Re: [PATCH net 1/2] ipv6: create multicast route with RTPROT_KERNEL

On Sat, Jan 16, 2021 at 5:36 AM David Ahern [off-list ref] wrote:

On 1/15/21 11:42 AM, Matteo Croce wrote:

quoted

From: Matteo Croce <redacted>

The ff00::/8 multicast route is created without specifying the fc_protocol
field, so the default RTPROT_BOOT value is used:

  $ ip -6 -d route
  unicast ::1 dev lo proto kernel scope global metric 256 pref medium
  unicast fe80::/64 dev eth0 proto kernel scope global metric 256 pref medium
  unicast ff00::/8 dev eth0 proto boot scope global metric 256 pref medium

As the documentation says, this value identifies routes installed during
boot, but the route is created when interface is set up.
Change the value to RTPROT_KERNEL which is a better value.

Signed-off-by: Matteo Croce <redacted>
---
 net/ipv6/addrconf.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/net/ipv6/addrconf.c b/net/ipv6/addrconf.c
index eff2cacd5209..19bf6822911c 100644
--- a/net/ipv6/addrconf.c
+++ b/net/ipv6/addrconf.c

@@ -2469,6 +2469,7 @@ static void addrconf_add_mroute(struct net_device *dev)
              .fc_flags = RTF_UP,
              .fc_type = RTN_UNICAST,
              .fc_nlinfo.nl_net = dev_net(dev),
+             .fc_protocol = RTPROT_KERNEL,
      };

      ipv6_addr_set(&cfg.fc_dst, htonl(0xFF000000), 0, 0, 0);

What's the motivation for changing this? ie., what s/w cares that it is
kernel vs boot?

A practical example: systemd-networkd explicitly ignores routes with
kernel flag[1]. Having a different flag leads the daemon to remove the
route sooner or later.

[1] https://github.com/systemd/systemd/blob/0b81225e5791f660506f7db0ab88078cf296b771/src/network/networkd-routing-policy-rule.c#L675-L677
-- 
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