Internet DRAFT - draft-abarbanel-idr-bgp4-te

draft-abarbanel-idr-bgp4-te



Network Working Group                                     Ben Abarbanel
Internet Draft                                         IPOptical, Inc.,
Document: draft-abarbanel-idr-bgp4-te-01.txt      Senthil Venkatachalam
Expiration Date: September, 2000                         Alcatel, U.S.A




                   BGP-4 support for Traffic Engineering

Status of this Memo

     This document is an Internet-Draft and is in full conformance with
     all provisions of Section 10 of RFC2026 [].

     This document is an Internet-Draft and is in full conformance with all
     provisions of Section 10 of RFC2026 except that the right to produce
     derivative works is not granted.

     This document is an Internet-Draft and is NOT offered in accordance
     with Section 10 of RFC2026, and the author does not provide the IETF
     with any rights other than to publish as an Internet-Draft

     Internet-Drafts are working documents of the Internet Engineering Task
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Abstract

     Currently, constraint routing (CR) and traffic engineering (TE)
     models do not take into consideration the big picture view of IP
     traffic traversing multiple autonomous systems (AS). Most of the
     traffic and constraint routing is based on IGP protocols such as
     OSPF/ISIS, etc. The resulting view of the Internet is limited to 
     one autonomous system and areas or systems within it. Hence, the 
     routing/forwarding functions do not select the optimum path for 
     packets that need to traverse several autonomous systems. 
     
     The proposal in this draft is that the BGP protocol can be utilized 
     to choose the best BGP routes based on traffic engineered (TE) 
     constraint weights. This information can be propagated between all 
     BGP peers and calculated by the BGP AS border routers before it is 
     deployed to their forwarding tables.


draft-abarbanel-idr-bgp4-te-01.txt                                   [page 2]

1. Conventions used in this document

     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 [].



2. Overview

     The Internet is composed of many autonomous systems(AS). BGP acts as
     the road map for selecting the best paths across these systems. Today's
     Internet infrastructure does not consider the Internet as one
     homogenous system but a collection of systems. Where each system is
     managed autonomously by an (ISP) provider. These providers tend to
     filter or block routes from each other. This in itself creates a
     non-optimum routing. Constraint based routing adds a level of traffic
     influence by defining the path (all the hops along the way) that a
     packet should take. It does this very well within an autonomous system
     and within the limitation of an OSPF/ISIS areas/levels. The area
     border routers inside the AS will need to compute the best path to
     other areas until the packet arrives at its destination within the
     autonomous system or leaves the AS to the next Autonomous System. The
     choice of which AS to select is based purely on a one dimensional
     level, by looking at the minimum number of AS hops to a given
     destination or providing various weights and preferences, that are
     local to the AS. The BGP Multi Exit Discriminator (MED)
     provides some level of inter-AS metric but is still limited to the
     adjacent AS.

     The approach discussed here is to view the Internet as one homogenous
     entity with many AS's. Each of the AS's can have a summary weight
     assigned to it based on a given traffic engineering criteria. This
     weight can be a type of quality of service, such as maximum IGP
     bandwidth available, maximum number of IGP hops, maximum IGP delay
     across the AS from one IBGP router to the other IBGP router, maximum
     bandwidth for a service class A, B, C, etc. These criteria levels are
     summarized by the IGP for a given network destination in a given AS
     and exported to BGP. The summarization within an AS can be achieved
     using IGP constraint based routing algorithms used within link state
     protocols such as OSPF and ISIS. In the case of OSPF, a new opaque LSA
     is defined to propagate the summarized weights between OSPF areas.

     This draft is organized as follows. Section 3 details the approach at 
     the BGP level between ASs and Section 4 discusses the approach at the
     IGP level within an AS. The various traffic engineering weights are
     discussed in Section 5. The following sections deal with the 
     redistribution of the traffic engineering weight information from IGP to 
     BGP, configuration issues, route flapping, and ISP issues.  The BGP and 
     IGP approaches together will provide a comprehensive traffic engineering 
     routing system across the internet.
 



draft-abarbanel-idr-bgp4-te-01.txt                                    [page 3]


3. BGP Level

   The method used to propagate constraint summarization weights for each AS 
   is to define a new attribute which contains QOS like sub fields that can 
   include such parameters as bandwidth, number of hops, delay, various QOS 
   service classes, and so on. Historical NLRI information is contained
   as well. These sub fields will be termed TE weights and each BGP router 
   would propagate this information to its peers. Making it possible for any 
   router that handles the data to have a traffic engineering view of all the 
   paths and their associated TE Weights for a given route to a given router.
 
   When the BGP RIB database is loaded with TE Weight information, a TE 
   capable BGP router would compute based on TE manual configurations 
   criteria the best BGP route for a given destination. The BGP Route 
   Selection process is extended to support a TE way of prioritizing the best 
   routes for any configured destination. In which the order and preference 
   of the routes can be changed to give the TE weight attribute a higher 
   priority than other attributes. Different TE Weight types could be 
   manually assigned a different level of priority in order to strategize a 
   system where the BGP route selection criteria could be further optimized.

3.1 BGP Routes Originating in Local AS
    Routes that originated within the same AS will not be calculated for
    TE weights since there is no BGP optimization that can be achieved.
    In this case, all TE Weight calculations are strictly done at the IGP
    level. As a rule, IBGP routers will not propagate to other IBGP routers  
    the new TE Weight attribute for routes that originated in the same AS. 
    Routes that came from other EBGP peers could contain the new TE Weight 
    attribute which will be propagated to IBGP peers.

3.2 Route Reflector Functionality 
    When a Route Reflector receives an update messages with the Aggregated TE 
    Weight attribute it will simply add it to the BGP RIB-IN/OUT for local  
    use and propagate it to other IBGP peers without modifying any of its 
    fields.   

3.3 When to Add TE Weight to BGP Update messages
    When an IBGP router receives an update message from another IBGP router 
    for a (route) destination outside its own AS, it will consult the local 
    FIB database for its reachability via the corresponding update message 
    BGP Next Hop. Using this BGP Next Hop it will check the associated TE 
    summary weight provided in the FIB by the extended IGP constraint routing 
    calculations. It will add or compare the IGP TE summary weight with the 
    Aggregated TE Weight that was propagated in the update message and create 
    the next level Aggregated TE weight. Next, it will add the Aggregated TE 
    weight to the local BGP RIB and use it for the BGP route selection 
    process. In addition, the current router will propagate the new 
    Aggregated TE weight value to all of its EBGP peers except the one that 
    introduced the route.    





 draft-abarbanel-idr-bgp4-te-01.txt                                   [page 4]

    Propagation, aggregating BGP TE Weights, and deploying into the BGP RIB  
    and FIB tables is performed from one router to the next such that the 
    only TE weight that is detected by any router along an AS path is 
    accurate enough to cover the TE measurements from a given router to the 
    route's point of origin.

3.4 Route Aggregation Impacts
    As routes are propagated from one AS to the next, it is possible that
    providers have configured their routers to aggregate more specific routes 
    into general ones. This condition will cause the specific routes and 
    their TE Weight attributes to get lost or reduced in accuracy.  In order 
    to keep track of this information, it is proposed that the specific 
    routes and their TE Weights be contained in the new TE Weight attribute 
    fields. It would be possible at any router along the route propagation 
    paths to determine the detail accuracy of the TE weights that made up the 
    super aggregate TE Weight. 

    Example 1: A single AS-Path with no route aggregation, and TE weights 
               are aggregated.

      In AS1            In AS2               Arriving in Dest AS3
    N1N2,AS1,TE1 ----> N1N2,AS2,(TE1+TE2) ----> N1N2,TE12  

    In AS3 all we need is the routes(N1N2) and the TE weight TE12, which is         
    the aggregate of TE1 and TE2.


    Example 2: Aggregating routes from multiple AS-Paths, and TE weights
               are super aggregated too.

      In AS1            In AS2             In Dest AS3
    N1N2,AS1,TE1 ----> N1N2,AS2,(TE1+TE2) --> N1N2,TE12 --> see below 

      In AS4            In AS5             In Dest AS3
    N3N4,AS5,TE5 ----> N3N4,AS5,(TE5+TE6) --> N3N4,TE56 --> see below

    At this point in AS3, routes N1N2 and N3N4 are aggregated together
    to form super aggregate route N13N24, 
    with the aggregated TE weight of (TE12+TE56) = Super aggregated TE WEIGHT 
    TE1256.

    In order to keep track of which routes made up TE12 and TE56 we keep 
    two TE Weight paths in the super aggregated route N13N24 as follows:

    N13N24/TE1256 = (N1N2/TE12, N3N4/TE56) in the TE Weight Attribute field.
 
    This list of historical routes can be as large as the number of route 
    aggregation points that are performed along the AS-Paths.

    *Note: For each list of historical routes and TE weights, there will be 
           one or several TE Weight types. See section 3.5 for details.
 



draft-abarbanel-idr-bgp4-te-01.txt                                   [page 5]


3.5 TE Weight Calculation Impacts
    As was seen in section 3.4, routes and TE Weights are aggregated together 
    into less specific information and as a result the TE weights become more 
    and more global. This affect creates sub optimal data for choosing the 
    best path across a series of ASs. If there is an historical trace of 
    route and TE weights that created the global aggregated route, than its 
    possible to make more accurate decision in choosing the best BGP route. 
    This is done during the route selection process which is run for the same 
    route from multiple BGP peers. With the information in the TE Weight 
    Attribute its possible to look inside an aggregated route and more 
    precisely see its composition (sub-aggregation of routes and more 
    specific TE weights) and determine the best TE route and related BGP Next 
    Hop.  

3.6 TE Weight Attribute Format 
    The BGP update message will contain a new Optional Transitive attribute 
    called TE Weight (type code ?). This contains one or several aggregated 
    TE Weight types and their historical sub aggregated routes and TE 
    weights. The amount of aggregation would depend on the number of AS's the 
    route had traversed from the point of origin to the current router.
   
    A TE Weight type must have the same consistency or granularity throughout 
    all the routers that have the software to aggregate, calculate, and 
    propagate it further.  

        |-- Optional(1) or well known(0) 
        | |-- transitive(1) or non-transitive(0)
        | | |-Attr Flags 
        | | |              1                   2                   3   
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 
       +-|-|-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-++    
       |1|1|   FLAGS  | Attr Type (?) | Number TE Weight Lists        |
       +-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-++
       +==============|===============|===============|===============+
       +    1st Super Aggregated TE Weight list entry                 |
       +==============|===============|===============|===============+
       | Number of TE | TE Weight     | 1st Super Aggregated TE Weight|
       | Weight types |  Type 1       |  Value                        |
       +-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-++
       | 2nd TE Weight | 2nd Super Aggregated TE Weight |nth TE Weight|
       |  Type        |     Value                     |type           |
       +-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-++
       |nth Super Aggregated TE Weight| Number of Aggregated Route    |
       |    Value                     |    Prefixes                   |
       +-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-++
       |route prefix 1| 1st Aggregated IP Route prefix                |
       |length        |             1st, 2nd, 3rd   byte              |
       +-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-++ 
       |1st route pref| route prefix n| nth Aggregated IP route prefix|
       | 4th byte     | length        |   1st, and 2nd byte           |
       +-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-++
       |nth Aggregated IP route prefix|                               |
       | 3rd and 4th byte             |          ...                  |
       +-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-++
       draft-ietf-abarbanel-bgp4-te.txt                            [page 6]

       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 
       +-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-++    
       +==============|===============|===============|===============+
       +    nth Super Aggregated TE Weight list entry                 |
       +==============|===============|===============|===============+
       | Number of TE | TE Weight     | 1st Super Aggregated TE Weight|
       | Weight types |  Type 1       |  Value                        |
       +-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-++
       | 2nd TE Weight| 2nd Super Aggregated TE Weight |nth TE Weight |
       |  Type        |     Value                     |type           |
       +-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-++
       |nth Super Aggregated TE Weight| Number of Aggregated Route    |
       |    Value                     |    Prefixes                   |
       +-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-++
       |route prefix 1| 1st Aggregated IP Route prefix                |
       |length        |             1st, 2nd, 3rd   byte              |
       +-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-++ 
       |1st route pref| route prefix n| nth Aggregated IP route prefix|
       | 4th byte     | length        |   1st, and 2nd byte           |
       +-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-++
       |nth Aggregated IP route prefix|                               |
       | 3rd and 4th byte             |          ...                  |
       +-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-++

       - Each TE Weight type could be:

         o Maximum Bandwidth Available
         o Maximum Number of IGP Hops
         o Maximum Transit Delay
         o Color
         o Etc.

       - Each TE Weight value can be in units relevant to its use:
         o For maximum bandwidth could be Megabits/second.
         o For Maximum transit delay could be in milliseconds.

       - Aggregated IP Route Prefix: Defines the aggregation of several 
         routes into a single route for a given AS.
   
       - Route Prefix Length: The number of significant bits from the   
         left side or high order byte of the IP address. As defined in CIDR.

         Example:  IP address 10.20.30.40, High order Byte is the 10.
                       
       - Super Aggregated TE Weight: Each TE weight will have a different 
          algorithm for aggregation and meaning. See section 5.0 for details.
    
 3.7 Phasing TE Weights 
     The use of TE weights can be manually configured on a destination route 
     prefix basis, and thus its possible to enable/disable TE Weights on any 
     BGP route. The functionality can be easily phased into an AS where some
     BGP routers are TE Weight capable and others are not. The new attribute 
     will be Optional and Transitive which implies that older BGP routers   
     will be required to propagate the new attribute in update messages to 
     their peers. 

 draft-abarbanel-idr-bgp4-te-01.txt                           [page 7]

    When not all of the BGP routers along a given TE Path support the TE
    Weight attribute, the TE weight calculations is not done there and the
    best BGP route selection computation will be less than optimal.
 
 4. IGP TE Constraints based Calculations and AS Summarization for TE

    The IGP level routing protocol used is generally either OSPF or ISIS.
    The basic OSPF and ISIS protocols allow routing based on a static
    metric. These protocols can be extended to take into consideration
    various traffic engineering criteria such as unreserved bandwidth,
    delay, colors, OSPF metric, etc. The approach detailed below is
    oriented more toward OSPF, but will be readily extended to ISIS.

    If the IGP inside a routing domain is OSPF, the AS is divided into
    areas - each of which is a collection of routers and networks. The
    routers within an area know the complete topology of the area by means
    of LSA database synchronization with their neighbors at all times.
    Through the use of the opaque LSAs [8], it is possible to maintain the
    traffic engineering topology (in addition to the regular network
    topology) and hence perform route calculations based on traffic
    engineering criteria within an area inside an AS that runs OSPF.
    However, this restricts the traffic engineering calculations to within
    an area.

    To determine the traffic engineering weight to any network or router
    in the AS, the approach proposed for OSPF is to define a new opaque
    LSA for traffic engineering that summarizes the traffic engineering
    weights of every network from the perspective of an area border router
    (ABR), for each area in the AS. This traffic engineering summary LSA
    is analogous to the summary LSA in OSPF. More details on this work can
    be found in [9].

    The destination network could either lie in the same area as the ASBR,
    or in a different area. If the destination network and the ASBR are in
    the same area, the opaque traffic engineering LSAs as defined in [8]
    for the area will suffice to calculate the traffic engineering metric
    to the destination network. If the destination network lies in a
    different area than the ASBR, the weight is a combination (such as
    simple addition, or max) of the weight to the ABR and the weight
    described in the traffic engineering summary LSA originated by the ABR
    that contains the destination network. In this manner, the traffic
    engineering weights for all the networks in an AS can be computed.
    Hence the ASBRs will also be able to determine the aggregate traffic
    engineering weights across the AS to other ASBRs and use this in the
    BGP advertisements.

 5. Weights

    The traffic engineering weights act as a cost or distance function,
    describing the quality of a path to a destination network 
    in traffic engineering terms. The traffic engineering weights 
    currently proposed are:

 
draft-abarbanel-idr-bgp4-te-01.txt                                  [page 8]

        1. Available Bandwidth (in bits/sec)
        2. Unreserved Bandwidth (in each of several classes)
        3. Colors (or class types) (8 types)
        4. Transit Delay  (in milliseconds)
        5. IGP Metric
        6. IGP Hops

    These traffic engineering weights can be dynamically measured or
    statically configured for each interface in a node. The weights can 
    be propagated within an IGP area using the opaque traffic engineering 
    LSA. The area border routers (ABRs) can summarize the traffic engineering 
    weights to destination networks in their area and flood this information 
    into the backbone through the use of the traffic engineering summary LSA 
    as proposed in [9]. The summary LSAs can then be flooded by other ABRs 
    into their areas.

    Any ASBR can determine the TE weight to a destination network by 
    examining its TE database and performing a simple dijkstra like 
    calculation by its associated IGP. This calculation can be a real 
    dijkstra if the weight is additive (delay, or hops or IGP metric), 
    or dijkstra like if the weight is a minimum to maximum constraint  
    (available bandwidth, unreserved bandwidth, and colors). 
    Depending on the level of processing desired, the number of supported TE 
    weights should be configured.

    These calculations result in a value for each TE Weight for each 
    destination network in the AS and for each ASBR across the AS.
    The weights from the IGP are then exported into BGP for propagation to     
    its EBGP peers. 

    The following two subsections deal specifically with the treatment of the
    available bandwidth and delay TE weights, during the calculations:

    Maximum Available Bandwidth: 
      IBGP/IGP router within a given AS will pick the smallest available 
      Bandwidth link from the ingress to the egress of the IBGP to IBGP path 
      and use that value as the summary TE weight. Next the egress IGP will 
      export this information to BGP which will use and propagate it to its 
      EBGP peers as the first aggregated TE Weight value. As the route is 
      propagate to each IBGP peer in another AS, the Aggregated TE weight 
      value in the message is compared with the summary TE weight for the BGP          
      Next Hop router defined in the message. Whichever value is the smaller       
      of the two, will be considered the next level of aggregation value and        
      propagated further to the next AS.   
      This mechanism will continue till the route reaches the furthest points 
      in the Internet. This way the smallest available bandwidth value will 
      be used as the overall Aggregated TE Weight value for any given route 
      along the TE path.  
  
    Maximum Delay: 
      IBGP/IGP router within a given AS will obtain the delay from the       
      ingress to the egress of the IBGP to IBGP path and use that value as  
      the summary TE "delay" weight. Next the egress IGP will export this   
      information to BGP

draft-abarbanel-idr-bgp4-te-01.txt                                    [page 9]
    

    which will use and propagate it to its EBGP peers as the first aggregated 
    TE Weight "delay" value. As the route is propagate to each IBGP peer in 
    another AS, the Aggregated TE weight value in the message is added with 
    the summary TE "delay" weight for the BGP Next Hop router defined in the
    message. The sum of the two is considered the next level of aggregation 
    and propagated further to the next AS. This mechanism will continue till the   
    route reaches the furthest points in the Internet.     
    
   *Note: See section 3.4 for Route Aggregation Impacts which must be        
          followed in order for this mechanism to be optimal. As mentioned             
          in section 3.4, historical routes/TE Weights are carried in this   
          new attribute for routes that are aggregated several times.

6. TE Weights Redistributed from the IGP to BGP
   In order for a given router to inherit the TE weights from IGP, a
   mechanism must be provided to do that. What is proposed is that the
   standard FDB database contain TE summary weight fields based in each
   route entry, with their TE weight type, TE weight value and
   associated AS number. In other words, in all the BGP routers, the
   running IGP will inject the TE summary weight information into the FDB
   database and signal BGP to import it to its BGP RIB database for
   propagation to other BGP peers.

7. Configuring the TE feature for BGP and IGP.

   In order to minimize the amount of information produced by the TE weight  
   parameters across the entire Internet as described in section 3.6, it is  
   recommended that the TE weight be configured on at the network route's    
   point of origin. Implying that the AS router that originated the route    
   into BGP will add the TE Weight attribute and all transit routers that    
   propagate this route will perform the TE Weight processing when they see  
   the TE Weight Attribute. This way it will be possible to limit the amount 
   of TE Weight information being propagated across the Internet.
     
   What is needed to manually configure the BGP Best Route Selection       
   criteria:

   I. To Enable TE Weight Feature for a given network prefix.

      a. Define each network prefix for TE Weight functionality.
         Once enabled all transit BGP TE routers will process the TE Weight
         aggregation and propagate the TE Weight attribute to their peers.

   II. To manually configure the BGP Best Route Selection Criteria in each
       BGP TE Router, configure the following parameters:

       a. TE Weight Type
          o Maximum Bandwidth Available (Megabits/sec)
          o Unreserved Bandwidth (in each of several classes)
          o Maximum Number of IGP Hops
          o IGP Metric
          o Maximum Transit Delay (in Milliseconds)
          o Color (or class types) (8 types)

draft-abarbanel-idr-bgp4-te-01.txt                                   [page 10]

 
       b. TE Weight Priority
          1st choice = Make this TE Weight the first choice  
                       for best BGP route selection criteria
          2nd choice = Make this TE Weight the 2nd choice
                       for best BGP route selection criteria
          nth choice = Make this TE Weight the 2nd choice
                       for best BGP route selection criteria

       c. Example of BGP TE Topology


                                                       AS2
  +---------+               70 MB                +--------------+
  |       R6+------------------------------------| R7--net1--R13|
  |  AS5   ||70MB                                |/ \     80MB| |
  |       R5|                                    /   \        | |
  |---------+                                   /|    \30MB   | |
             \                            30MB / |     \------R8|
              \70MB                           /  +------------+-+
               \           AS1               /                |
                +-------+--------|----------/+                |30MB
                | R2    |   30MB |         R3|\        +------+-------+
                | |   /-|--------|---------/ | \       |      R9-net2 |
                | |  /  |        |           |  \60MB  | 60MB /       |
        Source--+->R1/  | Area 0 |  Area 2   |   \     |     /        |
                |  \----+--------+--------\  |    \    |    /         |
                | Area 1|   30MB |        R4 |     \---+-R10   AS3    |
                +-------+--------|-----------+         +-- -\---------+
                                             \               \
                                              \30MB           \30MB
                                               \               \ 
                                                \+----------- --\----+
                                                 |R11----------- R12 |
                                                 |      30MB     /   |
                                                 |              /    |
                                                 |    AS4     net3   |
                                                 +-------------------+
          Figure 1. BGP TE Topology

















draft-abarbanel-idr-bgp4-te-01.txt                                   [page 11]

        Table 1. Router R1 BGP TE Weight Table

   +-+-+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+++-+-+-+-+-+-+-+-+-+-+-+-++
   |Entry #  | Route  |  BGP Next Hop |  Aggregated TE Weight   |
   |         |        |               |  Bandwidth              |
   +-+-+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+++-+-+-+-+-+-+-+-+-+-+-+-++
   |    1    | NET1   |  R7 via R3    |  30 MB                  |
   +-+-+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+-+-+-+-+-+-
   |    2    | *NET1  |  R5 via R2    |  70 MB                  |
   +-+-+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+-+-+-+-+-+-
   |    3    | NET1   |  R10 via R3   |  60 MB                  |
   +-+-+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+-+-+-+-+-+-
   |    4    | NET1   |  R11 via R4   |  30 MB                  |
   +-+-+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+-+-+-+-+-+-
   |    5    | NET2   |  R11 via R4   |  30 MB                  |
   +-+-+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+-+-+-+-+-+-
   |    6    | *NET2  |  R10 via R3   |  60 MB                  |
   +-+-+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+-+-+-+-+-+-
   |    7    | NET2   |  R7 via R3    |  30 MB                  |
   +-+-+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+-+-+-+-+-+-
   |    8    | NET2   |  R5 via R2    |  30 MB                  |
   +-+-+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+|+-+-+-+-+-+-+-+-+-+-+-+-+-

 
   *Note: Although we show only one TE weight type under each AS subfield
          it is possible to have multiple TE weight types and have
          them prioritized by manual configurations in each BGP TE router. 

   In Figure 1 we see that R1 is the current router receiving Update
   messages from R2, R3, and R4. All the Update message contain
   the new BGP TE Weight Attribute with the weights as shown in Table 1.
   From this data, we see that for NET1, Entry #2 is the best choice
   amongst other NET1 entries, because it guarantees that we get 70MB
   bandwidth from AS2 and AS5. Assumption, operator had configured the TE
   (bandwidth) weight as the highest priority criteria.

   Also for NET2 entries, entry #6 is the best choice, even though it
   includes more AS hops, but it guarantees that at least 60MB of
   bandwidth will be available. This case shows, how sometimes
   sacrificing more AS hops for guaranteed bandwidth service could work.

 8. Route Flapping and Impacts on BGP Aggregated TE Weights

    In the real world route flapping is a normal occurrence. It is
    expected that the router performing TE Weight Aggregation will be     
    notified by the IGP that routes have gone down/up and it will be 
    required to recalculate the aggregated TE Weight. Obviously, when a new 
    aggregated TE weight is defined for an aggregated route, the router 
    performing this calculation will be required to deploy it to its BGP 
    peers.




draft-abarbanel-idr-bgp4-te-01.txt                                   [page 12]

 9. BGP Confederations
    Since the IGP domain will cover the entire AS, any mapping of BGP        
    Confederation within each of the sub-ASs will not be used for BGP TE   
    aggregation.
    Internal Sub-AS BGP routers running either EBGP or IBGP will not   
    aggregate the new TE Weight attribute since that job will only be done 
    By the BGP ASBR routers. They will however, use these attributes in their
    Route selection criteria and propagate them further to all inter/intra sub- 
    AS peers.  

 10. ISP Issues and Dependencies
     TBD

 11. Conclusion

     As has been shown, the Internet is a complex WEB of systems within 
     systems. Traffic Engineering is the only solution that attempts to 
     control/contain the explosion of resources within routers. The technique 
     described in this manuscript defines a way for BGP routers to influence 
     and control the routing paths chosen for routes that are bound by 
     Traffic Engineering Weights. Thereby, enabling the Inter-AS providor a 
     more uniform method of allocating resources and providing gauranteed 
     service using BGP TE across multiple Autonomous Systems. 
      
 12. Security Considerations

     The new BGP TE Weight attribute does not change the underlying security 
     issues inherent in the existing BGP-4 design.

 13. References

    [1] "A Border Gateway Protocol 4 (BGP-4)", Y. Rekhter & T. Li,
        RFC1771, March 1995

    [2] Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M., McManus, J.,
        "Requirements for Traffic Engineering Over MPLS", RFC 2702, September
        1999.

    [3] Awduche, D., Rekhter, Y., Drake, J., Coltun, R., "Multi-Protocol
        Lambda Switching: Combining MPLS Traffic Engineering Control With
        Optical Crossconnects", draft-awduche-mpls-te-optical-01.txt.

    [4] Jamoussi, B. "Constraint-Based LSP Setup using LDP", Work in
        Progress, Internet Draft <draft-ietf-mpls-cr-ldp-03.txt>, September
        1999.

    [5] Braden, R., Zhang, L., Berson, S., Herzog, S., "Resource
        ReSerVation Protocol (RSVP) -- Version 1 Functional Specification", 
        RFC 2205, September 1997.

    [6] Awduche, D. et al "Extensions to RSVP for LSP Tunnels", Work in
        Progress, Internet Draft <draft-ietf-mpls-rsvp-lsp-tunnel-04.txt,
        September 1999.

    
draft-abarbanel-idr-bgp4-te-01.txt                                   [page 13]

    [7] Tang, Z. et al "Extensions to CR-LDP for Path Establishment in
        Optical Networks", Internet Draft <draft-tang-crldp-optical-00.txt>
        September 2000.

    [8] Katz, D. and Yeung D., "Traffic Engineering Extensions to OSPF",
        Internet Draft <draft-katz-yeung-ospf-traffic-00.txt>

    [9] Venkatachalam, Senthil and Abarbanel, B., "Traffic Engineering
        Summary Extensions to OSPF", work in progress.

    [10] Villamizar, "BGP Route Flap Damping", RFC2439, November 1998


 14.Acknowledgments
    To be supplied in future revisions.
     
 15. Author's Addresses

     Ben Abarbanel
     IPOptical, Inc.
     11480 Sunset Hills Rd, Suite 200E
     Reston, VA 20190
     email: ben.abarbanel@ipoptical.com

     Senthil Venkatachalam
     Alcatel USA
     45195 Business Court, Suite 400
     Dulles, VA 20166
     email: senthil.venkatachalam@usa.alcatel.com