Thursday, 13 October 2022

BGP Lab topology for AS123 (part one 1)

 


> Topology Overview:

- Routers RG 31/32 - peering routers 

- Routers RR-10 / RR-20 - route reflectors

- Ps and PEs - core and customer connectivity


BGP CONCEPTS


> Pourpouse of BGP:

- interconnect between different AS (interdomain communication)

- widely used in Service Provider, Large Enterprise and Datacenter enviroments

- multihomed customers

- scalable 

- created with stability in mind


> Main considerations

- trust one one - eBGP filter advertisment in and out 

- policy based 

- multiprotocol support IPv4/6, VPNv4/6 and VXLAN

- reliable updates

- triggered updates only

- uses rich metrics/attributes


> Internal BGP

- neighbourship between two nodes in the same AS

- AS-PAth is not updated when sending to iBGP

- BGP Split-horizon is used to prevent the loops, iBGP updates are not forwarded to any other iBGP peer

- BGP next-hop is not changed

- used to carry partial of full table of internet routing prefixes


> External BGP

- neigborship between two nodes with different AS numbers

- when router receives a route with its own AS in the AS Path the information is discarded  (loop prevention)

- used to exchange prefixes with other ASes

- implements routing policies


> RFC 4456 / Route Reflectors

- removes the need for Full Mesh IBGP

- loop prevention is done using non-transitive attribute called CLUSTER_LIST and adding it is own ID to it

- when router receives update which CLUSTER_LIST contains router's own cluster ID the update is discarded.

- By default BGP Router ID value is used for cluster ID - has to be 32bit and can be changed i.e.: 0.0.0.1

- Multiple cluster IDs (MCID) feature allows to assign per-neighbor cluster IDs


> Possible scenarios of route reflection

- Between client and non-client

- Between clients in the same cluster (intra-cluster)

- Between clients in different clusters (inter-cluster)

Plumbing... QoS

Rule no 1. QoS does not help in situations where there is no enough bandwidth but helps optimize performance by prioritization of the traffi...