Set broadcast IP address for static IPv4 config

When running the `"ip addr"` command, the broadcast IP address wasn't getting set properly: ``` 4: uap0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq qlen 1000 link/ether b4:8c:9d:9c:2a:0b brd ff:ff:ff:ff:ff:ff inet 172.16.61.1/24 brd 172.16.61.1 scope global uap0 valid_lft forever preferred_lft forever ``` I'm not sure when/how this started, but this commit fixes the issue by always setting it to the all-ones host (RFC 922): ``` 4: uap0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq qlen 1000 link/ether b4:8c:9d:9c:2a:0b brd ff:ff:ff:ff:ff:ff inet 172.16.61.1/24 brd 172.16.61.255 scope global uap0 valid_lft forever preferred_lft forever ``` The code supports /31 and /32 subnets to avoid raising should this ever be called for them.
nerves-networking · May 15, 2023 · c52dede · c52dede
1 parent c5808c6
commit c52dede
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diff --git a/lib/vintage_net/ip.ex b/lib/vintage_net/ip.ex
@@ -205,4 +205,25 @@ defmodule VintageNet.IP do
 
     {new_a, new_b, new_c, new_d, new_e, new_f, new_g, new_h}
   end
+
+  @doc """
+  Return the IPv4 broadcast address for the specified subnet and prefix
+
+  Examples:
+
+      iex> VintageNet.IP.ipv4_broadcast_address({192, 168, 1, 50}, 24)
+      {192, 168, 1, 255}
+
+      iex> VintageNet.IP.ipv4_broadcast_address({74, 125, 227, 0}, 29)
+      {74, 125, 227, 7}
+  """
+  @spec ipv4_broadcast_address(:inet.ip4_address(), VintageNet.prefix_length()) ::
+          :inet.ip4_address()
+  def ipv4_broadcast_address({a, b, c, d}, subnet_bits)
+      when subnet_bits >= 0 and subnet_bits <= 32 do
+    not_subnet_bits = 32 - subnet_bits
+    <<subnet::size(subnet_bits), _::size(not_subnet_bits)>> = <<a, b, c, d>>
+    <<new_a, new_b, new_c, new_d>> = <<subnet::size(subnet_bits), -1::size(not_subnet_bits)>>
+    {new_a, new_b, new_c, new_d}
+  end
 end
diff --git a/lib/vintage_net/ip/ipv4_config.ex b/lib/vintage_net/ip/ipv4_config.ex
@@ -202,6 +202,9 @@ defmodule VintageNet.IP.IPv4Config do
       ) do
     addr_subnet = IP.cidr_to_string(ipv4.address, ipv4.prefix_length)
 
+    broadcast_addr =
+      IP.ipv4_broadcast_address(ipv4.address, ipv4.prefix_length) |> IP.ip_to_string()
+
     route_manager_up =
       case ipv4[:gateway] do
         nil ->
@@ -223,7 +226,18 @@ defmodule VintageNet.IP.IPv4Config do
       up_cmds ++
         [
           {:run_ignore_errors, "ip", ["addr", "flush", "dev", ifname, "label", ifname]},
-          {:run, "ip", ["addr", "add", addr_subnet, "dev", ifname, "label", ifname]},
+          {:run, "ip",
+           [
+             "addr",
+             "add",
+             addr_subnet,
+             "dev",
+             ifname,
+             "broadcast",
+             broadcast_addr,
+             "label",
+             ifname
+           ]},
           {:run, "ip", ["link", "set", ifname, "up"]},
           route_manager_up,
           resolver_up

diff --git a/test/vintage_net/ip/ipv4_config_test.exs b/test/vintage_net/ip/ipv4_config_test.exs
@@ -135,7 +135,18 @@ defmodule VintageNet.IP.IPv4ConfigTest do
       ],
       up_cmds: [
         {:run_ignore_errors, "ip", ["addr", "flush", "dev", "eth0", "label", "eth0"]},
-        {:run, "ip", ["addr", "add", "192.168.1.2/24", "dev", "eth0", "label", "eth0"]},
+        {:run, "ip",
+         [
+           "addr",
+           "add",
+           "192.168.1.2/24",
+           "dev",
+           "eth0",
+           "broadcast",
+           "192.168.1.255",
+           "label",
+           "eth0"
+         ]},
         {:run, "ip", ["link", "set", "eth0", "up"]},
         {:fun, VintageNet.RouteManager, :set_route,
          ["eth0", [{{192, 168, 1, 2}, 24}], {192, 168, 1, 1}]},
@@ -182,7 +193,18 @@ defmodule VintageNet.IP.IPv4ConfigTest do
       ],
       up_cmds: [
         {:run_ignore_errors, "ip", ["addr", "flush", "dev", "eth0", "label", "eth0"]},
-        {:run, "ip", ["addr", "add", "192.168.1.2/24", "dev", "eth0", "label", "eth0"]},
+        {:run, "ip",
+         [
+           "addr",
+           "add",
+           "192.168.1.2/24",
+           "dev",
+           "eth0",
+           "broadcast",
+           "192.168.1.255",
+           "label",
+           "eth0"
+         ]},
         {:run, "ip", ["link", "set", "eth0", "up"]},
         {:fun, VintageNet.RouteManager, :clear_route, ["eth0"]},
         {:fun, VintageNet.NameResolver, :clear, ["eth0"]}
@@ -228,7 +250,18 @@ defmodule VintageNet.IP.IPv4ConfigTest do
       ],
       up_cmds: [
         {:run_ignore_errors, "ip", ["addr", "flush", "dev", "eth0", "label", "eth0"]},
-        {:run, "ip", ["addr", "add", "192.168.1.2/24", "dev", "eth0", "label", "eth0"]},
+        {:run, "ip",
+         [
+           "addr",
+           "add",
+           "192.168.1.2/24",
+           "dev",
+           "eth0",
+           "broadcast",
+           "192.168.1.255",
+           "label",
+           "eth0"
+         ]},
         {:run, "ip", ["link", "set", "eth0", "up"]},
         {:fun, VintageNet.RouteManager, :clear_route, ["eth0"]},
         {:fun, VintageNet.NameResolver, :setup, ["eth0", nil, [{1, 2, 3, 4}]]}