How it Works

This section provides a brief of how the Static IP Support feature works.

The SMF receives a framed IP address of the subscriber from external AAA servers, such as RADIUS. While IPAM is not involved in individual IP address management in this scenario, it still handles the route management and UPF management for static address ranges.

IPAM splits the ‘static’ address ranges equally according to number of UPFs present in the SMF configuration. Unlike dynamic IP, IPAM splits all static IP address ranges and assigns them for all configured UPFs. IPAM involves and selects an UPF when the external AAA server returns the framed IP of the subscriber. IPAM looks for the route which includes this static IP and then selects the UPF where the route is already configured.

The following figure shows how the static IP address is assigned to the configured UPFs.

Static IP Address Management Procedure


  1. IPAM splits the static ranges into equal number of address ranges based on the number of configured UPFs.

  2. The UPMGR programs the corresponding static routes on the associated UPFs.

  3. Subscribers get static IP from RADIUS server authorization response.

  4. SMF service selects the right UPF based on address ranges and UPF map allocation from the Node Manager.

Address Range Split

Splitting a given address range into smaller address ranges is a key functionality of the IPAM server and IPAM cache. The following guidelines determine address range split:

  • Size of a split address range depends on the configured value or the default value as per the Authority and Format Identifier (AFI) type.

  • Size of a split address range must be a power of 2 or at least to the closest of it. That is, it should be able to represent the split range in subnet/mask notation such that a route can be added in the data plane (user plane) if required.

  • Configured or default address range size must be at the power of 2.

The address range must be split into smaller ranges immediately on configuration or initial start-up. This helps in better sorting of address ranges based on size and faster allocation during actual address range allocation requests. The address range exchange between modules is always in the mentioned size.

Examples of IPv4 Address Range Split

Address Range

Split Size (number of addresses per range)

Split Ranges

(* Odd sized ranges)

Route Notation

209.165.200.225 - 209.165.200.254

128

[1] 209.165.200.225 – 209.165.200.254

[2] 209.165.202.129 – 209.165.202.158

[1] 209.165.200.224/27

[2] 209.165.202.128/27

209.165.201.1 – 209.165.201.30

256

[1] 209.165.200.224 – 209.165.200.254

[2] 209.165.201.0 – 209.165.201.30

[3] 209.165.202.128 – 209.165.202.158

...

[n] 209.165.200.225 – 209.165.200.253

[1] 209.165.201.1/27

[2] 209.165.200.224/27

[3] 209.165.202.128/27

...

[n] 209.165.201.0/27

209.165.200.229 – 209.165.200.253

256

[1] 209.165.201.1 – 209.165.201.30 *

[2] 209.165.202.129 – 209.165.202.158

[3] 209.165.200.225 – 209.165.200.253 *

[1] 209.165.201.0/27

[2] 209.165.200.224/27

[3] 209.165.202.128/27

Examples of IPv6 Address Range Split

Address Range

Split Size (number of addresses per range)

Split Ranges

(* Odd sized ranges)

Route Notation

1:: - 1::1000

1024

[1] 1:: – 1::3FF

[2] 1::400 – 1::7FF

[3] 1::800 – 1::BFF

[4] 1::C00 – 1::FFF

[1] 1::/118

[2] 1::400/118

[3] 1::800/118

[4] 1::C00/118

1::3 - 1::1DEF

1024

[1] 1::3 – 1::3FF *

[2] 1::400 – 1::7FF

[3] 1::800 – 1::BFF

[n] 1::1C00 – 1::1DEF *

[1] 1::/118

[2] 1::400/118

[3] 1::800/118

[n] 1::1C00/118

Examples of IPv6 Address Range Split

Prefix split needs two length fields for performing the split.

  • Network length

  • Host length

Prefixes are split between these two length fields and a new route is calculated.

Example 1: network-length = 48, prefix-length = 64

Total (64-48) = 16 bits (that is, 65536 prefixes are available for the split)

Example 2: network-length = 32, prefix-length = 56

Total (56-32) = 24 bits (that is, 16 million prefixes available for the split)

Note
For SMF, the host-length is hard-coded as ‘64’. Only network-length can be configured using the CLI.
Examples of IPv6 Address Range Split

Prefix Range

Split Size (number of addresses per range)

Split Ranges

(* Odd sized ranges)

Route Notation

1:2:3::

Nw-len = 48

Host-len = 64

8192

[1]1:2:3:: ... 1:2:3:1fff

[2]1:2:3:2000:: ... 1:2:3:2fff::

[3]1:2:3:3000:: ... 1:2:3:3fff::

...

[1]1:2:3::/51

[2]1:2:3:2000/51

[3]1:2:3:3000/51

...