rfc9107v3.txt   rfc9107.txt 
skipping to change at line 157 skipping to change at line 157
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
3. Modifications to BGP Route Selection 3. Modifications to BGP Route Selection
The core of this solution is the ability for an operator to specify The core of this solution is the ability for an operator to specify
the IGP location for which the route reflector calculates interior the IGP location for which the route reflector calculates interior
cost for the NEXT_HOP. The IGP location is defined as a node in the cost to the next hop. The IGP location is defined as a node in the
IGP topology, it is identified by an IP address of this node (e.g., a IGP topology, it is identified by an IP address of this node (e.g., a
loopback address), and it may be configured on a per-route-reflector loopback address), and it may be configured on a per-route-reflector
basis, per set of clients, or on a per-client basis. Such basis, per set of clients, or on a per-client basis. Such
configuration will allow the route reflector to select and distribute configuration will allow the route reflector to select and distribute
to a given set of clients routes with the shortest distance to the to a given set of clients routes with the shortest distance to the
next hops from the position of the selected IGP location. This next hops from the position of the selected IGP location. This
provides for freedom related to the route reflector's physical provides for freedom related to the route reflector's physical
location and allows transient or permanent migration of this network location and allows transient or permanent migration of this network
control plane function to an arbitrary location with no impact on IP control plane function to an arbitrary location with no impact on IP
transit. transit.
skipping to change at line 188 skipping to change at line 188
* It has a different position in the IGP topology. * It has a different position in the IGP topology.
* It can have a different routing policy. * It can have a different routing policy.
These factors correspond to the issues described earlier. These factors correspond to the issues described earlier.
This document defines, for BGP route reflectors [RFC4456], two This document defines, for BGP route reflectors [RFC4456], two
changes to the BGP route selection algorithm: changes to the BGP route selection algorithm:
* The first change, introduced in Section 3.1, is related to the IGP * The first change, introduced in Section 3.1, is related to the IGP
cost to the BGP Next Hop in the BGP Decision Process. The change cost to the BGP next hop in the BGP Decision Process. The change
consists of using the IGP cost from a different IGP location than consists of using the IGP cost from a different IGP location than
the route reflector itself. the route reflector itself.
* The second change, introduced in Section 3.2, is to extend the * The second change, introduced in Section 3.2, is to extend the
granularity of the BGP Decision Process, to allow for running granularity of the BGP Decision Process, to allow for running
multiple Decision Processes using different perspectives or multiple Decision Processes using different perspectives or
policies. policies.
A route reflector can implement either or both of the modifications A route reflector can implement either or both of the modifications
in order to allow it to choose the best path for its clients that the in order to allow it to choose the best path for its clients that the
skipping to change at line 262 skipping to change at line 262
3.2. Multiple Route Selections 3.2. Multiple Route Selections
A BGP route reflector as per [RFC4456] runs a single BGP Decision A BGP route reflector as per [RFC4456] runs a single BGP Decision
Process. BGP Optimal Route Reflection (BGP ORR) may require multiple Process. BGP Optimal Route Reflection (BGP ORR) may require multiple
BGP Decision Processes or subsets of the Decision Process in order to BGP Decision Processes or subsets of the Decision Process in order to
consider different IGP locations or BGP policies for different sets consider different IGP locations or BGP policies for different sets
of clients. This is very similar to what is defined in [RFC7947], of clients. This is very similar to what is defined in [RFC7947],
Section 2.3.2.1. Section 2.3.2.1.
If the required routing optimization is limited to the IGP cost to If the required routing optimization is limited to the IGP cost to
the BGP Next-Hop, only step e) and subsequent steps as defined in the BGP next hop, only step e) and subsequent steps as defined in
[RFC4271], Section 9.1.2.2 need to be run multiple times. [RFC4271], Section 9.1.2.2 need to be run multiple times.
If the routing optimization requires the use of different BGP If the routing optimization requires the use of different BGP
policies for different sets of clients, a larger part of the Decision policies for different sets of clients, a larger part of the Decision
Process needs to be run multiple times, up to the whole Decision Process needs to be run multiple times, up to the whole Decision
Process as defined in Section 9.1 of [RFC4271]. This is, for Process as defined in Section 9.1 of [RFC4271]. This is, for
example, the case when there is a need to use different policies to example, the case when there is a need to use different policies to
compute different degrees of preference during Phase 1. This is compute different degrees of preference during Phase 1. This is
needed for use cases involving traffic engineering or dedicating needed for use cases involving traffic engineering or dedicating
certain exit points for certain clients. In the latter case, the certain exit points for certain clients. In the latter case, the
skipping to change at line 284 skipping to change at line 284
for a set of clients. Regular path selection, including IGP for a set of clients. Regular path selection, including IGP
perspectives for a set of clients as per Section 3.1, is then applied perspectives for a set of clients as per Section 3.1, is then applied
to the candidate paths to select the final paths to advertise to the to the candidate paths to select the final paths to advertise to the
clients. clients.
4. Deployment Considerations 4. Deployment Considerations
BGP ORR provides a model for integrating the client's perspective BGP ORR provides a model for integrating the client's perspective
into the BGP route selection Decision Process for route reflectors. into the BGP route selection Decision Process for route reflectors.
More specifically, the choice of BGP path takes into account either More specifically, the choice of BGP path takes into account either
the IGP cost between the client and the NEXT_HOP (rather than the IGP the IGP cost between the client and the next hop (rather than the IGP
cost from the route reflector to the NEXT_HOP) or other user- cost from the route reflector to the next hop) or other user-
configured policies. configured policies.
The achievement of optimal routing between clients of different The achievement of optimal routing between clients of different
clusters relies upon all route reflectors learning all paths that are clusters relies upon all route reflectors learning all paths that are
eligible for consideration. In order to satisfy this requirement, eligible for consideration. In order to satisfy this requirement,
BGP ADD-PATH [RFC7911] needs to be deployed between route reflectors. BGP ADD-PATH [RFC7911] needs to be deployed between route reflectors.
This solution can be deployed in hop-by-hop forwarding networks as This solution can be deployed in hop-by-hop forwarding networks as
well as in end-to-end tunneled environments. To avoid routing loops well as in end-to-end tunneled environments. To avoid routing loops
in networks with multiple route reflectors and hop-by-hop forwarding in networks with multiple route reflectors and hop-by-hop forwarding
 End of changes. 4 change blocks. 
5 lines changed or deleted 5 lines changed or added

This html diff was produced by rfcdiff 1.48. The latest version is available from http://tools.ietf.org/tools/rfcdiff/