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fix(ipam): Avoid allocating IPv6 subnet-router anycast address (#21547)

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Ensure available IP selection for IPv6 non-pool prefixes excludes the
subnet-router anycast address (RFC 4291), so allocation starts at ::1
for typical prefixes (e.g. /64).
Add tests for IPv4/IPv6 pools and special cases (/31-/32, /127-/128).

Fixes #21347
This commit is contained in:
Martin Hauser
2026-03-03 17:26:44 +01:00
committed by GitHub
parent 53345f194a
commit 3f02309538
3 changed files with 145 additions and 5 deletions
Download Patch File Download Diff File Expand all files Collapse all files
netbox/ipam/models/ip.py
+5 -3
View File
@@ -432,9 +432,11 @@ class Prefix(ContactsMixin, GetAvailablePrefixesMixin, CachedScopeMixin, Primary
])
available_ips = prefix - child_ips - child_ranges
# IPv6 /127's, pool, or IPv4 /31-/32 sets are fully usable
if (self.family == 6 and self.prefix.prefixlen >= 127) or self.is_pool or (
self.family == 4 and self.prefix.prefixlen >= 31
# Pool, IPv4 /31-/32 or IPv6 /127-/128 sets are fully usable
if (
self.is_pool
or (self.family == 4 and self.prefix.prefixlen >= 31)
or (self.family == 6 and self.prefix.prefixlen >= 127)
):
return available_ips
netbox/ipam/tests/test_tables.py
+129
View File
@@ -39,3 +39,132 @@ class AnnotatedIPAddressTableTest(TestCase):
iprange_checkbox_count = html.count(f'name="pk" value="{self.ip_range.pk}"')
self.assertEqual(iprange_checkbox_count, 0)
def test_annotate_ip_space_ipv4_non_pool_excludes_network_and_broadcast(self):
prefix = Prefix.objects.create(
prefix=IPNetwork('192.0.2.0/29'), # 8 addresses total
status='active',
is_pool=False,
)
data = annotate_ip_space(prefix)
self.assertEqual(len(data), 1)
available = data[0]
# /29 non-pool: exclude .0 (network) and .7 (broadcast)
self.assertEqual(available.first_ip, '192.0.2.1/29')
self.assertEqual(available.size, 6)
def test_annotate_ip_space_ipv4_pool_includes_network_and_broadcast(self):
prefix = Prefix.objects.create(
prefix=IPNetwork('192.0.2.8/29'), # 8 addresses total
status='active',
is_pool=True,
)
data = annotate_ip_space(prefix)
self.assertEqual(len(data), 1)
available = data[0]
# Pool: all addresses are usable, including network/broadcast
self.assertEqual(available.first_ip, '192.0.2.8/29')
self.assertEqual(available.size, 8)
def test_annotate_ip_space_ipv4_31_includes_all_ips(self):
prefix = Prefix.objects.create(
prefix=IPNetwork('192.0.2.16/31'), # 2 addresses total
status='active',
is_pool=False,
)
data = annotate_ip_space(prefix)
self.assertEqual(len(data), 1)
available = data[0]
# /31: fully usable
self.assertEqual(available.first_ip, '192.0.2.16/31')
self.assertEqual(available.size, 2)
def test_annotate_ip_space_ipv4_32_includes_single_ip(self):
prefix = Prefix.objects.create(
prefix=IPNetwork('192.0.2.100/32'), # 1 address total
status='active',
is_pool=False,
)
data = annotate_ip_space(prefix)
self.assertEqual(len(data), 1)
available = data[0]
# /32: single usable address
self.assertEqual(available.first_ip, '192.0.2.100/32')
self.assertEqual(available.size, 1)
def test_annotate_ip_space_ipv6_non_pool_excludes_anycast_first_ip(self):
prefix = Prefix.objects.create(
prefix=IPNetwork('2001:db8::/126'), # 4 addresses total
status='active',
is_pool=False,
)
data = annotate_ip_space(prefix)
# No child records -> expect one AvailableIPSpace entry
self.assertEqual(len(data), 1)
available = data[0]
# For IPv6 non-pool prefixes (except /127-/128), the first address is reserved (subnet-router anycast)
self.assertEqual(available.first_ip, '2001:db8::1/126')
self.assertEqual(available.size, 3) # 4 total - 1 reserved anycast
def test_annotate_ip_space_ipv6_127_includes_all_ips(self):
prefix = Prefix.objects.create(
prefix=IPNetwork('2001:db8::/127'), # 2 addresses total
status='active',
is_pool=False,
)
data = annotate_ip_space(prefix)
self.assertEqual(len(data), 1)
available = data[0]
# /127 is fully usable (no anycast exclusion)
self.assertEqual(available.first_ip, '2001:db8::/127')
self.assertEqual(available.size, 2)
def test_annotate_ip_space_ipv6_128_includes_single_ip(self):
prefix = Prefix.objects.create(
prefix=IPNetwork('2001:db8::1/128'), # 1 address total
status='active',
is_pool=False,
)
data = annotate_ip_space(prefix)
self.assertEqual(len(data), 1)
available = data[0]
# /128 is fully usable (single host address)
self.assertEqual(available.first_ip, '2001:db8::1/128')
self.assertEqual(available.size, 1)
def test_annotate_ip_space_ipv6_pool_includes_anycast_first_ip(self):
prefix = Prefix.objects.create(
prefix=IPNetwork('2001:db8:1::/126'), # 4 addresses total
status='active',
is_pool=True,
)
data = annotate_ip_space(prefix)
self.assertEqual(len(data), 1)
available = data[0]
# Pools are fully usable
self.assertEqual(available.first_ip, '2001:db8:1::/126')
self.assertEqual(available.size, 4)
netbox/ipam/utils.py
+11 -2
View File
@@ -78,12 +78,21 @@ def annotate_ip_space(prefix):
records = sorted(records, key=lambda x: x[0])
# Determine the first & last valid IP addresses in the prefix
if prefix.family == 4 and prefix.mask_length < 31 and not prefix.is_pool:
if (
prefix.is_pool
or (prefix.family == 4 and prefix.mask_length >= 31)
or (prefix.family == 6 and prefix.mask_length >= 127)
):
# Pool, IPv4 /31-/32 or IPv6 /127-/128 sets are fully usable
first_ip_in_prefix = netaddr.IPAddress(prefix.prefix.first)
last_ip_in_prefix = netaddr.IPAddress(prefix.prefix.last)
elif prefix.family == 4:
# Ignore the network and broadcast addresses for non-pool IPv4 prefixes larger than /31
first_ip_in_prefix = netaddr.IPAddress(prefix.prefix.first + 1)
last_ip_in_prefix = netaddr.IPAddress(prefix.prefix.last - 1)
else:
first_ip_in_prefix = netaddr.IPAddress(prefix.prefix.first)
# For IPv6 prefixes, omit the Subnet-Router anycast address (RFC 4291)
first_ip_in_prefix = netaddr.IPAddress(prefix.prefix.first + 1)
last_ip_in_prefix = netaddr.IPAddress(prefix.prefix.last)
if not records: