User guide

Bridge Functional Description BRIDGE
2-39
iMG/RG Software Reference Manual (Switching)
To regenerate priority mapping, it can be configured for each port such that, whenever a tagged packet is
received with a specified priority in the tag header, it is mapped to the corresponding regenerated priority and
the tag header is reset with the new priority.
Additionally, it can be configured to prioritize traffic based on certain traffic classes defined for each outgoing
port. Based on these mappings, the regenerated priority is mapped to the corresponding traffic class priority,
which is set as the system buffer priority such that the transmitted packets are appropriately prioritized by the
lower layers. The actual priority transmission of packets is performed by the Scheduler device. The scheduler
device transmits packets with highest priority first, followed by lower priority packets and finally the lowest pri-
ority packets.
Priority handling has the following effect on the forwarding path:
• If the packet receive is untagged, assign the default priority of the port on which packet is received else
obtain the user priority from the tag header.
• Maps the user priority to the regenerated priority based on the configuration of the received port.
• If the packet is forwarded as tagged, it sets the regenerated priority in the tag header.
• If traffic class mapping is enabled, it obtains the traffic class mapping based on the configuration of the outgo-
ing port and sets the priority in the system buffer.
2.3.2.5 Multicast Traffic
The system supports configuration and handling of multicast MAC forwarding entries, forward all and forward
unregistered entries. Forwarding of the multicast packets is done based on these entries. By default, multicast
traffic is forwarded to all ports. With the addition of support for IGMP snooping in the Bridge, multicast for-
warding is further optimized, by intelligent forwarding of multicast traffic in the network..
Additionally, the system provides configuration of forward all and forward unregistered ports.
Forward all ports are the ports to which all multicast data will always be forwarded. Forward unregistered ports
are the ports to which the multicast data needs to be forwarded, for which there exists no multicast filtering
entry.
2.3.2.6 Learning
Learning is carried out for each unicast packet received by the bridge. Based on the source MAC address and
the source port on which the packet is received, the bridge updates it forwarding database so that whenever a
packet with destination as the learnt MAC address is received, it sends it to the appropriate port on which it
had learnt that MAC address.
The entries are aged out with a periodicity of filter age time configured by the user.
The entries are learnt only on those ports that are in either learning or forwarding state.
Learning is carried out in the following manner: