Connected: An Internet Encyclopedia
7. Required set of supported routing policies
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7. Required set of supported routing policies
7. Required set of supported routing policies
Policies are provided to BGP in the form of configuration
information. This information is not directly encoded in the
protocol. Therefore, BGP can provide support for very complex routing
policies. However, it is not required that all BGP implementations
support such policies.
We are not attempting to standardize the routing policies that must
be supported in every BGP implementation; we strongly encourage all
implementors to support the following set of routing policies:
- BGP implementations should allow an AS to control announcements
of BGP-learned routes to adjacent AS's. Implementations should
also support such control with at least the granularity of a
single address prefix. Implementations should also support
such control with the granularity of an autonomous system,
where the autonomous system may be either the autonomous system
that originated the route, or the autonomous system that
advertised the route to the local system (adjacent autonomous
system). Care must be taken when a BGP speaker selects a new
route that can't be announced to a particular external peer,
while the previously selected route was announced to that peer.
Specifically, the local system must explicitly indicate to the
peer that the previous route is now infeasible.
- BGP implementations should allow an AS to prefer a particular
path to a destination (when more than one path is available).
At the minimum an implementation shall support this
functionality by allowing to administratively assign a degree
of preference to a route based solely on the IP address of the
neighbor the route is received from. The allowed range of the
assigned degree of preference shall be between 0 and 2^(31) -
1.
- BGP implementations should allow an AS to ignore routes with
certain AS's in the AS_PATH path attribute. Such function can
be implemented by using the technique outlined in [2], and by
assigning "infinity" as "weights" for such AS's. The route
selection process must ignore routes that have "weight" equal
to "infinity".
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Connected: An Internet Encyclopedia
7. Required set of supported routing policies