Instances on a provider network is unreachable when more than 200 neutron routers are associated to the network

Issue

• Instances on a provider network is not reachable. Neither ping or arping work.

  $ arping -I eth1 10.0.0.10
  ARPING 10.0.0.10 from 10.0.0.1 eth1
  
  $ ping 10.0.0.10
  PING 10.0.0.10 (10.0.0.10) 56(84) bytes of data.
  From 10.0.0.1 icmp_seq=1 Destination Host Unreachable
  From 10.0.0.1 icmp_seq=2 Destination Host Unreachable
  From 10.0.0.1 icmp_seq=3 Destination Host Unreachable
  

• The instance is connected to the provider network

  $ openstack server show instance_01 -c addresses -c name
  +-----------+----------------------------------+
  | Field     | Value                            |
  +-----------+----------------------------------+
  | addresses | provider_network_01=10.0.0.10    |
  | name      | instance_01                      |
  +-----------+----------------------------------+
  

• Another instance which is connected to a private network and assigned a floating IP address is reachable

  $ openstack server create instance_02 --network proviate_network_01
  $ openstack create floating ip provider_network_01
  $ openstack server add floating ip instance_02 10.0.0.11
  $ openstack server show instance_02 -c addresses -c name
  +-----------+--------------------------------------------+
  | Field     | Value                                      |
  +-----------+--------------------------------------------+
  | addresses | private_network_01=10.0.0.11, 192.168.0.11 |
  | name      | instance_02                                |
  +-----------+--------------------------------------------+
  
  $ ping 10.0.0.11
  PING 10.0.0.11 (10.0.0.11) 56(84) bytes of data.
  64 bytes from 10.0.0.11: icmp_seq=1 ttl=62 time=9.61 ms
  64 bytes from 10.0.0.11: icmp_seq=2 ttl=62 time=1.96 ms
  64 bytes from 10.0.0.11: icmp_seq=3 ttl=62 time=1.10 ms
  

• The provider network has more than 200 associated neutron routers

  $ openstack router list|grep ACTIVE |wc -l
  250
  $ openstack port list --network provider_network_01 --long |grep router |wc -l
  250