Subject: RE: RA and Default routes?

From: "Richard Draves" <[email-masked]>
Date: Fri, 16 Feb 2001 10:20:31 -0800

> > => you mix up router lifetime (which is in fact the 
> lifetime as a default
> > router) and prefix lifetimes (which are the lifetimes of 
> the prefix).
> > The router is removed from the default router list when 
> *its* lifetime
> > is expired, this should have no effect on the prefix list.
> 
> Actually, I had the misunderstanding that RA prefix option with L=0
> and A=0 was a useful way for router to inform, that it is willing to
> route the matching addresses. I though this was a nice feature...
> 
> So, if I see prefix option with L=0 and A=0, it should be totally
> ignored? (and not give the useful semantics to it?).

Yes, your processing of a prefix option should be based on which flag
bits are enabled. If all the flag bits are off, then the prefix option
is totally ignored.

See draft-draves-ipngwg-router-selection-00 for the functionality you
were thinking about.

Rich
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From: Markku Savela <[email-masked]>
Date: Mon, 19 Feb 2001 12:18:51 +0200

Continuing my "explanations" on prefix option handling. What I had
coded, did basicly for each prefix option something like (for L-bit):

  if (L == 1)
      AddRoute(prefix, ONLINK);
  else
      AddRoute(prefix, GATEWAY, router);

That is, I assumed that each router advertising a prefix without
specifying it onlink, also was willing to route to all destinations
matching this prefix.

The plus side of this logic was

  - you could have multihomed network where routers come and go
    advertising different or same prefixes (WLAN with mobile
    client?). Routers can be configured independently (even if one
    client sees two routers, routers could be too far away and not see
    each other).

The minus is of course, that above implicit gateway route will not
work, if router is not also a default router (if it does not support
"my little extension" :-).

However, yes, I will change my implementation to match the RFC (by
removing the "else" part :-).

> See draft-draves-ipngwg-router-selection-00 for the functionality you

Yes, appears that the same effect can be achieved. I'm still unsure
whether a separate option is really needed. Prefix option could just
have a separate bit (instead of my implicit L==0), and preference
bits (maybe into Reserved2).