CS641 Advanced Computer Networks Lecture 04 Bhaskaran Raman - - PowerPoint PPT Presentation
CS641 Advanced Computer Networks Lecture 04 Bhaskaran Raman Department of CSE, IIT Bombay http://www.cse.iitb.ac.in/~br/ http://www.cse.iitb.ac.in/synerg/doku.php?id=public:courses:cs641-autumn10:start Outline for Today Recall: routing
http://www.cse.iitb.ac.in/~br/ http://www.cse.iitb.ac.in/synerg/doku.php?id=public:courses:cs641-autumn10:start
– DV, LS, Path-Vector, Hierarchical routing
– Link-State – Distance-Vector – Path-Vector
– Path-vector based protocol – Data path is reverse of control path – Allows for policy-based routing
– For initialization, exchange of AS numbers
– Main routing messages – Route announcements and withdrawals
– Periodic heart-beat to keep BGP session alive
– Before closing a connection
– To implement the path vector protocol
– IP address of the external next-hop for this route
– How the route to the prefix was learnt – Three possibilities: IGP, EGP, Redistributed
– With MED=10 on Link A, MED=50 on Link B
– I-BGP used between routers of the same AS – This is NOT the same as IGP
– LOCAL-PREF – AS-PATH – MED – IGP origin preferred over EGP origin – IGP cost
– Has poor convergence properties in practice – Can take up to a few min. to recover from failure – Overlay networks (later in course)
– Largest distributed system to date – A router may have as many as 250,000 entries!
– Its a surprise that it works!
– Policy control, convergence, and other issues
– [LMJ97] C. Labovitz, G. R. Malan, and F.