[ovs-dev] [PATCH] ovn: Prevent erroneous duplicate IP address

Mark Michelson mmichels at redhat.com
Wed Aug 28 18:05:40 UTC 2019

When using dynamic address assignment for logical switches, OVN reserves
the first address in the subnet for the attached router port to use.

In commit 488d153ee87841c042af05bc0eb8b5481aaa98cf, the IPAM code was
modified to add assigned router port addresses to IPAM. The use case for
this was when a switch was joined to multiple routers, and all router
addresses were dynamically assigned.

However, that commit also made it so that when a router rightly claimed
the first address in the subnet, ovn-northd would issue a warning about
a duplicate IP address being set. This change fixes the issue by adding
a special case so that we don't add the router's IP address to IPAM if
it is the first address in the subnet. This prevents the warning message
from appearing.

Signed-off-by: Mark Michelson <mmichels at redhat.com>
Acked-by: Numan Siddique <nusiddiq at redhat.com>
Acked-by: Han ZHou <hzhou8 at ebay.com>
This is a backport of a patch from the ovn repo.
 ovn/northd/ovn-northd.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/ovn/northd/ovn-northd.c b/ovn/northd/ovn-northd.c
index 2abf1f897..7827830b6 100644
--- a/ovn/northd/ovn-northd.c
+++ b/ovn/northd/ovn-northd.c
@@ -1194,7 +1194,14 @@ ipam_add_port_addresses(struct ovn_datapath *od, struct ovn_port *op)
         for (size_t i = 0; i < lrp_networks.n_ipv4_addrs; i++) {
             uint32_t ip = ntohl(lrp_networks.ipv4_addrs[i].addr);
-            ipam_insert_ip(op->peer->od, ip);
+            /* If the router has the first IP address of the subnet, don't add
+             * it to IPAM. We already added this when we initialized IPAM for
+             * the datapath. This will just result in an erroneous message
+             * about a duplicate IP address.
+             */
+            if (ip != op->peer->od->ipam_info.start_ipv4) {
+                ipam_insert_ip(op->peer->od, ip);
+            }

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