Understanding Load Balancing Using Source or Destination IP Only
In deep packet inspection (DPI) networks with per-subscriber awareness or transparent caches, all of the PE routers in the service provider network should route all traffic to and from a particular subscriber through the specific content server that maintains subscriber state for that subscriber. To reach the same server consistently, the traffic must be hashed onto the same link towards that specific server for traffic in both directions.
In order to accomplish this consistency, certain MX Series routers can be configured to make load-balancing decisions based solely on the source IP address or the destination IP address of the traffic. From a service provider perspective, using only the source IP for inbound traffic, and the destination IP for outbound traffic limits the criteria used in hashing, making it more likely that a particular link will be chosen to forward the traffic.
This feature will only work on IP-based traffic. In the
case of L3VPN traffic, only MPLS lookup will be performed on the PE
routers when the default label assignment scheme is used. In order
to use source-or-destination only load-balancing with L3VPN, you can
either configure vrf-table-label or add a vt- interface
in the routing instance.