Specifications

Extreme Networks Technical Brief
© 2010 Extreme Networks, Inc. All rights reser ved. SummitStack Stacking Technology—Page 4
topologies and will allow for standard interface media such
as XENPAK, XFP, SFP+ or 10GBASE-T RJ45 to create stack
links. With this technology it is now possible to create stack
links that are much more than five meters in length, and
stacking can now be used between physical locations. It is
important to note that once a 10 GbE stacking port is
configured into stacking mode, the port cannot be used for
any other use, and is unusable for Ethernet traffic.
• Stacking is only supported using 10 GbE ports.
(10/100/1000 Mbps ports are not usable for stacking)
• Stacking ports must be directly connected between the
two nodes in the stack. (No devices active or passive in
between.)
About SummitStack
Logging Messages
Each node may generate log messages through the usual
logging mechanism.
On backup and standby nodes, a log target and related filter
is automatically installed. The log target is the master node.
The filter allows all messages that have a log level of
warning, error, or critical to be saved in the log file of the
master node.
If the master node changes the log target is updated on all
the remaining nodes.
You can also log in to any node in the active topology and
see the complete log of the node.
About Quality of Service
in Stacking
Each SummitStack uses Quality of Service (QoS) on the
stacking links to prioritize the following traffic within the stack:
• Stack topology control packets
• ExtremeXOS control packets
• Data packets
For stack performance and reliability, the priority of control
packets is elevated over that of data packets. This is done to
prevent control packet loss and avoid the timed retries that
can lower performance. It is also done to prevent unneeded
stack topology changes that can occur if enough stack
topology information packets are lost. For these reasons,
SummitStack reserves one QoS profile to provide higher
priority to control packets.
When the stack restarts, if a switch becomes the master and
its selected configuration file was not created in stacking
mode, the configuration file is deselected, and the stack
completes its restart using a default configuration. In
addition, if the previously selected file was named with one
of the default names (primary.cfg or secondary.cfg), the
file is renamed to old_non_stack.cfg.
Similarly, if a switch is configured not to operate in stacking
mode and the selected configuration file was created in
stacking mode, the configuration file is deselected, and the
switch boots with a default configuration. In addition, if the
file was named with one of the default names (primary.cfg
or secondary.cfg), the file is renamed to old_stack.cfg.
The renamed file replaces any file that exists with the same
name; the existing file is deleted.
Understanding Stacking Link
Over Commitment
The stack is formed by each node supplying a pair of
full-duplex 10 Gbps stacking ports. Each node can operate
on a stack with up to 20 Gbps full duplex throughput.
Even though two links are available, the links might not be
fully utilized. For example, suppose there is a ring of eight
nodes and the nodes are numbered clockwise from 1 to 8.
Suppose node 1 wants to send 10 Gbps of unicast traffic to
each of node 2 and node 3. The shortest path topology forces
all traffic from node 1 over the link to node 2. Traffic from
node 1 to node 3 passes through node 2. Thus, there is only
10 Gbps available. However, if node 1 wanted to send 10
Gbps to node 2 and node 8, there would be 20 Gbps available
because both links connected to node 1 would be used.
In a ring of eight nodes, between any two nodes (with one
exception), only one link is used. If the devices provide 48
1 Gbps Ethernet ports, the over commitment ratio between
two such nodes is approximately 5:1. The exception is if
there is an equal distance between the nodes. In this case, if
both nodes are 48-port nodes, the nodes are grouped into
two groups of 24 ports (by the hardware architecture), and
thus it is possible to use both directions around the stack.
About SummitStack-V Stacking
Using 10 GbE Ports
With ExtremeXOS version 12.5, a stack can be connected
using 10 GbE ports. These ports are the optional 10 GbE
ports provided on the stackable switches but are repur-
posed to allow the stacking function to utilize these ports.
This technology will provide greater distances for stacking