Posted: June 12, 2017 in BGP, Routing, SDN

BGP SDN enables central control over distributed routing.
This is based on routing protocol BGP and its ability to signal third party next hop using policy based routing.

We are using standard community to set next-hop which will define path to reach destination

This approach is kind of similar to Fibbing: OSPF and SDN (Hybrid model) where we set third party next hop with help of LSA5

All devices are running EBGP with each other via directly connected interface and controller will speak IBGP with every router
Controller can be any device which is capable of speaking BGP . I am using Cisco router and local-as feature to form IBGP with all routers as controller. In below diagram R5 is contoller


When we try to reach IP 100.100.100.l00 from IP we have 1 path available via path R4-R2-R1(marked with blue line)
R1 before

R2 before

R3 before

R4 before

Before Trace

Now with help of controller R5 I am sending prefix to all routers with community set to {4:2 2:3 3:1} and local preference set to 120
we can move the traffic from IP to IP via path R4-R2-R3-R1(marked with red line).

These communities are user defined and locally significant to the router mapped with next hop value
e.g if you want move packet from AS4 to AS2 set community 4:2 (this community is local to R4) in controller and next hop will be set to once R4 receives the update.
similarly to move packet frmo AS2 to AS3 set community 2:3 in controller and next hop will be set to once R4 receives the update.

R1 after

R2 after

R3 after

R4 after

After trace

Please check below link for more information

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