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Merge pull request #1029 from hedrok/T6962-frr-zebra-kernel-routes
T6962: frr: fix wrong kernel routes updates
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‎scripts/package-build/frr/patches/frr/0007-zebra-remove-kernel-route-on-last-address-deletion.patch‎

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From 1ba7319656c548075e466a8ad1d068f7b1d66756 Mon Sep 17 00:00:00 2001
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From: Kyrylo Yatsenko <hedrok@gmail.com>
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Date: Thu, 11 Sep 2025 17:43:08 +0300
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Subject: [PATCH] zebra: remove kernel route on last address deletion
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Fixes issue #13561
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Linux kernel deletes IPv4 routes when last interface IPv4 address
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is deleted, but intentionally doesn't send RTM_DELROUTE in this case.
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FRR has function rib_update_handle_kernel_route_down_possibility
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that handles setting interface down, but not removal of last address.
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To fix the situation:
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* Add RIB_UPDATE_KERNEL_LAST_ADDRESS_DELETED to enum rib_update_event
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* In zebra_if_addr_update_ctx make more specific check that last
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address is deleted and trigger RIB_UPDATE_KERNEL_LAST_ADDRESS_DELETED
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instead of RIB_UPDATE_KERNEL in this case. If it was not last address,
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don't emit any RIB_UPDATE.
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* Call rib_update_handle_kernel_route_down_possibility not only
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for event RIB_UPDATE_INTERFACE_DOWN, but also for
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RIB_UPDATE_KERNEL_LAST_ADDRESS_DELETED.
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* Change rib_update_handle_kernel_route_down_possibility not to
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consider IPv4 route alive when interface is up, but there
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are no IPv4 addresses left.
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Relevant kernel code:
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* net/ipv4/fib_frontend.c fib_inetaddr_event
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* net/ipv4/fib_semantics.c fib_sync_down_dev
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Comment from kernel networking author that RTM_DELROUTE isn't sent
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intentionally:
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https://bugzilla.kernel.org/show_bug.cgi?id=207089
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Signed-off-by: Kyrylo Yatsenko <hedrok@gmail.com>
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---
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lib/if.c | 12 +++++++++++
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lib/if.h | 1 +
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zebra/interface.c | 8 ++++---
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zebra/rib.h | 1 +
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zebra/zebra_rib.c | 55 +++++++++++++++++++++++++++++++++++++++--------
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5 files changed, 65 insertions(+), 12 deletions(-)
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diff --git a/lib/if.c b/lib/if.c
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index 8f15230f23..2402d17992 100644
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--- a/lib/if.c
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+++ b/lib/if.c
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@@ -899,6 +899,18 @@ nbr_connected_log(struct nbr_connected *connected, char *str)
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zlog_info("%s", logbuf);
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}
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+/* Return true if there is at least one connected address in the given family */
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+bool if_has_connected_with_family(struct interface *ifp, int family)
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+{
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+ struct connected *connected;
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+
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+ frr_each (if_connected, ifp->connected, connected)
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+ if (connected->address->family == family)
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+ return true;
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+
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+ return false;
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+}
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+
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/* count the number of connected addresses that are in the given family */
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unsigned int connected_count_by_family(struct interface *ifp, int family)
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{
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diff --git a/lib/if.h b/lib/if.h
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index 0dc56bd210..233213ca84 100644
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--- a/lib/if.h
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+++ b/lib/if.h
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@@ -606,6 +606,7 @@ extern struct connected *connected_lookup_prefix(struct interface *ifp,
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const struct prefix *p);
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extern struct connected *connected_lookup_prefix_exact(struct interface *ifp,
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const struct prefix *p);
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+extern bool if_has_connected_with_family(struct interface *ifp, int family);
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extern unsigned int connected_count_by_family(struct interface *ifp, int family);
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extern struct nbr_connected *nbr_connected_new(void);
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extern void nbr_connected_free(struct nbr_connected *connected);
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diff --git a/zebra/interface.c b/zebra/interface.c
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index e2c2b4a80c..48343355ba 100644
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--- a/zebra/interface.c
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+++ b/zebra/interface.c
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@@ -1313,11 +1313,13 @@ static void zebra_if_addr_update_ctx(struct zebra_dplane_ctx *ctx,
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}
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/*
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- * Linux kernel does not send route delete on interface down/addr del
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+ * Linux kernel does not send route delete on interface down/last addr del
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* so we have to re-process routes it owns (i.e. kernel routes)
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+ * See rib_update_handle_kernel_route_down_possibility for more details
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*/
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- if (op != DPLANE_OP_INTF_ADDR_ADD)
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- rib_update(RIB_UPDATE_KERNEL);
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+ if (op != DPLANE_OP_INTF_ADDR_ADD && addr->family == AF_INET &&
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+ !if_has_connected_with_family(ifp, AF_INET))
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+ rib_update(RIB_UPDATE_KERNEL_LAST_ADDRESS_DELETED);
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}
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static void zebra_if_update_ctx(struct zebra_dplane_ctx *ctx,
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diff --git a/zebra/rib.h b/zebra/rib.h
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index 5fedb07335..2f1954de9d 100644
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--- a/zebra/rib.h
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+++ b/zebra/rib.h
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@@ -330,6 +330,7 @@ enum rib_update_event {
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RIB_UPDATE_KERNEL,
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RIB_UPDATE_RMAP_CHANGE,
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RIB_UPDATE_OTHER,
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+ RIB_UPDATE_KERNEL_LAST_ADDRESS_DELETED,
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RIB_UPDATE_MAX
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};
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void rib_update_finish(void);
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diff --git a/zebra/zebra_rib.c b/zebra/zebra_rib.c
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index 752f8282df..eaba976265 100644
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--- a/zebra/zebra_rib.c
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+++ b/zebra/zebra_rib.c
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@@ -4465,6 +4465,9 @@ static const char *rib_update_event2str(enum rib_update_event event)
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case RIB_UPDATE_OTHER:
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ret = "RIB_UPDATE_OTHER";
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break;
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+ case RIB_UPDATE_KERNEL_LAST_ADDRESS_DELETED:
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+ ret = "RIB_UPDATE_KERNEL_LAST_ADDRESS_DELETED";
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+ break;
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case RIB_UPDATE_MAX:
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break;
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}
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@@ -4487,13 +4490,45 @@ rib_update_handle_kernel_route_down_possibility(struct route_node *rn,
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bool alive = false;
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for (ALL_NEXTHOPS(re->nhe->nhg, nexthop)) {
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+ if (!nexthop->ifindex || nexthop->type == NEXTHOP_TYPE_BLACKHOLE) {
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+ /* blackhole nexthops have no interfaces */
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+ alive = true;
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+ break;
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+ }
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+
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struct interface *ifp = if_lookup_by_index(nexthop->ifindex,
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nexthop->vrf_id);
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- if ((ifp && if_is_up(ifp)) || nexthop->type == NEXTHOP_TYPE_BLACKHOLE) {
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+ if (!ifp || !if_is_up(ifp)) {
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+ /* interface is not up, not alive */
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+ continue;
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+ }
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+
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+ /*
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+ * Kernel deletes IPv4 routes from interface when last IPv4 address is deleted
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+ * It is not important whether nexthop is reachable after address
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+ * is deleted - route is deleted only after last address deletion.
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+ *
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+ * See net/ipv4/fib_frontend.c fib_inetaddr_event,
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+ * net/ipv4/fib_semantics.c fib_sync_down_dev
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+ */
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+
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+ /* If not IPv4, set alive
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+ * Check rn->p->family: for nexthop->type=NEXTHOP_TYPE_IFINDEX it
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+ * depends on destination only
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+ */
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+ if (rn->p.family != AF_INET) {
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alive = true;
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break;
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}
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+
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+ /* Check if there are any IPv4 addresses connected, if yes - set alive */
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+ if (if_has_connected_with_family(ifp, AF_INET)) {
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+ alive = true;
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+ break;
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+ }
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+
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+ /* Otherwise kernel deletes the route */
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}
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if (!alive) {
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@@ -4518,8 +4553,9 @@ static void rib_update_route_node(struct route_node *rn, int type,
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bool re_changed = false;
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RNODE_FOREACH_RE_SAFE (rn, re, next) {
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- if (event == RIB_UPDATE_INTERFACE_DOWN && type == re->type &&
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- type == ZEBRA_ROUTE_KERNEL)
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+ if ((event == RIB_UPDATE_INTERFACE_DOWN ||
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+ event == RIB_UPDATE_KERNEL_LAST_ADDRESS_DELETED) &&
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+ type == re->type && type == ZEBRA_ROUTE_KERNEL)
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rib_update_handle_kernel_route_down_possibility(rn, re);
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else if (type == ZEBRA_ROUTE_ALL || type == re->type) {
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SET_FLAG(re->status, ROUTE_ENTRY_CHANGED);
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@@ -4562,17 +4598,18 @@ void rib_update_table(struct route_table *table, enum rib_update_event event,
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* If we are looking at a route node and the node
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* has already been queued we don't
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* need to queue it up again, unless it is
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- * an interface down event as that we need
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- * to process this no matter what.
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+ * an interface down event or last address down event
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+ * as that we need
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+ * to process these no matter what.
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*/
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- if (rn->info &&
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- CHECK_FLAG(rib_dest_from_rnode(rn)->flags,
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- RIB_ROUTE_ANY_QUEUED) &&
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- event != RIB_UPDATE_INTERFACE_DOWN)
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+ if (rn->info && CHECK_FLAG(rib_dest_from_rnode(rn)->flags, RIB_ROUTE_ANY_QUEUED) &&
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+ event != RIB_UPDATE_INTERFACE_DOWN &&
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+ event != RIB_UPDATE_KERNEL_LAST_ADDRESS_DELETED)
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continue;
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switch (event) {
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case RIB_UPDATE_INTERFACE_DOWN:
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+ case RIB_UPDATE_KERNEL_LAST_ADDRESS_DELETED:
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case RIB_UPDATE_KERNEL:
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rib_update_route_node(rn, ZEBRA_ROUTE_KERNEL, event);
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break;
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--
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2.50.1
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