WEBINAR TUESDAY: Can We Make IPv4 Great Again?

valdis.kletnieks at vt.edu valdis.kletnieks at vt.edu
Tue Mar 7 23:46:50 UTC 2017

On Tue, 07 Mar 2017 18:27:06 -0500, Dennis Bohn said:

> AFAICT, Cisco V6 HSRP (mentioning that brand only because it caused me to
> try to figure something out, a coincidence that this is in reply to Jakob
> from Cisco but is based on what he wrote)  relies on Link Local addresses.
> I didn't understand why link locals should be there in the first place
> seemed klugey and have googled, looked at rfcs and tried to understand why
> link local addresses were baked into V6. The only thing I found was that it
> enabled interfaces on point to point links to be unaddressed in V6. (To
> save address space!??) Can anyone point me in a direction to understand the
> reasoning for link local addressing?

Because there are a lot of corner cases where you may want to talk to the
network before you find out what your network address is.  And if it's a
stand-alone network, it may not *have* a well-define network prefix to use
for SLAAC auto-config addressing.

Think about all the places in IPv4 where you toss packets on the net with your
MAC address or a bogus placeholder IP address because you don't have an IP
address yet (ARP, DHCP for starters).  Link-Local is basically the same thing
in the IPv6 world.

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