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

Route Aggregation · Lesson 01 of 01

Aggregating without losing the detail

Aggregation shrinks the table, but a naive aggregate throws away the AS_PATH history and can create loops. as-set fixes that.

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

Written lesson

summary-only and the components

aggregate-address 10.0.0.0 255.0.0.0 advertises the /8 but, by default, keeps advertising the more specific components too. Add summary-only and the components are suppressed, so only the aggregate leaves — the point of aggregating. The aggregate needs at least one component in the BGP table to be generated; it does not conjure a route from nothing.

Configuration

Aggregate with as-set and summary-only

IOS / IOS XE
router bgp 65001
 address-family ipv4 unicast
  aggregate-address 10.0.0.0 255.0.0.0 as-set summary-only

as-set and flap

With as-set, the aggregate's AS_PATH changes whenever the set of contributing components changes — so a flapping component can flap the aggregate's attributes. It is the trade-off for correct loop prevention; weigh it in unstable edges.

Key notes

Aggregation checklist

  • A component must exist in the BGP table for the aggregate to appear.
  • `summary-only` is what actually shrinks the table.
  • `as-set` preserves path history and loop prevention.
  • ATOMIC_AGGREGATE marks a route whose detail was lost to aggregation.