Summary Data

Some Routers and switches in the core network balances packet load that crosses multiple links in LAG or ECMP by calculating a hash value based on packet header fields. To have a better load balance of traffic on core network fabric, it is essential to support randomized GTP-U source port functionality on the VPP-enabled ASR 5500 platform.

On the S5/S8 interface, the GTP header encapsulates the downlink user traffic with same destination/source IP address, destination/source port, and subscriber TEID. If there are incoming packets of 5 Gbps or higher single UE throughput traffic, the GTP-U traffic’s IP addresses, ports, and TEID are all the same. GTP-U header fields hash polarization leads to uneven load distribution among LAG and ECMP member links and causes packets drop.

For the Downlink Traffic, the VPP does source port randomization based on the inner packet flow. The source port of the outer header (GTP-U packet) is randomized on the S5/S8 interface.

To enable randomized GTP-U source port, in the GTP-U Service Configuration Mode, the source-port non-standard CLI command is added. The port range supported is 32768–33791.

Note	P-GW uses GTP-U interheader to do hashing for load balance and distributes the load evenly to all LAG/interfaces.

Use the following configuration command to enable source port randomization.

configure 
   context context_name 
      gtpu-service service_name 
         source-port non-standard  
   end 

NOTES:

• source-port non-standard : Configures randomized non-standard source port downlink to GTP-U data packets.

show gtpu-service name

The show gtpu-service name gtpu_service_name CLI command now includes the value for the GTPU Source-port non-standard value.