So why is "IPv4 with longer addresses" a problem anyway?

Benedikt Stockebrand me at
Tue Jun 1 16:36:44 CEST 2010

Hi once more,

Nick Hilliard <nick at> writes:

> RFC 2461, section 6.3.4:

just for completeness sake: That one's been obsoleted by RFC 4861
since September 2007.

> "the receipt of a Router Advertisement MUST NOT invalidate all information
> received in a previous advertisement or from another source.  However, when
> received information for a specific parameter (e.g., Link MTU) or option
> (e.g., Lifetime on a specific Prefix) differs from information received
> earlier, and the parameter/option can only have one value, the most
> recently-received information is considered authoritative."
> ... and the rest of section 6.3.4, which provides the mechanism for RA
> Default Router List timeout.
> Please read this section carefully.  You are simply not guaranteed quick
> failover when using RA.  Yes, you can tune things down, but it's never
> going to be anything like a router failover protocol.

The timeout you are referring to determines how long a router is kept
in the list of default routers on a host, not for how long it is
actually used.

The timeout determining which router is actually used is the NUD
timeout at 30s plusminus 15s.

> I'd be happy to retract a statement like that if you can provide a
> reference.

In <4C03BADF.3080902 at> you write:

] - loss of service measured in (by default) minutes in the case of router
] failure 


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Benedikt Stockebrand, Dipl.-Inform.

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