Subject: [imss] Re: IMSS WG last call on Transmission of IPv6, IPv4 and ARP Packets over Fibre Channel

From: Claudio DeSanti <[email-masked]>
Date: Tue, 15 Mar 2005 12:34:41 -0800

Hi Elizabeth,

let's do some last call work! :-)

I recently realized that with a small change to the specification we may 
greatly improve the mapping of IP multicast over Fibre Channel. Currently 
the specification requires to map an IP multicast packet to a broadcast 
Fibre Channel Information Unit, carrying in the destination N_Port_Name 
field of the Network_Header the value 0x10-00-FF-FF-FF-FF-FF-FF.

If the destination N_Port_Name field of the Network_Header was set to the 
mapped MAC multicast address associated with an IP multicast address, this 
would allow a receiving N_Port to distinguish if a received broadcast 
Sequence is mapping a broadcast packet (e.g., an ARP request) or a 
multicast IP packet. The receiving Nx_Port would be then able to filter at 
the driver level the broadcast Sequences it receives, passing to the upper 
layers (or to the operating system) only the Information Units addressed to 
the IP multicast groups to which the N_Port joined (which is what an 
Ethernet card normally does).

So, I propose to change the following sentence in section 10:

"The Destination N_Port_Name field of the FC Network_Header MUST be set to 
the value
0x10-00-FF-FF-FF-FF-FF-FF."

to:

"The Destination N_Port_Name field of the FC Network_Header MUST be set to 
the value:
-  for broadcast ARP and IPv4 packets: 0x10-00-FF-FF-FF-FF-FF-FF;
-  for multicast IPv6 packets: 0x10-00-33-33-XX-YY-ZZ-QQ,
    where XX-YY-ZZ-QQ are the four least significant octets of the
    multicast destination IPv6 address;
-  for multicast IPv4 packets: 0x10-00-01-00-5E-XX-YY-ZZ,
    where the 23 least significant bits of XX-YY-ZZ are the 23 least
    significant bits of the multicast destination IPv4 address and the
    most significant bit of XX-YY-ZZ is set to zero."

On the sending side this change may simplify implementations, because 
several current Fibre Channel drivers for IP present an Ethernet-like 
interface to the O.S. When the O.S. passes a multicast IP packet to the 
driver, it already puts the appropriate destination multicast MAC address 
in place. The Fibre Channel driver has then simply to take the passed 
value, pre-pend it with 0x10-00 in the Network_Header, and then transmit 
the Sequence, which is the same processing performed for sending unicast 
traffic. So, with the proposed new wording unicast and multicast 
transmission can be handled in exactly the same way, while the current 
wording in the specification requires an implementation to check if a 
multicast MAC address is passed and to replace it with the value 
0x10-00-FF-FF-FF-FF-FF-FF in the destination N_Port_Name field of the 
Network_Header.

This is a small technical change to RFC 3831, but given that there are not 
yet implementations of RFC 3831 in the field this change does not introduce 
any backward compatibility problem and greatly improves the handling of IP 
multicast over Fibre Channel.

Best regards,

                             Claudio.

At 04:58 PM 2/22/2005 -0800, [email-masked] wrote:
>Hello all,
>
>I would like to announce IMSS working group last call on the Transmission of
>IPv6, IPv4 and ARP Packets over Fibre Channel working group draft.
>
>Details:
>Name: Transmission of IPv6, IPv4 and ARP Packets over Fibre Channel
>URL: 
>http://www.ietf.org/internet-drafts/draft-ietf-imss-ip-over-fibre-channel-00.txt
>Editor/Authors: Claudio DeSanti ([email-masked]), Craig Carlson
>([email-masked]) and Bob Nixon ([email-masked])
>Last Call period: Three weeks, ending March 17 at 11:59pm EST.
>
>Thanks,
>
>Elizabeth Rodriguez
>IMSS Chair

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