ARRIS 2247-N8-10NA (v9.1.x) Admin Handbook - Manual (Page 34)

Administrator’s Handbook
34
set gfs name filterset_name rule number match number value [ value (category-specific) ]
Queue commands
Queue configuration typically requires a classification component to set a QoS marker to a packet and a queue-
ing component to schedule the marked packets to the link. This is accomplished using filtersets (
“Filterset com-
mands” on page 29 ).
The basic queue 's size and “ length ” are controls for how many packets and total bytes can be enqueued
before it is considered to be full. Once it is full, any attempts to enqueue another packet will result in a “tail-
drop.”
Both constraints are simultaneously used, such that it is full when either packet count OR byte count exceeds
the limit. This allows flexibility in obtaining a balance, where a large number of small packets, but only a small
number of large packets can be enqueued.
If there are no tail-drops – that is, the queue is not blocked from sending and doesn't over-fill and dump pack-
ets – then these queue size/bytes parameters do not affect anything. Their only function is to adjust the
threshold at which the queue is considered full, which dictates when tail drops will occur. So if there are no
tail-drops, then increasing the queue length will have no effect. Increasing the queue length has no effect
unless there are tail-drops.
The maximum size/bytes of a queue balances how much burstiness can be buffered versus having a queue that
is simply too long.
Burstiness smoothing requires queueing up the buffers. For example, if the upstream line rate is 1mbps, but
the traffic source sends 100mbps bursts for 10ms every second (which coincidentally averages 1mbps) then
the router will have to buffer enough (about a full second worth of traffic) so that the burst of traffic doesn't
get tail-dropped when it arrives and is enqueued at the same time in the same burst.
On the other hand, it is undesirable to buffer too much data in the queue(s) since the packets may be stale by
the time they are sent. It may be desirable to drop the traffic sufficiently that there are queuing disciplines
such as Random Early Discard (
red ) that don't drop from the tail of the queue. Instead, red drops packets
towards the front of the queue, so that the congestion is noticed more quickly in order for the sender to scale
back bandwidth usage to avoid drops.
the following types of queue “building blocks” are supported:
‹ basic queue
‹ ingress queue
‹ priority queue
‹ wfq (weighted fair queue)
NOTE:
A rule cannot contain data that specifies both IPv6 and IPv4 at the same time, and thus be applicable to nei-
ther iptables nor ip6tables; however, a rule can be IP-version-agnostic, in which case it will be applied to both
iptables and ip6tables, given the proper conditions. For instance, if a LAN-side device has both an IPv4
address and a routable IPv6 address, then one can specify a rule for this device by referring to its MAC
address, and if no other match attributes of the rule preclude its use in both tables, the rule will be applied to
both iptables and ip6tables (given the assumption that the LAN Host Discovery database contains both
addresses).