Subject: Subnet anycast address

From: "Niveda Monyvannan" <[email-masked]>
Date: Mon, 23 Oct 2000 17:53:22 +0530

Hello,
          IPv6 specs says that 'IPv6 router should take receive the
packet destined to Subnet anycast address and the Subnet anycast address
is nothing but the subnet prefix +  interface ID as 0'

When a packet with Destination address as ' Subnet anycast address' is
generated?

How a source of the packet in a subnet ensures that the packet is
delivered to only one person in the subnet?

Regards,
Niveda

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From: Ignatios Souvatzis <[email-masked]>
Date: Tue, 24 Oct 2000 14:08:46 +0200

> is nothing but the subnet prefix +  interface ID as 0'

No, it does not, at least the versions I have access to. What you describe
is the subnet _router_ anycast address.

> delivered to only one person in the subnet?

The source doesn't care. The router knows, when it sees such a packet, that
it is for itself, and grabs it.

Regards,
	-is

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From: Francis Dupont <[email-masked]>
Date: Sat, 28 Oct 2000 12:29:45 +0200

In your previous mail you wrote:

   
=> when someone wants to send a packet to any router (anycast works only
for routers) in the subnet. I know no real usage of this as a final
destination but this can be used in source routing if you'd like to
go through a subnet, ie. this is a cheap & nice way to implement
some kind of policy routing...

=> first the source doesn't need to be in the subnet (only the knowledge
of the subnet is needed). The packet is delivered to only one router
in the subnet by definition of what is anycast. This is realized by
one of these two cases:
 - if the packet comes from the exterior then the entry router can get
   the packet for him (it should be one of the routers in the anycast group)
 - if the packet is on the link of the subnet then the neighbor discovery
   (neighbor advertisements for an anycast address) will select one of
   the routers in the anycast group.
This works for other anycast addresses (mobility home agent for instance)
but in general the first case is less common for others.

Regards

[email-masked]