linux-cp: handle ipv4 routes when link goes down

Type: improvement

Currently, when the link goes down on an interface, routes that resolve
through that interface and created with Nexthop API are removed by the
kernel. However, IPv4 routes remain in the FIB because the kernel
doesn't send any notifications about that.

And for the plugin working with user-space applications that create
routes in the kernel using Nexthop API there should be a mechanism to
synchronize the FIB and the kernel in this case.

With this change, add two new startup configuration options to the
plugin to be able to control what should happen with static and dynamic
routes managed by the plugin on link down:
  - del-static-on-link-down (disabled by default, delete routes created
    with the linux-cp static FIB source on link down),
  - del-dynamic-on-link-down (disabled by default, delete routes created
    with the linux-cp dynamic FIB source on link down).

Then, monitor link state changes on interfaces for which a linux-cp pair
exists. If the link goes down on one of the interfaces, process routes
that resolve through that interface according to the new configurations.

Signed-off-by: Alexander Chernavin <achernavin@netgate.com>
Change-Id: I0fbaeeca3f3d1fcd22e8eebb08a0a4a3d0dfe5b8

1 files changed, 60 insertions, 0 deletions

diff --git a/src/plugins/linux-cp/lcp_router.c b/src/plugins/linux-cp/lcp_router.c
index 34d0500b0c5..4fc824ca5ad 100644
--- a/src/plugins/linux-cp/lcp_router.c
+++ b/src/plugins/linux-cp/lcp_router.c
@@ -468,6 +468,66 @@ lcp_router_link_sync_end (void)
   LCP_ROUTER_INFO ("End synchronization of interface configurations");
 }
 
+static clib_error_t *
+lcp_router_link_up_down (vnet_main_t *vnm, u32 hw_if_index, u32 flags)
+{
+  vnet_hw_interface_t *hi;
+  index_t lipi;
+
+  hi = vnet_get_hw_interface_or_null (vnm, hw_if_index);
+  if (!hi)
+    return 0;
+
+  lipi = lcp_itf_pair_find_by_phy (hi->sw_if_index);
+  if (lipi == INDEX_INVALID)
+    return 0;
+
+  /* When the link goes down on an interface, the kernel processes routes which
+   * resolve through that interface depending on how they were created:
+   *   - Legacy Route API: the kernel retains the routes and marks them as
+   *     "linkdown";
+   *   - Nexthop API: the kernel removes the next-hop objects and the routes
+   *     which reference them.
+   *
+   * For IPv4 routes created with Nexthop API, the kernel will not send any
+   * explicit RTM_DELROUTE messages about removing them. In order to
+   * synchronize with the kernel, affected routes need to be manually removed
+   * from the FIB.
+   *
+   * The behavior is different for IPv6 routes created with Nexthop API. The
+   * kernel will send explicit RTM_DELROUTE messages about IPv6 routes being
+   * removed.
+   */
+  if (!(flags & VNET_HW_INTERFACE_FLAG_LINK_UP) &&
+      (lcp_get_del_static_on_link_down () ||
+       lcp_get_del_dynamic_on_link_down ()))
+    {
+      u32 fib_index;
+      lcp_router_table_t *nlt;
+
+      fib_index = fib_table_get_index_for_sw_if_index (FIB_PROTOCOL_IP4,
+						       hi->sw_if_index);
+
+      pool_foreach (nlt, lcp_router_table_pool)
+	{
+	  if (fib_index == nlt->nlt_fib_index &&
+	      FIB_PROTOCOL_IP4 == nlt->nlt_proto)
+	    {
+	      if (lcp_get_del_static_on_link_down ())
+		lcp_router_table_flush (nlt, hi->sw_if_index, lcp_rt_fib_src);
+	      if (lcp_get_del_dynamic_on_link_down ())
+		lcp_router_table_flush (nlt, hi->sw_if_index,
+					lcp_rt_fib_src_dynamic);
+	      break;
+	    }
+	}
+    }
+
+  return 0;
+}
+
+VNET_HW_INTERFACE_LINK_UP_DOWN_FUNCTION (lcp_router_link_up_down);
+
 static fib_protocol_t
 lcp_router_proto_k2f (uint32_t k)
 {