Lectures notes for 2010 - KTH

BGP does not transmit metrics.
However, each path is a list of attributes:
• well-known attributes (which every router must understand)
• well-known mandatory attribute - must appear in the description of a route
• well-known discretionary attribute - may appear, but must be recognized, in the description
of a route
• optional attributes
• optional transitive attribute - must be passed to the next router
• optional nontransitive attribute - the receiving router must discarded it if does not recognize it
For examples of the use of an attribute see [18] and [19]
BGP detects failures (either links or hosts) by sending keepalive messages to its
neighbors. Generally sent every 30 seconds and as they are only 19 bytes each ⇒
only ~5 bits/second of bandwidth, but with very long lived TCP connections
(semi-permanent connections)
A major feature of BGP version 4 is its ability to do aggregation - to handle CIDR
and supernetting. For more information on aggregation see chapter 5 of [13].
Maguire BGP operation 7: 42 of 70
maguire@kth.se 2010.03.21 Internetworking/Internetteknik