Allow IPv4 link-local nexthops (sonic-net#1903)

*Orchagent (NeighOrch) currently ignores IPv4 link-local neighbours. Any route pointing to such a nexthop is not added to the ASIC DB. Such routes are expected and should be supported.
Signed-off-by: Utpal Kant Pintoo [email protected]

orchagent/neighorch.cpp

@@ -685,19 +685,6 @@ void NeighOrch::doTask(Consumer &consumer)
 
  IpAddress ip_address(key.substr(found+1));
 
- /* Verify Ipv4 LinkLocal and skip neighbor entry added for RFC5549 */
- if ((ip_address.getAddrScope() == IpAddress::LINK_SCOPE) && (ip_address.isV4()))
- {
- /* Check if this prefix is not a configured ip, if so allow */
- IpPrefix ipll_prefix(ip_address.getV4Addr(), 16);
- if (!m_intfsOrch->isPrefixSubnet (ipll_prefix, alias))
- {
- SWSS_LOG_NOTICE("Skip IPv4LL neighbor %s, Intf:%s op: %s ", ip_address.to_string().c_str(), alias.c_str(), op.c_str());
- it = consumer.m_toSync.erase(it);
- continue;
- }
- }
-
  NeighborEntry neighbor_entry = { ip_address, alias };
 
  if (op == SET_COMMAND)
@@ -807,6 +794,18 @@ bool NeighOrch::addNeighbor(const NeighborEntry &neighborEntry, const MacAddress
  memcpy(neighbor_attr.value.mac, macAddress.getMac(), 6);
  neighbor_attrs.push_back(neighbor_attr);
 
+ if ((ip_address.getAddrScope() == IpAddress::LINK_SCOPE) && (ip_address.isV4()))
+ {
+ /* Check if this prefix is a configured ip, if not allow */
+ IpPrefix ipll_prefix(ip_address.getV4Addr(), 16);
+ if (!m_intfsOrch->isPrefixSubnet (ipll_prefix, alias))
+ {
+ neighbor_attr.id = SAI_NEIGHBOR_ENTRY_ATTR_NO_HOST_ROUTE;
+ neighbor_attr.value.booldata = 1;
+ neighbor_attrs.push_back(neighbor_attr);
+ }
+ }
+
  MuxOrch* mux_orch = gDirectory.get<MuxOrch*>();
  bool hw_config = isHwConfigured(neighborEntry);