I.2) Overview of the study case: BGP tutorial , best practices and multihoming techniques on ISP proposing IP transit services.
1. The information given below will be used as references for the whole tutorial described in this document.
2. The objective of the tutorial is to show a practical example of some BGP best practices with multihoming techniques for a Tier3-4 ISP which desires to proposes IP Transit services. The study implies the use of load-balancing, communities, and active/passive backup configurations.For these topics, many notions related to BGP will be aborted and explained in details such as peering agreements, next-hop, choice of tools for traffic engineering, basic template connectivity for Ebgp and Ibgp setup, debug/verification commands, monitoring processes and analyzes of results, etc.
3. The entire study case will focus on the ISP-A, which has the as-number 1000 and owns two routers in its core-network: RT-A and RT-B.ISP-A is connected to the Internet, provided by the transit/upstream providers ISP-B, ISP-C and ISP-D.ISP-A also provides Internet transit services to Customer-B, C, D-E and G.All the tasks required for multihoming a BGP network using two routers with multiple paths to the three service providers, will be exposed. The use of Cisco commands (network and BGP) related to this case and how they are used in practice; will also be presented in the document for information.The study case is not complicated, and can be clustered up from 2 to 6-8 routers: above these numbers, we recommend the use of reflectors routes. The document still requires to the reader minimum basic BGP knowledge.
4. The first router “RT-A” of ISP-A is connected directly to:
- The upstream/transit provider “ISP-D”, with the as-number 500, through two external BGP sessions. The 1st session will be referenced as ISP-D-Link1 and the 2nd one as ISP-D-Link2.
5. The second router “RT-B” has two different Ebgp speakers this time, and is connected directly to:
- the provider ISP-B (with the as-number 300) through one Ebgp session;
- and ISP-C (as-Number 400) through another Ebgp session.
The two routers are physically linked, and shared an Ibgp session layered on an IS-IS setup. Let’s note that in this design, we will try to respect that ideally there will be no interaction between BGP and IGP sessions.
Plz click on the picture below in order to zoom in.