Software Overview
December 2000 8 - 15
802.1q Priority Mapping
By default, devices with IronClad QoS assign 802.1q tagged VLAN packets into one of the four QoS queues
based on the prioritization value in the tag field. You can bias tagged traffic to lower or higher queues by
remapping the prioritization values.
Queue Assignment by Traffic Type
You can assign the following traffic types to one of the four QoS queues:
• IP source and destination addresses
• Layer 4 source and destination information (for all IP addresses or specific IP addresses)
• Static MAC entry
• AppleTalk socket number
• Layer 2 port-based VLAN membership
NOTE: This part of QoS was supported in earlier software releases too, but always used the default queue
weights.
In addition, IronClad QoS allows you to assign packets to a QoS queue based on the incoming (ingress) port.
Layer 2 Switching Features
The following sections describe the Layer 2 Switching features listed in Table 8.1 on page 8-2.
MAC Switching
All Foundry devices support MAC switching. MAC switching enables intelligent wire-speed bridging of Layer 2
packets. The first time a Foundry 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, Foundry routers that are enabled for MAC switching can switch traffic for routed protocols that are not
supported in the routing software. If IPX routing is disabled on a router, the router can switch the IPX packets
instead.
To avoid accumulating stale cache entries, Foundry 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 10-33 for more information about configuring MAC switching
parameters.
NOTE: By default, all ports in a Foundry 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 8-17.
Static MAC Entries
MAC entries that the Foundry 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
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