Category: Routing Protocols

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BGP Route-Reflector Design

A route learned by one ibgp peer won’t be advertised to another ibgp peer. This is called BGP split horizon rule. This rule is used to avoid loop in ibgp cases.

To mitigate this, we have following option by which one ibgp learned routes can be advertised to another ibgp peer.

  1. BGP full mesh
  2. BGP confederation
  3. BGP route-reflector

In this article we will discuss about the 3rd option i.e BGP route-reflector.

BGP route reflector rule.

Whenever a RR learn route from its client it adds two attributes to the route.

  1. Cluster id – (32-bit identifier, which can be set, by defaults its bgp router-id)
  2. Originator id- (router id of client who send the route)
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Different Static Route Options

The IP assignment on interface is shown as above.

We will demonstrate the following case study.

Case Study 1: Static routes using exit interface

Case Study 2:Static routes using IP as next hop

Case Study 3:Static routes using exit interface and IP add as next hop

Let’s understand how the communication takes place in Ethernet or multi-access networks.

  1. Whenever router want to reach a particular destination, it basically needs two information viz the destination IP address where it wants to go and the L2 address with respect to the destination.
  2. The router must check first whether the outgoing interface is point to point or ethernet/multi-access. In case it is Ethernet then it must resolve L2 address
  3. For getting the L2 address the router must generated ARP request for the destination subset. The router must know on which outgoing interface it needs to generate ARP so the router do routing recursive process to know the outgoing interface for a particular destination.

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BGP Over GRE

Topology

Objective:
To implement BGP over GRE , the topology shown above. In topology R1 & R3 running BGP 100 whereas R2 running only IGP.R1-R4 & R3-R5 running ebgp and advertising prefix 4.4.4.4 and 5.5.5.5 respectively.
R1-R2-R3 running ospf under area 0.
Bgp over GRE can be configured in scenario where end to end BGP is not running or where we want to bypass non bgp peer to peering with BGP peer.

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