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

Neighbor Sessions and the FSM · Lesson 02 of 02

Loopback peering, multihop and authentication

iBGP peers on loopbacks for resilience; eBGP sometimes needs multihop; both often need a password.

  • 13 min lesson
  • 00:00 video
  • Foundation
Written lessonConfiguration

Written lesson

Why iBGP peers on loopbacks

iBGP sessions are usually built between loopback addresses, not physical interfaces, so the session survives the loss of any single link as long as the IGP can still reach the loopback another way. Because the loopback is not the outgoing interface, you must tell BGP which source address to use, and the IGP must carry the loopbacks. eBGP, by contrast, is normally built on the directly connected interface addresses.

Configuration

update-source, multihop and a password

IOS / IOS XE
router bgp 65001
 neighbor 10.0.0.2 remote-as 65001
 neighbor 10.0.0.2 update-source Loopback0
 neighbor 203.0.113.9 remote-as 65003
 neighbor 203.0.113.9 ebgp-multihop 2
 neighbor 203.0.113.9 update-source Loopback0
 neighbor 203.0.113.9 password C1sco123

Multihop and next-hop

eBGP-multihop changes how the next hop is reached but not the next-hop value itself. Combine loopback eBGP with a route to the peer loopback (static or IGP) or the session will form and then fail to forward traffic.