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Flow of Packets in a Services Control Gateway Network

 

TDF subscriber-aware services are supported only on XLP-based line cards. All other services configured as part of next-hop style services can be either on XLR/XLP/Trio (inline). Interface style service on the access interface is not supported.

Uplink Packet Flow

The following events occur during the packet flow from subscriber edge network element facing Interface to internet (Uplink)

  1. A packet enters the subscriber edge network element facing interface or the access-facing interface from a subscriber. If it matches the exclude implicit filters configured on the TDF subscriber demultiplexer next-hop, then subscriber TDF Lookup is bypassed and the packet is sent to route lookup. If the packet is a RADIUS control packet, it matches the route implicit filter; so it is steered to the session PIC using a load- balancing algorithm. If the packet is not a RADIUS control packet, then it is TDF non-Subscriber traffic and the packet undergoes route lookup for being forwarded.

  2. If the received packet on subscriber edge network element facing interface does not match the exclude implicit filters, then it undergoes route lookup in the subscriber demux table and steered to TDF logical interface (mif) ingress processing. On the mif- interface, packet that matches the subscriber service filter is steered to the service Packet Forwarding Engine for subscriber-aware services and unmatched packets are subjected to route lookup and forwarded to the Internet.

  3. Packet that do not match the learned subscriber route prefix in the subscriber route table is sent to one of the available service PFEs through the mif- interface using prefix (source IP prefix) based load-balancing algorithm.

Downlink Packet Flow

The following events occur during the packet flow from the PDN (Internet) facing interface to the subscriber edge network element (downlink):

  1. A packet enters the PDN-facing interface. Route lookup on the packet results in sending the packet to subscriber edge network element facing interface for egress processing.

  2. On the subscriber edge network element-facing interface egress processing, if the packet matches the exclude filters then it is considered as a TDF non-subscriber packet and it is transmitted out. On the subscriber edge network element-facing Interface egress processing, if the packet does not match the exclude filters , then it is subjected to destination IP based subscriber demultiplex lookup, which results in running the mif- topology.

  3. On the mif- interface, the packet that matches the subscriber service filter is steered to the service Packet Forwarding Engine for subscriber-aware services and any unmatched packet is sent back to subscriber edge network element facing egress processing by looping back on the local Interface. Packets that do not match the subscriber learned prefix in the subscriber demultiplexer table are sent to one of the available service PFEs through the mif- interface egress processing using prefix (destination IP prefix)-based load balancing algorithm. Packets that correspond and map to the subscriber learned prefix are sent to the control plane-configured service Packet Forwarding Engine for subscriber-aware processing.

  4. After performing the subscriber services on the services Packet Forwarding Engine, a route lookup is performed, which causes the packet to be sent to the subscriber edge network element facing interface’s egress processing for a second parsing. Subscriber-aware services are already done in the first parsing, which causes TDF Subscriber demux NH to be excluded and the packet is propagated out of the interface.