Figure 40: Queuing on Constituent Links
When LFI is enabled, all large packets are fragmented. These packet fragments have a multilink header that contains a multilink sequence number. The sequence numbers on the fragments must be preserved so that the remote router receiving these fragments can correctly reassemble them into a complete packet. To accommodate this requirement, the software queues all fragmented packets on constituent links of a multilink bundle to a single queue (Q0), by default.
Although they are not fragmented, data packets smaller than the fragmentation threshold are also queued to Q0.
When you configure CRTP with LFI, CRTP packets on a multilink bundle from queues other than Q2 are queued to Q2 (instead of Q0) on the constituent links. Because CRTP packets are compressed and do not require fragmentation, they are treated as LFI (voice) packets and are sent to Q2 on the constituent links.
Figure 40 shows how traffic is queued on an MLPPP or MLFR multilink bundle and its constituent links. Irrespective of the packet queuing on the multilink bundle, the packets on the constituent links are queued according to the default setting so that traffic from all queues except Q2 is mapped to Q0.
Figure 40: Queuing on Constituent Links
On a multilink bundle, packet fragments from all queues except Q2 are transmitted to Q0 on constituent links. On the Q0s of constituent links, the packets are queued in a weighted round-robin fashion to enable per-fragment load balancing.
Figure 41 shows how queuing is performed on the constituent links.
Figure 41: Queuing on Q0 of Constituent Links
Packet fragments from the multilink bundle are queued to constituent links one by one in a weighted round-robin fashion. Packet 1 from Q0 on the multilink bundle is queued to Q0 on Constituent Link 1, packet 2 from Q1 on the multilink bundle is queued to Q0 on Constituent Link 2, packet 3 from Q3 on the multilink bundle is queued to Q0 on Constituent Link 1,and so on.
On a multilink bundle, all Q2 traffic (LFI traffic) from the multilink bundle is queued to Q2 of constituent links based on a hash computed from the source address, destination address, and IP protocol of the packet. If the IP payload is TCP or UDP traffic, the hash also includes the source port and destination port. As a result of this hash algorithm, all traffic belonging to one traffic flow is queued to Q2 of one constituent link.