Re: Why specify a default router?
On Tue, Jul 05, 2005 at 12:07:53AM -0700, The Orange Rider wrote:
> Hey all, I'm just entering the IPv6 world and I have a question I'm
> hoping someone can answer:
>
> Time and time again I read about how hosts don't need to have a
> default gateway configured statically in IPv6 as they did in IPv4
> becuase they will automatically discover the router via Neighbor
> Discovery Protocol (through Router Solicitations and Router
> Advertisments and all that).
IPv4 can also be dynamically configured with a default gateway (DHCP). I
don't think this is very different in principle from IPv6 neighbour
discovery or DHCPv6. A host connected to the global IPv6 network will need a
default gateway to communicate with the rest of the network.
> This is all well and good, except that Linux still supports the manual
> configuration of a router (route add -inet6 [ipv6_address]). What I
> don't understand is why this is supported at all. Since IPv6 lacks ARP
> requests, it seems as though a host would still have to resolve the
Although I can't remember having heard about ARP for IPv6, I can't imagine
that something like ARP is not used, because ARP provides mapping from L3
addresses to L2 and that is certainly not guaranteed to be derivable from
the L3 address alone.
> router via NDP even if it is manually configured with a default
> router. Can anyone clarify how specifying the L3 address of the
> gateway without an L2 address along with it is useful to the host?
That's the same in IPv4, ARP is used to fill the ARP table.
Cheers
Simon
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