Hi,
On 03.07.2011 19:03, Karl Auer wrote:
> Which RFCs (or other sources) describe how IPv6 subnet anycast *works*?
> In particular how it works when there are multiple routers in a single
> subnet?
That's a good question. I was also looking for that. It's distributed
across various RFCs:
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RFC4291:
"A node is required to compute and join (on the appropriate interface)
the associated Solicited-Node multicast addresses for all unicast and
anycast addresses that have been configured for the node's interfaces
(manually or automatically)."
RFC 4861:
7.2.7. Anycast Neighbor Advertisements
From the perspective of Neighbor Discovery, anycast addresses are
treated just like unicast addresses in most cases. Because an
anycast address is syntactically the same as a unicast address, nodes
performing address resolution or Neighbor Unreachability Detection on
an anycast address treat it as if it were a unicast address. No
special processing takes place.
Nodes that have an anycast address assigned to an interface treat
them exactly the same as if they were unicast addresses with two
exceptions. First, Neighbor Advertisements sent in response to a
Neighbor Solicitation SHOULD be delayed by a random time between 0
and MAX_ANYCAST_DELAY_TIME to reduce the probability of network
congestion. Second, the Override flag in Neighbor Advertisements
SHOULD be set to 0, so that when multiple advertisements are
received, the first received advertisement is used rather than the
most recently received advertisement.
As with unicast addresses, Neighbor Unreachability Detection ensures
that a node quickly detects when the current binding for an anycast
address becomes invalid.
RFC 4862:
- Duplicate Address Detection MUST NOT be performed on anycast
addresses (note that anycast addresses cannot syntactically be
distinguished from unicast addresses).
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Multiple Routers are usually not a problem since
only one gets the packet for forwarding into the subnet.
Regards,
Roland
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