Overlapping IP Pool

Overlapping pools share and use an IP address range. Overlapping pools can either be of Static or Private type. Public pools cannot 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 APNs.

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

With this functionality, UPF handles chunks from two different overlapping pools. So, a single UPF 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 a particular pool is installed on UPF, its corresponding vrf-name is sent along with the chunk.

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

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

UE IP VRF is a custom IE that encapsulates the VRF name of N4 SESSION ESTABLISHMENT REQUEST message.

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 addresses 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 addresses are associated to different VRFs. 0 1 1
5 Both IPv4 and IPv6 UE IP addresses are associated to a common VRF. 1 1 1