Stop allocating network and broadcast addresses

When an allocation pool range is not defined by the operator, we should
not include network and broadcast addresses in the list of IP addresses
to give to hosts.

Change-Id: Id6e14286b5eb2b767a515e7edfc56741fb8d2c78
Story: 2006267
Task: 35958

ansible/roles/ip-allocation/library/ip_allocation.py

@@ -147,6 +147,9 @@ def update_allocation(module, allocations):
             allocation_pool = netaddr.IPSet(allocation_pool)
         else:
             allocation_pool = netaddr.IPSet([network])
+            if network.prefixlen != 32:
+                reserved_ips = [network.network, network.broadcast]
+                allocation_pool -= netaddr.IPSet(reserved_ips)
         free_ips = allocation_pool - allocated_ips
         for free_cidr in free_ips.iter_cidrs():
             ip = free_cidr[0]

doc/source/configuration/network.rst

@@ -157,10 +157,12 @@ To configure a network called ``example`` with VLAN ID ``123``:
 IP Address Allocation
 =====================
 
-IP addresses are allocated automatically by Kayobe from the
-allocation pool
-defined by ``allocation_pool_start`` and ``allocation_pool_end``.  The
-allocated addresses are stored in
+IP addresses are allocated automatically by Kayobe from the allocation pool
+defined by ``allocation_pool_start`` and ``allocation_pool_end``. If these
+variables are undefined, the entire network is used, except for network and
+broadcast addresses. IP addresses are only allocated if the network ``cidr`` is
+set and DHCP is not used (see ``bootproto`` in
+:ref:`configuration-network-per-host`). The allocated addresses are stored in
 ``${KAYOBE_CONFIG_PATH}/network-allocation.yml`` using the global per-network
 attribute ``ips`` which maps Ansible inventory hostnames to allocated IPs.
 
@@ -264,6 +266,8 @@ To configure a network called ``example`` with a default route and a
      - cidr: 10.1.0.0/24
        table: exampleroutetable
 
+.. _configuration-network-per-host:
+
 Per-host Network Configuration
 ==============================
 

releasenotes/notes/restrict-ip-allocation-8e20022110c2283e.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    Stops allocating network and broadcast addresses to hosts when an allocation pool
+    is not defined.