- Enterasys Security Router User's Guide

IP Routing Protocols
5-22 Configuring IP
Figure 5-7 WAN Interface to VLAN Ethernet Topology
For sample configurations, refer to “Configuring VLAN Examples” on page 5-46.
QoS with VLAN
The XSR’s support for Quality of Service (QoS) with VLAN is described in the chapter
“Configuring Quality of Service” on page 12-1.
Policy Based Routing
IP packets typically are forwarded according to the route chosen by traditional routing protocols
RIP, OSPF, BGP or static routes. Selection is based only on the destination of the packet. Policy
Based Routing (PBR) allows you to selectively forward some patterned packets through alternative
paths. It is not meant to replace routing protocols but is complementary while adding flexibility. If
any packets do not meet policy criteria, the destination-based routing table will be searched.
PBR is beneficial for the following reasons:
• Flexible Transit Provider Selection - Internet service providers and others can set priorities for
their customers and use PBR to route traffic according to their users' priorities through
different Internet connections across policy routers.
• Cost Savings - PBR can cut networking costs by distributing traffic among low-cost and high-
cost paths.
• Load Sharing - You can implement policies to distribute traffic among multiple paths based on
traffic characteristics as opposed to traditional load sharing. With PBR, the same traffic flow
will go through the same path but different traffic flow will be directed over a different path
according to the policy.
Accessing the Global Routing Policy Table
Policy-based routing can be applied to incoming packets only and can be enabled on any interface
with the
ip policy command. It works as follows:
1. If a packet is a candidate for PBR, the XSR consults a global routing policy table in the form of
a route-map table having multiple entries. Each entry is assigned a sequence number and are
sequentially ordered from low to high. The
route-map pbr command specifies the sequence
number and acquires PBR configuration mode. You can display this information with the
show route-map pbr command.
1
2
3
Incoming Serial frame
F1.1
VLAN 1200
IP 1.2.3.4/24
Ethernet VLAN Tag IP: 9.9.9.1
PPP IP: 9.9.9.1
Priority CFI VLAN: 1200
IP 3.2.3.4/24
Serial 1
IP Routing Table
1.2.3.0/24 F1.1
3.3.2.0/24 Serial 1
9.9.9.0/24 Serial 1 (Static)
Outgoing VLAN tagged frame
PPP encapsulation
Note: Policy-based routing takes precedence over destination-based routing.