Full Mesh Dual Homed BGP Connection with External Network

Full Mesh Dual Homed BGP Connection with External Network

This section explains how to set up a dual-homed, full-mesh eBGP peering for that we need to build a BGP policy model, where both incoming and outgoing paths of specifics networks can be controlled via Border Leaf switches without doing any changes in external routers Ext-Ro01 and Ext-Ro02.

The policy defined in this section prevents the External network AS64555 to use VXLAN Fabric as a transit network between Ext-Ro01 and Ext-Ro02 in case of backbone failure in AS65055.

OSPF is used as an IGP inside the AS64555. Routes learned from BGP are redistributed into OSPF. Ext-Ro01 redistributes routes with metric 10 while the Ext-Ro02 uses metric 100. This way the Ext-Ro03 will prefer route learned from the Ext-Ro01.

Below figure shows the Full-Mesh External BGP Peering Topology.

In order to to achieve this topology , lets see the configuration done on Border Leaf-102 and Leaf-103.

Below is the configuration done on EXT-Ro01

Below is the configuration done on EXT-R02

Below shows that the Border Leaf-102 has learned route 172.16.10.0/24 from Ext-R01 (best), from Ext-Ro02 and from Spine-11. This decision is based on the lower RID of Ext-Ro01 (Ext-Ro01 BGP RID 172.16.55.55 and Ext-Ro02 BGP RID 172.16.55.56).

Below figure shows that also the Border Leaf-103 has learned route 172.16.10.0/24 from Ext-R01 (best), from Ext-Ro02 and from Spine-11. This decision is also based on the lower RID of Ext-Ro01. Note that both Border Leaf switches are receiving BGP Update about 172.16.10.0/24 also from the VXLAN Fabric Spine switch, which is BGP Route-Reflector. Since the internal BGP has worse Administrative Distance (200) than an external BGP (20), it is only a third-best route.

At this point, there is no BGP policy between the eBGP peers. The IP connectivity between the network 192.168.11.0/24 in AS65000 and network 172.16.10.0/24 in AS64577 is tested by pinging from host Cafe (192.168.11.101) to address 172.16.10.1 (Loopback on Ext-Ro03)

Now Lets configure the BGP Policy to influence the traffic .