ipv6 next-hop link-local

S.P.Zeidler spz at serpens.de
Mon Feb 21 09:05:48 CET 2011


Thus wrote George Bonser (gbonser at seven.com):

> Looking right now at a box in a data center.  Two different vlan
> interfaces on the same box.  One is:
> inet6 addr: fe80::221:28ff:fe57:3412/64
> and the other is:
> inet6 addr: fe80::221:28ff:fe57:3412/64

Speaking at least for the KAME stack, that is a red herring, because a
linklocal address always has a scope which tells it which interface
it refers to.

So you don't have fe80::221:28ff:fe57:3412/64 and
fe80::221:28ff:fe57:3412/64, but fe80::221:28ff:fe57:3412%if1/64 and

> Same netmask, same IP address, two different networks.  On which one
> will I find fe80:ab:cd?  I need to do ND on all of them until I find it,
> I suppose.

Not much different from "where is the MAC address I see acting up
located". If you are instead intending to set up communications with
another machine via linklocal, you presumably know which network it is on
beforehand. Remember that a linklocal address is only addressable with

> If I were making the rules, link local would only mean "I don't have
> enough information to build a 'real' IP address so I am using this
> placeholder in the meantime.  Once a "real" address is configured, the
> link-local would be dropped. 

I've used linklocal for eg NFS and the 'will not cross routers' feature
was quite welcome as a built-in security mechanism. Thus, I disagree.

spz at serpens.de (S.P.Zeidler)

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