IPv6 and data link layer

[tirke_cisco]

As we have learned, layer design is made to make us and Vendors happy about new inventions on a network field. If so, how come up this statement:

The following data links are supported for IPv6:

ATM permanent virtual circuit (PVC) and ATM LANE,

Ethernet, Fast Ethernet, Gigabit Ethernet,

FDDI,

Frame Relay PVC,

Cisco High-Level Data Link Control (HDLC),

PPP over Packet over SONET (PoS),

ISDN, serial interfaces

dynamic packet transport (DPT).

Is this truth that IPv6 (L3) is connected to lower layer (layer 2)?

Best Regards,

Tirke

[WSLH OIS NOC - OIS Infrastructure]

> Is this truth that IPv6 (L3) is connected to lower layer (layer 2)?

Well, they have to be, or you couldn't send layer 3 IP packets over the layer 2 links.  In IPv4 the connection between layer 3 (IP) and layer 2 (say, ethernet) is most often via the Address Resolution Protocol, layer 2 ethernet type 0x0806 (IPv4 being 0x0800 and IPv6 0x86dd).

In IPv6 the connection is instead via the ICMPv6 neighbor discovery protocol.  Neighbor discovery was invented with goals like getting more uniformity into the layer 3->2 transition over different link types, and better duplicate and dead address detection.

-- Jim Leinweber, WI State Lab of Hygiene

[tirke_cisco]

I was thinking that Layers are 100% independent but now I see that the story is not so simple as it looks. 

Thanks

Saša

[Peter Koltl]

You have to specify in the Layer2 header what kind of packet is in the L2 payload. Typically, the Ethernet Type field is set to 0x86DD if the payload is an IPv6 packet. Otherwise the TCP/IP stack could not decide how to interpret the payload.

Similarly, you have to specify in the Layer3 header what kind of segment is in the  L3 payload. Typically, the IP Protocol field is set to 6 if the  payload is an TCP segment. Otherwise the TCP/IP stack could not decide  how to interpret the payload.