[Docs] [txt|pdf] [Tracker] [WG] [Email] [Nits]

Versions: 00 01 02 03 04 05 06 RFC 4098

Benchmarking Terminology Working Group                  H.Berkowitz

Internet Draft
S.Hares
draft-ietf-bmwg-conterm-00.txt                          A.Retana

Expires February 2002
P.Krishnaswamy
                                                        M.Lepp

                                                         July 2001

        Terminology for Benchmarking External Routing Convergence Measurements

Status of this Memo

This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026 [1].

Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.

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."

The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.

The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.


Abstract

    This draft establishes terminology to standardize the description of
benchmarking methodology for measuring eBGP convergence in the control
plane of a single router. Future documents will address iBGP
convergence, the initiation of forwarding based on converged control
plane information and internet-wide convergence.

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].

Table of Contents
1       Introduction                                                    3
1.1     Overview and Roadmap                                            3
1.2     Definition Format                                               4
2       Constituent elements of a router or  network  of routers.       5
2.1     BGP Peer                                                        5
2.2     Default Route, Default Free Table, and Full Table               5
2.2.1   Default Route
        6                       2.2.2   Default Free Routing Table
                                        6
2.2.3   Full Default Free Table                                         7
2.2.4   Full Provider Internal Table                                    7
2.3     Classes of BGP-Speaking Routers                                 8
2.3.1   Provider Edge Router                                            8
2.3.2   Subscriber Edge Router                                          8
2.3.3   Interprovider Border Router                                     9
2.3.4   Intraprovider Core Router                                       9
3       Routing Data Structures                                         9
3.1     Routing Information Base (RIB)                                  9
3.1.1   Adj-RIB-In and Adj-RIB-Out                                      10
3.1.2   Loc-RIB                                                         10
3.2     Policy                                                          11
3.3     Policy Information Base                                         11
3.4     The Forwarding Information Base (FIB)                           12
4       Components and characteristics of Routing information           13
4.1     Prefix                                                          13
4.2     Route                                                           13
4.3     BGP Route                                                       14
4.4     Route Instance                                                  14
4.5     Active Route                                                    15
4.6     Unique Route                                                    15
4.7     Non-Unique Route                                                15
4.8     Route Packing                                                   16
4.9     Update Train                                                    16
4.10    Route Flap                                                      16
5       Route Changes and Convergence                                   17
5.1     Route Change Events                                             17
5.2     Convergence                                                     18
6       Factors that impact the performance of the convergence process  19
6.1     General factors affecting BGP convergence                       19
6.1.1   Number of peers                                                 19
6.1.2   Number of routes per peer                                       20
6.1.3   Policy processing/reconfiguration                               20
6.1.4   Interactions with other protocols.                              20
6.1.5   Flap Damping                                                    20
6.1.6   Churn                                                           21
6.2     Implementation-specific and other factors affecting BGP
        convergence                                                     21
6.2.1   Forwarded  traffic                                              21
6.2.2   Timers                                                          22
6.2.3   TCP parameters underlying BGP transport                         22
6.2.4   Authentication                                                  22
7       Security Considerations                                         22
8       References                                                      22
9       Acknowledgments                                                 22
10      Author's Addresses                                              23



1       Introduction

    This document defines terminology for use in  characterizing the
convergence
performance of BGP processes in routers or other devices that instantiate
BGP
functionality. It  is the first part of a two document series, of which  the
subsequent document will contain the associated tests and methodology.

The following observations underly the approach adopted in this, and the
companion document:

-The principal  objective is to derive methodologies to standardize
conducting and
reporting convergence-related measurements for BGP.
-It is  necessary to  remove  ambiguity from many frequently used terms that
arise in
the context of such measurements.
-As convergence characterization is a complex process, it is desirable to
restrict the initial focus in this set of  documents to specifying how to
take basic control plane measurements towards  characterizing BGP
convergence.
For  path vector protocols such as BGP, the  primary initial focus will
therefore  be on network and system control-plane activity consisting of the
arrival, processing, and propagation of routing information

Subsequent drafts will explore the more intricate aspects of convergence
measurement, such as the impacts of the presence of policy processing,
simultaneous traffic on the control and data paths within the DUT, and other
realistic performance modifiers. Convergence of
Interior Gateway Protocols will also be considered in separate drafts.



1.1     Overview and Roadmap

A characterization of the BGP convergence performance of a device must take
into account
all distinct stages and aspects of BGP functionality. This requires that the
relevant terms
and metrics be as specifically defined as possible. Such definition is the
goal of this document.

    The necessary definitions are classified into two separate
    categories:
           . Descriptions of the constituent elements of a network or a
    router that is undergoing convergence
           . Descriptions of factors that impact convergence processes

1.2     Definition Format

       The definition format is equivalent to that defined in [RFC1812],
and
    is repeated here for convenience:

       X.x Term to be defined. (e.g., Latency)

       Definition:
              The specific definition for the term.

       Discussion:
              A brief discussion about the term, its application and any
              restrictions on measurement procedures.


Measurement units:
              The units used to report measurements of this term, if
              applicable.

       Issues:

              List of issues or conditions that affect this term.

       See Also:
              List of other terms that are relevant to the discussion of
    this term.

2       Constituent elements of a router or  network  of routers.

    Many terms included in this list of definitions were described
    originally in previous standards or papers. They are included here
    because of their pertinence to this discussion. Where relevant,
    reference is made to these sources. An effort has been made to keep
    this list complete with regard to the necessary concepts without
    over definition.

2.1      BGP Peer

    Definition:

    A BGP peer is another BGP instance to which the the Device Under Test
(DUT) has established a TCP connection over which a BGP session is
active.  In the test scenarios in the methodology discussion that will
follow this draft, peers send BGP advertisements to the DUT and receive
DUT-originated advertisements.

    Discussion:

    This is a protocol-specific definition, not to be confused  with
    another frequent usage, which refers to the  business/economic
    definition for the exchange of routes without financial
    compensation.

    It is worth noting that a BGP peer, by this definition is associated
with a BGP peering session, and  there may be more than one such active
session on a router or on a tester.  The peering sessions referred to
here may exist between various classes of BGP routers (see section 2.3)
.

    Measurement units: number of BGP peers

    Issues:

    See Also:

2.2     Default Route, Default Free Table, and Full Table

An individual router's routing table may not necessarily contain a
default route.  Not having a default route, however, is not synonymous
with having a full default-free table.

It should be noted that the references to number of routes in this
section are to routes installed in the loc-RIB, not route instances, and
that the total number of route instances may be 4 to 10 times the number
of routes.
MPLS speaking routers are outside the scope of this document

2.2.1    Default Route

    Definition:

    A Default Route is a route entry that can match any prefix. If a
    router does not have a route for a particular packet's destination
    address, it forwards this packet to the next hop in the default
    route entry, provided its Forwarding Table (Forwarding Information
    Base (FIB) )  contains one. The notation for a default
    route is 0.0.0.0/0

    Discussion:


    Measurement units: N.A.

    Issues:

    See Also: default free routing table, route, route instance

2.2.2   Default Free Routing Table
    Definition:

A routing table with no default routes, as typically seen in routers at
the core or top tier.

    Discussion:

    The term originates from the concept that  routers at the core or
    top tier of the Internet will not be configured with a default route
    (Notation 0.0.0.0/0). Thus they will forward every prefix to a
    specific nexthop based on the longest match on the IP addresses.

Default free routing table size is commonly used as an indicator of
    the magnitude of reachable Internet address space. However, default
    free routing tables  may also include routes internal to the router's
AS.
Measurements: The number of routes

See Also: Full Default Free

2.2.3  Full Default Free Table

    Definition:

    A set of BGP routes generally accepted to be the complete set of
    BGP routes announced by all autonomous systems to the public
    Internet.  Due to the dynamic nature of the Internet, the exact
    size and composition of this table may vary slightly depending where
    it is observed.

    Discussion:

    Several investigators [Bates, Smith] measure this
    on a weekly basis; June 2001 measurements put the table at
    approximately 105,000 routes, growing exponentially.

    It is generally accepted that a full table, in this usage, does not
contain the infrastructure routes or individual subaggregates of routes
that are otherwise aggregated by the provider before announcement to
other autonomous systems.

    Measurement Units: number of routes

    Issues:

    See Also: Routes, Route Instances, Default Route


2.2.4  Full Provider Internal Table

    Definition:

    A superset of the full routing table that contains infrastructure and
    non-aggregated routes.

    Discussion:

    Experience has shown that this table can contain 1.3 to 1.5 times the
    number of routes in the externally visible full table.  Tables of
    this size, therefore, are a real-world requirement for key internal
    provider routers.

    Measurement Units: number of routes

    Issues:

    See Also: Routes, Route Instances, Default Route

2.3     Classes of BGP-Speaking Routers
A given router may perform more than one of the following functions,
based on its logical location in the network.

2.3.1   Provider Edge Router

Definition:

A router at the edge of a provider's network, configured to speak BGP,
which peers with a BGP speaking router operated by the end-user. The
traffic that transits this router may be destined to, or originate from
non-contiguous autonomous systems.

Discussion:
Such a router will always speak eBGP and may speak iBGP.

Measurement units:

Issues:

See Also:


2.3.2   Subscriber Edge Router

Definition:

A BGP-speaking router belonging to an end user organization that may be
multi-homed, which carries traffic only to and from that end user AS.

Discussion:
Such a router will always speak eBGP and may speak iBGP.

Measurement units:

Issues:

See Also:

2.3.3   Interprovider Border Router


Definition:

A BGP speaking router that maintains BGP sessions with another BGP
speaking router in another provider AS.  Traffic transiting this router
may be directed to or from another AS that has no direct connectivity
with this provider's AS.

Discussion:

Such a router will always speak eBGP and may speak iBGP.

Measurement units:

Issues:

See Also:

2.3.4   Intraprovider Core Router

     Definition:  A provider router speaking iBGP to the provider's edge
routers, other intraprovider core routers, or the provider's
interprovider border routers.

Discussion:

Such a router will always speak iBGP and may speak eBGP.

Measurement units:

Issues:

MPLS speaking routers are outside the scope of this document.  It is
entirely likely, however, that core Label Switched Routers, especially
in the P router role of RFC 2547, may contain little or no BGP
information.

See Also:
3       Routing Data Structures
3.1     Routing Information Base (RIB)
The RIB collectively consists of a set of logically (not necessarily
literally) distinct databases, each of which is enumerated below. The
RIB contains all destination prefixes to which the router may forward,
and one or more currently reachable next hop addresses for them.
Routes included in this set potentially have been selected from several
sources of information,including hardware status, interior routing
protocols, and exterior routing protocols. RFC 1812 contains a basic set
of route selection criteria relevant in an all-source  context. Many
implementations impose additional criteria.  A common implementation-
specific criterion is the preference given to different routing
information sources.

3.1.1   Adj-RIB-In and Adj-RIB-Out
Definition:
Adj-RIB-In and Adj-RIB-Out are "views" of
    routing information from the perspective of individual peer routers.
    The Adj-RIB-In contains information advertised to the DUT by a
    specific peer.  The Adj-RIB-Out contains the information the DUT
    will advertise to the peer.

See RFC 1771
Discussion:

Issues:

Measurement Units: Number of route instances

See Also: Route, BGP Route, Route Instance, Loc-RIB, FIB

3.1.2     Loc-RIB

    Definition:

    The Loc-RIB contains the set of best routes selected from
    the various Adj-RIBs, after applying local policies and the BGP route
    selection algorithm.

    Discussion:

    The separation implied between the various RIBs is logical. It does
    not necessarily follow that these RIBs are distinct and separate
    entities in any given implementation.

    Issues:

    Specifying the RIB is important because the types and relative
    proportions of routes in it can affect the convergence efficiency.
    Types of routes can include internal BGP, external BGP,interface,
    static and IGP routes.
    Measurement Units: Number of route instances.

    See Also: Route, BGP Route, Route Instance, Adj-RIB-in, Adj-RIB-out,
FIB


3.2     Policy

    Definition:

    Policy is "the ability to define conditions for accepting,
    rejecting, and modifying routes received in advertisements"[16]

    Discussion:

    RFC 1771 [RFC1771] further constrains policy to be within the
    hop-by-hop routing paradigm.
    Policy is implemented using filters and associated policy
    actions.

    Measurement Units:

    Issues:

    See Also: Policy Information Base.

3.3     Policy Information Base

     Definition:

    A policy information base is the set of incoming and outgoing
    policies.


    Discussion:

All references to the phase of the BGP selection process
    here are made with respect to RFC 1771 [RFC1771] definition of these
    phases.
    Incoming policies are applied in Phase 1 of the BGP selection
    process [RFC1771]to the Adj-RIB-In routes to set the metric for the
    Phase 2 decision process.   Outgoing Policies are applied in Phase 3 of
    the BGP process to the Adj-RIB-Out routes preceding  route (prefix
    and path attribute tuple) announcements to a specific peer.


      Policies in the Policy Information Base have matching and action
conditions.  Common information to match include route prefixes, AS paths,
communities,
etc.  The action on match may be to drop the update and not pass it to the
Loc-RIB, or
to modify the update in some way, such as changing local preference (on
input) or MED
(on output), adding or deleting communities, prepending AS in the AS path,
etc.

    The amount of policy processing (both in terms of route maps and
    filter/access lists) will impact the convergence time and properties
    of the distributed BGP algorithm.    The amount of policy processing may
vary from a    simple policy which accepts all routes and sends all routes
to complex
    policy with a substantial fraction of the prefixes being filtered by
    filter/access lists.

3.4     The Forwarding Information Base (FIB)

    Definition:

The Forwarding Information Base is generated from
    the RIB. The FIB is referred to in [RFC1771] as well as [RFC1812] but
not defined in either. For the purposes of this document, the FIB is the
subset of the RIB used by the forwarding plane to make per-packet
forwarding decisions.

    Discussion:

    Most current implementations have full, non-cached FIBs
    per router interface. All the route computation and convergence
    occurs before a route is downloaded into a FIB.

    Measurement Units: N.A.

    Issues:

    See Also: Route, RIB

4       Components and characteristics of Routing information
4.1     Prefix

    Definition:

    A destination address in CIDR format.
    Expressed as prefix/length. The definition in [RFC1812] is "A
    network prefix is à a contiguous set of bits at the more significant
    end of the address that defines a set of systems; host numbers select
    among those systems."

    Discussion:

     A prefix is expressed as a portion of an IP address followed by the
    associated mask such as 10/8.

    Measurement Units: N.A.

    Issues:

    See Also


4.2     Route

    Definition:

    In general, a 'route' is the n-tuple <prefix, nexthop [,other non-
routing protocol attributes] >.  A route is not end-to-end, but is
defined with respect to a specific next hop that will move traffic
closer to the destination defined by the prefix. In this usage, a route
is  the basic unit of information about a target destination distilled
from routing protocols.

    Discussion:

    This term refers to the concept of a route common to all
    routing protocols. With reference to the definition above, typical
non-routing-protocol attributes would be associated with diffserv or
traffic engineering.

Measurement Units: N.A.

    Issues: None.

    See Also: BGP route

4.3     BGP Route

    Definition:

    The n-tuple <prefix, nexthop, aspath [, other BGP attributes]>.

Discussion:

    Nexthop is one type of attribute.  Attributes are defined in RFC 1771
[RFC1771],   and are the  qualifying
    data that accompanies a prefix in a BGP route. From RFC 1771:
    " For purposes of this protocol a route is defined as a unit of
    information that pairs a destination with the attributes of a path
    to that destination... A variable length sequence of path attributes
    is present in every UPDATE.  Each path attribute is a triple
    <attribute type, attribute length, attribute value> of variable
    length."
    Measurement Units:N.A.

    Issues:

    See Also: Route, prefix, Adj-RIB-in.

4.4     Route Instance

    Definition:

A single occurrence of a route sent by a BGP Peer for a particular
prefix. When a router has multiple peers from which it accepts routes,
routes to the same prefix may be received from several peers. This
is then  an example of multiple route instances.

    Discussion:

    Each route instance is associated with a specific peer.
A specific route instance may be rejected by the BGP selection algorithm
due to local policy.

    Measurement Units: number of route instances

    Issues:
    The number of route instances in the Adj-RIB-in bases will vary based
on the function to be performed by a router. An interprovider router,
located in the default free zone will likely receive more route
instances than an provider edge router, located closer to the end-users
of the network.
See Also:

4.5     Active Route
Definition:
Route for which there is a FIB entry corresponding to a RIB entry.

Discussion:

Measurement Units:

Issues:
See also: RIB.
4.6     Unique Route

D efinition:

    A unique route is a prefix for which there is just one
    route instance across all Adj-Ribs-In.

    Discussion:

    Measurement Units: N.A.

    Issues:

    See Also: route, route instance

4.7     Non-Unique Route

    Definition:
     A Non-unique route is a prefix for which there is at least one other
route in a set including more than one Adj-RIB-in.

    Discussion:

    Measurement Units: N.A.

    Issues:

    See Also: route, route instance, unique active route.
4.8     Route Packing
    Definition:

    Number of  route prefixes that exist in a single Routing
    Protocol Update or Withdraw Message.

    Discussion:

    In general, a routing protocol update MAY contain more than one
    prefix.  In BGP, a single  update MAY contain multiple prefixes with
    identical attributes.

    Protocols that do not support such a concept implicitly have a Route
    Packing of 1. "

4.9     Update Train
Definition:

     A set of updates, containing one or more route prefixes, which an
external router desires to send to the DUT.  When there is more than one
prefix in the set, the multiple updates (including withdrawals) may be
sent as individual BGP UPDATE packets, or as one or more BGP packets
with multiple routes packed (q.v.) into them.

Discussion:
    The more individual update packets that are sent, the more TCP and
BGP header processing will be imposed on the receiving router that is
the DUT.

An update train may be caused by a variety of network conditions.  For
example,  an update train could be caused by an influx of UPDATES from
different peers that have been received  and  moved to RIB-out or caused
by a peer coming up and advertising its routes, or by a local or remote
peer flapping a link.  Other causes are, of course, possible.

Measurement units:  Number of prefixes and update packets in the train.
Issues:
See Also:
4.10     Route Flap
Definition:  RIPE 210 [RIPE]define a route flap as "the announcement and
withdrawal of prefixes."  For our purposes we define a route flap as the
rapid withdrawal/announcement or announcement/withdrawal/ of a prefix in
the Adj-RIB-in.

A route flap is not a problem until a route is flapped several times in
close succession.   This  causes negative repercussions throughout the
internet.

    Discussion:
Route flapping can be considered a special and pathological case of
update trains.

       A practical interpretation of what may be considered excessively
rapid is the RIPE recommendation of "four flaps in a row".  See
Section 6.1.5 on flap damping for further discussion.

Measurement units
       Flapping events per unit time.

Issues:
Specific Flap events can be found in Section 5.1Route Change Events.  A
bench-marker should use a mixture of different route change events in
testing.

See Also: Route change events, flap damping, packet train

5       Route Changes and Convergence

The following two definitions are central to  the benchmarking of
external routing convergence, and so are singled out for more extensive
discussion.

5.1      Route Change Events

A taxonomy characterizing routing information changes seen in
operational networks is proposed in [Ahuja et al] as well as Labovitz
et al[4]. These papers describe BGP protocol-centric events, and event
sequences in the course of an analysis of  network behavior. The
terminology in the two papers addresses similar but slightly different
behaviors with some overlap. We would like to apply these taxonomies to
categorize the tests under definition where possible, because these
tests must tie in to phenomena that arise in actual networks. We avail
of, or may extend, this terminology as necessary for this purpose.

A route can be changed implicitly by replacing it with another route or
explicitly by withdrawal followed by the introduction of a new route.
In either case the change may be an actual change, no change, or a
duplicate. The notation and definition of individual categorizable route
change events is adopted from [Labovitz et al] and given below.


a)      AADiff: Implicit withdrawal of a route and replacement by a
route different in some path attribute.
b)      AADup: Implicit withdrawal of a route and replacement by route
that is identical in all path attributes.
c)      WADiff: Explicit withdrawal of a route and replacement by a
different route.
d)      WADup: Explicit withdrawal of a route and replacement by a
route that is identical in all path attributes.
To apply this taxonomy in the benchmarking context, we need both terms
to describe the sequence of events from the update train perspective, as
listed above, as well as event indications in the time domain so as to
be able to measure activity  from the perspective of the DUT.
With this in mind, we incorporate and extend the definitions of [4] to
the following:
a)      Tup (TRx): Route advertised to the DUT by Test Router x
b)      Tdown: Route being withdrawn
c)      Tupinit: The initial announcement of a route to a unique prefix
d)      TWF: Route fail over after an explicit withdrawal.

    The basic criterion for selecting a "better" route is the final
    tiebreaker defined in RFC1771, the router ID. As a consequence, this
    memorandum uses the following descriptor events.
        a)Tbest -- The current best path.
        b)Tbetter -- Advertise a path that is better than Tbest.
        c)Tworse -- Advertise a path that is worse than Tbest.

5.2     Convergence

    Definition:

    A router is said to have converged onto a route
    advertised to it, given that the route is the best route instance for
    a prefix(if multiple choices exist for that prefix), when this route
    is advertised to its downstream peers.

    Discussion:

The convergence process can be subdivided into three distinct phases:

     -convergence across the entire Internet,
     -convergence within an Autonomous System,
     -convergence with respect to a single router.

Convergence with respect to a single router can be
         -convergence with regard to the routing process(es), the
focus of this document
         -convergence with regard to data forwarding process(es).

    It is of key importance to benchmark the
    performance of each phase of convergence separately before proceeding
to a composite
    characterization of routing convergence, where implementation-
specific dependencies are
    allowed to interact.

    The preferred route
    instance must be unambiguous during test
    setup/definition.



    Measurement Units: N.A.

Issues:

    See Also:

6       Factors that impact the performance of the convergence process

    While this is not a complete list, all of the items discussed below
have a significant affect on BGP convergence.  Not all of them can be
addressed in the baseline measurements described in this document.


6.1     General factors affecting BGP convergence
These factors are conditions of testing external to the router Device
Under Test (DUT).

6.1.1   Number of peers

    As the number of peers increases, the BGP route selection algorithm
is increasingly exercised. In addition, the phasing and frequency of
updates from the various peers will have an increasingly marked effect
on the convergence process on a router as the number of peers grows.

6.1.2   Number of routes per peer

    The number of routes per BGP peer is an obvious stressor to the
    convergence process. The number, and relative proportion, of
    multiple route instances and distinct routes being added or
    withdrawn by each peer will affect the convergence process, as will
    the mix of overlapping route instances, and IGP routes.

6.1.3   Policy processing/reconfiguration

       The number of routes and attributes being filtered, and
    set, as a fraction of the target route table size is another
    parameter that will affect BGP convergence.
       Extreme examples are

       -Minimal Policy: receive all, send all,
       -Extensive policy: up to 100% of the total routes
        have applicable policy.

6.1.4   Interactions with other protocols.
There are interactions in the form of precedence, synchronization,
duplication and the addition of timers, and route selection
criteria.  Ultimately, understanding BGP4 convergence must include
understanding of the interactions with both the IGPs and the
protocols associated with the physical media, such as Ethernet,
SONET, DWDM.
6.1.5   Flap Damping
   A router can use flap damping to  respond to route flapping.   Use of
flap damping is not mandatory, so the decision to enable the feature,
and to change parameters associated with it, can be considered a matter
of routing policy.

The timers are defined by RFC 2439 [RFC 2439] and discussed in RIPE 210
[17].
If this feature is in effect, it requires that the router keep
additional state to carry out the damping, which can have a direct
impact on the control plane due to increased processing.  In addition,
flap damping may delay the arrival of real changes in a route, and
affect convergence times

6.1.6   Churn
In theory, a BGP router could receive a set of updates that completely
defined the Internet, and could remain in a steady state, only sending
appropriate KeepAlives.  In practice, the Internet will always be
changing.

Churn refers to control plane processor activity caused by announcements
received and sent by the router.  It does not include KeepAlives.

Churn is caused by both normal and pathological events.  For example, if
an interface of the local router goes down and the associated prefix is
withdrawn, that withdrawal is a normal activity, although it contributes
to churn.  If the local router receives a withdrawal of a route it
already advertises, or an announcement of a route it did not previously
know, and readvertises this information, again these are normal
constituents of churn. Routine updates can range from single
announcement or withdrawals, to announcements of an entire default-free
table.  The latter is completely reasonable as an initialization
condition.

Flapping routes  are a pathological contributor to churn, as is MED
oscillation [medosc].  The goal of flap damping is to reduce the
contribution of flapping to churn.

The effect of churn on overall convergence depends on the processing
power available to the control plane, and whether the same processor(s)
are used for forwarding and for control.

6.2     Implementation-specific and other factors affecting BGP convergence
These factors are conditions of testing internal to the router Device
Under Test (DUT), although they may affect its interactions with test
devices.

6.2.1   Forwarded  traffic

     The presence of actual traffic in the router may stress the control
    path in some fashion if both the offered load due to data and the
    control traffic (FIB updates and downloads as a consequence of
    flaps)are excessive. The addition of data traffic presents a more
accurate reflection of realistic operating
    scenarios than if only control traffic is present

6.2.2   Timers
Settings of delay and hold-down timers at the link level as well as for
BGP4, can introduce or ameliorate delays.  As part of a test report, all
relevant timers should be reported if they use non-default value.  Also,
any variation in standard behavior, such as overriding TCP slow start,
should be documented.

6.2.3   TCP parameters underlying BGP transport
Since all BGP traffic and interactions occur over TCP, all relevant
parameters characterizing the TCP sessions should be provided: eg Max
window size, Maximum segment size, timers.


6.2.4   Authentication

    Authentication in BGP is currently done using the TCP MD5 Signature
    Option [Heff].  The processing of the MD5 hash, particularly in routers
    with a large number of BGP peers and a large amount of update
    traffic can have an impact on the control plane of the router.
7       Security Considerations
     The document explicitly considers authentication as a performance-
     affecting feature, but does not consider the overall security of
     the routing system.




8       References

1. [RFC 2026]Bradner, S., "The Internet Standards Process -- Revision
              3", BCP 9, RFC 2026, October 1996


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


3. [RFC 1771]"A Border Gateway Protocol 4 (BGP-4)", RFC 1771,  Y.
              Rekhter, T. Li. March 1995.


4. [RFC 2539]""BGP Route Flap Damping", RFC 2439, C. Villamizar, R.
              Chandra, R. Govindan. November 1998."


5. [RFC 1812]"Requirements for IP Version 4 Routers", RFC 1812, F.
              Baker. June 1995.

6.  [Ahuja et al]"An Experimental Study of Delayed Internet Routing
              Convergence." Abha Ahuja, Farnam Jahanian, Abhijit Bose,
              Craig Labovitz, RIPE 37 - Routing WG.
7. [Labovitz et al] "Origins of Internet Routing Instability," Infocom 99
              Craig Labovitz, G. Robert Malan, Farnam Jahanian],

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

9.[RIPE]RIPE 210, "RIPE Routing-WG Recommendation for coordinated
              route-flap damping parameters, Tony Barber, Sean Doran,
              Daniel Karrenberg, Christian Panigl, Joachim Schmitz
10.[Heff]"Protection of BGP Sessions via the TCP MD5 Signature
              Option", RFC 2385, A. Heffernan. August 1998.


11. [medosc]<draft-ietf-idr-route-oscillation-00.txt>, BGP Persistent Route
Oscillation Condition,McPhersonm, Gill, Walton, Retana




9       Acknowledgments
    Thanks to Francis Ovenden and Elwyn Davies for review and Abha Ahuja for
    encouragement. Much appreciation to Jeff Haas, Matt Richardson, and
    Shane Wright at Nexthop for comments and input. Debby Stopp and Nick
    Ambrose contributed the concept of route packing.



10      Author's Addresses

    Howard Berkowitz
    Nortel Networks
    5012 S. 25th St
    Arlington VA 22206
    Phone: +1 703 998-5819 (ESN 451-5819)
    Fax:   +1 703 998-5058
    EMail: hberkowi@nortelnetworks.com

    Susan Hares
    Nexthop Technologies
    517 W. William
    Ann Arbor, Mi 48103
    Phone:
    Email: skh@nexthop.com

    Padma Krishnaswamy
    Nexthop  Technologies
    517 W William
    Ann Arbor, Mi 48103
    Phone: 734 973 2200
    Email: kri@nexthop.com

    Marianne Lepp
    Juniper Networks
    51 Sawyer Road
    Waltham, MA 02453
    Phone: 617 645 9019
    Email: mlepp@juniper.net

    Alvaro Retana
    Cisco Systems, Inc.
    7025 Kit Creek Rd.
    Research Triangle Park, NC 27709
    Email: aretana@cisco.com



Full Copyright Statement

Copyright (C) The Internet Society (2000). All Rights Reserved.

This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implmentation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph
are included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.

The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.

This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDIN
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Html markup produced by rfcmarkup 1.109, available from https://tools.ietf.org/tools/rfcmarkup/