5G UE disconnects if IPv6 IP Block and APN PTN are not correctly provisioned

[jblakley]

In Magma 5G, a UE will connect to gNB/AGW for roughly 10 seconds and then disconnect. The root cause of this issue is not provisioning of IPv6 address space in Orchestrator (even if IPv6 is not used in the deployment).

Your Environment

• Version: pre-1.9
• Affected Component: Orchestrator, Access Gateway, and NMS
• Affected Subcomponent: mobilityd
• Deployment Environment: Local Orc8r and containerized AGW with Sercomm gNB & Global Telecomm Titan 5000 5G gateway

Describe the Issue

If the network admin fails to specify a) an IPv6 address range in the EPC and b) set the APN PTN to IPv4v6, a 5G UE will initially connect to the network but, after 10 seconds, the connection will drop. A warning message appears in mobilityd log: IPv4/IPv6 IP address allocation not successful. Reconnection may require a UE reboot.

In lte/gateway/python/magma/mobilityd/rpc_servicer.py
the following code throws an exception when IPv6 addresses are not configured.

try:
    ipv4_address = ipv4_response.ip_list[0]
    ipv6_address = ipv6_response.ip_list[0]
except IndexError:
    logging.warning("IPv4/IPv6 IP address allocation not successful")
    resp = AllocateIPAddressResponse()
else:
    resp = AllocateIPAddressResponse(
        ip_list=[ipv4_address, ipv6_address],
        vlan=ipv4_response.vlan,
    )

To Reproduce

1. Create a network in Orc8r and configure for 5G per this.

2. In NMS, don't configure IPv6

   • Equipment->Gateway->GW-ID->EPC->Edit. Leave IPv6 Block empty
   • Traffic->APN->APN ID. Leave PDN Type as IPv4

3. Provision and connect gNB

4. Provision and connect UE

Expected behavior

If the network admin configures the network only for IPv4, magma should ignore IPv6 errors during UE connection and assign IPv4 addresses only.

Some possible solutions:

• Change code to handle failure to assign IP block more smoothly
• Pre-populate the IPv6 Block with default addresses
• Update documentation to make clear ramifications of failure to populate

Screenshots

The disconnect looks as follows in wireshark.

The zipped pcap file is attached.
ue-connect-release-while-pinging-2023-02-16.zip

Additional context

See this github issue for more detail/background.