I'm upgrading my MCSA to MCITP and IPV6 is something I'm expecting to see ... which I know next to nothing about. I also don't really know anything about load balancing, which leads to my confusion here, I think.

In my reading, I saw "Unicast. ... RF 2373 allows multiple interfaces to use the same address, provided that these interfaces appear as a single interface to the IPv6 implementation on the host. This accommodates load balancing systems."

Now, I get how it would be beneficial to load balancing, but I don't really get how it works Is this multiple interfaces on a single server? That wouldn't make sense for the load balancing; so if it's for multiple machines, how does it actually distribute traffic between them, do hosts receive all traffic for the address and control which server handles a request via communication on a different interface?

I thought this might be a dupe but I couldn't find one.


RFC2373 was obsoleted by RFC3513; you can't do what is being described with Global Unicast addresses unless you use interface bonding (with which you would also be able to assign a single IPv4) - Site Local (AKA ULA addresses) also behave in this manner.

IPv6 Link-Local addresses behave a bit differently in that they require an interface identifier for the system to know which interface to send the packet out of, and thus you can assign identical link-local addresses to multiple NICs on a single system - however, doing so must not break neighbour discovery - or in other words, if the two NICs exist on the same VLAN, don't do it. Additionally, if you do have multiple identical Link-Local identifiers on a single host, it's usually a requirement that you specify the interface you wish to send the packets from.

  • Well. That answers my question well enough ... mostly it tells me I have a lot of reading to do :) Thank you. – Daniel B. Jul 23 '11 at 23:52

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