netdev - Re: [PATCH v2] net: bonding: alb disable balance for IPv6 multicast related mac

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Message-ID: <20201103130559.0335c353@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Tue, 3 Nov 2020 13:05:59 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     LIU Yulong <liuyulong.xa@...il.com>
Cc:     netdev@...r.kernel.org, LIU Yulong <i@...yulong.me>,
        Jay Vosburgh <j.vosburgh@...il.com>,
        Veaceslav Falico <vfalico@...il.com>,
        Andy Gospodarek <andy@...yhouse.net>
Subject: Re: [PATCH v2] net: bonding: alb disable balance for IPv6 multicast
 related mac

On Mon,  2 Nov 2020 15:56:43 +0800 LIU Yulong wrote:
> According to the RFC 2464 [1] the prefix "33:33:xx:xx:xx:xx" is defined to
> construct the multicast destination MAC address for IPv6 multicast traffic.
> The NDP (Neighbor Discovery Protocol for IPv6)[2] will comply with such
> rule. The work steps [6] are:
>   *) Let's assume a destination address of 2001:db8:1:1::1.
>   *) This is mapped into the "Solicited Node Multicast Address" (SNMA)
>      format of ff02::1:ffXX:XXXX.
>   *) The XX:XXXX represent the last 24 bits of the SNMA, and are derived
>      directly from the last 24 bits of the destination address.
>   *) Resulting in a SNMA ff02::1:ff00:0001, or ff02::1:ff00:1.
>   *) This, being a multicast address, can be mapped to a multicast MAC
>      address, using the format 33-33-XX-XX-XX-XX
>   *) Resulting in 33-33-ff-00-00-01.
>   *) This is a MAC address that is only being listened for by nodes
>      sharing the same last 24 bits.
>   *) In other words, while there is a chance for a "address collision",
>      it is a vast improvement over ARP's guaranteed "collision".
> Kernel related code can be found at [3][4][5].

Please make sure you keep maintainers CCed on your postings, adding bond
maintainers now.

> +static inline bool is_ipv6_multicast_ether_addr(const u8 *addr)
> +{
> +	return (addr[0] == 0x33) && (addr[1] == 0x33);
> +}

nit: brackets are not necessary here.