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Lectures notes for 2010 - KTH

Lectures notes for 2010 - KTH

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BGP operation<br />

BGP routers exchange in<strong>for</strong>mation based on traffic which transits the AS, derives<br />

a graph of AS connectivity; with loop pruning.<br />

Routing policy decisions can be en<strong>for</strong>ced as to what is allowed to transit whom<br />

⇒ policy-based routing<br />

• based on economic/security/political/… considerations.<br />

• BGP does not implement the policy decisions, but allows the<br />

in<strong>for</strong>mation on which such decisions can be made to propagate as<br />

necessary<br />

Uses TCP (port 179) to create a session between BGP routers:<br />

• initially two systems exchange their entire BGP routing table,<br />

• then they simply send updates as necessary.<br />

BGP is a path-vector protocol - which enumerates the route to each destination<br />

(i.e., the sequence of AS numbers which a packet would have to pass through from<br />

a source to its destination) = a path vector<br />

Maguire BGP operation 7: 41 of 70<br />

maguire@kth.se <strong>2010</strong>.03.21 Internetworking/Internetteknik

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