Policy Route - ZyXEL Communications NXC2500 User Manual

• Policy routes are only used within the NXC itself. Static routes can be propagated to other
routers.
• Policy routes take priority over static routes. If you need to use a routing policy on the NXC and
propagate it to other routers, you could configure a policy route and an equivalent static route.
DiffServ
QoS is used to prioritize source-to-destination traffic flows. All packets in the same flow are given
the same priority. CoS (class of service) is a way of managing traffic in a network by grouping
similar types of traffic together and treating each type as a class. You can use CoS to give different
priorities to different packet types.
DiffServ (Differentiated Services) is a class of service (CoS) model that marks packets so that they
receive specific per-hop treatment at DiffServ-compliant network devices along the route based on
the application types and traffic flow. Packets are marked with DiffServ Code Points (DSCPs)
indicating the level of service desired. This allows the intermediary DiffServ-compliant network
devices to handle the packets differently depending on the code points without the need to
negotiate paths or remember state information for every flow. In addition, applications do not have
to request a particular service or give advanced notice of where the traffic is going.
DSCP Marking and Per-Hop Behavior
DiffServ defines a new DS (Differentiated Services) field to replace the Type of Service (TOS) field
in the IP header. The DS field contains a 2-bit unused field and a 6-bit DSCP field which can define
up to 64 service levels. The following figure illustrates the DS field.
DSCP is backward compatible with the three precedence bits in the ToS octet so that non-DiffServ
compliant, ToS-enabled network device will not conflict with the DSCP mapping.
The DSCP value determines the forwarding behavior, the PHB (Per-Hop Behavior), that each packet
gets across the DiffServ network. Based on the marking rule, different kinds of traffic can be
marked for different kinds of forwarding. Resources can then be allocated according to the DSCP
values and the configured policies.

9.2 Policy Route

Click Configuration > Network > Routing to open this screen. Use this screen to see the
configured policy routes and turn policy routing based bandwidth management on or off.
A policy route defines the matching criteria and the action to take when a packet meets the criteria.
The action is taken only when all the criteria are met. The criteria can include the user name,
source address and incoming interface, destination address, schedule, IP protocol (ICMP, UDP, TCP,
etc.) and port.
The actions that can be taken include:
• Routing the packet to a different gateway or outgoing interface.
• Limiting the amount of bandwidth available and setting a priority for traffic.
Chapter 9 Policy and Static Routes
DSCP (6 bits)
NXC Series User's Guide
Unused (2 bits)
139