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I2RS Working Group                                              K. Patel
Internet-Draft                                               R. Fernando
Intended status: Informational                             Cisco Systems
Expires: January 5, 2015                                      H. Gredler
                                                        Juniper Networks
                                                               S. Amante
                                                                   Apple
                                                                R. White
                                                                Ericsson
                                                                S. Hares
                                                                  Huawei
                                                            July 4, 2014


               Use Cases for an Interface to BGP Protocol
                draft-keyupate-i2rs-bgp-usecases-04.txt

Abstract

   A network routing protocol like BGP is typically configured and
   analyzed through some form of Command Line Interface (CLI) or
   NETCONF.  These interactions to control BGP and diagnose its
   operation encompass: configuration of protocol parameters, display of
   protocol data, setting of certain protocol state and debugging of the
   protocol.

   Interface to the Routing System's (I2RS) Programmatic interfaces
   provides an alternate way to control and diagnose the operation of
   the BGP protocol.  I2RS may be used for the configuration,
   manipulation, analyzing or collecting the protocol data.  This
   document describes set of use cases for which I2RS can be used for
   BGP protocol.  It is intended to provide a base for the solution
   draft describing a set of interfaces to the BGP protocol.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."



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   This Internet-Draft will expire on January 5, 2015.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
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   Without obtaining an adequate license from the person(s) controlling
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
     1.2.  Requirements for I2S  . . . . . . . . . . . . . . . . . .   4
   2.  Summary of Requirements for I2RS  . . . . . . . . . . . . . .   4
   3.  BGP Protocol Operation  . . . . . . . . . . . . . . . . . . .   6
     3.1.  BGP Error Handling for Internal BGP Sessions  . . . . . .   6
     3.2.  Summary of I2RS Capabilities and Interactions . . . . . .   7
   4.  BGP Route Manipulation  . . . . . . . . . . . . . . . . . . .   7
     4.1.  Customized Best Path Selection Criteria . . . . . . . . .   7
     4.2.  Flowspec Routes . . . . . . . . . . . . . . . . . . . . .   8
     4.3.  Route Filter Routes for Legacy Routers  . . . . . . . . .   8
     4.4.  Optimized Exit Control  . . . . . . . . . . . . . . . . .   9
     4.5.  Summary of I2RS Capabilities and Interactions . . . . . .   9
   5.  BGP Events  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     5.1.  Notification of Routing Events  . . . . . . . . . . . . .  10
     5.2.  Tracing Dropped BGP Routes  . . . . . . . . . . . . . . .  11
     5.3.  BGP Protocol Statistics . . . . . . . . . . . . . . . . .  12



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     5.4.  Summary of I2RS Capabilities and Interactions for Event
           statistics  . . . . . . . . . . . . . . . . . . . . . . .  13
   6.  Central membership computation for MPLS based VPNs  . . . . .  14
   7.  Marking Overlapping Traffic Engineering Routes for Removal  .  15
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  15
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  16
     10.2.  Informative References . . . . . . . . . . . . . . . . .  16
   Appendix A.  BGP Configuration  . . . . . . . . . . . . . . . . .  17
     A.1.  BGP Protocol Configuration  . . . . . . . . . . . . . . .  18
     A.2.  BGP Policy Configuration  . . . . . . . . . . . . . . . .  19
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  20

1.  Introduction

   Typically, a network routing protocol like BGP is configured and
   results of its operation are analyzed through some form of Command
   Line Interface (CLI) or NETCONF.  These interactions to control BGP
   and diagnose its operation encompass: configuration of protocol
   parameters, display of protocol data, setting of certain protocol
   state and debugging of the protocol.

   The I2RS architecture document [I-D.ietf-i2rs-architecture] describes
   a mechanism to control network protocols like BGP using a set of
   programmatic interfaces.  These programmatic interfaces allow one to
   control the BGP protocol by analyzing its operational state and
   routing protocol data, plus manipulating BGP's configuration to
   achieve various goals.  The I2RS is not intended to replace any
   existing configuration mechanisms, (i.e.: Command Line Interface or
   NETCONF).  Instead, I2RS is intended to augment those existing
   mechanisms by defining a standardized set of programmatic interfaces
   to enable easier configuration, interrogation and analysis of the BGP
   protocol.

   This document describes set of use cases for which I2RS's
   programmatic interfaces can be used to control and analyze the
   operation of BGP.  The use cases described in this document cover the
   following aspects of BGP: protocol parameter configuration, protocol
   route manipulation and tracking of protocol events.  The goal is to
   inform the community's understanding of where the I2RS BGP extensions
   fit within the overall I2RS architecture.  It is intended to provide
   a basis for the solutions draft describing the set of Interfaces to
   the BGP protocol.







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1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

1.2.  Requirements for I2S

   Each of the sections below (BGP protocol operation, BGP Route
   Manipulation, BGP Events, Central Membership for MPLS based VPNs, and
   Marking Overlapping BGP Routes) have specified a use case
   descriptions followed by a summary of I2RS requirements.  Each
   requirement listed in these sections is given an number [REQnn] where
   nn is the unique BGP Requirement.  Requirements duplicated from
   previous sections are repeated with the original requirements number.

2.  Summary of Requirements for I2RS

   This is a summary of the requirements listed in this document.

   o  BGP-REQ01: I2RS client/agent exchange SHOULD support the read,
      write and quick notification of status of the BGP peer operational
      state on each router within a given Autonomous System (AS).  This
      operational status includes the quick notification of protocol
      events that proceed a destructive tear-down of BGP session

   o  BGP-REQ02: I2RS client SHOULD be able to push BGP routes with
      custom cost communities to specific I2RS agents on BGP routers for
      insertion in specific BGP Peer(s) to aid Traffic engineering of
      data paths.  These routes SHOULD be tracked by the I2RS Agent as
      specific BGP routes with customer cost communities.  These routes
      (will/will not) installed via the RIB-Info.

   o  BGP-REQ03: I2RS client SHOULD be able to track via read/
      notifications all Traffic engineering changes applied via I2RS
      agents to BGP route processes in all routers in a network.

   o  BGP-REQ04: I2RS Agents SHOULD support identification of routers as
      BGP ASBRs, PE routers, and IBGP routers.

   o  BGP-REQ05: I2RS client-agent SHOULD support writing traffic flow
      specifications to I2RS Agents that will install them in associated
      BGP ASBRs and the PE routers.

   o  BGP-REQ06: I2RS Client SHOULD be able to track flow specifications
      installed within a IBGP Cloud within an AS via reads of BGP Flow
      Specification information in I2RS Agent, or via notifications from
      I2RS agent



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   o  BGP-REQ07: I2RS client-agent exchange SHOULD support the I2RS
      client being able to prioritize and control BGP's announcement of
      flow specifications after status information reading BGP ASBR and
      PE router's capacity.  BGP ASBRs and PE routers functions within a
      router MAY forward traffic flow specifications received from EBGP
      speakers to I2RS agents, so the I2RS Agent SHOULD be able to send
      these flow specifications from EBGP sources to a client in
      response to a read or notification.

   o  BGP-REQ08: I2RS Client SHOULD be able to read BGP route filter
      information from I2RS Agents associated with legacy BGP routers,
      and write filter information via the I2RS agent to be installed in
      BGP RR.  The I2RS Agent SHOULD be able to install these routes in
      the BGP RR, and engage a BGP protocol action to push these routers
      to ASBR and PE routers.

   o  BGP-REQ09: I2RS client(s) SHOULD be able to request the I2RS agent
      to read BGP routes with all BGP parameters that influence BGP best
      path decision, and write appropriate changes to the BGP Routes to
      BGP and to the RIB-Info in order to manipulate BGP routes

   o  BGP-REQ10: I2RS client SHOULD be able instruct the I2RS agent(s)
      to notify the I2RS client when the BGP processes on an associated
      routing system observe a route change to a specific set of IP
      Prefixes and associated prefixes.  Route changes include: 1)
      prefixes being announced or withdrawn, 2) prefixes being
      suppressed due to flap damping, or 3) prefixes using an alternate
      best-path for a given IP Prefix.  The I2RS agent should be able to
      notify the client via publish or subscribe mechanism.

   o  BGP-REQ11: I2RS client SHOULD be able to read BGP route
      information from BGP routers on routes in received but rejected
      from ADJ-RIB-IN due to policy, on routes installed in ADJ-RIB-IN,
      but not selected as best path, and on route not sent to IBGP peers
      (due to non-selection).

   o  BGP-REQ12: I2RS client SHOULD be able to request the I2RS agent to
      read installed BGP Policies.

   o  BGP-REQ13: I2RS client SHOULD be able to instruct the I2RS Agent
      to write BGP Policies into the running BGP protocols and into the
      BGP configurations.

   o  BGP-REQ14: I2RS client-agent SHOULD be able to read BGP statistics
      associated with Peer, and to receive notifications when certain
      statistics have exceeded limits.  An example of one of these
      protocol statistics is the max-prefix limit.




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   o  BGP-REQ15: The I2RS client via the I2RS agent MUST have the
      ability to read the loc-RIB-In BGP table that gets all the routes
      that the CE has provided to a PE router.

   o  BGP-REQ16: The I2RS client via the I2RS agent MUST have the
      ability to install destination based routes in the local RIB of
      the PE devices.  This must include the ability to supply the
      destination prefix (NLRI), a table identifier, a route preference,
      a route metric, a next-hop tunnel through which traffic would be
      carried

   o  BGP-REQ17: The I2RS client via the I2RS agent SHOULD have the the
      ability to read the loc-RIB-in BGP table to discover overlapping
      routes, and determine which may be safely marked for removal.

   o  BGP-REQ18: The I2RS client via the I2RS Agent SHOULD have the
      ability to modify filtering rules and initiate a re-computation of
      the local BGP table through those policies to cause specific
      routes to be marked for removal at the outbound eBGP edge.

3.  BGP Protocol Operation

   It is increasingly common for services facilitated via BGP to be
   subject to severe, widespread disruptions (outages), primarily due to
   the destructive teardown of BGP sessions as a result of receiving
   malformed BGP attributes.  Unfortunately, more fine-grained BGP error
   handling solutions, which would result in little to no impact on the
   operation of BGP protocol, remain elusive.

   A planned Graceful must also carefully be handled to limit the amount
   of traffic loss during a the shutdown.  While operational
   requirements for the BGP mechanism for graceful shutdown of a (set
   of) BGP sessions is describe din [RFC6198], and the operational
   procedures are described in [I-D.ietf-grow-bgp-gshut], additional
   fine-grained BGP error handling could improve graceful shutdown of
   BGP sessions.

   This section discussed how I2RS information could improve both the
   destructive teardown and the graceful teardown of sessions.

3.1.  BGP Error Handling for Internal BGP Sessions

   It is possible that I2RS could enable enhanced error handling
   techniques for Internal BGP sessions.  At a minimum, I2RS-capable BGP
   routers could signal an event such as "Malformed Attribute Received"
   via an I2RS agent toward an I2RS client(s).  I2RS client(s) may
   already have a real-time view of BGP routes, and corresponding BGP
   attributes, or may dynamically interrogate BGP routers in the network



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   to identify the present propagation scope of the BGP route(s) that
   are affected.  Finally, the I2RS client(s) could then signal back to
   I2RS agents on BGP routers to apply a filter that would block
   propagation of the BGP attribute or BGP route, as necessary, in order
   to temporarily aid in consistency of BGP routing information across
   the entire network until a permanent fix can be developed and
   deployed within BGP routers.

   I2RS would enable the global visibility and global control over the
   operational state of BGP, within a given Autonomous System, that is
   necessary to facilitate the learning of, rapid response to and more
   fine-grained isolation/scoping of BGP protocol events that currently
   cause a destructive tear-down of BGP sessions that lead to widespread
   disruptions of services.

3.2.  Summary of I2RS Capabilities and Interactions

   o  BGP-REQ01: I2RS client/agent exchange SHOULD support the read,
      write and quick notification of status of the BGP peer operational
      state on each router within a given Autonomous System (AS).  This
      operational status includes the quick notification of protocol
      events that proceed a destructive tear-down of BGP session

4.  BGP Route Manipulation

   Multiprotocol BGP [RFC4760] provides support to carry routing
   information for different BGP address families.  Route manipulation
   is heavily done across these different address families for different
   reasons.  BGP IPv4 and IPv6 address families use BGP Communities
   [RFC1997] and other IBGP and EBGP attributes to manipulate BGP routes
   for Traffic Engineering purpose.  BGP VPN address families use
   Extended Communities [RFC4360] to filter unwanted BGP routes.  BGP
   Flowspec address family [RFC5575] is used to install Flow based
   filters to filter unwanted data traffic.  The following sub-sections
   describe the use of IRS towards BGP Route Manipulation for different
   BGP address families.

4.1.  Customized Best Path Selection Criteria

   The BGP customized Bestpath facilitates custom bestpath computations
   within a BGP speaking network.  It is usually used within an IBGP
   network.  Customized bestpaths use special extended communities known
   as cost communities.  Cost communities carry enough information;
   Point of Insertion (POI) and the cost value to signal where in BGP
   bestpath the customize checks need to be done.  Both, the traffic
   engineering as well as backdoor (SHAM) links use customized bestpath
   computation.




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   With I2RS, it would be possible for an I2RS client to push routes
   with custom cost communities on the BGP routers for Traffic
   Engineering purpose.  I2RS client now can act as a central entity
   keeping track of all Traffic engineering data that get applied to BGP
   routes within an IBGP network.

4.2.  Flowspec Routes

   The BGP flowspec address family is used to disseminate the traffic
   flow specification to the BGP Autonomous System Border Routers
   (ASBRs) and Provider Edge (PE) routers.  Both, the BGP ASBRs and the
   PEs would translate the received BGP traffic flow specification into
   an Access Control List (ACL) and install it in router's forwarding
   path.  Using such ACLs routers can now classify, shape, rate limit,
   filter, or redirect traffic flows.

   With I2RS, it would be possible for an I2RS client to push traffic
   flow specifications to the BGP ASBRs and the PE routers.  I2RS client
   can act as a central entity tracking all the traffic flow
   specifications that are installed within an IBGP network.  I2RS
   client could also prioritize and control the announcement of traffic
   flow specifications according to various ASRBs and PE router's
   capacity.  BGP ASBRs and PE routers MAY forward traffic flow
   specifications received from EBGP speakers to I2RS Agents.  This
   would allow I2RS agents to centrally manage and track any externally
   received traffic flow specifications.

4.3.  Route Filter Routes for Legacy Routers

   The BGP Route Filter address family is used to disseminate the Route
   Target filter information between VPN BGP speakers.  This information
   is then used to build a route distribution graph that helps in
   limiting the propagation of VPN NLRI (network Layer Reachabilty
   Information) within a VPN network.  However, it requires that all the
   BGP VPN routers are upgraded to support this functionality.
   Otherwise, the graph information is incomplete when a VPN network
   consists of legacy routers that participates in VPN but does not
   implement the BGP route filter address family.

   With I2RS, it would be possible for an I2RS client to push router
   filter information to BGP RR routers on behalf of all legacy routers
   that participates in VPN but does not support or implement the BGP
   route filter address family.  I2RS client can act as a central entity
   tracking all the configured Route Filters for legacy routers and push
   them on appropriate RRs who in turn would push it to ASBRs and PE
   routers.  In this way, I2RS agents help build an optimal route
   distribution graph that would assist in filtering of VPN NLRIs in a
   VPN network.



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4.4.  Optimized Exit Control

   Optimized Exit Control is used to provide route optimization and load
   distribution for multiple network connections between networks.
   Network operators can monitor IP traffic flows and then could define
   policies and rules based on traffic class performance, link bandwidth
   monetary costs, link load distribution, traffic types, link failures,
   etc.

   With I2RS, it would be possible for an I2RS client to manipulate BGP
   routes and its parameters that influence BGP bestpath decisions.
   I2RS client could act as a central entity that would monitor and
   manipulate BGP routes based on central network based policies.  Such
   routes would then be injected by a I2RS client into the network so as
   to get the load distribution for multiple network connections.

4.5.  Summary of I2RS Capabilities and Interactions

   o  BGP-REQ02: I2RS client SHOULD be able to push BGP routes with
      custom cost communities to specific I2RS agents on BGP routers for
      insertion in specific BGP Peer(s) to aid Traffic engineering of
      data paths.  These routes SHOULD be tracked by the I2RS Agent as
      specific BGP routes with customer cost communities.  These routes
      (will/will not) installed via the RIB-Info.

   o  BGP-REQ03: I2RS client SHOULD be able to track via read/
      notifications all Traffic engineering changes applied via I2RS
      agents to BGP route processes in all routers in a network.

   o  BGP-REQ04: I2RS Agents SHOULD support identification of routers as
      BGP ASBRs, PE routers, IBGP routers.

   o  BGP-REQ05: I2RS client-agent SHOULD support writing traffic flow
      specifications to I2RS Agents that will install them in associated
      BGP ASBRs and the PE routers.

   o  BGP-REQ06: I2RS Client SHOULD be able to track flow specifications
      installed within a IBGP Cloud within an AS via reads of BGP Flow
      Specification information in I2RS Agent, or via notifications from
      I2RS agent.

   o  BGP-REQ07: I2RS client-agent exchange SHOULD support the I2RS
      client being able to prioritize and control BGP's announcement of
      flow specifications after status information reading BGP ASBR and
      PE router's capacity.  BGP ASBRs and PE routers functions within a
      router MAY forward traffic flow specifications received from EBGP
      speakers to I2RS agents, so the I2RS Agent SHOULD be able to send




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      these flow specifications from EBGP sources to a client in
      response to a read or notification.

   o  BGP-REQ08: I2RS Client SHOULD be able to read BGP route filter
      information from I2RS Agents associated with legacy BGP routers,
      and write filter information via the I2RS agent to be installed in
      BGP RR.  The I2RS Agent SHOULD be able to install these routes in
      the BGP RR, and engage a BGP protocol action to push these routers
      to ASBR and PE routers.

   o  BGP-REQ09: I2RS client(s) SHOULD be able to request the I2RS agent
      to read BGP routes with all BGP parameters that influence BGP best
      path decision, and write appropriate changes to the BGP Routes to
      BGP and to the RIB-Info in order to manipulate BGP routes

5.  BGP Events

   Given the extremely large number of BGP Routes in networks, it is
   critical to have scalable mechanisms that can be used to monitor for
   events affecting routing state and, consequently, reachability.  In
   addition, similar tools are needed in order to monitor BGP protocol
   statistics, which help operators and developers better understand
   scalability of software and hardware that BGP utilizes.

   I2RS could provide a publish-subscribe capability to applications to:

   o  request monitoring of BGP routes and related events; and,

   o  subscribe to the I2RS client to receive events related to BGP
      routes or other protocol-related events of interest.

5.1.  Notification of Routing Events

   There are certain IP prefixes, for example those that are arbitrarily
   classified by a given network operator as "high visibility" by its
   end-users, for which immediate notification of changes in their state
   are extremely useful to know about.  Upon notification of such
   events, a Network Operations Center (NOC) could respond to customer
   inquiries in a more timely fashion; alternatively, the NOC may decide
   to perform Traffic Engineering to restore service, etc.

   Currently, the only way to learn of such events is for a BGP
   monitoring system to establish a BGP session with a multitude of BGP
   routers in an AS.  Then, the BGP monitoring system needs to look
   through all BGP UPDATE's in order to identify those events that are
   of interest to it.  Note, this doesn't account for the fact that
   there are several applications that might be simultaneously
   interested in learning of events to a given IP prefix nor the fact



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   that some applications may want to dynamically insert or remove "IP
   prefixes of interest", depending on the needs of their constituent
   applications.

   With I2RS, it is conceivable that applications could tell an I2RS
   client, through a North-Bound API, their "IP prefixes" (or,
   AS_PATH's, BGP communities, etc.) that are of interest.  For example,
   a NOC application may be interested in changes to high visibility
   content or service-provider Web sites; alternatively, a security
   application may be interested in events associated with a different
   set of IP prefixes.  The I2RS client would then consolidate the list
   of IP prefixes, and associated characteristics, to be monitored and
   program BGP routers in an AS to observe this subset of routes for
   changes.  Some examples of changes in routing state might include:

   o  an IP prefix being announced or withdrawn

   o  an IP prefix being suppressed, due to route flap dampening

   o  an alternative best-path being chosen for a given IP prefix

   When the requisite events for a BGP Route are observed by a BGP
   router, it would notify I2RS agents.

   The I2RS agents would have a publish/subscribe mechanism whereby
   various sets of applications may subscribe to events of interest.
   The I2RS client would then publish these events so applications would
   immediately receive them and take the appropriate domain-specific
   action necessary.

5.2.  Tracing Dropped BGP Routes

   It is extremely useful to operators to be able to rapidly identify
   instances where a BGP route is not being propagated within an
   Autonomous System.  At a minimum, this could result in sub-optimal
   performance when attempting to reach such destinations.

   There are two instances when this scenario will occur.  First, when a
   Service Provider is using "Soft Reconfiguration Inbound", it allows
   their ASBR routers to receive a copy of a BGP route, but show that
   route was not permitted into the Adj-RIB-In most likely as a result
   of the inbound BGP policy not permitting that IP prefix.  Thus, this
   BGP route is not even eligible for BGP Path Selection.  The second
   instance is where the BGP route is permitted by the inbound BGP
   policy into the Adj-RIB-In, but due to BGP Path Selection (i.e.:
   lower LOCAL_PREF, longer AS_PATH length, etc.) was not chosen as the
   best path and, subsequently, this particular BGP route is not
   forwarded on to other internal BGP speakers in the AS.  In both



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   instances, the BGP route is only visible within the ASBR on which
   that BGP route was first learned.  Needless to say, in large Service
   Provider networks with a numerous interconnects to a single customer
   it can be very time-consuming to discover where such a BGP route is
   learned before ultimately determining why the route was blocked or
   not preferred.

   With I2RS, it would be possible for an I2RS client to rapidly gather
   information from across a large set of BGP routers in the network to
   determine at what ASBR's the BGP route is being learned.  Next, the
   I2RS client could interrogate those routers BGP policies to determine
   the root cause of why the route was either not learned or not
   preferred in BGP.  Finally, if necessary, the I2RS client(s) could
   amend BGP policies and push them out to BGP routers to permit the BGP
   route or make it a preferred route according to the BGP path
   selection algorithm.

5.3.  BGP Protocol Statistics

   There are a variety of statistics related to the operation of BGP
   that are invaluable to network operators.  These statistics generally
   help operators, and developers, understand the present state and
   future scalability of BGP.

   One statistic that is invaluable to operators is the current number
   of BGP routes learned through an eBGP session.  Operators then apply
   a command against each eBGP session to limit the maximum number of
   BGP routes that may be learned through that eBGP session before a
   warning message is triggered and/or the eBGP session is torn down
   completely.  This configuration capability is often referred to as a
   "max-prefix limit".  This command must be routinely audited and, if
   necessary, adjusted in order to not trigger a false warning or
   teardown due to the natural organic growth in BGP routes learned from
   a given BGP neighbor.

   I2RS agents could provide an invaluable capability to help audit and
   re-program the "max-prefix limit" on a periodic basis, which is
   generally once per day.  Specifically, the first task would be for an
   I2RS client to validate that there is a "max-prefix limit" applied to
   every eBGP session.  (If there is not, that should either trigger a
   red alarm to the NOC to manually fix this condition or for the I2RS
   client to automatically apply a "max-prefix limit" that would
   alleviate this hazardous condition).  Assuming there is a "max-prefix
   limit" already in place, the I2RS client would simultaneously
   retrieve, from each BGP router, the current number of BGP routes
   learned through a BGP session and value used for the "max-prefix
   limit" on that same BGP session.  These two values could then be
   handed off to an application that determines if adjustments in the



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   "max-prefix limit" value are required for each BGP session.  The
   application would then notify the I2RS client of the subset of eBGP
   sessions and their associated change in "max-prefix limit" value,
   whereby the I2RS client would then adjust the BGP protocol
   configuration on each requisite BGP router in the network.  Finally,
   it should be noted that the above is just one method whereby "max-
   prefix limit" values are adjusted.  It's similarly possible that the
   BGP routers may, through the I2RS, pull the "max-prefix limit" values
   for each eBGP neighbor they have on-board on a periodic basis and
   validate their accuracy.

   The above is just one use case related to BGP protocol statistics.
   There are wealth of other BGP protocol statistics or state
   information that would be invaluable to have programmatic visibility
   into that operators do not have today.

5.4.  Summary of I2RS Capabilities and Interactions for Event statistics

   I2RS SHOULD have the ability to:

   o  BGP-REQ10: I2RS client SHOULD be able instruct the I2RS agent(s)
      to notify the I2RS client when the BGP processes on an associated
      routing system observe a route change to a specific set of IP
      Prefixes and associated prefixes.  Route changes include: 1)
      prefixes being announced or withdrawn, 2) prefixes being
      suppressed due to flap damping, or 3) prefixes using an alternate
      best-path for a given IP Prefix.  The I2RS agent should be able to
      notify the client via publish or subscribe mechanism.

   o  BGP-REQ11: I2RS client SHOULD be able to read BGP route
      information from BGP routers on routes in received but rejected
      from ADJ-RIB-IN due to policy, on routes installed in ADJ-RIB-IN,
      but not selected as best path, and on route not sent to IBGP peers
      (due to non-selection).

   o  BGP-REQ12: I2RS client SHOULD be able to request the I2RS agent to
      read installed BGP Policies

   o  BGP-REQ13: I2RS client SHOULD be able to instruct the I2RS Agent
      to write BGP Policies into the running BGP protocols and into the
      BGP configurations.

   o  BGP-REQ14: I2RS client-agent SHOULD be able to read BGP statistics
      associated with Peer, and to receive notifications when certain
      statistics have exceeded limits.  An example of one of these
      protocol statistics is the max-prefix limit.





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6.  Central membership computation for MPLS based VPNs

   MPLS based VPNs use route target extended communities to express
   membership information.  Every PE router holds incoming BGP NLRI and
   processes them to determine membership and then import the NLRI into
   the appropriate MPLS/VPN routing tables.  This consumes resources,
   both memory and compute on each of the PE devices.

   An alternative approach is to monitor routing updates on every PE
   from the attached CEs and then compute membership in a central
   manner.  Once computed the routes are pushed to the VPN RIBs of the
   participating PEs.

   This centralization of membership control has a few advantages.

   o  The membership mechanism (route-targets) need not be configured in
      each of the PEs and can be expressed once centrally.

   o  No resources in the PEs need to be spent to categorize routes into
      the VRF tables that they belong and to filter out unwanted state.

   o  Doing it centrally means the availability of almost unlimited
      compute capacity to compute membership and hence can be done in a
      scaleable manner.

   o  More sophisticated routing policies and filters can be applied
      during the central import/export process than can be expressed and
      performed using the traditional route target mechanism.

   o  Routes can be selectively pushed only to the participating PE's
      further reducing the memory load on the individual routers in the
      network.  This further obviates for a distributed mechanisms such
      as rt constraints to reduce unnecessary path state in the routers.

   Note that centrally computation of membership can be applied to other
   scenarios as well such as VPLS, MVPNs, MAC VPNs and others.
   Depending on the scenario, what gets monitored from the CE might
   vary.  Central computation will especially help VPLS where multi-
   homing and load balancing using distributed techniques has
   particularly been a challenge.

   Also note that one of the biggest promises of central route
   computation is simplification and reduction of computation and memory
   load on all devices in the network.  This use case is just one
   example that illustrates these benefits of central computation very
   well.

   Summary of I2RS Capabilities and Interactions:



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   o  BGP-REQ15:The I2RS client via the I2RS agent MUST have the ability
      to read the loc-RIB-In BGP table that gets all the routes that the
      CE has provided to a PE router.

   o  BGP-REQ16:The I2RS client via the I2RS agent MUST have the ability
      to install destination based routes in the local RIB of the PE
      devices.  This must include the ability to supply the destination
      prefix (NLRI), a table identifier, a route preference, a route
      metric, a next-hop tunnel through which traffic would be carried

7.  Marking Overlapping Traffic Engineering Routes for Removal

   It is often the case that routes are advertised not to provide
   reachability (in the strict sense), but rather to provide optimal
   reachability, or to engineer the path traffic takes to a particular
   destination.  While this can improve the efficiency of a network's
   operation, it can also increase the amount of state carried in the
   control plane beyond the point where the additional state has any
   real effect on traffic flow.  Removing Overlapping Routes
   [I-D.white-grow-overlapping-routes] provides a mechanism designed to
   remove these traffic engineering routes once they are beyond the
   point of actually impacting traffic flows in the network.

   Summary of I2RS Capabilities and Interactions:

   o  BGP-REQ17: The I2RS client via the I2RS agent SHOULD have the the
      ability to read the loc-RIB-in BGP table to discover overlapping
      routes, and determine which may be safely marked for removal.

   o  BGP-REQ18: The I2RS client via the I2RS Agent SHOULD have the
      ability to modify filtering rules and initiate a re-computation of
      the local BGP table through those policies to cause specific
      routes to be marked for removal at the outbound eBGP edge.

8.  Security Considerations

   The BGP use cases described in this document assumes use of I2RS
   programmatic interfaces described in the I2RS framework mentioned in
   [I-D.ietf-i2rs-architecture].  This document does not change the
   underlying security issues inherent in the existing in
   [I-D.ietf-i2rs-architecture].

9.  Acknowledgements

   The authors would like to thank Ed Crabbe, Joel Halpern, Wes George,
   Carlos Pignataro, Jon Mitchell and Bill Atwood for their comments and
   suggestions.




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10.  References

10.1.  Normative References

   [I-D.ietf-i2rs-architecture]
              Atlas, A., Halpern, J., Hares, S., Ward, D., and T.
              Nadeau, "An Architecture for the Interface to the Routing
              System", draft-ietf-i2rs-architecture-03 (work in
              progress), May 2014.

   [RFC1997]  Chandrasekeran, R., Traina, P., and T. Li, "BGP
              Communities Attribute", RFC 1997, August 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2629]  Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
              June 1999.

   [RFC3392]  Chandra, R. and J. Scudder, "Capabilities Advertisement
              with BGP-4", RFC 3392, November 2002.

   [RFC3552]  Rescorla, E. and B. Korver, "Guidelines for Writing RFC
              Text on Security Considerations", BCP 72, RFC 3552, July
              2003.

   [RFC4271]  Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
              Protocol 4 (BGP-4)", RFC 4271, January 2006.

   [RFC4360]  Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
              Communities Attribute", RFC 4360, February 2006.

   [RFC4760]  Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
              "Multiprotocol Extensions for BGP-4", RFC 4760, January
              2007.

10.2.  Informative References

   [I-D.ietf-grow-bgp-gshut]
              Francois, P., Decraene, B., Pelsser, C., Patel, K., and C.
              Filsfils, "Graceful BGP session shutdown", draft-ietf-
              grow-bgp-gshut-05 (work in progress), January 2014.

   [I-D.mcpherson-irr-routing-policy-considerations]
              McPherson, D., Amante, S., Osterweil, E., and L. Blunk,
              "IRR & Routing Policy Configuration Considerations",
              draft-mcpherson-irr-routing-policy-considerations-01 (work
              in progress), September 2012.



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   [I-D.white-grow-overlapping-routes]
              White, R., Retana, A., and S. Hares, "Filtering of
              Overlapping Routes", draft-white-grow-overlapping-
              routes-01 (work in progress), February 2013.

   [RFC2622]  Alaettinoglu, C., Villamizar, C., Gerich, E., Kessens, D.,
              Meyer, D., Bates, T., Karrenberg, D., and M. Terpstra,
              "Routing Policy Specification Language (RPSL)", RFC 2622,
              June 1999.

   [RFC2858]  Bates, T., Rekhter, Y., Chandra, R., and D. Katz,
              "Multiprotocol Extensions for BGP-4", RFC 2858, June 2000.

   [RFC5156]  Blanchet, M., "Special-Use IPv6 Addresses", RFC 5156,
              April 2008.

   [RFC5575]  Marques, P., Sheth, N., Raszuk, R., Greene, B., Mauch, J.,
              and D. McPherson, "Dissemination of Flow Specification
              Rules", RFC 5575, August 2009.

   [RFC5735]  Cotton, M. and L. Vegoda, "Special Use IPv4 Addresses",
              RFC 5735, January 2010.

   [RFC6198]  Decraene, B., Francois, P., Pelsser, C., Ahmad, Z.,
              Elizondo Armengol, A., and T. Takeda, "Requirements for
              the Graceful Shutdown of BGP Sessions", RFC 6198, April
              2011.

Appendix A.  BGP Configuration

   The configuration of BGP is arduous to establish and maintain,
   particularly on networks whose services have a requirement for
   complex routing policies.  This need is magnified by the need to
   routinely perform changes to large numbers of BGP routers to, for
   example: add or remove customer's BGP sessions, announce or withdraw
   (customer) IP prefixes in BGP, modify BGP policies to effect changes
   in Traffic Engineering, audit BGP routers to ensure they have
   consistent and appropriate BGP policies, and others.

   There are three categories of BGP configuration:

   1.  Local BGP routing protocol configuration: local Autonomous System
       Number (ASN), BGP path selection properties of the router,
       injection of (aggregate) routes into BGP, etc.

   2.  Local BGP policies: policies designed to filter and/or manipulate
       BGP attributes associated with BGP routes learned through BGP
       sessions.  These policies typically live in the global



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       configuration of a BGP router, but are applied on a per-BGP
       neighbor basis (or, group of BGP neighbors); and,

   3.  BGP neighbor sessions: remote ASN, remote IP address, address
       families, BGP policies to applied to routes, max-prefix limits,
       etc.

   The sum total of BGP configuration on a BGP router is typically the
   largest quantify of configuration on Service Provider's BGP routers,
   by a fairly large margin.  When that is combined with the large set
   of routine configuration changes, mentioned above, it should be
   fairly clear that systematic reading, configuration and control of
   BGP routers through a mechanism like I2RS would greatly benefit all
   operators of BGP routers.

   While it may not be possible to provide programmatic APIs for
   esoteric vendor-specific policy configuration, it is possible to
   provide such API's for BGP protocol specific configuration and the
   more commonly used BGP routing policies.

A.1.  BGP Protocol Configuration

   Ability to enable and disable new address families within a BGP
   protocol for a network of BGP speaking routers is a challenge.  The
   challenge is mainly in keeping track of BGP speaker's feature
   capabilities and then configuration of new address families on a
   multiple BGP speakers within a given network.  With the necessary
   information, I2RS agents allow a network operator to push
   configuration information for enabling and disabling of new address
   families on a partial or entire set of BGP speakers within a given
   network.  This would assist in building BGP overlay networks as
   needed.

   For VPN address families, the main challenge lies in the complex VPN
   configuration required to setup the control plane for Customer VPNs.
   The configuration involves creating a Virtual Routing and Forwarding
   instance (VRF), a Route Distinguisher (RD) that ensures each customer
   prefixes remains unique across VPNs, and Route Targets (RT) that help
   ensure that the Customer prefixes are segregated appropriately so
   that they do not cross the VPN boundaries.  I2RS would allow a
   network operator to push such configuration from a central location
   where a global VPN provisioning information could be stored.  This
   helps avoid manual configuration of a VPN on multiple routers.
   Instead the configuration is controlled and pushed though a central
   I2RS client using a programmatic set of APIs on targeted set of BGP
   speakers.





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   Use of I2RS agents to announce protocol configuration information
   would simplify and automate configuration of BGP protocol in IBGP
   deployments where the protocol based policies are seldom used.  To
   facilitate such a centralized configuration model, BGP speakers could
   be extended to use programmatic APIs to announce their feature
   capabilities as part of protocol initialization to the centralize
   I2RS agents.  This would assist I2RS agents to auto-discover BGP
   protocol capabilities of various BGP speakers in a given network.
   I2RS agents in turn would use the information towards enabling/
   disabling of BGP specific features on BGP speakers.

A.2.  BGP Policy Configuration

   Filtering of BGP routes is strongly recommended to control the
   announcements of BGP prefixes across the internet.  Most providers
   make extensive use of BGP prefix filtering policies at the edge of
   their networks.  The reasons for filtering BGP prefixes are:

   o  Avoid Unwanted Route Announcements.  Filter prefixes that MUST not
      be routed [RFC5735], [RFC5156].  Filter prefixes that are not
      allocated by Internet Routing Registries.

   o  Facilitate Route Summarization.  Filter prefixes beyond certain
      agreed prefix mask length between providers.  Route Summarization
      helps control BGP RIB and FIB table size.

   o  Defensive Security.  Filter prefixes from Stub customer ASes that
      are not owned by the customers.  Filter customer prefixes
      announced by other providers.  This helps avoid prefix hijacking.

   A set of standards-based schemas to enable configuration of Local BGP
   policies and BGP neighbor sessions was realized through the Routing
   Policy Specification Language (RSPL) [RFC2622].  The RPSL defined a
   standards-based schemas, or 'objects' as it called them, that
   defined:

   o  binding of IP prefixes to (one or more) Origin AS, (route
      objects);

   o  collections of routes (route-set objects);

   o  collections of Autonomous Systems (as-set objects); and,

   o  routing policy of an Autonomous System to/from its adjacent
      neighbor AS'es, (aut-num objects)

   Each ASN is responsible for creation, modification and deletion of
   its RPSL objects in an Internet Routing Registry (IRR).  IRR's are



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   typically operated by Regional Internet Registries (RIR's) and a few
   dozen larger ISP's and independent organizations.  The IRR's provide
   a well-known location for all organizations attached to the Internet
   to retrieve or update RPSL objects.

   While still widely and actively used by Internet Service Providers,
   the prevailing belief is that the data contained in the IRR's is
   inaccurate, primarily due to a lack of deployed authorization method
   with respect to the creation of modification of RPSL objects.  It
   should be noted that this criticism is not directed at the previously
   defined RPSL schemas, but rather at the data contained in RPSL
   schemas by end-users of the IRR system.  Please refer to the IRR And
   Routing Policy Configuration Considerations
   [I-D.mcpherson-irr-routing-policy-considerations] document for a more
   thorough discussion of the history and present state of the IRR's.

   Currently, RPSL schemas are exchanged between non-routing systems
   (servers) used within the IRR system.  In addition, open-source and
   proprietary applications create or modify RPSL schemas, as necessary,
   to signal the announcement (or, withdrawal) of an IP prefix from an
   ASN or the creation (or, teardown) of a neighbor relationship between
   two adjacent ASN's.  Most importantly, these RPSL schemas are
   consumed by similar applications to automatically build routing
   policies, (i.e.: lists of IP prefixes, corresponding Origin ASN's
   and/or AS_PATH's), that then get translated to device-specific syntax
   (i.e.: CLI) before being pushed into individual BGP routers to effect
   routing policy on the network.  It is common for Internet Service
   Providers to perform updates to these routing policies across their
   entire network on a daily basis.

   With I2RS it would be desirable to change the last step in the above
   process so that BGP policies derived from RPSL schemas, and other
   information sources, are translated into standards-based schemas that
   are then pushed, or pulled, into individual BGP routers.  More
   generally, I2RS agents could use API's to gather information required
   to build various types of BGP routing policies plus the corresponding
   set of Autonomous System Border Routers (ASBR's) where such policies
   need to be applied in the network and, finally, making those changes
   to individual network elements so those BGP policies take effect in
   the network.  In doing so, a network operator now has a centralized
   way of building and making these policies take effect across the
   network in a coordinated manner.

Authors' Addresses







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   Keyur Patel
   Cisco Systems
   170 W. Tasman Drive
   San Jose, CA  95134
   USA

   Email: keyupate@cisco.com


   Rex Fernando
   Cisco Systems
   170 W. Tasman Drive
   San Jose, CA  95134
   USA

   Email: rex@cisco.com


   Hannes Gredler
   Juniper Networks
   1194 N. Mathilda Ave
   Sunnyvale, CA  94089
   USA

   Email: hannes@juniper.net


   Shane Amante
   Apple


   Russ White
   Ericsson

   Email: russw@riw.us


   Susan Hares
   Huawei

   Email: shares@ndzh.com










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