DVR: Increase the link-local address pair range

The current dvr_fip_ns.py file has FIP_LL_SUBNET configured
with a subnet prefixlen of /23 which only allows 255 pairs of
link-local addresses to be generated. If the number of routers
per-node increases beyond the 255 limit it raises an assertion.

This patch increases the link-local address cidr to be a /18
to allow for 8K routers. The new range was chosen to not
overlap with the original, allowing for in-place upgrades
without affecting existing routers.

Closes-Bug: #1562110
Change-Id: I6e11622ea9cc74b1d2428757f16aa0de504ac31a
(cherry picked from commit 7b1b8c2de5)

neutron/agent/l3/dvr_fip_ns.py

@@ -31,7 +31,7 @@ FIP_2_ROUTER_DEV_PREFIX = 'fpr-'
 ROUTER_2_FIP_DEV_PREFIX = namespaces.ROUTER_2_FIP_DEV_PREFIX
 # Route Table index for FIPs
 FIP_RT_TBL = 16
-FIP_LL_SUBNET = '169.254.30.0/23'
+FIP_LL_SUBNET = '169.254.64.0/18'
 # Rule priority range for FIPs
 FIP_PR_START = 32768
 FIP_PR_END = FIP_PR_START + 40000

neutron/agent/l3/item_allocator.py

@@ -74,7 +74,9 @@ class ItemAllocator(object):
             self.pool.update(self.remembered.values())
             self.remembered.clear()
             if not self.pool:
-                # More than 256 routers on a compute node!
+                # The number of address pairs allocated from the
+                # pool depends upon the prefix length specified
+                # in FIP_LL_SUBNET
                 raise RuntimeError("Cannot allocate item of type:"
                                    " %s from pool using file %s"
                                    % (self.ItemClass, self.state_file))

neutron/agent/linux/keepalived.py

@@ -31,7 +31,7 @@ VALID_AUTH_TYPES = ['AH', 'PASS']
 HA_DEFAULT_PRIORITY = 50
 PRIMARY_VIP_RANGE_SIZE = 24
 # TODO(amuller): Use L3 agent constant when new constants module is introduced.
-FIP_LL_SUBNET = '169.254.30.0/23'
+FIP_LL_SUBNET = '169.254.64.0/18'
 KEEPALIVED_SERVICE_NAME = 'keepalived'
 GARP_MASTER_DELAY = 60