Marking and Re-marking
The OpenArchitect switch can mark or remark packets using the TOS field or 802.1p tag. This is
also controlled through the Linux
iptables
utility.
Scheduling
The servicing of configured queues by the switching fabric is referred to as scheduling. The
OpenArchitect switch has three built-in scheduling algorithms. The type of scheduling algorithm
used is implied, rather than being explicitly specified, based on the number of queues and which
options are configured. The following scheduling algorithms are provided:
First In First Out (FIFO) – When only one queue is configured per port, packets are serviced in
the order in which they arrive. This is the default for the OpenArchitect switch.
Strict Priority – This algorithm is used when more than one queue is provisioned on the port. The
highest priority queue, which is also the highest numbered one, is always serviced first (Example:
If four queues are configured, queue three is of higher priority than queue zero). As long as there
are packets in the highest priority queue, the lower priority queues are not serviced. The danger is
that higher priority traffic could block lower priority traffic.
Weighted Round Robin (WRR) – This algorithm is similar to Strict Priority scheduling, but it
provides fairness with quanta for each queue. Each queue is assigned a number of packets, known
as
weight
, that it is allowed to transmit before it yields to a lower priority queue. Note that with
WRR, the priorities of the queues are dependent on the weights allocated. A higher priority queue
with a smaller weight will get less wire-time than a lower priority queue configured with a larger
weight. The relative weights used for priority queues on a port can be set using the
zcos
command (this is a switch-wide parameter).
ztmd
Explained
ztmd
is a traffic management daemon which accepts messages from traffic filtering and quality
of service applications and sets up the hardware.
zfilterd
Explained
zfilterd
is a daemon that intercepts filtering rules entered by the user via
iptables
, checks
them for validity and then passes them on to
ztmd
for entry in the switch.
Running
zfilterd
Before starting
zfilterd
,
ztmd
must be running. Your can start both from within a script, or
directly from the command line. For example,
ztmd
zfilterd
iptables
rules can be entered at any time. If your
iptables
filtering rules set is extensive,
Ethernet Switch Blade User's Guide
release 3.2.2j
page 58
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