Riverstone Networks WICT1-12 - Manual (Page 112)

6-12 Riverstone Networks RS Switch Router User Guide Release 8.0
SmartTRUNK Load Redistribution SmartTRUNK Configuration Guide
Redistribution of IP Flows
The
smarttrunk set load-redistribution-params
command is used to specify the redistribution of layer-3
flows by setting the
ip-redistribute
parameter. For example:
Layer-3 flows, as well as layer-2 flows, will now be affected by SLR on SmartTRUNK
st.4
.
Typically, IP (layer-3) flows are short-lived compared to layer-2 flows. For example, a customer decides to surf the
web. As the customer moves from site to site, layer-3 flows are established and then torn down. Depending on the
amount of time the customer spends at each site, these layer-3 flows could be fairly short-lived. In this case, it would
be a waste of switch resources to redistribute these flows along with the layer-2 flows. On the other hand, if you provide
a service that requires long-lived layer-3 flows (for example, streaming video), you may want to consider including
Layer-3 flows for redistribution.
Using Low Water-Mark Events
A low water-mark event occurs than traffic on a SmartTRUNK port falls below the low water-mark threshold. By
default, SLR ignores low water-mark events. However, low water mark events can help SLR to determine whether a
port is being under utilized. If a port experiences many low water mark events, SLR will attempt to even out traffic
across the SmartTRUNK by redistributing flows to the under utilized port.
The
smarttrunk set load-redistribution-params
command is used to specify the use of low water-mark
events by setting the
dont-ignore-lwm-events
parameter. For example:
However, using low water-mark events with SmartTRUNKs that contain ports of widely varying bandwidth can cause
problems. This is why low water-mark events are disabled by default. To understand why using low water-mark events
can be an issue, consider the following scenario:
• A SmartTRUNK consists of five 100 Megabit Ethernet ports and one Gigabit Ethernet port, and
dont-ignore-lwm-events
is specified.
• By default, the low water-mark is set at 20%. This means that on the 100 Megabit ports 20% of
bandwidth is 20 Megabits/sec, while on the Gigabit Ethernet port, 20% of bandwidth is 200
Megabits/sec.
• The large bandwidth of the Gigabit Ethernet port causes it to trigger many low water-mark events,
which indicate to SLR that the Gigabit Ethernet link is vastly under utilized. As a result, most flows
are moved to the Gigabit Ethernet port, while the remaining links go under utilized.
The best use for low water-mark events is with SmartTRUNKs that are made up of links that have equal bandwidth.
In such configurations, low water-mark events combine with high water-mark events to increase the efficiency of
SLR’s redistribution process.
rs(config)#smarttrunk set load-redistribution-params st.4 redistribute-ip
rs(config)#smarttrunk set load-redistribution-params st.4 dont-ignore-lwm-events