Subject: Doubt on Dual IP layer in RFC 1933

From: Murali Krishna Ch <[email-masked]>
Date: Tue, 21 Mar 2000 17:53:11 +0530

There are two mechanisms 

1) Dual IP layer
2) Tunneling

to keep IPv6 hosts/routers compatible with 
IPv4 hosts/routers.

Query 1: If Dual IP layer mechansim is used alone, how does
	an ipv6 packet from ipv6 host/router will be processed	 
	at ipv4-only node? 
Query 2: Is it necessry to have tunnelling mechanism to be 
	compatible with IPv4?

Thanks in advance,
murali.

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From: Steve Deering <[email-masked]>
Date: Tue, 21 Mar 2000 07:33:58 -0800

>	an ipv6 packet from ipv6 host/router will be processed	 

If a dual IP-layer mechanism is used *alone*, that means all IPv6-capable
nodes are also IPv4-capable.  Such a dual IP-layer node sends only IPv4
packets to IPv4-only nodes, so your question is not meaningful.

For an IPv6-only (i.e., *not* dual IP-layer) node to send a packet to an
IPv4-only node, there must be some sort of translator or gateway in the
path, to perform the necessary header conversion.  The translator or gateway
itself will have dual IP layers.

>Query 2: Is it necessry to have tunnelling mechanism to be 

No.  Tunneling (of IPv6 inside IPv4) is used for IPv6-to-IP6 communication
only, when the routers between the source and destination IPv6 nodes do
not all support IPv6.

Steve

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From: Wang Hui <[email-masked]>
Date: Thu, 23 Mar 2000 20:36:57 +0800 (CST)

> 	an ipv6 packet from ipv6 host/router will be processed	 
     Should there be a v6-to-v4 translator?  
     And should we standize a translating rules?
     I think we need both of them.     

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From: Erik Nordmark <[email-masked]>
Date: Thu, 23 Mar 2000 14:18:25 -0800 (PST)

>      Should there be a v6-to-v4 translator?  

It might be useful in certain transition scenarios.
But in other scenarios socks (draft-ietf-ngtrans-socks-gateway-03.txt)
or application layer gateways (web proxies, mail relays) on a dual-stack
machine will suffice.

>      I think we need both of them.     

See RFC 2765 (SIIT) and 2766 (NAT-PT).

  Erik