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Full Mesh Dual Homed BGP Connection with External Network

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 .


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