Cisco Systems 3200 User Manual
C-7
Cisco 3200 Series Router Hardware Reference
OL-5816-10
Appendix C Switch Port Functionality
802.1P CoS
Disabling VTP (VTP Transparent Mode) Example
The following example shows how to configure the switch as VTP transparent:
Router# vlan database
Router(vlan)# vtp transparent
Setting device to VTP TRANSPARENT mode.
Router(vlan)# exit
APPLY completed.
Exiting....
Router#
VTP Version 2 Example
The following example shows how to enable VTP version 2:
Router# vlan database
Router(vlan)# vtp v2-mode
V2 mode enabled.
Router(vlan)# exit
APPLY completed.
Exiting....
Router#
802.1P CoS
The IEEE 802.1P specification defines eight levels of priority (0 thru 7), with priority 7 being the highest
priority. This information is carried in the 3-bit priority field of the VLAN tag header.
priority. This information is carried in the 3-bit priority field of the VLAN tag header.
The FESMIC supports up to four class of service (CoS) queues per port. For the tagged packets, the
incoming packet priority can be mapped into one of the four queues, based on the priority field in the
tag header or from the result of filtering mechanism. For untagged packets, the CoS priority is derived
either from a programmable field within the ARL (MAC address table) or from the result of filtering
mechanism.
incoming packet priority can be mapped into one of the four queues, based on the priority field in the
tag header or from the result of filtering mechanism. For untagged packets, the CoS priority is derived
either from a programmable field within the ARL (MAC address table) or from the result of filtering
mechanism.
After the packets are mapped into a CoS queue, they are forwarded or conditioned using these scheduling
algorithms:
algorithms:
•
Strict priority-based scheduling—Any packets residing in the higher priority queues are transmitted
first. Only when these queues are empty will packets of lower priority be transmitted. The
disadvantage of this scheme is the potential starvation of packets in lower priority queues.
first. Only when these queues are empty will packets of lower priority be transmitted. The
disadvantage of this scheme is the potential starvation of packets in lower priority queues.
•
Weighted round-robin scheduling—This scheme alleviates the starvation of packets in lower priority
queues by providing a certain minimum bandwidth to all queues for transmission. This bandwidth
is programmable as the maximum number of packets of each CoS.
queues by providing a certain minimum bandwidth to all queues for transmission. This bandwidth
is programmable as the maximum number of packets of each CoS.
The FESMIC 10/100 Fast Ethernet interfaces default to use the strict priority-based scheduling. After
system boots, you can enable weighted round-robin scheduling.
system boots, you can enable weighted round-robin scheduling.
Mapping 802.1P priority to IP precedence bits is not supported.