Benchmarking Working Group H.Berkowitz, Gett Communications
Internet Draft S.Hares, Nexthop
Document: draft-ietf-bmwg-conterm-03.txt A.Retana, Cisco
Expires January 2003 P.Krishnaswamy, Consultant
M.Lepp, Juniper Networks
E.Davies, Nortel Networks
July 2002
Terminology for Benchmarking BGP Device Convergence
in the Control Plane
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.
A revised version of this draft document will be submitted to the RFC
editor as a Informational document for the Internet Community.
Discussion and suggestions for improvement are requested.
This document will expire before January 2003 . Distribution of this
draft is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract
This draft establishes terminology to standardize the description of
benchmarking methodology for measuring eBGP convergence in the
control plane of a single BGP device. Future documents will address
iBGP convergence, the initiation of forwarding based on converged
control plane information and multiple interacting BGP devices. This
terminology is applicable to both IPv4 and IPv6. Illustrative
examples of each version are included where relevant.
Berkowitz, et al Expires: January 2003 [Page 1]
INTERNET DRAFT Terminology for Benchmarking BGP July, 2002
Table of Contents
1. Introduction....................................................3
1.1 Overview and Roadmap.......................................3
1.2 Definition Format..........................................3
2. Constituent elements of a router or network of routers.........4
2.1 BGP Instance or Device.....................................4
2.2 BGP Peer...................................................5
2.3 Default Route, Default Free Table, and Full Table..........5
2.4 Classes of BGP-Speaking Routers............................8
3. Routing Data Structures.........................................9
3.1 Routing Information Base (RIB).............................9
3.2 Policy....................................................11
3.3 Policy Information Base...................................11
3.4 Forwarding Information Base (FIB).........................12
4. Components and characteristics of Routing information..........13
4.1 (Network) Prefix..........................................13
4.2 Network Prefix Length.....................................13
4.3 Route.....................................................14
4.4 BGP Route.................................................14
4.5 BGP Route Attributes and BGP Timers.......................15
4.6 Route Instance............................................16
4.7 Active Route..............................................17
4.8 Unique Route..............................................17
4.9 Non-Unique Route..........................................17
4.10 BGP UPDATE message.....................................17
4.11 Characterization of sets of update messages............18
4.12 Route Flap.............................................20
5. Route Changes and Convergence..................................21
5.1 Route Change Events.......................................21
5.2 Device Convergence in the Control Plane...................22
6. BGP Operation Events...........................................23
6.1 Hard reset................................................24
6.2 Soft reset................................................24
7. Factors that impact the performance of the convergence process.24
7.1 General factors affecting device convergence..............24
7.2 Implementation-specific and other factors affecting BGP
convergence............................................26
8. Security Considerations........................................27
9. References.....................................................27
10. Acknowledgments...............................................28
11. Author's Addresses............................................29
Berkowitz, et al Expires: January 2003 [Page 2]
INTERNET DRAFT Terminology for Benchmarking BGP July, 2002
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 (see RFC1771 [1]). It is the first
part of a two document series, of which the subsequent document will
contain the associated tests and methodology. This terminology is
applicable to both IPv4 and IPv6. Illustrative examples of each
version are included where relevant.
The following observations underlie 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 as a
first step to 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
Characterizations 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 [3], and is
repeated here for convenience:
X.x Term to be defined. (e.g., Latency)
Definition:
Berkowitz, et al Expires: January 2003 [Page 3]
INTERNET DRAFT Terminology for Benchmarking BGP July, 2002
One or more sentences forming the body of the definition.
Discussion:
A brief discussion of the term, its application and any
restrictions that there might be on measurement
procedures.
Measurement units:
The units used to report measurements of this term, if
applicable.
Issues:
List of issues or conditions that could affect this term.
See Also:
List of related terms that are relevant to the definition
or discussion of this term.
2. Constituent elements of a router or network of routers.
Many terms included in this list of definitions were originally
described 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 Instance or Device
Definition:
A BGP instance is a process with a single Loc-RIB that
runs on a BGP device.
Discussion:
We have chosen to use "device" as the general case, to
deal with the understood [e.g. [9]] and yet-to-be-invented
cases where the control processing may be separate from
forwarding [12]. A BGP device may be a traditional
router, a route server, a BGP-aware traffic steering
device, a device using BGP to exchange topology
information with a GMPLS environment, etc. A device such
as a route server, for example, never forwards traffic, so
forwarding-based measurements would be meaningless for it.
Measurement units: N/A
Issues:
See Also:
Berkowitz, et al Expires: January 2003 [Page 4]
INTERNET DRAFT Terminology for Benchmarking BGP July, 2002
2.2 BGP Peer
Definition:
A BGP peer is another BGP instance to which 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:
2.3 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(DFT).
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.
The actual path setup and forwarding of MPLS speaking routers are
outside the scope of this document. A device that computes BGP
routes, which a sub-IP device can use to set up paths, has its BGP
aspects within scope.
Berkowitz, et al Expires: January 2003 [Page 5]
INTERNET DRAFT Terminology for Benchmarking BGP July, 2002
2.3.1 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 for IPv4 is
0.0.0.0/0 and for IPv6 it is 0:0:0:0:0:0:0:0 or ::/0.
Discussion:
Measurement units: N.A.
Issues:
See Also: default free routing table, route, route instance
2.3.2 Default Free Routing Table
Definition:
A default free routing table has no default routes and is
typically seen in routers in the core or top tier of
routers in the network.
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 in IPv4 0.0.0.0/0 and in
IPv6 0:0:0:0:0:0:0:0 or ::/0). Thus they will forward
every prefix to a specific next hop 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, Default Route
Berkowitz, et al Expires: January 2003 [Page 6]
INTERNET DRAFT Terminology for Benchmarking BGP July, 2002
2.3.3 Full Default Free Table
Definition:
A full default free table is a set of BGP routes generally
accepted to be the complete set of BGP routes collectively
announced by the complete set of autonomous systems making
up the public Internet. Due to the dynamic nature of the
Internet, the exact size and composition of this table may
vary slightly depending where and when it is observed.
Discussion:
Several investigators ([17],[18],[19]) measure this on a
daily and/or 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
sub-aggregates 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
2.3.4 Full Provider Internal Table
Definition:
A full provider internal table is 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
Berkowitz, et al Expires: January 2003 [Page 7]
INTERNET DRAFT Terminology for Benchmarking BGP July, 2002
2.4 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.
2.4.1 Provider Edge Router
Definition:
A provider edge router is 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:
2.4.2 Subscriber Edge Router
Definition:
A subscriber edge router is a BGP-speaking router
belonging to an end user organization that may be multi-
homed, and 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:
2.4.3 Inter-provider Border Router
Definition:
An inter-provider border router is a BGP speaking router
which 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:
Berkowitz, et al Expires: January 2003 [Page 8]
INTERNET DRAFT Terminology for Benchmarking BGP July, 2002
Issues:
See Also:
2.4.4 Intra-provider Core Router
Definition:
An intra-provider core router is a provider router
speaking iBGP to the provider's edge routers, other intra-
provider core routers, or the provider's inter-provider
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 [10], 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.
Berkowitz, et al Expires: January 2003 [Page 9]
INTERNET DRAFT Terminology for Benchmarking BGP July, 2002
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[1].
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.
Types of routes can include internal BGP, external
BGP,interface, static and IGP routes.
Issues:
Measurement Units: Number of route instances.
See Also: Route, BGP Route, Route Instance, Adj-RIB-in,
Adj-RIB-out,FIB
Berkowitz, et al Expires: January 2003 [Page 10]
INTERNET DRAFT Terminology for Benchmarking BGP July, 2002
3.2 Policy
Definition:
Policy is "the ability to define conditions for accepting,
rejecting, and modifying routes received in
advertisements"[9].
Discussion:
RFC 1771 [1] further constrains policy to be within the
hop-by-hop routing paradigm. Policy is implemented using
filters and associated policy actions. Many AS's
formulate and document their policies using the Routing
Policy Specification Language (RPSL) [6] and then
automatically generate configurations for the BGP
processes in their routers from the RPSL specifications.
Measurement Units: Number of policies; length of policies
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
below are made with respect to RFC 1771 [1] definition of
these phases.
Incoming policies are applied in Phase 1 of the BGP
selection process [1] 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 the current AS
in the AS path, etc.
Berkowitz, et al Expires: January 2003 [Page 11]
INTERNET DRAFT Terminology for Benchmarking BGP July, 2002
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.
Measurement Units: Number and length of policies
Issues:
See Also:
3.4 Forwarding Information Base (FIB)
Definition:
As according to the definition in Appendix B of [4]:
"The table containing the information necessary to forward
IP Datagrams is called the Forwarding Information Base.
At minimum, this contains the interface identifier and
next hop information for each reachable destination
network prefix."
Discussion:
The forwarding information base describes a database
indexing network prefixes versus router port identifiers.
The forwarding information base is distinct from the
"routing table" (the Routing Information Base or RIB),
which holds all routing information received from routing
peers. The Forwarding Information Base is generated from
the RIB. For the purposes of this document, the FIB is
effectively the subset of the RIB used by the forwarding
plane to make per-packet forwarding decisions.
Most current implementations have full, non-cached FIBs
per router interface. All the route computation and
convergence occurs before entries are downloaded into a
FIB.
Measurement units: N.A.
Issues:
See Also: Route, RIB
Berkowitz, et al Expires: January 2003 [Page 12]
INTERNET DRAFT Terminology for Benchmarking BGP July, 2002
4. Components and characteristics of Routing information
4.1 (Network) Prefix
Definition:
"A network prefix is . . . 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."
(This definition is taken directly from section 2.2.5.2,
"Classless Inter Domain Routing (CIDR)", in [3].)
Discussion:
In the CIDR context, the network prefix is the network
component of an IP address.
Measurement Units: N.A.
Issues:
See Also
4.2 Network Prefix Length
Definition:
The network prefix length is the number of bits used to
define the network prefix.
Discussion:
A common alternative to using a bit-wise mask to
communicate this component is the use of "slash (/)
notation." Slash notation binds the notion of network
prefix length (see 4.2) in bits to an IP address. E.g.,
141.184.128.0/17 indicates the network component of this
IPv4 address is 17 bits wide. Similar notation is used for
IPv6 network prefixes e.g. :FF02:20::/24
When referring to groups of addresses, the network prefix
length is often used as a means of describing groups of
addresses as an equivalence class. For example,
'one hundred /16 addresses' refers to 100 addresses whose
network prefix length is 16 bits.
Measurement units: bits
Issues:
See Also: network prefix
Berkowitz, et al Expires: January 2003 [Page 13]
INTERNET DRAFT Terminology for Benchmarking BGP July, 2002
4.3 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
4.4 BGP Route
Definition:
A BGP route is an n-tuple
<prefix, nexthop, ASpath [, other BGP attributes]>.
Discussion:
BGP Attributes, such as Nexthop or AS path are defined in
RFC 1771[1], where they are known as Path Attributes, and
are the qualifying data that accompanies the network
prefixes in a BGP route UPDATE message. (An UPDATE message
may contain multiple prefixes that share a common set of
attributes).
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, NLRI.
Berkowitz, et al Expires: January 2003 [Page 14]
INTERNET DRAFT Terminology for Benchmarking BGP July, 2002
4.5 BGP Route Attributes and BGP Timers
The definitions in this section refer to items that are originally
defined in RFC 1771 [1] and are repeated here for convenience, and to
allow for some discussion beyond the definitions in RFC 1771.
4.5.1 Network Level Reachability Information (NLRI)
Definition:
The NRLI consists of one or more network prefixes that
share all other BGP path attributes and are distributed in
the update portion (as opposed to the unfeasible routes
portion) of a BGP UPDATE message.
Discussion:
Each prefix in the NLRI is combined with the (common)
path attributes in the UPDATE message to form a BGP route.
The NLRI encapsulates a set of destinations to which
packets can be routed (from this point in the network)
along a common route described by the path attributes.
Measurement Units: N.A.
Issues:
See Also: Route Packing, Network Prefix, BGP Route, NLRI
4.5.2 MinRouteAdvertisementInterval (MRAI)
Definition:
(Paraphrased from 1771[1]) The MRAI timer determines the
minimum time between advertisements of routes to a
particular destination (prefix) from a single BGP device.
The timer is applied on a pre-prefix basis, although the
timer is set on a per BGP device basis.
Discussion:
Given that a BGP instance may manage in excess of 100,000
routes, RFC 1771 allows for a degree of optimization in
order to limit the number of timers needed. The MRAI does
not apply to routes received from BGP speakers in the same
AS or to explicit withdrawals.
RFC 1771 also recommends that random jitter is applied to
MRAI in an attempt to avoid synchronization effects
between the BGP instances in a network.
In this document we define RIB convergence by measuring
the time an NLRI is advertised to the DUT to the time it
is advertised from the DUT. Clearly any delay inserted by
the MRAI will have a significant effect on this
measurement.
Measurement Units: seconds.
Berkowitz, et al Expires: December 2002 [Page 15]
INTERNET DRAFT Terminology for Benchmarking BGP July, 2002
Issues:
See Also: NLRI, BGP route
4.5.3 MinASOriginationInterval (MAOI)
Definition:
The MAOI specifies the minimum interval between
advertisements of locally originated routes from this BGP
instance.
Discussion:
Random jitter is applied to MAOI in an attempt to avoid
synchronization effects between BGP instances in a
network.
Measurement Units: seconds
Issues:
See Also: MRAI, BGP route
4.6 Route Instance
Definition:
A route instance is 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.
The BGP selection algorithm may reject a specific route
instance 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
inter-provider router, located in the default free zone
will likely receive more route instances than a provider
edge router, located closer to the end-users of the
network.
See Also:
Berkowitz, et al Expires: January 2003 [Page 16]
INTERNET DRAFT Terminology for Benchmarking BGP July, 2002
4.7 Active Route
Definition:
Route for which there is a FIB entry corresponding to a
RIB entry.
Discussion:
Measurement Units: Number of routes.
Issues:
See also: RIB.
4.8 Unique Route
Definition:
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
4.9 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.
4.10BGP UPDATE message
Definition:
An UPDATE message is an advertisement of a single NLRI,
possibly containing multiple prefixes, and multiple
withdrawals of unfeasible routes. See RFC 1771 ([1]) for
details.
Discussion:
Measurement Units: N.A.
Berkowitz, et al Expires: January 2003 [Page 17]
INTERNET DRAFT Terminology for Benchmarking BGP July, 2002
Issues:
4.11Characterization of sets of update messages
This section contains a sequence of definitions that build up to the
definition of an Update Train, a concept originally introduced by
Jain and Routhier [11]. This is a formalization of the sort of test
stimulus that is expected as input to a DUT running BGP. This data
could be a well-characterized, ordered and timed set of hand-crafted
BGP UPDATE packets. It could just as well be a set of BGP UPDATE
packets that have been captured from a live router.
Characterization of route mixtures and Update Trains is an open area
of research. The particular question of interest for this work is
the identification of suitable Update Trains, modeled or taken from
live traces that reflect realistic sequences of UPDATEs and their
contents.
4.11.1 Route Packing
Definition:
Route packing is the number of route prefixes accommodated
in a single Routing Protocol UPDATE Message either as
updates (additions or modifications) or withdrawals.
Discussion:
In general, a routing protocol update may contain more
than one prefix. In BGP, a single UPDATE may contain two
sets of multiple network prefixes: one set of additions
and updates with identical attributes (the NLRI) and one
set of unfeasible routes to be withdrawn.
Measurement Units:
Number of prefixes.
Issues:
See Also: route, BGP route, route instance, update train, NLRI.
4.11.2 Route Mixture
Definition:
A collection of routes such as an NLRI, a set of UPDATE
messages or a RIB.
Discussion:
A route mixture is the input data for the benchmark. The
particular route mixture used as input must be selected to
suit the question being asked of the benchmark.
Data containing simple route mixtures, such as 100,000 /32
routes might test the performance limits of the BGP
device.
Berkowitz, et al Expires: January 2003 [Page 18]
INTERNET DRAFT Terminology for Benchmarking BGP July, 2002
Using live data, or input that simulates live data, should
improve understanding of how the BGP device will operate
in a live network. The data for this kind of test must be
route mixtures that model the patterns of arriving control
traffic in the live Internet.
To accomplish that kind of modeling it is necessary to
identify the key parameters that characterize a live
Internet route mixture. The parameters and how they
interact is an open research problem. However, we
identify the following as affecting the route mixture:
- Path length distribution
- Attribute distribution
- Prefix distribution
- Packet packing
- Probability density function of inter-arrival times of
UPDATES Each of the items above is more
complex than a singlenumber. For example, one could
consider the distribution of prefixes by AS or
distribution of prefixes by length.
Measurement Units: Probability density functions
Issues:
See Also: NLRI, RIB.
4.11.3 Update Train
Definition:
An update train is a set of Routing Protocol UPDATE
messages sent by a router to a BGP peer.
Discussion:
The arrival pattern of UPDATEs can be influenced by many
things, including TCP parameters, hold-down timers, BGP
header processing, a peer coming up or multiple peers
sending at the same time. Network conditions such as a
local or remote peer flapping a link can also affect the
arrival pattern.
Measurement units:
Probability density function for the inter-arrival times
of UPDATE packets in the train.
Issues:
Characterizing the profiles of real world UPDATE trains is
a matter for future research. In order to generate
realistic UPDATE trains as test stimuli a formal
mathematical scheme or a proven heuristic is needed to
drive the selection of prefixes. Whatever mechanism is
Berkowitz, et al Expires: January 2003 [Page 19]
INTERNET DRAFT Terminology for Benchmarking BGP July, 2002
selected it must generate Update trains that have similar
characteristics to those measured from live routers.
See Also: Route Mixture, MRAI, MAOI
4.11.4 Randomness in Update Trains
As we have seen from the previous sections, an update train used as a
test stimulus has a considerable number of parameters that can be
varied, to a greater or lesser extent, randomly and independently.
A random Update Train will contain:
- A route mixture randomized across
- NLRIs
- updates and withdrawals
- prefixes
- inter-arrival times of the UPDATEs
and possibly across other variables.
This is intended to simulate the unpredictable asynchronous nature of
the network, whereby UPDATE packets may have arbitrary contents and
be delivered at random times.
It is important that the data set be randomized sufficiently to avoid
favoring one vendor's implementation over another's.
Specifically, the distribution of prefixes could be structured to
favor the internal organization of the routes in a particular
vendor's databases. This is to be avoided.
4.12Route Flap
Definition:
RIPE 210 [7] 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.
Berkowitz, et al Expires: January 2003 [Page 20]
INTERNET DRAFT Terminology for Benchmarking BGP July, 2002
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 [4] as well as Labovitz et al[5].
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 categorizes 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 ourselves 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 [5] 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, and event indications in the time
Berkowitz, et al Expires: January 2003 [Page 21]
INTERNET DRAFT Terminology for Benchmarking BGP July, 2002
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 [5] to the following:
a) Tup (TDx): Route advertised to the DUT by Test Device x
b) Tdown(TDx): Route being withdrawn by Device x
c) Tupinit(TDx): The initial announcement of a route to a unique
prefix
d) TWF(TDx): Route fail over after an explicit withdrawal.
But we need to take this a step further. Each of these events can
involve a single route, a "short" packet train, or a "full" routing
table. We further extend the notation to indicate how many routes are
conveyed by the events above:
a) Tup(1,TDx) means Device x sends 1 route
b) Tup(S,TDx) means Device x sends a train, S, of routes
c) Tup(DFT,TDx) means Device x sends an approximation of a full
default-free table.
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, which are routes
selected by the BGP selection process rather than simple updates:
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 Device Convergence in the Control Plane
Definition
A routing device is said to have converged at the point in
time when the DUT has performed all actions in the control
plane needed to react to changes in topology in the
context of the test condition.
Discussion:
For example, when considering BGP convergence, a change
that alters the best route instance for a single prefix at
a router would be deemed to have converged when this route
is advertised to its downstream peers. Similarly, OSPF
convergence concludes when SPF calculations have been
performed and the required link states advertised onwards.
The convergence process, in general, can be subdivided
into three distinct phases:
- convergence across the entire Internet,
- convergence within an Autonomous System,
- convergence with respect to a single device.
Berkowitz, et al Expires: January 2003 [Page 22]
INTERNET DRAFT Terminology for Benchmarking BGP July, 2002
Convergence with respect to a single device can be
- convergence with regard to data forwarding process(es)
- convergence with regard to the routing process(es), the
focus of this document.
It is the latter, convergence with regard to the routing
process, that we describe in this and the methodology
documents.
Because we are trying to benchmark the routing protocol
performance which is only a part of the device overall,
this definition is intended (so far as is possible) to
exclude any additional time such as is needed to download
and install the forwarding information base in the data
plane. This definition should be usable for different
families of protocols.
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 time resolution needed to measure the device
convergence depends to some extent on the types of the
interfaces on the router. For modern routers with gigabit
or faster interfaces, an individual UPDATE may be
processed and re-advertised in very much less than a
millisecond so that time measurements must be made to a
resolution of hundreds to tens of microseconds or better.
Measurement Units:
Time period.
Issues:
See Also:
6. BGP Operation Events
The BGP speaker process(es) in a device restarts completely, for
example, because of operator intervention or a power failure, or
fails partially because a TCP session has terminated for a particular
link. Until recently the BGP process would have to re-advertise all
relevant routes on reestablished links potentially triggering updates
across the network. Recent work is focused on limiting the volume of
updates due to operational events and the amount of processing
resulting from these events: This work includes soft refresh[12], a
graceful restart mechanism [13] and cooperative route filtering
(e.g.[14]).
Berkowitz, et al Expires: January 2003 [Page 23]
INTERNET DRAFT Terminology for Benchmarking BGP July, 2002
6.1 Hard reset
Definition:
An event which triggers a complete re-initialization of
the routing tables on one or more BGP sessions, resulting
in exchange of a full routing table on one or more links
to the router.
Discussion:
Measurement Units: N/A
Issues:
See Also:
6.2 Soft reset
Definition:
An event which results in a complete or partial restart of
the BGP session(s) on a BGP device, but which avoids the
exchange of a full table by maintaining state across the
restart.
Discussion:
Measurement Units: N/A
Issues:
See Also:
7. 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.
7.1 General factors affecting device convergence
These factors are conditions of testing external to the router Device
Under Test (DUT).
7.1.1 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. Increasing the number of peers also increases the processing
workload for TCP and BGP keepalives.
Berkowitz, et al Expires: January 2003 [Page 24]
INTERNET DRAFT Terminology for Benchmarking BGP July, 2002
7.1.2 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.
7.1.3 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.
7.1.4 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.
7.1.5 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 [2] and discussed in RIPE-229 [7].
If this feature is in effect, it requires that the device 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
7.1.6 Churn
In theory, a BGP device 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 and TCP processing.
Churn is caused by both normal and pathological events. For example,
if an interface of the local router goes down and the associated
Berkowitz, et al Expires: January 2003 [Page 25]
INTERNET DRAFT Terminology for Benchmarking BGP July, 2002
prefix is withdrawn, that withdrawal is a normal activity, although
it contributes to churn. If the local device receives a withdrawal
of a route it already advertises, or an announcement of a route it
did not previously know, and re-advertises 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 [16]. 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.
7.2 Implementation-specific and other factors affecting BGP convergence
These factors are conditions of testing internal to the Device Under
Test (DUT), although they may affect its interactions with test
devices.
7.2.1 Forwarded traffic
The presence of actual traffic in the device 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.
7.2.2 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.
7.2.3 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
Slow start, max window size, maximum segment size, or timers.
7.2.4 Authentication
Authentication in BGP is currently done using the TCP MD5 Signature
Option [8]. The processing of the MD5 hash, particularly in devices
with a large number of BGP peers and a large amount of update traffic
can have an impact on the control plane of the device.
Berkowitz, et al Expires: January 2003 [Page 26]
INTERNET DRAFT Terminology for Benchmarking BGP July, 2002
8. Security Considerations
The document explicitly considers authentication as a performance-
affecting feature, but does not consider the overall security of the
routing system.
9. References
Normative
[1] Rekhter, Y. and Li, T., "A Border Gateway
Protocol 4 (BGP-4)", RFC 1771, March 1995.
[2] Villamizar, C., Chandra, R. and Govindan, R.,
"BGP Route Flap Damping", RFC 2439,
November 1998."
[3] Baker, F.,"Requirements for IP Version 4
Routers", RFC 1812. June 1995.
[4] Ahuja, A., Jahanian, F., Bose, A. and Labovitz,
C.,
"An Experimental Study of Delayed Internet
Routing Convergence", RIPE 37 - Routing WG.
[5] Labovitz, C., Malan, G.R. and Jahanian, F.,
"Origins of Internet Routing Instability,"
Infocom 99.
[6] Alaettinoglu, C., Villamizar, C., Gerich, E.,
Kessens, D., Meyer, D., Bates, T., Karrenberg,
D. and Terpstra, M., "Routing Policy
Specification Language (RPSL)", RFC 2622, June
1999.
[7] Barber, T., Doran, S., Karrenberg, D., Panigl,
C., Schmitz, J., "RIPE Routing-WG Recommendation
for coordinated route-flap damping parameters",
RIPE 210.
[8] Heffernan, A., "Protection of BGP Sessions via
the TCP MD5 Signature Option", RFC 2385, August
1998.
[9] Juniper Networks,"Junos(tm) Internet Software
Configuration Guide Routing and Routing
Protocols, Release 4.2"
http://www.juniper.net/techpubs/software/junos42/
swconfig-routing42/html/glossary.html#1013039.
September 2000 (and other releases).
[10] Rosen, E. and Rekhter, Y., "BGP/MPLS VPNs", RFC
2547, March 1999.
Berkowitz, et al Expires: January 2003 [Page 27]
INTERNET DRAFT Terminology for Benchmarking BGP July, 2002
[11] Jain, R. and Routhier, S.A., "Packet trains --
measurement and a new model for computer network
traffic," IEEE Journal on Selected Areas in
Communication, 4(6)September 1986.
Illustrative
[12] Chen, E., "Route Refresh for BGP-4", RFC 2918,
September 2000.
[13] Ramachandra, S., Rekhter, Y., Fernando, R.,
Scudder, J.G. and Chen, E.,
"Graceful Restart Mechanism for BGP",
draft-ietf-idr-restart-02.txt, January 2002,
work in progress.
[14] Chen, E. and Rekhter, Y, "Cooperative Route
Filtering Capability for BGP-4",
draft-ietf-idr-route-filter-05.txt, January 2002,
work in progress.
[15] T. Anderson et al. "Requirements for Separation
of IP Control and Forwarding",
draft-ietf-forces-requirements-02.txt,
February 2002, work in progress.
[16] McPherson, Gill, Walton, Retana, "BGP Persistent
Route Oscillation Condition",
<draft-ietf-idr-route-oscillation-01.txt>,
February 2002, work In progress.
[17] Bates, T., "The CIDR Report",
http://www.employees.org/~tbates/cidr-report.html
Internet statistics relevant to inter-domain
routing updated daily.
[18] Smith, P. (designer), APNIC Routing Table
Statistics, http://www.apnic.net/stats/bgp/,
Statistics derived from a daily analysis of a
core router in Japan.
[19] Huston, G., Telstra BGP table statistics,
http://www.telstra.net/ops/bgp/index.html,
Statistics derived daily from the BGP tables of
Telstra and other AS's routers.
For Internet Draft consistency purposes only
[20] Bradner, S., "The Internet Standards Process --
Revision 3", BCP 9, RFC 2026, October 1996
10.Acknowledgments
Berkowitz, et al Expires: January 2003 [Page 28]
INTERNET DRAFT Terminology for Benchmarking BGP July, 2002
Thanks to Francis Ovenden 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.
11.Author's Addresses
Howard Berkowitz
Gett Communications
5012 S. 25th St
Arlington VA 22206
Phone: +1 703 998-5819
Fax: +1 703 998-5058
EMail: hcb@gettcomm.com
Elwyn Davies
Nortel Networks
London Road
Harlow, Essex CM17 9NA
UK
Phone: +44-1279-405498
Email: elwynd@nortelnetworks.com
Susan Hares
Nexthop Technologies
517 W. William
Ann Arbor, Mi 48103
Phone:
Email: skh@nexthop.com
Padma Krishnaswamy
Email: kri1@earthlink.net
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 (2002). 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 implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
Berkowitz, et al Expires: January 2003 [Page 29]
INTERNET DRAFT Terminology for Benchmarking BGP July, 2002
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.
Berkowitz, et al Expires: January 2003 [Page 30]
