Why does ibgp require a full mesh

In the network above, R1 is advertising the Therefore, R2 will not advertise that route to R3. This rule is required to prevent routing loops within the AS. This prevents routing loops in EBGP sessions. Notice that R1 is the originator of the route next hop is 0.

The configuration addition on R1 and R3 is as follows:. Note that the IBGP session is only a logical one; i. I have also used static routes to establish underlying connectivity.

As such, there are two methods by which this requirement can be relaxed, as we will now consider. When talking about route reflection, there are two types of internal peers related to the RR: client peers and non-client peers.

The private AS number ranges from to , where private AS numbers are available. If the IP fabric network has more than switches, the public AS numbers not recommended in data centers or 4-byte private AS numbers must be used.

CE series switches support 4-byte private AS numbers in a range from to or from The following describes BGP in specific network architecture scenarios. In the DC1 scenario, there are five rows of racks, which are arranged into a spine-leaf network architecture. Each spine or leaf switch has its own AS number. AS numbers AS and AS can be assigned to the first row of racks, and then the AS number of each device increases by 1 sequentially. The same method can be used in DC2, as shown in Figure and Figure Figure IBGP.

You simply establish a BGP session from the route reflector to each internal peer and the iBGP full-mesh requirement is met. Figure 1 shows the configuration of a single cluster with one route reflector.

RR is configured as a route reflector redistributing routes among the connected internal peers. As shown in Figure 2, you can have multiple clusters with the route reflectors configured as fully meshed internal peers.

When a router advertises to RR1, RR1 further distributes the routes to the rest of route reflectors. These, in turn, readvertise the routes to their clients. Rather than fully mesh these reflectors they can be grouped in a separate cluster for which RR1 will be the route reflector. All the routes advertised to RR2 will be readvertised within Cluster 2 and then, readvertised to RR1. RR1, in turn, distributes the routes among the Level 2 reflectors that further propagate the routes down their clusters.