HP ProCurve 5308XL-48G Supplementary Manual page 14

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 ProCurve 5300xl Switch 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 ProCurve 5300xl Switch 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 ProCurve'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.
•
Unlike a router, no packet modification is required as it travels through the switch.
Figure 2. Switch Meshing
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