ZyXEL Communications ZyWALL 110 Series, User Manual, Page: 189 / 562

Chapter 9 Policy and Static Routes
ZyWALL 110/310/1100 Series User’s Guide
189
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.
Finding Out More
• See Section 9.4 on page 197 for more background information on policy routing.
9.2 Policy Route Screen
Click Configuration > Network > Routing to open the Policy Route 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, outgoing interface, VPN tunnel, or trunk.
• Limiting the amount of bandwidth available and setting a priority for traffic.
IPPR follows the existing packet filtering facility of RAS in style and in implementation.
If you enabled IPv6 in the Configuration > System > IPv6 screen, you can also configure policy
routes used for your IPv6 networks on this screen.
DSCP (6 bits) Unused (2 bits)