TrainSignal Chapter 6, Lecture 10 - Route Reflector Lab

R4 is in AS4, and will advertise its loopback (4.4.4.4/32) into BGP

Straight away we can see an issue, whereby the R4's loopback network which is being advertised into BGP, and since R3 learned this via eBGP when it advertises this into its iBGP peers it will retain R4's Eth0 as the next-hop address ......

So lets apply the next-hop-self to R3 to correct this

(We could have configured dynamic routing or static routing to get a route to 4.4.4.4 in R1's IP routing table, or configure next hop self on R3 - as we did)

So, does R1 see any BGP routes ........ NO, no it does and why not? .....

Well it would of learnt this route (4.4.4.4) from another internal BGP speaker, then trying to advertise it to another iBGP peer ...... therefore BGP Split Horizon would stop this

The same is true if R2 wants to advertise its loopback (2.2.2.2/32) to R3

We can fix this by configuring R1 as a route reflector :0)

TrainSignal Chapter 6, Lecture 9 - Route Reflector Theory

TrainSignal Chapter 6, Lecture 8 - Adjusting the Weight Attribute

TrainSignal Chapter 6, Lecture 5 - Med & Local Preference

TrainSignal Chapter 6, Lecture 6 - Local Pref Change

Lets look at the routing table on R2, here we can see alittle of what we looked at early (which we cured with update-self) R1 is learning about the 172.12.34.0/24 network from its eBGP peer and then advertising to its iBGP peers .... BUT by default it will leave the next hop address along, so it stays as R3 (10.1.1.3), however we can cure this with the local-preference command

TrainSignal Chapter 6, Lecture 6 - Local Pref Change with Route-Map

This is te preferred way to change the path (real world) as it would be very rare for you to change the the local pref on a router for all routes.

So we will undo the default local-preference command and add in a new link between R3 and R4 (210.1.1.0/24)