2. Border Gateway Protocol BGP-4 BGP environment How BGP works BGP information BGP administration

3. Routing and Routers IGP (internal gateway protocols) Distance vector protocols Link state protocols EGP (external gateway protocols BGP (boarder gateway protocol) First version BGP 1 (1989) Current standard de facto (1993)

4. BGP - Requirements No restriction on the network deployment Scalability Loop-free routing Manageable routing policy CIDR support

5. CIDR Format Networks represented by tuple E.G. represents 198.24.160.0 255.255.224.0 1100110.00011000.10100000.00000000 1111111.11111111.11100000.00000000  --------19 bit ------- 

6. BGP Environment Autonomous system (AS) definition Single technical administration Single routing policy Unique identifying number

7. AS Topology Stub AS Multihomed AS Transit Non transit

8. How BGP Works ? Using TCP (port 179) as a transport layer Establish connection Establish BGP session Data base export / import Incremental updates Decision process

9. Information Sources EGP IGP Dynamic Semi-dynamic Static routes

10. BGP Data Base Input table (incoming routes) Local routing table IP forwarding table Output table

11. BGP Update Structure Withdrawn list Path attribute Network layer Reachability information (NLRI)

12. Route Information (The Path Attribute) NEXT_HOP AS_PATH Local preference MULTI_EXIT_DISC Origin Community Atomic aggregation Aggregator

13. BGP Decision Process Next hop is inaccessible Largest local preference Locally originated path Shortest AS_PATH IGP before EGP Lowest MED Shortest internal path (IGP) Lowest router ID

14. Administrator Intervention (Policy) Identify route (match) Filtering (accept \ reject) Manipulate attributes (action) Local preference As path

15. AS_PATH Manipulation

16. Conclusion Topology restriction Scalability Loop-free routing CIDR Manageable Segregation to ASs Support the current internet deployment The path attribute BGP syntax Static routes, Filtering policy, attribute manipulation