CCIE Enterprise Infrastructure · BGP

BGP — CCIE Enterprise Infrastructure

The complete BGP learning path for CCIE Enterprise Infrastructure: how sessions form, how prefixes are chosen and shaped, how the protocol scales with route reflection and confederations, and how it is designed, secured and repaired in production.

  • 24 complete lessons
  • 5 hr 20 min
  • Foundation

Routing Policy and Filtering · Lesson 01 of 01

Filtering and route-maps

Prefix-lists decide which prefixes; filter-lists decide which AS paths; route-maps do both and set attributes. Order of operations matters.

  • 15 min lesson
  • 00:00 video
  • Foundation
Written lessonConfigurationKey notes

Written lesson

The right tool per job

A prefix-list matches network and length — 'permit 10.0.0.0/8 le 24' means any 10-prefix up to /24. A filter-list matches an AS-path access-list, filtering by who a route came through rather than what it is. A route-map is the general instrument: it can match either of those (and communities), permit or deny, and set attributes on what it permits. Use the narrow tool when a narrow tool fits; reach for the route-map when you need to set as well as match.

Configuration

Inbound policy on one session

IOS / IOS XE
ip prefix-list CUST seq 5 permit 198.51.100.0/24
!
route-map FROM-CUST permit 10
 match ip address prefix-list CUST
 set local-preference 200
route-map FROM-CUST deny 20
!
router bgp 65001
 address-family ipv4 unicast
  neighbor 203.0.113.9 route-map FROM-CUST in

Changing inbound policy needs a refresh

A new inbound policy only affects routes received after it is applied unless you trigger a soft refresh: clear bgp ipv4 unicast 203.0.113.9 soft in. With route-refresh capability (default on modern IOS) this re-requests the routes without tearing down the session.

Key notes

Order of operations

  • Inbound: route-map/filter is applied as routes arrive, before best-path.
  • A route-map's implicit deny drops anything not explicitly permitted.
  • `soft in` re-applies inbound policy without a hard reset.
  • Outbound policy shapes the Adj-RIB-Out per neighbour.