Chapter 8 Routing
USG FLEX H Series User’s Guide
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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.
NAT and SNAT
NAT (Network Address Translation - NAT, RFC 1631) is the translation of the IP address in a packet in one
network to a different IP address in another network. Use SNAT (Source NAT) to change the source IP
address in one network to a different IP address in another network.
Assured Forwarding (AF) PHB for DiffServ
Assured Forwarding (AF) behavior is defined in RFC 2597. The AF behavior group defines four AF classes.
Inside each class, packets are given a high, medium or low drop precedence. The drop precedence
determines the probability that routers on the network will drop packets when congestion occurs. If
congestion occurs between classes, the traffic in the higher class (smaller numbered class) is generally
given priority. Combining the classes and drop precedence produces the following twelve DSCP
encodings from AF11 through AF43. The decimal equivalent is listed in brackets.
8.2 Policy Route Screen
Click 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, VTI interface, or trunk.
Table 73 Assured Forwarding (AF) Behavior Group
CLASS 1 CLASS 2 CLASS 3 CLASS 4
Low Drop Precedence AF11 (10) AF21 (18) AF31 (26) AF41 (34)
Medium Drop Precedence AF12 (12) AF22 (20) AF32 (28) AF42 (36)
High Drop Precedence AF13 (14) AF23 (22) AF33 (30) AF43 (38)
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