All HP devices support MAC switching. MAC switching enables intelligent wire-speed bridging of Layer 2
packets. The first time an HP device receives a packet from a given MAC destination, the device makes an entry
in its Layer 2 cache. The entry consist of the packet's source MAC address and the port on which the device
received the packet.
When the device receives a bridge packet destined for the cached address, the device does not need to send the
packet as a broadcast through all the ports within the broadcast domain. Instead, the device can intelligently send
the packet only through the port to which the destination device is connected. Thus, even though Layer 2
domains are typically broadcast domains, MAC switching enhances performance in the domain by reducing the
amount of broadcast traffic in the domain.
In addition, HP routing switches that are enabled for MAC switching can switch traffic for routed protocols that are
not supported in the routing switch software. If IPX routing is disabled on a routing switch, the routing switch can
switch the IPX packets instead.
To avoid accumulating stale cache entries, HP devices use an aging mechanism. The aging mechanism removes
a learned entry from the cache after the entry has remained unused for a specified interval (by default, 300
seconds). You can change or disable the aging interval.
See "Configuring Basic Layer 2 Parameters" on page 9-29 for more information about configuring MAC switching
NOTE: By default, all ports in an HP device belong to a common Layer 2 broadcast domain, VLAN 1. You can
configure port-based VLANs (Virtual LANs) to create smaller broadcast domains that use subsets of the device's
ports. See "Port-Based Virtual LANs (VLANs)" on page 7-16.
Static MAC Entries
MAC entries that the HP device learns and caches are subject to an aging time. After a cached entry remains
unused for the duration of the aging time, the software removes the entry from the Layer 2 cache. If you want
certain MAC addresses to always be present in the device's Layer 2 address table, you can add them as static
A static MAC entry, like a cached (dynamic) MAC entry, maps a MAC address to the HP device's port attached to
Unlike cached MAC entries, static MAC entries provide the following benefits:
You can assign a QoS priority to a static MAC entry.
You can specify VLAN membership for a static MAC entry.
A static entry prevents broadcast storms that can be caused when a server's MAC entry is removed. For
example, if the server goes down long enough for the server's entry to age out, the HP device sends packets
addressed to the server as broadcasts until the device relearns the cache entry for the server.
You can specify port priority (QoS) and VLAN membership (VLAN ID) for the MAC address. On switches, you
also can specify the device type (router or host) for the entry.
NOTE: On HP routing switches, you also can create static IP routes, ARP entries, and RARP entries. HP
switches support only static MAC addresses.
For more details on configuring static MAC addresses, see "Configuring Static MAC Entries" on page 9-31.
Standard Spanning Tree Protocol (STP)
The Spanning Tree Protocol (STP) is a protocol for detecting and eliminating logical loops in a Layer 2
broadcast domain. STP is described in the IEEE 802.1d bridge protocols standard. STP is supported on all HP
switches and routing switches.
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