Network Working Group H. Berkowitz
Request for Comments: 4098 Gett Communications & CCI Training
Category: Informational E. Davies, Ed.
Folly Consulting
S. Hares
Nexthop Technologies
P. Krishnaswamy
SAIC
M. Lepp
Consultant
June 2005
Terminology for Benchmarking BGP Device Convergence
in the Control Plane
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document 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.
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Table of Contents
1. Introduction ....................................................3
1.1. Overview and Road Map ......................................4
1.2. Definition Format ..........................................5
2. Components and Characteristics of Routing Information ...........5
2.1. (Network) Prefix ...........................................5
2.2. Network Prefix Length ......................................6
2.3. Route ......................................................6
2.4. BGP Route ..................................................7
2.5. Network Level Reachability Information (NLRI) ..............7
2.6. BGP UPDATE Message .........................................8
3. Routing Data Structures and Route Categories ....................8
3.1. Routing Information Base (RIB) .............................8
3.1.1. Adj-RIB-In and Adj-RIB-Out ..........................8
3.1.2. Loc-RIB .............................................9
3.2. Prefix Filtering ...........................................9
3.3. Routing Policy ............................................10
3.4. Routing Policy Information Base ...........................10
3.5. Forwarding Information Base (FIB) .........................11
3.6. BGP Instance ..............................................12
3.7. BGP Device ................................................12
3.8. BGP Session ...............................................13
3.9. Active BGP Session ........................................13
3.10. BGP Peer .................................................13
3.11. BGP Neighbor .............................................14
3.12. MinRouteAdvertisementInterval (MRAI) .....................14
3.13. MinASOriginationInterval (MAOI) ..........................15
3.14. Active Route .............................................15
3.15. Unique Route .............................................15
3.16. Non-Unique Route .........................................16
3.17. Route Instance ...........................................16
4. Constituent Elements of a Router or Network of Routers .........17
4.1. Default Route, Default-Free Table, and Full Table .........17
4.1.1. Default Route ......................................17
4.1.2. Default-Free Routing Table .........................18
4.1.3. Full Default-Free Table ............................18
4.1.4. Default-Free Zone ..................................19
4.1.5. Full Provider-Internal Table .......................19
4.2. Classes of BGP-Speaking Routers ...........................19
4.2.1. Provider Edge Router ...............................20
4.2.2. Subscriber Edge Router .............................20
4.2.3. Inter-provider Border Router .......................21
4.2.4. Core Router ........................................21
5. Characterization of Sets of Update Messages ....................22
5.1. Route Packing .............................................22
5.2. Route Mixture .............................................23
5.3. Update Train ..............................................24
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5.4. Randomness in Update Trains ...............................24
5.5. Route Flap ................................................25
6. Route Changes and Convergence ..................................25
6.1. Route Change Events .......................................25
6.2. Device Convergence in the Control Plane ...................27
7. BGP Operation Events ...........................................28
7.1. Hard Reset ................................................28
7.2. Soft Reset ................................................29
8. Factors That Impact the Performance of the Convergence
Process ........................................................29
8.1. General Factors Affecting Device Convergence ..............29
8.1.1. Number of Peers ....................................29
8.1.2. Number of Routes per Peer ..........................30
8.1.3. Policy Processing/Reconfiguration ..................30
8.1.4. Interactions with Other Protocols ..................30
8.1.5. Flap Damping .......................................30
8.1.6. Churn ..............................................31
8.2. Implementation-Specific and Other Factors Affecting BGP ...31
8.2.1. Forwarded Traffic ..................................31
8.2.2. Timers .............................................32
8.2.3. TCP Parameters Underlying BGP Transport ............32
8.2.4. Authentication .....................................32
9. Security Considerations ........................................32
10. Acknowledgements ..............................................32
11. References ....................................................33
11.1. Normative References ....................................33
11.2. Informative References ..................................34
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 'A Border Gateway Protocol
4 (BGP-4)' [RFC1771], referred to as RFC 1771 in the remainder of the
document.) 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.
However, this document is primarily targeted for BGP-4 in IPv4
networks. IPv6 will require the use of MP-BGP [RFC2858], as
described in RFC 2545 [RFC2545], but this document will not address
terminology or issues specific to these extensions of BGP-4. Also
terminology and issues specific to the extensions of BGP that support
VPNs as described in RFC 2547 [RFC2547] are out of scope for this
document.
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The following observations underlie the approach adopted in this
document, and in the companion document:
o The principal objective is to derive methodologies that
standardize conducting and reporting convergence-related
measurements for BGP.
o It is necessary to remove ambiguity from many frequently used
terms that arise in the context of these measurements.
o 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 in characterizing BGP convergence.
For path-vector protocols, such as BGP, the primary initial focus
will therefore be on network and system control-plane [RFC3654]
activity consisting of the arrival, processing, and propagation of
routing information.
We note that for testing purposes, all optional parameters SHOULD be
turned off. All variable parameters SHOULD be at their default
setting unless the test specifies otherwise.
Subsequent documents will explore the more intricate aspects of
convergence measurement, such as the impacts of the presence of
Multiprotocol Extensions for BGP-4, policy processing, simultaneous
traffic on the control and data paths within the Device Under Test
(DUT), and other realistic performance modifiers. Convergence of
Interior Gateway Protocols (IGPs) will also be considered in separate
documents.
1.1. Overview and Road Map
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 separate categories:
o Components and characteristics of routing information
o Routing data structures and route categories
o Descriptions of the constituent elements of a network or a router
that is undergoing convergence
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o Characterization of sets of update messages, types of route-change
events, as well as some events specific to BGP operation
o Descriptions of factors that impact the performance of convergence
processes
1.2. Definition Format
The definition format is equivalent to that defined in 'Requirements
for IP Version 4 Routers' [RFC1812], and is repeated here for
convenience:
X.x Term to be defined (e.g., Latency).
Definition:
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. This item may
not be applicable (N.A.).
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. Components and Characteristics of Routing Information
2.1. (Network) Prefix
Definition:
"A network prefix is a contiguous set of bits at the more
significant end of the address that collectively designates the
set of systems within a network; host numbers select among those
systems." (This definition is taken directly from section 2.2.5.2,
"Classless Inter Domain Routing (CIDR)", of RFC 1812.)
Discussion:
In the CIDR context, the network prefix is the network component
of an IP address. In IPv4 systems, the network component of a
complete address is known as the 'network part', and the remaining
part of the address is known as the 'host part'. In IPv6 systems,
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the network component of a complete address is known as the
'subnet prefix', and the remaining part is known as the 'interface
identifier'.
Measurement units: N.A.
Issues:
See also:
2.2. Network Prefix Length
Definition:
The network prefix length is the number of bits, out of the total
constituting the address field, that define the network prefix
portion of the address.
Discussion:
A common alternative to using a bit-wise mask to communicate this
component is the use of slash (/) notation. This binds the notion
of network prefix length in bits to an IP address. For example,
141.184.128.0/17 indicates that the network component of this IPv4
address is 17 bits wide. Similar notation is used for IPv6
network prefixes; e.g., 2001:db8:719f::/48. 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.
2.3. Route
Definition:
In general, a 'route' is the n-tuple <prefix, nexthop [, other
routing or non-routing protocol attributes]>. A route is not
end-to-end, but is defined with respect to a specific next hop
that should take packets on the next step toward their destination
as defined by the prefix. In this usage, a route is the basic
unit of information about a target destination distilled from
routing protocols.
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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.
2.4. 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, where they are known as Path Attributes, and they are the
qualifying data that define the 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."
Measurement units: N.A.
Issues:
See also:
Route, Prefix, Adj-RIB-In, Network Level Reachability Information
(NLRI)
2.5. Network Level Reachability Information (NLRI)
Definition:
The NLRI consists of one or more network prefixes with the same
set of path attributes.
Discussion:
Each prefix in the NLRI is combined with the (common) path
attributes 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.
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Measurement units: N.A.
Issues:
See also:
Route Packing, Network Prefix, BGP Route, NLRI.
2.6. BGP UPDATE Message
Definition:
An UPDATE message contains an advertisement of a single NLRI
field, possibly containing multiple prefixes, and multiple
withdrawals of unfeasible routes. See RFC 1771 for details.
Discussion:
From RFC 1771: "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.
See also:
3. Routing Data Structures and Route Categories
3.1. Routing Information Base (RIB)
The RIB collectively consists of a set of logically (not necessarily
physically) 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.
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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 among 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 that need
to be considered include internal BGP, external BGP, interface,
static, and IGP routes.
Issues:
Measurement units:
Number of routes.
See also:
Route, BGP Route, Route Instance, Adj-RIB-In, Adj-RIB-Out, FIB.
3.2. Prefix Filtering
Definition:
Prefix Filtering is a technique for eliminating routes from
consideration as candidates for entry into a RIB by matching the
network prefix in a BGP Route against a list of network prefixes.
Discussion:
A BGP Route is eliminated if, for any filter prefix from the list,
the Route prefix length is equal to or longer than the filter
prefix length and the most significant bits of the two prefixes
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match over the length of the filter prefix. See 'Cooperative
Route Filtering Capability for BGP-4' [BGP-4] for examples of
usage.
Measurement units:
Number of filter prefixes; lengths of prefixes.
Issues:
See also:
BGP Route, Network Prefix, Network Prefix Length, Routing Policy,
Routing Policy Information Base.
3.3. Routing Policy
Definition:
Routing Policy is "the ability to define conditions for accepting,
rejecting, and modifying routes received in advertisements"
[GLSSRY].
Discussion:
RFC 1771 further constrains policy to be within the hop-by-hop
routing paradigm. Policy is implemented using filters and
associated policy actions such as Prefix Filtering. Many ASes
formulate and document their policies using the Routing Policy
Specification Language (RPSL) [RFC2622] 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:
Routing Policy Information Base, Prefix Filtering.
3.4. Routing Policy Information Base
Definition:
A routing 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 definition of these phases.
Incoming policies are applied in Phase 1 of the BGP selection
process to the Adj-RIB-In routes to set the metric for the Phase 2
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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 includes route prefixes,
AS paths, communities, etc. The action on match may be to drop
the update and not to 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. 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 that accepts all routes and sends them according to a
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:
3.5. Forwarding Information Base (FIB)
Definition:
According to the definition in Appendix B of RIPE-37 [RIPE37]:
"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. It is a data plane construct and is
used for the forwarding of each packet. 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.
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Measurement units: N.A.
Issues:
See also:
Route, RIB.
3.6. BGP Instance
Definition:
A BGP instance is a process with a single Loc-RIB.
Discussion:
For example, a BGP instance would run in routers or test
equipment. A test generator acting as multiple peers will
typically run more than one instance of BGP. A router would
typically run a single instance.
Measurement units: N.A.
Issues:
See also:
3.7. BGP Device
Definition:
A BGP device is a system that has one or more BGP instances
running on it, each of which is responsible for executing the BGP
state machine.
Discussion:
We have chosen to use "device" as the general case, to deal with
the understood (e.g., [GLSSRY]) and yet-to-be-invented cases where
the control processing may be separate from forwarding [RFC2918].
A BGP device may be a traditional router, a route server, a BGP-
aware traffic steering device, or a non-forwarding route
reflector. BGP instances such as route reflectors or servers, for
example, never forward traffic, so forwarding-based measurements
would be meaningless for them.
Measurement units: N.A.
Issues:
See also:
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3.8. BGP Session
Definition:
A BGP session is a session between two BGP instances.
Discussion:
Measurement units: N.A.
Issues:
See also:
3.9. Active BGP Session
Definition:
An active BGP session is one that is in the established state.
(See RFC 1771.)
Discussion:
Measurement units: N.A.
Issues:
See also:
3.10. BGP Peer
Definition:
A BGP peer is another BGP instance to which the DUT is in the
Established state. (See RFC 1771.)
Discussion:
In the test scenarios for the methodology discussion that will
follow this document, peers send BGP advertisements to the DUT and
receive DUT-originated advertisements. We recommend that the
peering relation be established before tests begin. It might also
be interesting to measure the time required to reach the
established state. 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 4.2).
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Measurement units:
Number of BGP peers.
Issues:
See also:
3.11. BGP Neighbor
Definition:
A BGP neighbor is a device that can be configured as a BGP peer.
Discussion:
Measurement units:
Issues:
See also:
3.12. MinRouteAdvertisementInterval (MRAI)
Definition:
(Paraphrased from RFC 1771) 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 routing plane convergence by measuring from 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.
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Issues:
See also:
NLRI, BGP Route.
3.13. 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:
It is not known what, if any, relationship exists between the
settings of MRAI and MAOI.
See also:
MRAI, BGP Route.
3.14. 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.
3.15. Unique Route
Definition:
A unique route is a prefix for which there is just one route
instance across all Adj-Ribs-In.
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Discussion:
Measurement units: N.A.
Issues:
See also:
Route, Route Instance.
3.16. 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.
3.17. Route Instance
Definition:
A route instance is one of several possible occurrences of a route
for a particular prefix.
Discussion:
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. Each route
instance is associated with a specific peer. The BGP algorithm
that arbitrates between the available candidate route instances
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 border router, located in the default-free zone (see
Section 4.1.4), will likely receive more route instances than a
provider edge router, located closer to the end-users of the
network.
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See also:
4. 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.
4.1. 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). Also, a
router that has a full set of routes as in a DFT, but that also has a
'discard' rule for a default route would not be considered default
free.
Note that in this section the references to number of routes are to
routes installed in the loc-RIB, which are therefore unique routes,
not route instances. Also note that the total number of route
instances may be 4 to 10 times the number of routes.
4.1.1. Default Route
Definition:
A default route can match any destination address. If a router
does not have a more specific route for a particular packet's
destination address, it forwards this packet to the next hop in
the default route entry, provided that its Forwarding Table
(Forwarding Information Base, or 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.
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4.1.2. 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 packet to a specific next hop
based on the longest match between the destination IP address and
the routes in the forwarding table.
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.
Measurement units:
The number of routes.
See also:
Full Default-Free Table, Default Route.
4.1.3. Full Default-Free Table
Definition:
A full default-free table is the union of all sets of BGP routes
taken from all the default-free BGP routing tables 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 on where and when it is observed.
Discussion:
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:
The full default-free routing table is not the same as the union
of all reachable unicast addresses. The table simply does not
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contain the default prefix (0/0) and does contain the union of all
sets of BGP routes from default-free BGP routing tables.
See also:
Routes, Route Instances, Default Route.
4.1.4. Default-Free Zone
Definition:
The default-free zone is the part of the Internet backbone that
does not have a default route.
Discussion:
Measurement units:
Issues:
See also:
Default Route.
4.1.5. 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 might 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.
4.2. 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.
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4.2.1. Provider Edge Router
Definition:
A provider edge router is a router at the edge of a provider's
network that speaks eBGP to a BGP speaker in another AS.
Discussion:
The traffic that transits this router may be destined to or may
originate from non-adjacent autonomous systems. In particular,
the MED values used in the Provider Edge Router would not be
visible in the non-adjacent autonomous systems. Such a router
will always speak eBGP and may speak iBGP.
Measurement units:
Issues:
See also:
4.2.2. Subscriber Edge Router
Definition:
A subscriber edge router is router at the edge of the subscriber's
network that speaks eBGP to its provider's AS(s).
Discussion:
The router belongs to an end user organization that may be multi-
homed, and that carries traffic only to and from that end user AS.
Such a router will always speak eBGP and may speak iBGP.
Measurement units:
Issues:
This definition of an enterprise border router (which is what most
Subscriber Edge Routers are) is practical rather than rigorous.
It is meant to draw attention to the reality that many enterprises
may need a BGP speaker that advertises their own routes and
accepts either default alone or partial routes. In such cases,
they may be interested in benchmarks that use a partial routing
table, to see whether a smaller control plane processor will meet
their needs.
See also:
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4.2.3. Inter-provider Border Router
Definition:
An inter-provider border router is a BGP speaking router that
maintains BGP sessions with other BGP speaking routers in other
providers' ASes.
Discussion:
Traffic transiting this router may be originated in or destined
for another AS that has no direct connectivity with this
provider's AS. Such a router will always speak eBGP and may speak
iBGP.
Measurement units:
Issues:
See also:
4.2.4. Core Router
Definition:
An core router is a provider router internal to the provider's
net, speaking iBGP to that 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:
By this definition, the DUTs that are eBGP routers aren't core
routers.
See also:
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5. Characterization of Sets of Update Messages
This section contains a sequence of definitions that build up to the
definition of an update train. The packet train concept was
originally introduced by Jain and Routhier [PKTTRAIN]. It is here
adapted to refer to a train of packets of interest in BGP performance
testing.
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 on or taken
from live traces that reflect realistic sequences of UPDATEs and
their contents.
5.1. 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 as 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.
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5.2. Route Mixture
Definition:
A route mixture is the demographics of a set of routes.
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 might be suitable to test the performance limits of
the BGP device. Using live data or input that simulates live data
will 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 this 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 length distribution
* Packet packing
* Probability density function of inter-arrival times of UPDATES
Each of the items above is more complex than a single number. For
example, one could consider the distribution of prefixes by AS or by
length.
Measurement units:
Probability density functions.
Issues:
See also:
NLRI, RIB.
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5.3. 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, upstream 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 selected, it must generate update trains that have
similar characteristics to those measured in live networks.
See also:
Route Mixture, MRAI, MAOI.
5.4. 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.
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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.
5.5. Route Flap
Definition:
A route flap is a change of state (withdrawal, announcement,
attribute change) for a route.
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 229 [RIPE229], which
contains current guidelines on flap-damping parameters.
Measurement units:
Flapping events per unit time.
Issues:
Specific Flap events can be found in Section 6.1. A bench-marker
SHOULD use a mixture of different route change events in testing.
See also:
Route Change Events, Flap Damping, Packet Train
6. Route Changes and Convergence
The following two definitions are central to the benchmarking of
external routing convergence and are therefore singled out for more
extensive discussion.
6.1. Route Change Events
A taxonomy characterizing routing information changes seen in
operational networks is proposed in RIPE-37 [RIPE37] and Labovitz et
al [INSTBLTY]. 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.
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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 [INSTBLTY] and
given below.
1. AADiff: Implicit withdrawal of a route and replacement by a route
different in some path attribute.
2. AADup: Implicit withdrawal of a route and replacement by route
that is identical in all path attributes.
3. WADiff: Explicit withdrawal of a route and replacement by a
different route.
4. 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 terms to
describe the sequence of events from the update train perspective, as
listed above, and event indications in the time domain in order to
measure activity from the perspective of the DUT. With this in mind,
we incorporate and extend the definitions of [INSTBLTY] to the
following:
1. Tup (TDx): Route advertised to the DUT by Test Device x
2. Tdown(TDx): Route being withdrawn by Device x
3. Tupinit(TDx): The initial announcement of a route to a unique
prefix
4. 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:
1. Tup(1,TDx) means Device x sends 1 route
2. Tup(S,TDx) means Device x sends a train, S, of routes
3. Tup(DFT,TDx) means Device x sends an approximation of a full
default-free table.
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The basic criterion for selecting a "better" route is the final
tiebreaker defined in RFC 1771, 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:
1. Tbest -- The current best path.
2. Tbetter -- Advertise a path that is better than Tbest.
3. Tworse -- Advertise a path that is worse than Tbest.
6.2. 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, the convergence
resulting from a change that alters the best route instance for a
single prefix at a router would be deemed to have occurred when
this route is advertised to its downstream peers. By way of
contrast, OSPF convergence concludes when SPF calculations have
been performed and the required link states are advertised onward.
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.
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
that we describe herein and in 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 (as far as is possible) to exclude any
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additional time needed to download and install the
forwarding information base in the data plane. This definition is
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.
Care also needs to be taken to ensure that the convergence time is
not influenced by policy processing on downstream peers.
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:
7. BGP Operation Events
The BGP process(es) in a device might restart because operator
intervention or a power failure caused a complete shutdown. In this
case, a hard reset is needed. A peering session could be lost, for
example, because of action on the part of the peer or a dropped TCP
session. A device can reestablish its peers and re-advertise all
relevant routes in a hard reset. However, if a peer is lost, but
the BGP process has not failed, BGP has mechanisms for a "soft
reset."
7.1. Hard Reset
Definition:
An event that 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:
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See also:
7.2. Soft Reset
Definition:
A soft reset is performed on a per-neighbor basis; it does not
clear the BGP session while re-establishing the peering relation
and does not stop the flow of traffic.
Discussion:
There are two methods of performing a soft reset: (1) graceful
restart [GRMBGP], wherein the BGP device that has lost a
peer continues to forward traffic for a period of time before
tearing down the peer's routes and (2) soft
refresh [RFC2918], wherein a BGP device can request a peer's
Adj-RIB-Out.
Measurement units: N.A.
Issues:
See also:
8. Factors That Impact the Performance of the Convergence Process
Although this is not a complete list, all the items discussed below
have a significant effect on BGP convergence. Not all of them can be
addressed in the baseline measurements described in this document.
8.1. General Factors Affecting Device Convergence
These factors are conditions of testing external to the router Device
Under Test (DUT).
8.1.1. 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, depending on the quantity of updates generated by each
additional peer. Increasing the number of peers also increases the
processing workload for TCP and BGP keepalives.
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8.1.2. 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.
8.1.3. 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.
The following are extreme examples:
o Minimal policy: receive all, send all.
o Extensive policy: up to 100% of the total routes have applicable
policy.
8.1.4. 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 an
understanding of the interactions with both the IGPs and the
protocols associated with the physical media, such as Ethernet,
SONET, and DWDM.
8.1.5. 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 [RFC2439] and discussed in RIPE-
229 [RIPE229]. 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.
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8.1.6. Churn
In theory, a BGP device could receive a set of updates that
completely define 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
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 it re-advertises this information, these
are normal constituents of churn. Routine updates can range from
single announcements 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 [RFC3345]. 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 on whether the same
processor(s) are used for forwarding and control.
8.2. 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.
8.2.1. 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 would be presented
if only control traffic were present.
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8.2.2. 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 MUST be reported if they use non-default
values.
8.2.3. TCP Parameters Underlying BGP Transport
Because all BGP traffic and interactions occur over TCP, all relevant
parameters characterizing the TCP sessions MUST be provided; e.g.,
slow start, max window size, maximum segment size, or timers.
8.2.4. Authentication
Authentication in BGP is currently done using the TCP MD5 Signature
Option [RFC2385]. 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.
9. Security Considerations
The document explicitly considers authentication as a performance-
affecting feature, but does not consider the overall security of the
routing system.
10. Acknowledgements
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.
Alvaro Retana was a key member of the team that developed this
document, and made significant technical contributions regarding
route mixes. The team thanks him and regards him as a co-author in
spirit.
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11. References
11.1. Normative References
[RFC1771] Rekhter, Y. and T. Li, "A Border Gateway Protocol 4
(BGP-4)", RFC 1771, March 1995.
[RFC2439] Villamizar, C., Chandra, R., and R. Govindan, "BGP Route
Flap Damping", RFC 2439, November 1998.
[RFC1812] Baker, F., "Requirements for IP Version 4 Routers", RFC
1812, June 1995.
[RIPE37] Ahuja, A., Jahanian, F., Bose, A., and C. Labovitz, "An
Experimental Study of Delayed Internet Routing
Convergence", RIPE-37 Presentation to Routing WG,
November 2000,
<http://www.ripe.net/ripe/meetings/archive/
ripe-37/presentations/RIPE-37-convergence/>
.
[INSTBLTY] Labovitz, C., Malan, G., and F. Jahanian, "Origins of
Internet Routing Instability", Infocom 99, August 1999.
[RFC2622] Alaettinoglu, C., Bates, T., Gerich, E., Karrenberg, D.,
Meyer, D., Terpstra, M., and C. Villamizar, "Routing
Policy Specification Language (RPSL)", RFC 2280, January
1998.
[RIPE229] Panigl, C., Schmitz, J., Smith, P., and C. Vistoli,
"RIPE Routing-WG Recommendation for coordinated route-
flap damping parameters, version 2", RIPE 229, October
2001.
[RFC2385] Heffernan, A., "Protection of BGP Sessions via the TCP
MD5 Signature Option", RFC 2385, August 1998.
[GLSSRY] Juniper Networks, "Junos(tm) Internet Software
Configuration Guide Routing and Routing Protocols,
Release 4.2", Junos 4.2 and other releases, September
2000,
<http://www.juniper.net/techpubs/software/junos/junos42/
swcmdref42/html/glossary.html>
.
[RFC2547] Rosen, E. and Y. Rekhter, "BGP/MPLS VPNs", RFC 2547,
March 1999.
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[PKTTRAIN] Jain, R. and S. Routhier, "Packet trains -- measurement
and a new model for computer network traffic", IEEE
Journal on Selected Areas in Communication 4(6),
September 1986.
11.2. Informative References
[RFC2918] Chen, E., "Route Refresh Capability for BGP-4", RFC
2918, September 2000.
[GRMBGP] Sangli, S., Rekhter, Y., Fernando, R., Scudder, J., and
E. Chen, "Graceful Restart Mechanism for BGP", Work in
Progress, June 2004.
[BGP-4] Chen, E. and Y. Rekhter, "Cooperative Route Filtering
Capability for BGP-4", Work in Progress, March 2004.
[RFC3654] Khosravi, H. and T. Anderson, "Requirements for
Separation of IP Control and Forwarding", RFC 3654,
November 2003.
[RFC3345] McPherson, D., Gill, V., Walton, D., and A. Retana,
"Border Gateway Protocol (BGP) Persistent Route
Oscillation Condition", RFC 3345, August 2002.
[RFC2858] Bates, T., Rekhter, Y., Chandra, R., and D. Katz,
"Multiprotocol Extensions for BGP-4", RFC 2858, June
2000.
[RFC2545] Marques, P. and F. Dupont, "Use of BGP-4 Multiprotocol
Extensions for IPv6 Inter-Domain Routing", RFC 2545,
March 1999.
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Authors' Addresses
Howard Berkowitz
Gett Communications & CCI Training
5012 S. 25th St
Arlington, VA 22206
USA
Phone: +1 703 998-5819
Fax: +1 703 998-5058
EMail: hcb@gettcomm.com
Elwyn B. Davies
Folly Consulting
The Folly
Soham
Cambs, CB7 5AW
UK
Phone: +44 7889 488 335
EMail: elwynd@dial.pipex.com
Susan Hares
Nexthop Technologies
825 Victors Way
Ann Arbor, MI 48108
USA
Phone: +1 734 222-1610
EMail: skh@nexthop.com
Padma Krishnaswamy
SAIC
331 Newman Springs Road
Red Bank, New Jersey 07701
USA
EMail: padma.krishnaswamy@saic.com
Marianne Lepp
Consultant
EMail: mlepp@lepp.com
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Full Copyright Statement
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contained in BCP 78, and except as set forth therein, the authors
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Berkowitz, et al. Informational [Page 36]
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