Network Router User Manual
Table Of Contents
- Notices
- Contents
- About This Manual
- Introduction
- Hot Swapping Line Cards and Control Modules
- Bridging Configuration Guide
- Bridging Overview
- VLAN Overview
- Configuring SSR Bridging Functions
- Monitoring Bridging
- Configuration Examples
- SmartTRUNK Configuration Guide
- ATM Configuration Guide
- Packet-over-SONET Configuration Guide
- DHCP Configuration Guide
- IP Routing Configuration Guide
- IP Routing Protocols
- Configuring IP Interfaces and Parameters
- Configuring IP Interfaces to Ports
- Configuring IP Interfaces for a VLAN
- Specifying Ethernet Encapsulation Method
- Configuring Jumbo Frames
- Configuring Address Resolution Protocol (ARP)
- Configuring Reverse Address Resolution Protocol (RARP)
- Configuring DNS Parameters
- Configuring IP Services (ICMP)
- Configuring IP Helper
- Configuring Direct Broadcast
- Configuring Denial of Service (DOS)
- Monitoring IP Parameters
- Configuring Router Discovery
- Configuration Examples
- VRRP Configuration Guide
- RIP Configuration Guide
- OSPF Configuration Guide
- BGP Configuration Guide
- Routing Policy Configuration Guide
- Route Import and Export Policy Overview
- Configuring Simple Routing Policies
- Configuring Advanced Routing Policies
- Multicast Routing Configuration Guide
- IP Policy-Based Forwarding Configuration Guide
- Network Address Translation Configuration Guide
- Web Hosting Configuration Guide
- Overview
- Load Balancing
- Web Caching
- IPX Routing Configuration Guide
- Access Control List Configuration Guide
- Security Configuration Guide
- QoS Configuration Guide
- Performance Monitoring Guide
- RMON Configuration Guide
- LFAP Configuration Guide
- WAN Configuration Guide
- WAN Overview
- Frame Relay Overview
- Configuring Frame Relay Interfaces for the SSR
- Monitoring Frame Relay WAN Ports
- Frame Relay Port Configuration
- Point-to-Point Protocol (PPP) Overview
- Configuring PPP Interfaces
- Monitoring PPP WAN Ports
- PPP Port Configuration
- WAN Configuration Examples
- New Features Supported on Line Cards

SmartSwitch Router User Reference Manual 131
Chapter 12: BGP Configuration Guide
AS-Path Regular Expression Examples
To import MCI routes with a preference of 165:
To import all routes (.* matches all AS paths) with the default preference:
To export all active routes from 284 or 813 or 814 or 815 or 816 or 3369 or 3561 to
autonomous system 64800.
Using the AS Path Prepend Feature
When BGP compares two advertisements of the same prefix that have differing AS paths,
the default action is to prefer the path with the lowest number of transit AS hops; in other
words, the preference is for the shorter AS path length. The AS path prepend feature is a
way to manipulate AS path attributes to influence downstream route selection. AS path
prepend involves inserting the originating AS into the beginning of the AS prior to
announcing the route to the exterior neighbor.
Lengthening the AS path makes the path less desirable than would otherwise be the case.
However, this method of influencing downstream path selection is feasible only when
comparing prefixes of the same length because an instance of a more specific prefix
always is preferable.
On the SSR, the number of instances of an AS that are put in the route advertisement is
controlled by the as-count option of the bgp set peer-host command.
ip-router policy create bgp-import-source mciRoutes aspath-regular-
expression "(.* 3561 .*)" origin any sequence-number 10
ip-router policy import source mciRoutes network all preference 165
ip-router policy create bgp-import-source allOthers aspath-regular-
expression "(.*)" origin any sequence-number 20
ip-router policy import source allOthers network all
ip-router policy create bgp-export-destination to-64800 autonomous-
system 64800
ip-router policy create aspath-export-source allRoutes aspath-regular-
expression "(.*(284|813|814|815|816|3369|3561) .*)" origin any
protocol all
ip-router policy export destination to-64800 source allRoutes network
all