Draft

T oS-based high-priority forwarding

Note: This interpretation of Type of Service (ToS) predates the RFC 2474/2475 DiffServ specification.

You can prioritize IP traffic based on the IP ToS precedence bits within the received IP packet.

Note: This feature requires ARU3 ASICs (-B version modules or higher).

By comparing the ToS precedence bits in the incoming IP packet with a user-configurable ToS-threshold value, the switch determines if the packet will be placed in the High Priority Queue. By default, the ToS priority is disabled (Threshold Value of 7). If the packet's ToS precedence value is less than or equal to the Threshold Value, the packet is treated normally. If it is higher than the Threshold Value, the packet is placed in the High Priority Queue.

If you use IP filtering and the ToS feature simultaneously, the ToS value takes precedence. That is, the ingressing packet's ToS value will be compared first with the ToS threshold set for the switch to determine if the packet is high priority; then the packet will be filtered. So if the filter raises the packet's ToS precedence above the threshold, the packet is treated as low priority.

You enable the high-priority mode on the switch prior to setting the TOS threshold. By enabling the high-priority mode, you request TOS-based high-priority forwarding.

To set ToS-based priority for the routing switch:

1. Choose IP Routing > DiffServ.

The DiffServ dialog box opens.

The table below describes the items in the DiffServ dialog box.

2. To enable ToS-based prioritizing, click the TosPriorityEnable check box.
3. Select the desired threshold by clicking the appropriate box, levels 0 (lowest threshold) to 7 (highest threshold).
4. Click Apply.