Re: Command to Display Prefixes and Default router entries in Linux

[Dheeraj Kandula <dkandula@gmail.com>]

Thanks, Bjorn for the response.

The R flag is set in the NA as the sender is a router.

Dheeraj

On Fri, Jun 24, 2022 at 4:08 AM Bjørn Mork <bjorn@mork.no> wrote:

Dheeraj Kandula <dkandula@gmail.com> writes:

> Thanks Povl.
>
> In the "ip neighbor" output, I see entries listed with "router". Maybe it
> is a RA Default router learnt entry.

Nope.  That's the 'router' flag in the neigbour advertisment.  Lots of
systems will set this flag without sending RAs. Linux will set it if
forwarding is enable on the interface where the NA is going out.

>From net/ipv6/addrconf.c:

        /* send unsolicited NA if enabled */
        if (send_na &&
            (ifp->idev->cnf.ndisc_notify ||
             dev_net(dev)->ipv6.devconf_all->ndisc_notify)) {
                ndisc_send_na(dev, &in6addr_linklocal_allnodes, &ifp->addr,
                              /*router=*/ !!ifp->idev->cnf.forwarding,
                              /*solicited=*/ false, /*override=*/ true,
                              /*inc_opt=*/ true);
        }


Bjørn