Ole Troan wrote:
A router might (and probably should) be hard-coded not to
forward link-local packets, as there is no reason to ever
forward them.
However, a router that might ever need have multiple
interfaces in a single site can't be hard-coded not to
forward site-locals. Whether or not they will be forwarded is
the result of configuration.
Actually, a router can forward link-locals between interfaces on the
same link. In particular, a router can forward a packet with link-local
dest and/or source back out the interface from which it arrived (and
presumably generate a Redirect too).
If you are implementing link-locals properly, it's really very little
additional code to support site-locals. At least that's my experience.
could you comment on routing code? (RIPng, OSPFv3) i still think
it's way too tough to support multi-sited node.
RIPng is relatively simple. link-state protocols require congruent
areas and sites. there are some open issues with regards to multicast
and PIM I believe. routing protocol support is required in any case
for VPNs.
The actual routing protocol changes in RIPng is dependent on
how you structure your RIBs. I hacked RIPng to make an SBR
using a monolithic RIB with an additional index (the zone id).
It was an additional 800-900 lines of code to deal with
figuring out which RIB entries needed to be advertised on each
interface.
Then there are the changes to configure and maintain the zone
IDs.
The biggest hit is actually in the forwarding. Each packet
gets at least one additional table lookup (for the incoming
zone id). Then there are the checks to ensure that the source
address is valid (e.g. a site-local SA and global DA trying
to cross a site border).
The extra cost? Performance drops around 25-30% for a SBR
between 3 sites. Of course, this was all software based,
but even a hardware-based solution will take the extra lookup
hits.
Brian
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