Overlapping IP Pool

Overlapping pools share and use an IP address range. Overlapping pools can either be of type STATIC or PRIVATE. No public pools can be configured as overlapping pools. Each overlapping pool is part of a different VRF (routing domain) and pool-group. Since an APN can use only one pool-group, overlapping pools are part of different APN as well.

Without this functionality, overlapping pools can be configured at SMF. However, chunks from two overlapping pools can't be sent to the same UPF. That is, the UP can't handle chunks from two different overlapping pools. So, same number of UPFs and overlapping pools are required for sharing the same IP address range.

With this functionality, UPF can handle chunks from two different overlapping pools. So, a single UP can handle any number of overlapping pools sharing the same IP range.

The functionality of overlapping pools in the same UPF includes:

  • When a chunk from particular pool is installed on an UP, its corresponding vrf-name is sent along with the chunk.

  • The UPs are made VRF-aware of chunks and therefore, UPs install chunks on the corresponding VRFs and the chunk database is populated under the VRFs.

  • During call allocation, release, recovery, or any communication toward VPNMgr, the corresponding SessMgr at UP includes vrf-id. This enables VPNMgr to select the correct chunk for that IP under the provided vrf-id for processing.

A custom IE, UE IP VRF, is introduced to encapsulate VRF name of UE IP in N4 SESSION ESTABLISHMENT REQUEST message.

SessMgr in UPF converts the received vrf- name into UP VRF CONTEXT ID and passes it on to UPFs VPNMgr in IP allocation request. This UP VRF CONTEXT ID is also used when release request is sent to UPFs VPNMgr. UPFs VPNMgr is made aware of the VRF to which that chunk belongs to by sending vrf-name in each chunk-related communication between SMF and UPF. This enables UPFs VPNMgr to create database of chunks under each VRF enabling support of overlapping pools in the same UPF.

UE IP VRF Information Element

The following is the IE format of the private UE IP VRF.

UE IP VRF Format
Bits
Octets 8 7 6 5 4 3 2 1
1 to 2 Type = 242 (decimal)
3 to 4 Length = n
5 Spare Identical VRF flag IPv6 VRF Valid IPv4 VRF Valid
m to m+1 VRF-1 Name Length = p
m+1 to m+1+p VRF-1 Name
n to n+1 VRF-2 Name Length = q
m+1 to m+1+q VRF-2 Name

The following table shows the possible values of the "UE IP VRF" fields.

Cases UE IP VRF Value (binary)
Bit 3 Bit 2 Bit 1
1 None of the IPv4 and IPv6 UE IP address are associated to VRF. 0 0 0
2 Only IPv4 UE IP address is associated to a VRF 0 0 1
3 Only IPv6 UE IP address is associated to VRF 0 1 0
4 Both IPv4 and IPv6 UE IP address are associated to VRF and are different VRF. 0 1 1
5 Both IPv4 and IPv6 UE IP address are associated to VRF and is common VRF. 1 1 1