandre Petrescu" <[e-mail]>;
<[e-mail]>
Sent: Saturday, January 09, 2016 6:26 AM

> On 1/8/2016 8:05 AM, Alexandre Petrescu wrote:
> > RFC1122 "Reqs for Internet Hosts -- Communication Layers" does not
> > mention longest-prefix match.
>
> Section 3.3.2.3 (source address selection) refers to Section 3.3.1,
> which includes a set of mechanisms in Section 3.3.1.2 for selecting
> among multiple gateways.
>
> Note that this algorithm involves using a route cache with ICMP
> redirects that help the system learn the "best" (quote from the RFC)
> next-hop. Those entries are described in terms of host routes, but
there
> is a discussion about aggregating those entries in 3.3.1.3.
>
> The net result of that aggregation is effectively longest-prefix
matching.
>
> So you're strictly correct - RFC1122 does not require longest prefix,
> but a large number of entries in the route cache is more effectively
> handled as such.

But then RFC1122 does not mention classless addressing or Variable
Length Subnet Masks - as I recall, they did not exist at that time.
Rather, RFC1122 deals with 32 bit Host addresses and Classful Networks,
ie 8 or 16 or 24 bit addresses, so while you might have more than one
entry in the cache for a given destination, they will all be the same
length so the concept of longest-prefix (and of course, the term prefix
has no meaning at that date) match does not come into consideration.

Tom Petch

> Joe
>