Understanding the working of Optimistic DAD Feature.

[Chinmay Agarwal]

Hi Team,

Had a doubt regarding Optimistic DAD implementation in linux kernel.


The RFC of Optimistic DAD states:



"Section 3.3

        A router SHOULD NOT configure an Optimistic Address."

To check the same there is a condition in kernel code wherein we check if ipv6.devconf_all is set.
Now, my query is that we are checking if forwarding is enabled on all interfaces, then we consider the system to be a router.
But even if forwarding is enabled from few interfaces(not all) isn't the system behaving like a router?


void addrconf_add_linklocal<https://elixir.bootlin.com/linux/latest/ident/addrconf_add_linklocal>(struct inet6_dev<https://elixir.bootlin.com/linux/latest/ident/inet6_dev> *idev<https://elixir.bootlin.com/linux/latest/ident/idev>,

                     const struct in6_addr<https://elixir.bootlin.com/linux/latest/ident/in6_addr> *addr, u32<https://elixir.bootlin.com/linux/latest/ident/u32> flags)

{

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#ifdef<https://elixir.bootlin.com/linux/latest/ident/ifdef> CONFIG_IPV6_OPTIMISTIC_DAD

  if ((dev_net<https://elixir.bootlin.com/linux/latest/ident/dev_net>(idev<https://elixir.bootlin.com/linux/latest/ident/idev>->dev)->ipv6.devconf_all->optimistic_dad ||

       idev<https://elixir.bootlin.com/linux/latest/ident/idev>->cnf.optimistic_dad) &&

      !dev_net<https://elixir.bootlin.com/linux/latest/ident/dev_net>(idev<https://elixir.bootlin.com/linux/latest/ident/idev>->dev)->ipv6.devconf_all->forwarding<https://elixir.bootlin.com/linux/latest/ident/forwarding>)

          cfg<https://elixir.bootlin.com/linux/latest/ident/cfg>.ifa_flags |= IFA_F_OPTIMISTIC<https://elixir.bootlin.com/linux/latest/ident/IFA_F_OPTIMISTIC>;

#endif



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}

Thanks
Chinmay

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