Topology Address Pools

Lab topology transformation code assigns IPv4 and IPv6 subnets (prefixes) to individual links and loopback interfaces from address pools. Node addresses are then assigned from the prefixes assigned to individual links.

Tip

You can assign a static prefix to a link with prefix link attribute and static IP address to an interface with an ipv4 or ipv6 attribute of node-on-link data. For more details, see static link addressing.

netsim-tools use multiple predefined address pools:

  • mgmt pool: Management IPv4 and MAC addresses. IPv6 addresses are assigned if specified, but not used at the moment.

  • loopback pool: Loopback IPv4 and IPv6 addresses.

  • lan pool: IPv4 and IPv6 addresses used all links apart from P2P links (links with more or less than two nodes attached to them), or links with type set to lan.

  • p2p pool: IPv4 and IPv6 addresses used on point-to-point links

  • router_id pool is used to allocate BGP router IDs in IPv6-only networks.

  • l2only pool has no IPv4 or IPv6 addresses. You can use it to create L2-only links. See layer-2-only pools and Using l2only Address Pool for details.

  • vrf_loopback pool: IPv4 and IPv6 prefixes used on optional VRF loopback interfaces.

You can specify additional address pools, and use them with the role link attribute.

Default IPv4 address pools are defined in system settings:

addressing:
  loopback:
    ipv4: 10.0.0.0/24
  router_id:
    ipv4: 10.0.0.0/24
    prefix: 32
  lan:
    ipv4: 172.16.0.0/16
  p2p:
    ipv4: 10.1.0.0/16
  mgmt:
    ipv4: 192.168.121.0/24
    start: 100
    mac: 08-4F-A9-00-00-00
  l2only:
  vrf_loopback:
    ipv4: 10.2.0.0/24
    prefix: 32

You can override or augment them in topology addressing element. You can also override individual defaults.addressing components.

Dual-Stack Support

Every address pool could have an IPv4 and an IPv6 prefix, supporting IPv4-only, dual-stack or IPv6-only deployments. Pool address space is specified in ipv4 or ipv6 CIDR prefix. Size of individual IPv4 address allocations is specified with the prefix parameter, IPv6 prefixes are currently fixed (/64).

Specifying Address Pools

Address pools could be specified:

  • In addressing or defaults.addressing part of topology YAML file

  • In addressing part of local or global defaults file.

Notes:

  • Local defaults file is specified with --defaults CLI option (default value: topology-defaults.yml in current directory)

  • Global defaults file is topology-defaults.yml in netsim package directory.

Each address pool specification is a dictionary of address pools. Individual address pools are specified with these parameters:

  • ipv4 – IPv4 CIDR prefix or true for unnumbered IPv4 links

  • ipv6 – IPv6 CIDR prefix or true for LLA-only IPv6 links.

  • unnumbered – unnumbered address pool. Interfaces attached to nodes based on this address pool will have IPv4 and/or IPv6 enabled based on the protocols enabled on node’s loopback interface.

  • prefix - IPv4 subnet allocation size. IPv6 subnets use /64 prefixes that cannot be changed.

  • start - first subnet or first IP address offset. Used primarily with loopback pool to ensure the first devices gets x.x.x.1/32 IP address, and with mgmt pool to specify the first management IP address.

Notes:

  • Default IPv4 subnet allocation size is 32 for loopback pool, 24 for lan pool and 30 for p2p pool. All other pools must specify the prefix parameter whenever the ipv4 parameter is specified.

  • IPv4 loopback pool starts at .1 (start parameter is assumed to be 1)

  • IPv6 loopback pool starts at the second subnet to make loopback IPv6 address similar to its IPv4 counterpart.

Address Pool Configuration Example

This is the default addressing configuration from global topology-defaults.yml:

addressing:
  loopback:
    ipv4: 10.0.0.0/24
  lan:
    ipv4: 172.16.0.0/16
  p2p:
    ipv4: 10.1.0.0/16
  mgmt:
    ipv4: 192.168.121.0/24
    start: 100
    mac: 08-4F-A9-00-00-00
  • It specifies IPv4-only addressing scheme

  • Loopback IP addresses are assigned from 10.0.0.0/24 CIDR block. The first assigned address is 10.0.0.1/32 (see notes above for details).

  • LAN IP addresses are assigned from 172.16.0.0/16 CIDR block. Subnet prefix is /24 (see notes above for details).

  • P2P IP addresses are /30 subnets from 10.1.0.0/16 CIDR block.

  • Management IP addresses are assigned from 192.168.121.0/24 CIDR block. The first IP address is 192.168.121.101 (start offset plus node ID)

  • MAC addresses of management interfaces start with 08-4F-A9. The last byte of the MAC address is the node ID.

Unnumbered Interface Support

netsim-tools supports unnumbered IPv4 and IPv6 interfaces:

  • Unnumbered IPv4 interfaces are not supported on all platforms and use loopback address as the proxy address of the unnumbered interface.

  • Unnumbered IPv6 interfaces use only LLA IPv6 address – IPv6 is enabled on an interface, but no static IPv6 address is assigned to it.

You can create unnumbered interfaces in two ways:

  • Create a custom pool with no ipv4 or ipv6 attribute and set unnumbered attribute true. Interfaces using this address pool will get IPv4 and/or IPv6 enabled based on protocols enabled on the loopback interface.

  • Use ipv4: true or ipv6: true instead of specifying an IPv4 or IPv6 prefix for the address pool. See Specifying Address Pools section for details.

For more details, see Unnumbered Interface Example below.

Layer-2-only Pools

An address pool with no attributes is a layer-2-only pool. Links using such a pool have no IPv4/IPv6 prefix, and interfaces attached to such links get no IPv4/IPv6 address assigned from the on-link prefix.

netsim-tools has predefined l2only pool that you can use to create layer-2-only links, for example:

# CLNS lab
#
nodes: [ r1, r2, r3 ]

links:
- r1:
  r2:
  r3:
  role: l2only

Merging Defaults

Numerous default address pool configurations are merged during the topology processing:

  • Local defaults and global defaults are deep-merged with defaults dictionary in topology file

  • defaults.addressing topology section is deep-merged with addressing topology section

  • Legacy parameters (release 0.1 syntax) from the defaults topology section are deep-merged with the addressing section (making them least-preferred).

For more information on deep merging, please read the topology defaults document.

Example

The following address configuration in lab topology file…

addressing:
  loopback:
    ipv6: 2001:db8:0::/48
  lan:
    ipv4: 10.2.0.0/16
    ipv6: 2001:db8:1::/48
    prefix: 26

… results in the following address pools when combined with the global defaults (see above):

lan:
  ipv4: 10.2.0.0/16
  ipv6: 2001:db8:1::/48
  prefix: 26
loopback:
  ipv4: 10.0.0.0/24
  ipv6: 2001:db8:0::/48
  prefix: 32
mgmt:
  ipv4: 192.168.121.0/24
  mac: 08-4F-A9-00-00-00
  start: 100
p2p:
  ipv4: 10.1.0.0/16
  prefix: 30

Unnumbered Interface Example

The following topology file creates a LAN and an unnumbered P2P link between a pair of Cisco CSR1000v routers:

addressing:
  core:
    unnumbered: true

defaults:
  device: csr

nodes:
- r1
- r2

links:
- name: Unnumbered link between R1 and R2
  r1:
  r2:
  role: core

- name: LAN link between R1 and R2
  r1:
  r2:
  type: lan

The topology results in the following Ansible inventory data for R1 (please note ipv4: true attribute and lack of IPv4/IPv6 addresses on the first link).

---
box: cisco/csr1000v
links:
- ifindex: 2
  ifname: GigabitEthernet2
  ipv4: true
  linkindex: 1
  name: Unnumbered link between R1 and R2
  neighbors:
    r2:
      ifname: GigabitEthernet2
      ipv4: true
  remote_id: 2
  remote_ifindex: 2
  role: core
  type: p2p
  unnumbered: true
- bridge: X_2
  ifindex: 3
  ifname: GigabitEthernet3
  ipv4: 172.16.0.1/24
  linkindex: 2
  name: LAN link between R1 and R2
  neighbors:
    r2:
      ifname: GigabitEthernet3
      ipv4: 172.16.0.2/24
  type: lan
loopback:
  ipv4: 10.0.0.1/32
mgmt:
  ifname: GigabitEthernet1
  ipv4: 192.168.121.101
  mac: 08-4F-A9-00-00-01