HP ProCurve Switch 5300xl Series Reviewer’s Guide
2.3.3 Switch Meshing (LAN Aggregation)
The HP ProCurve Switch 5300xl Series family supports
HP’s Switch Meshing, a way to interconnect these switches
in a meshed topology at Layer 2. Meshed switch-to-switch
links can all be used simultaneously to their full advantage,
with traffic being load-balanced through redundant links
based on dynamically determined latency on the different
possible paths between switches. Highly available, fault
tolerant networks can be easily built with very low network
administration required.
Figure 2. Switch Meshing
Note, however, that routing and Switch Meshing cannot be used in the same switch at the same time.
In traditional switched environments, meshed topologies are not allowed without the use of the Rapid
or original Spanning Tree Protocol (802.1w or IEEE 802.1D). Spanning Tree detects loops in the
topology and logically blocks as many links as necessary to avoid traffic loops. If one of the active links
fails, Spanning Tree enables another link to re-establish the path, if possible. Unfortunately, Spanning
Tree requires links to be available that are not being used for data, letting available bandwidth go
unused.
Although RSTP and STP are supported by the HP ProCurve Switch 5300xl Series, Switch Meshing is
superior since all available links are used between switches. With Switch Meshing, the switch selects
the best traffic path for each new destination end-node it learns based on dynamically determined
latency on each of the possible paths to the node. Recalculation of path latency in each switch is done
every 30 seconds and is based on link speeds, input and output buffer queue lengths, and knowledge of
any dropped packets on particular ports.
Redundancy is also provided by Switch Meshing. If one of the links fails between switches, traffic is
redirected through another path, if available. The switchover time of typically less than 1 second is
very fast. Very robust high availability solutions can be implemented with a switch mesh.
Switch Meshing allows multiple HP ProCurve Switch 5300xl Series to form a virtual backplane
between the switches, allowing reliable high port density environments to be made inexpensively.
Up to 12 switches can participate in a Switch Meshing domain, with up to 5 switch hops between the
most distant switches in the mesh. Multiple Switch Meshing domains can exist in a single LAN
environment, but not within the same switch.
Routing switches and routers use a similar technique through routing protocols such as RIP or OSPF.
In many situations Switch Meshing is an improvement over these routing protocols because:
•
The path decision in HP’s Switch Meshing is made using dynamically determined latency
through the switches. Routing protocols do not take latency into account, only path costs
based on link speeds (OSPF) or simply the lowest number of router hops (RIP).
•
Switch Meshing works for all Layer 3 protocols, as well as non-routable protocols such as DEC
LAT or NET BIOS, because path specification is performed using Layer 2 MAC addresses.
Routing specifies paths based on supported Layer 3 protocols (usually IP, sometimes IPX
and rarely AppleTalk), otherwise the router must simply bridge the packet and use
Spanning Tree.
•
Configuration of Switch Meshing is trivial. Specifying which ports are part of the Switch
Meshing domain is all that is needed. The switch takes care of the rest. This is in sharp
contrast to configuration of routing protocols which can be challenging.
•
Convergence time (time to recover from a lost link) is fast - typically less than one second. This
is much faster than RIP and faster or on par with OSPF using triggered updates.
© Hewlett-Packard Co. 2002, 2003
Rev 1.1 – 2/11/2003
http://www.hp.com/go/hpprocurve
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