Unsupported MLPPP Features

The router does not support the following MLPPP features:

• Short sequence numbers
• Resequencing out-of-order packets in the absence of fragmentation

  Given the location in the network where the router resides, the NxT1 links to a customer site represent one of many places across the IP network where packets might be received out of order. For example, if the router has multiple uplinks to a core router, packets might be received out of order across these links.

  You can lose packets if you transmit layer 2 traffic on an MPLS LSP that passes over an MLPPP link bundle.

  Packets are passed along to the next protocol layer in the order that they are processed. Packet resequencing is therefore performed at the end station rather than the aggregation router. IP datagrams can be resequenced by the end station using the IP identification field.

  Layer 2 packets such as Ethernet/MPLS and ATM-AAL5/MPLS have no sequence number information and are sent in the order received. The packets are dropped if their out-of-order condition is detected by a downstream device.

  Frame Relay/MPLS packets do have a native sequence number in the header and are rejected at the end of the LSP if the MLPPP sequence number order is violated.

  To ensure that the router maintains the proper packet order when transmitting high-priority (non-best-effort) packets such as voice and video, you can use the ppp hash-link-selection command to enable use of a hash-based algorithm to select the link on which the router transmits high-priority packets on an MLPPP interface. For details, see MLPPP Link Selection.