BGP Route Reflector

Good Morning Guys,

This is a very old post of mine, and actually, this was the first post of mine back in 2013. Since I am migrating to my new website, hence I am republishing it here but I will never delete that post in my old blog.

Here you Go……

Route reflectors do one very important thing in an iBGP network, and that’s to disable the iBGP ‘split-horizon rule’.

iBGP Split-Horizon rule says that if I am a router running iBGP and I learn a route from another iBGP peer, I will never advertise that route to another iBGP peer.

i.e x-R1——–R2——–R3

All the routers above are running iBGP. R1 has a network x….It will advertise network x to R2. However, R2 will never tell R3 of network x, because of the iBGP Split-Horizon rule. This has severely hampered the propagation of routes in our network.

There are two ways of solving this. One, you could create a full mesh, meaning every router is connected to every other router; that would mean connecting R1 to R3 in our case, as shown below. That way, R1 is connected to R3 and can tell R3 of network x without going through R2. (as shown below) 

R1
/
R2——R3

This may work in our example of 3 routers, but it is not a scalable solution in a larger network.

That’s where route-reflectors come in.

x-R1——–R2——–R3

Here, we simply designate R2 as a route-reflector, by telling it that R1 and R3 are its route-reflector clients with the command “neighbor R2 route-reflector-client”……..R2 will, therefore, reflect or pass on as it were the routes it receives from R1 like network x to R3 and vice versa…..

This way, we have disabled the split-horizon rule for iBGP, to enable prefix propagation and thereby create a very scalable iBGP network…..

Am sure this is much easier than performing redistribution 🙂

Architect/Consultant in IT/Telecom/Networking Support Industry with over 13+ years of Experience. Mainly working with Cisco Products other than Cisco worked with VMware NSX/Juniper/Riverbed/Meraki & Citrix Products, and worked with various clients like PSU Banks, Petroleum Corporations, different government sector clients, BPO Sector, Telecom NOC and ISP. Global Certifications: VMware vSphere Foundation 6 CCNA Routing & Switching CCNP Routing & Switching ITIL V3 Foundation RTSA-W RTSS-W RSA RTSA-NPM RTSS-NPM Aspiring Certifications: VCP-NV

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