Virtual output queue allocation using dynamic drain bandwidth

A network device comprising:

• a plurality of forwarding units each comprising a packet forwarding engine and an interface;
• a switch fabric connecting the plurality of forwarding units, wherein an ingress forwarding unit for a packet flow internally forwards packets of the packet flow to an egress one of the forwarding units for the packet flow by the switch fabric;
• an output queue of the egress forwarding unit, wherein the output queue is associated with the interface of the egress forwarding unit;
• a Virtual Output Queue (VOQ) of the ingress forwarding unit that comprises a logical queue that corresponds to an output queue of the egress forwarding unit, wherein a size of the VOQ comprises a portion of a logical size of the output queue, wherein the logical size of the output queue is divided among a plurality of VOQs of a plurality of respective ingress forwarding units for the packet flow that includes at least the ingress forwarding unit;
• and
• a congestion manager of the ingress forwarding unit that determines a change in a drain rate at which network packets are forwarded from a Virtual Output Queue (VOQ) of an ingress forwarding unit of the network device to an egress forwarding unit of the network device, wherein the drain rate of the VOQ is based on a respective drain rate for each of the VOQs of the plurality of respective ingress forwarding units that is forwarding network packets to the egress forwarding unit,
• wherein the congestion manager, in response to determining the change in the drain rate, modifies the size of the VOQ in direct proportion to the determined change in the drain rate.