draft-ietf-grow-ix-bgp-route-server-operations-05.txt   rfc7948.txt 
GROW Working Group N. Hilliard Internet Engineering Task Force (IETF) N. Hilliard
Internet-Draft INEX Request for Comments: 7948 INEX
Intended status: Informational E. Jasinska Category: Informational E. Jasinska
Expires: December 10, 2015 BigWave IT ISSN: 2070-1721 BigWave IT
R. Raszuk R. Raszuk
Mirantis Inc. Bloomberg LP
N. Bakker N. Bakker
Akamai Technologies B.V. Akamai Technologies B.V.
June 8, 2015 September 2016
Internet Exchange BGP Route Server Operations Internet Exchange BGP Route Server Operations
draft-ietf-grow-ix-bgp-route-server-operations-05
Abstract Abstract
The popularity of Internet exchange points (IXPs) brings new The popularity of Internet Exchange Points (IXPs) brings new
challenges to interconnecting networks. While bilateral eBGP challenges to interconnecting networks. While bilateral External BGP
sessions between exchange participants were historically the most (EBGP) sessions between exchange participants were historically the
common means of exchanging reachability information over an IXP, the most common means of exchanging reachability information over an IXP,
overhead associated with this interconnection method causes serious the overhead associated with this interconnection method causes
operational and administrative scaling problems for IXP participants. serious operational and administrative scaling problems for IXP
participants.
Multilateral interconnection using Internet route servers can Multilateral interconnection using Internet route servers can
dramatically reduce the administrative and operational overhead dramatically reduce the administrative and operational overhead
associated with connecting to IXPs; in some cases, route servers are associated with connecting to IXPs; in some cases, route servers are
used by IXP participants as their preferred means of exchanging used by IXP participants as their preferred means of exchanging
routing information. routing information.
This document describes operational considerations for multilateral This document describes operational considerations for multilateral
interconnections at IXPs. interconnections at IXPs.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This document is not an Internet Standards Track specification; it is
provisions of BCP 78 and BCP 79. published for informational purposes.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 7841.
This Internet-Draft will expire on December 10, 2015. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7948.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3 1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3
2. Bilateral BGP Sessions . . . . . . . . . . . . . . . . . . . 3 2. Bilateral BGP Sessions . . . . . . . . . . . . . . . . . . . 3
3. Multilateral Interconnection . . . . . . . . . . . . . . . . 4 3. Multilateral Interconnection . . . . . . . . . . . . . . . . 4
4. Operational Considerations for Route Server Installations . . 5 4. Operational Considerations for Route Server Installations . . 6
4.1. Path Hiding . . . . . . . . . . . . . . . . . . . . . . . 5 4.1. Path Hiding . . . . . . . . . . . . . . . . . . . . . . . 6
4.2. Route Server Scaling . . . . . . . . . . . . . . . . . . 6 4.2. Route Server Scaling . . . . . . . . . . . . . . . . . . 6
4.2.1. Tackling Scaling Issues . . . . . . . . . . . . . . . 7 4.2.1. Tackling Scaling Issues . . . . . . . . . . . . . . . 7
4.2.1.1. View Merging and Decomposition . . . . . . . . . 7 4.2.1.1. View Merging and Decomposition . . . . . . . . . 7
4.2.1.2. Destination Splitting . . . . . . . . . . . . . . 8 4.2.1.2. Destination Splitting . . . . . . . . . . . . . . 8
4.2.1.3. NEXT_HOP Resolution . . . . . . . . . . . . . . . 8 4.2.1.3. NEXT_HOP Resolution . . . . . . . . . . . . . . . 8
4.3. Prefix Leakage Mitigation . . . . . . . . . . . . . . . . 8 4.3. Prefix Leakage Mitigation . . . . . . . . . . . . . . . . 8
4.4. Route Server Redundancy . . . . . . . . . . . . . . . . . 9 4.4. Route Server Redundancy . . . . . . . . . . . . . . . . . 9
4.5. AS_PATH Consistency Check . . . . . . . . . . . . . . . . 9 4.5. AS_PATH Consistency Check . . . . . . . . . . . . . . . . 9
4.6. Export Routing Policies . . . . . . . . . . . . . . . . . 9 4.6. Export Routing Policies . . . . . . . . . . . . . . . . . 10
4.6.1. BGP Communities . . . . . . . . . . . . . . . . . . . 10 4.6.1. BGP Communities . . . . . . . . . . . . . . . . . . . 10
4.6.2. Internet Routing Registries . . . . . . . . . . . . . 10 4.6.2. Internet Routing Registries . . . . . . . . . . . . . 10
4.6.3. Client-accessible Databases . . . . . . . . . . . . . 10 4.6.3. Client-Accessible Databases . . . . . . . . . . . . . 10
4.7. Layer 2 Reachability Problems . . . . . . . . . . . . . . 10 4.7. Layer 2 Reachability Problems . . . . . . . . . . . . . . 11
4.8. BGP NEXT_HOP Hijacking . . . . . . . . . . . . . . . . . 11 4.8. BGP NEXT_HOP Hijacking . . . . . . . . . . . . . . . . . 11
4.9. BGP Operations and Security . . . . . . . . . . . . . . . 13
5. Security Considerations . . . . . . . . . . . . . . . . . . . 13 5. Security Considerations . . . . . . . . . . . . . . . . . . . 13
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13 6.1. Normative References . . . . . . . . . . . . . . . . . . 13
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 6.2. Informative References . . . . . . . . . . . . . . . . . 14
8.1. Normative References . . . . . . . . . . . . . . . . . . 13 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 15
8.2. Informative References . . . . . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction 1. Introduction
Internet exchange points (IXPs) provide IP data interconnection Internet Exchange Points (IXPs) provide IP data interconnection
facilities for their participants, using data link layer protocols facilities for their participants, using data link-layer protocols
such as Ethernet. The Border Gateway Protocol (BGP) [RFC4271] is such as Ethernet. The Border Gateway Protocol (BGP) [RFC4271] is
normally used to facilitate exchange of network reachability normally used to facilitate exchange of network reachability
information over these media. information over these media.
As bilateral interconnection between IXP participants requires As bilateral interconnection between IXP participants requires
operational and administrative overhead, BGP route servers operational and administrative overhead, BGP route servers [RFC7947]
[I-D.ietf-idr-ix-bgp-route-server] are often deployed by IXP are often deployed by IXP operators to provide a simple and
operators to provide a simple and convenient means of interconnecting convenient means of interconnecting IXP participants with each other.
IXP participants with each other. A route server redistributes BGP A route server redistributes BGP routes received from its BGP clients
routes received from its BGP clients to other clients according to a to other clients according to a prespecified policy, and it can be
pre-specified policy, and it can be viewed as similar to an eBGP viewed as similar to an EBGP equivalent of an Internal BGP (IBGP)
equivalent of an iBGP [RFC4456] route reflector. [RFC4456] route reflector.
Route servers at IXPs require careful management and it is important Route servers at IXPs require careful management, and it is important
for route server operators to thoroughly understand both how they for route server operators to thoroughly understand both how they
work and what their limitations are. In this document, we discuss work and what their limitations are. In this document, we discuss
several issues of operational relevance to route server operators and several issues of operational relevance to route server operators and
provide recommendations to help route server operators provision a provide recommendations to help route server operators provision a
reliable interconnection service. reliable interconnection service.
1.1. Notational Conventions 1.1. Notational Conventions
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
skipping to change at page 3, line 45 skipping to change at page 3, line 45
The phrase "BGP route" in this document should be interpreted as the The phrase "BGP route" in this document should be interpreted as the
term "Route" described in [RFC4271]. term "Route" described in [RFC4271].
2. Bilateral BGP Sessions 2. Bilateral BGP Sessions
Bilateral interconnection is a method of interconnecting routers Bilateral interconnection is a method of interconnecting routers
using individual BGP sessions between each pair of participant using individual BGP sessions between each pair of participant
routers on an IXP, in order to exchange reachability information. If routers on an IXP, in order to exchange reachability information. If
an IXP participant wishes to implement an open interconnection policy an IXP participant wishes to implement an open interconnection policy
- i.e. a policy of interconnecting with as many other IXP -- i.e., a policy of interconnecting with as many other IXP
participants as possible - it is necessary for the participant to participants as possible -- it is necessary for the participant to
liaise with each of their intended interconnection partners. liaise with each of their intended interconnection partners.
Interconnection can then be implemented bilaterally by configuring a Interconnection can then be implemented bilaterally by configuring a
BGP session on both participants' routers to exchange network BGP session on both participants' routers to exchange network
reachability information. If each exchange participant interconnects reachability information. If each exchange participant interconnects
with each other participant, a full mesh of BGP sessions is needed, with each other participant, a full mesh of BGP sessions is needed,
as shown in Figure 1. as shown in Figure 1.
___ ___ ___ ___
/ \ / \ / \ / \
..| AS1 |..| AS2 |.. ..| AS1 |..| AS2 |..
skipping to change at page 4, line 23 skipping to change at page 4, line 23
: | / \ | : : | / \ | :
: _|_/____\_|_ : : _|_/____\_|_ :
: / \ / \ : : / \ / \ :
..| AS3 |..| AS4 |.. ..| AS3 |..| AS4 |..
\___/ \___/ \___/ \___/
Figure 1: Full-Mesh Interconnection at an IXP Figure 1: Full-Mesh Interconnection at an IXP
Figure 1 depicts an IXP platform with four connected routers, Figure 1 depicts an IXP platform with four connected routers,
administered by four separate exchange participants, each of them administered by four separate exchange participants, each of them
with a locally unique autonomous system number: AS1, AS2, AS3 and with a locally unique Autonomous System (AS) number: AS1, AS2, AS3,
AS4. The lines between the routers depict BGP sessions; the dotted and AS4. The lines between the routers depict BGP sessions; the
edge represents the IXP border. Each of these four participants dotted edge represents the IXP border. Each of these four
wishes to exchange traffic with all other participants; this is participants wishes to exchange traffic with all other participants;
accomplished by configuring a full mesh of BGP sessions on each this is accomplished by configuring a full mesh of BGP sessions on
router connected to the exchange, resulting in 6 BGP sessions across each router connected to the exchange, resulting in six BGP sessions
the IXP fabric. across the IXP fabric.
The number of BGP sessions at an exchange has an upper bound of The number of BGP sessions at an exchange has an upper bound of
n*(n-1)/2, where n is the number of routers at the exchange. As many n*(n-1)/2, where n is the number of routers at the exchange. As many
exchanges have large numbers of participating networks, the amount of exchanges have large numbers of participating networks, the amount of
administrative and operation overhead required to implement an open administrative and operation overhead required to implement an open
interconnection scales quadratically. New participants to an IXP interconnection scales quadratically. New participants to an IXP
require significant initial resourcing in order to gain value from require significant initial resourcing in order to gain value from
their IXP connection, while existing exchange participants need to their IXP connection, while existing exchange participants need to
commit ongoing resources in order to benefit from interconnecting commit ongoing resources in order to benefit from interconnecting
with these new participants. with these new participants.
3. Multilateral Interconnection 3. Multilateral Interconnection
Multilateral interconnection is implemented using a route server Multilateral interconnection is implemented using a route server
configured to distribute BGP routes among client routers. The route configured to distribute BGP routes among client routers. The route
server preserves the BGP NEXT_HOP attribute from all received BGP server preserves the BGP NEXT_HOP attribute from all received BGP
routes and passes them with unchanged NEXT_HOP to its route server routes and passes them with unchanged NEXT_HOP to its route server
clients according to its configured routing policy, as described in clients according to its configured routing policy, as described in
[I-D.ietf-idr-ix-bgp-route-server]. Using this method of exchanging [RFC7947]. Using this method of exchanging BGP routes, an IXP
BGP routes, an IXP participant router can receive an aggregated list participant router can receive an aggregated list of BGP routes from
of BGP routes from all other route server clients using a single BGP all other route server clients using a single BGP session to the
session to the route server instead of depending on BGP sessions with route server instead of depending on BGP sessions with each router at
each other router at the exchange. This reduces the overall number the exchange. This reduces the overall number of BGP sessions at an
of BGP sessions at an Internet exchange from n*(n-1)/2 to n, where n Internet exchange from n*(n-1)/2 to n, where n is the number of
is the number of routers at the exchange. routers at the exchange.
Although a route server uses BGP to exchange reachability information Although a route server uses BGP to exchange reachability information
with each of its clients, it does not forward traffic itself and is with each of its clients, it does not forward traffic itself and is
therefore not a router. therefore not a router.
In practical terms, this allows dense interconnection between IXP In practical terms, this allows dense interconnection between IXP
participants with low administrative overhead and significantly participants with low administrative overhead and significantly
simpler and smaller router configurations. In particular, new IXP simpler and smaller router configurations. In particular, new IXP
participants benefit from immediate and extensive interconnection, participants benefit from immediate and extensive interconnection,
while existing route server participants receive reachability while existing route server participants receive reachability
skipping to change at page 5, line 36 skipping to change at page 5, line 36
: IXP / \ : : IXP / \ :
: | RS | : : | RS | :
: \____/ : : \____/ :
: / \ : : / \ :
: / \ : : / \ :
: __/ \__ : : __/ \__ :
: / \ / \ : : / \ / \ :
..| AS3 |..| AS4 |.. ..| AS3 |..| AS4 |..
\___/ \___/ \___/ \___/
Figure 2: IXP-based Interconnection with Route Server Figure 2: IXP-Based Interconnection with Route Server
As illustrated in Figure 2, each router on the IXP fabric requires As illustrated in Figure 2, each router on the IXP fabric requires
only a single BGP session to the route server, from which it can only a single BGP session to the route server, from which it can
receive reachability information for all other routers on the IXP receive reachability information for all other routers on the IXP
which also connect to the route server. that also connect to the route server.
Multilateral and bilateral interconnections between different
autonomous systems are not exclusive to each other, and it is not
unusual to have both sorts of sessions configured in parallel at an
IXP. This configuration will lead to additional paths being
available to the BGP Decision Process, which will calculate a best
path as normal.
4. Operational Considerations for Route Server Installations 4. Operational Considerations for Route Server Installations
4.1. Path Hiding 4.1. Path Hiding
"Path hiding" is a term used in [I-D.ietf-idr-ix-bgp-route-server] to "Path hiding" is a term used in [RFC7947] to describe the process
describe the process whereby a route server may mask individual paths whereby a route server may mask individual paths by applying
by applying conflicting routing policies to its Loc-RIB. When this conflicting routing policies to its Loc-RIB. When this happens,
happens, route server clients receive incomplete information from the route server clients receive incomplete information from the route
route server about network reachability. server about network reachability.
There are several approaches which may be used to mitigate against There are several approaches that may be used to mitigate against the
the effect of path hiding; these are described in effect of path hiding; these are described in [RFC7947]. However,
[I-D.ietf-idr-ix-bgp-route-server]. However, the only method which the only method that does not require explicit support from the route
does not require explicit support from the route server client is for server client is for the route server itself to maintain an
the route server itself to maintain a individual Loc-RIB for each individual Loc-RIB for each client that is the subject of conflicting
client which is the subject of conflicting routing policies. routing policies.
4.2. Route Server Scaling 4.2. Route Server Scaling
While deployment of multiple Loc-RIBs on the route server presents a While deployment of multiple Loc-RIBs on the route server presents a
simple way to avoid the path hiding problem noted in Section 4.1, simple way to avoid the path-hiding problem noted in Section 4.1,
this approach requires significantly more computing resources on the this approach requires significantly more computing resources on the
route server than where a single Loc-RIB is deployed for all clients. route server than where a single Loc-RIB is deployed for all clients.
As the [RFC4271] BGP decision process must be applied to all Loc-RIBs As the BGP Decision Process [RFC4271] must be applied to all Loc-RIBs
deployed on the route server, both CPU and memory requirements on the deployed on the route server, both CPU and memory requirements on the
host computer scale approximately according to O(P * N), where P is host computer scale approximately according to O(P * N), where P is
the total number of unique paths received by the route server and N the total number of unique paths received by the route server, and N
is the number of route server clients which require a unique Loc-RIB. is the number of route server clients that require a unique Loc-RIB.
As this is a super-linear scaling relationship, large route servers As this is a super-linear scaling relationship, large route servers
may derive benefit from deploying per-client Loc-RIBs only where they may derive benefit from deploying per-client Loc-RIBs only where they
are required. are required.
Regardless of whether any Loc-RIB optimization technique is Regardless of whether any Loc-RIB optimization technique is
implemented, the route server's theoretical upper-bound network implemented, the route server's theoretical upper-bound network
bandwidth requirements will scale according to O(P_tot * N), where bandwidth requirements will scale according to O(P_tot * N), where
P_tot is the total number of unique paths received by the route P_tot is the total number of unique paths received by the route
server and N is the total number of route server clients. In the server, and N is the total number of route server clients. In the
case where P_avg (the arithmetic mean number of unique paths received case where P_avg (the arithmetic mean number of unique paths received
per route server client) remains roughly constant even as the number per route server client) remains roughly constant even as the number
of connected clients increases, the total number of prefixes will of connected clients increases, the total number of prefixes will
equal the average number of prefixes multiplied by the number of equal the average number of prefixes multiplied by the number of
clients. Symbolically, this can be written as P_tot = P_avg * N. If clients. Symbolically, this can be written as P_tot = P_avg * N. If
we assume that in the worst case, each prefix is associated with a we assume that in the worst case, each prefix is associated with a
different set of BGP path attributes, so must be transmitted different set of BGP path attributes, so must be transmitted
individually, the network bandwidth scaling function can be rewritten individually, the network bandwidth scaling function can be rewritten
as O((P_avg * N) * N) or O(N^2). This quadratic upper bound on the as O((P_avg * N) * N) or O(N^2). This quadratic upper bound on the
network traffic requirements indicates that the route server model network traffic requirements indicates that the route server model
may not scale well for larger numbers of clients. may not scale well for larger numbers of clients.
In practice, most prefixes will be associated with a limited number In practice, most prefixes will be associated with a limited number
of BGP path attribute sets, allowing more efficient transmission of of BGP path attribute sets, allowing more efficient transmission of
BGP routes from the route server than the theoretical analysis BGP routes from the route server than the theoretical analysis
suggests. In the analysis above, P_tot will increase monotonically suggests. In the analysis above, P_tot will increase monotonically
according to the number of clients, but will have an upper limit of according to the number of clients, but it will have an upper limit
the size of the full default-free routing table of the network in of the size of the full default-free routing table of the network in
which the IXP is located. Observations from production route servers which the IXP is located. Observations from production route servers
have shown that most route server clients generally avoid using have shown that most route server clients generally avoid using
custom routing policies and consequently the route server may not custom routing policies, and consequently, the route server may not
need to deploy per-client Loc-RIBs. These practical bounds reduce need to deploy per-client Loc-RIBs. These practical bounds reduce
the theoretical worst-case scaling scenario to the point where route- the theoretical worst-case scaling scenario to the point where route
server deployments are manageable even on larger IXPs. server deployments are manageable even on larger IXPs.
4.2.1. Tackling Scaling Issues 4.2.1. Tackling Scaling Issues
The problem of scaling route servers still presents serious practical The problem of scaling route servers still presents serious practical
challenges and requires careful attention. Scaling analysis challenges and requires careful attention. Scaling analysis
indicates problems in three key areas: route processor CPU overhead indicates problems in three key areas: route processor CPU overhead
associated with BGP decision process calculations, the memory associated with BGP Decision Process calculations, the memory
requirements for handling many different BGP path entries, and the requirements for handling many different BGP path entries, and the
network traffic bandwidth required to distribute these BGP routes network traffic bandwidth required to distribute these BGP routes
from the route server to each route server client. from the route server to each route server client.
4.2.1.1. View Merging and Decomposition 4.2.1.1. View Merging and Decomposition
View merging and decomposition, outlined in [RS-ARCH], describes a View merging and decomposition, outlined in [RS-ARCH], describes a
method of optimising memory and CPU requirements where multiple route method of optimizing memory and CPU requirements where multiple route
server clients are subject to exactly the same routing policies. In server clients are subject to exactly the same routing policies. In
this situation, multiple Loc-RIB views can be merged into a single this situation, multiple Loc-RIB views can be merged into a single
view. view.
There are several variations of this approach. If the route server There are several variations of this approach. If the route server
operator has prior knowledge of interconnection relationships between operator has prior knowledge of interconnection relationships between
route server clients, then the operator may configure separate Loc- route server clients, then the operator may configure separate
RIBs only for route server clients with unique routing policies. As Loc-RIBs only for route server clients with unique routing policies.
this approach requires prior knowledge of interconnection As this approach requires prior knowledge of interconnection
relationships, the route server operator must depend on each client relationships, the route server operator must depend on each client
sharing their interconnection policies, either in a internal sharing their interconnection policies either in an internal
provisioning database controlled by the operator, or else in an provisioning database controlled by the operator or in an external
external data store such as an Internet Routing Registry Database. data store such as an Internet Routing Registry Database.
Conversely, the route server implementation itself may implement Conversely, the route server implementation itself may implement
internal view decomposition by creating virtual Loc-RIBs based on a internal view decomposition by creating virtual Loc-RIBs based on a
single in-memory master Loc-RIB, with delta differences for each single in-memory master Loc-RIB, with delta differences for each
prefix subject to different routing policies. This allows a more prefix subject to different routing policies. This allows a more
fine-grained and flexible approach to the problem of Loc-RIB scaling, fine-grained and flexible approach to the problem of Loc-RIB scaling,
at the expense of requiring a more complex in-memory Loc-RIB at the expense of requiring a more complex in-memory Loc-RIB
structure. structure.
Whatever method of view merging and decomposition is chosen on a Whatever method of view merging and decomposition is chosen on a
route server, pathological edge cases can be created whereby they route server, pathological edge cases can be created whereby they
will scale no better than fully non-optimised per-client Loc-RIBs. will scale no better than fully non-optimized per-client Loc-RIBs.
However, as most route server clients connect to a route server for However, as most route server clients connect to a route server for
the purposes of reducing overhead, rather than implementing complex the purposes of reducing overhead, rather than implementing complex
per-client routing policies, edge cases tend not to arise in per-client routing policies, edge cases tend not to arise in
practice. practice.
4.2.1.2. Destination Splitting 4.2.1.2. Destination Splitting
Destination splitting, also described in [RS-ARCH], describes a Destination splitting, also described in [RS-ARCH], describes a
method for route server clients to connect to multiple route servers method for route server clients to connect to multiple route servers
and to send non-overlapping sets of prefixes to each route server. and to send non-overlapping sets of prefixes to each route server.
As each route server computes the best path for its own set of As each route server computes the best path for its own set of
prefixes, the quadratic scaling requirement operates on multiple prefixes, the quadratic scaling requirement operates on multiple
smaller sets of prefixes. This reduces the overall computational and smaller sets of prefixes. This reduces the overall computational and
memory requirements for managing multiple Loc-RIBs and performing the memory requirements for managing multiple Loc-RIBs and performing the
best-path calculation on each. best-path calculation on each.
In practice, the route server operator would need all route server In practice, the route server operator would need all route server
clients to send a full set of BGP routes to each route server. The clients to send a full set of BGP routes to each route server. The
route server operator could then selectively filter these prefixes route server operator could then selectively filter these prefixes
for each route server by using either BGP Outbound Route Filtering for each route server by using either BGP Outbound Route Filtering
[RFC5291] or else inbound prefix filters configured on client BGP [RFC5291] or inbound prefix filters configured on client BGP
sessions. sessions.
4.2.1.3. NEXT_HOP Resolution 4.2.1.3. NEXT_HOP Resolution
As route servers are usually deployed at IXPs where all connected As route servers are usually deployed at IXPs where all connected
routers are on the same layer 2 broadcast domain, recursive routers are on the same Layer 2 broadcast domain, recursive
resolution of the NEXT_HOP attribute is generally not required, and resolution of the NEXT_HOP attribute is generally not required and
can be replaced by a simple check to ensure that the NEXT_HOP value can be replaced by a simple check to ensure that the NEXT_HOP value
for each received BGP route is a network address on the IXP LAN's IP for each received BGP route is a network address on the IXP LAN's IP
address range. address range.
4.3. Prefix Leakage Mitigation 4.3. Prefix Leakage Mitigation
Prefix leakage occurs when a BGP client unintentionally distributes Prefix leakage occurs when a BGP client unintentionally distributes
BGP routes to one or more neighboring BGP routers. Prefix leakage of BGP routes to one or more neighboring BGP routers. Prefix leakage of
this form to a route server can cause serious connectivity problems this form to a route server can cause serious connectivity problems
at an IXP if each route server client is configured to accept all BGP at an IXP if each route server client is configured to accept all BGP
routes from the route server. It is therefore RECOMMENDED when routes from the route server. It is therefore RECOMMENDED when
deploying route servers that, due to the potential for collateral deploying route servers that, due to the potential for collateral
damage caused by BGP route leakage, route server operators deploy damage caused by BGP route leakage, route server operators deploy
prefix leakage mitigation measures in order to prevent unintentional prefix leakage mitigation measures in order to prevent unintentional
prefix announcements or else limit the scale of any such leak. prefix announcements or else limit the scale of any such leak.
Although not foolproof, per-client inbound prefix limits can restrict Although not foolproof, per-client inbound prefix limits can restrict
the damage caused by prefix leakage in many cases. Per-client the damage caused by prefix leakage in many cases. Per-client
inbound prefix filtering on the route server is a more deterministic inbound prefix filtering on the route server is a more deterministic
and usually more reliable means of preventing prefix leakage, but and usually more reliable means of preventing prefix leakage but
requires more administrative resources to maintain properly. requires more administrative resources to maintain properly.
If a route server operator implements per-client inbound prefix If a route server operator implements per-client inbound prefix
filtering, then it is RECOMMENDED that the operator also builds in filtering, then it is RECOMMENDED that the operator also builds in
mechanisms to automatically compare the Adj-RIB-In received from each mechanisms to automatically compare the Adj-RIB-In received from each
client with the inbound prefix lists configured for those clients. client with the inbound prefix lists configured for those clients.
Naturally, it is the responsibility of the route server client to Naturally, it is the responsibility of the route server client to
ensure that their stated prefix list is compatible with what they ensure that their stated prefix list is compatible with what they
announce to an IXP route server. However, many network operators do announce to an IXP route server. However, many network operators do
not carefully manage their published routing policies and it is not not carefully manage their published routing policies, and it is not
uncommon to see significant variation between the two sets of uncommon to see significant variation between the two sets of
prefixes. Route server operator visibility into this discrepancy can prefixes. Route server operator visibility into this discrepancy can
provide significant advantages to both operator and client. provide significant advantages to both operator and client.
4.4. Route Server Redundancy 4.4. Route Server Redundancy
As the purpose of an IXP route server implementation is to provide a As the purpose of an IXP route server implementation is to provide a
reliable reachability brokerage service, it is RECOMMENDED that reliable reachability brokerage service, it is RECOMMENDED that
exchange operators who implement route server systems provision exchange operators who implement route server systems provision
multiple route servers on each shared Layer-2 domain. There is no multiple route servers on each shared Layer 2 domain. There is no
requirement to use the same BGP implementation or operating system requirement to use the same BGP implementation or operating system
for each route server on the IXP fabric; however, it is RECOMMENDED for each route server on the IXP fabric; however, it is RECOMMENDED
that where an operator provisions more than a single server on the that where an operator provisions more than a single server on the
same shared Layer-2 domain, each route server implementation be same shared Layer 2 domain, each route server implementation be
configured equivalently and in such a manner that the path configured equivalently and in such a manner that the path
reachability information from each system is identical. reachability information from each system is identical.
4.5. AS_PATH Consistency Check 4.5. AS_PATH Consistency Check
[RFC4271] requires that every BGP speaker which advertises a BGP [RFC4271] requires that every BGP speaker that advertises a BGP route
route to another external BGP speaker prepends its own AS number as to another external BGP speaker prepends its own AS number as the
the last element of the AS_PATH sequence. Therefore the leftmost AS last element of the AS_PATH sequence. Therefore, the leftmost AS in
in an AS_PATH attribute should be equal to the autonomous system an AS_PATH attribute should be equal to the AS number of the BGP
number of the BGP speaker which sent the BGP route. speaker that sent the BGP route.
As [I-D.ietf-idr-ix-bgp-route-server] suggests that route servers As [RFC7947] suggests that route servers should not modify the
should not modify the AS_PATH attribute, a consistency check on the AS_PATH attribute, a consistency check on the AS_PATH of a BGP route
AS_PATH of an BGP route received by a route server client would received by a route server client would normally fail. It is
normally fail. It is therefore RECOMMENDED that route server clients therefore RECOMMENDED that route server clients disable the AS_PATH
disable the AS_PATH consistency check towards the route server. consistency check towards the route server.
4.6. Export Routing Policies 4.6. Export Routing Policies
Policy filtering is commonly implemented on route servers to provide Policy filtering is commonly implemented on route servers to provide
prefix distribution control mechanisms for route server clients. A prefix distribution control mechanisms for route server clients. A
route server "export" policy is a policy which affects prefixes sent route server "export" policy is a policy that affects prefixes sent
from the route server to a route server client. Several different from the route server to a route server client. Several different
strategies are commonly used for implementing route server export strategies are commonly used for implementing route server export
policies. policies.
4.6.1. BGP Communities 4.6.1. BGP Communities
Prefixes sent to the route server are tagged with specific standard Prefixes sent to the route server are tagged with specific standard
[RFC1997] or extended [RFC4360] BGP community attributes, based on BGP Communities [RFC1997] or Extended Communities [RFC4360]
pre-defined values agreed between the operator and all clients. attributes, based on predefined values agreed between the operator
Based on these community tags, BGP routes may be propagated to all and all clients. Based on these Communities values, BGP routes may
other clients, a subset of clients, or none. This mechanism allows be propagated to all other clients, a subset of clients, or none.
route server clients to instruct the route server to implement per- This mechanism allows route server clients to instruct the route
client export routing policies. server to implement per-client export routing policies.
As both standard and extended BGP community values are currently As both standard BGP Communities and Extended Communities values are
restricted to 6 octets or fewer, it is not possible for both the restricted to 6 octets or fewer, it is not possible for both the
global and local administrator fields in the BGP community to fit a global and local administrator fields in the BGP Communities value to
4-octet autonomous system number. Bearing this in mind, the route fit a 4-octet AS number. Bearing this in mind, the route server
server operator SHOULD take care to ensure that the predefined BGP operator SHOULD take care to ensure that the predefined BGP
community values mechanism used on their route server is compatible Communities values mechanism used on their route server is compatible
with [RFC4893] 4-octet ASNs. with 4-octet AS numbers [RFC6793].
4.6.2. Internet Routing Registries 4.6.2. Internet Routing Registries
Internet Routing Registry databases (IRRDBs) may be used by route Internet Routing Registry databases (IRRDBs) may be used by route
server operators to construct per-client routing policies. [RFC2622] server operators to construct per-client routing policies. "Routing
Routing Policy Specification Language (RPSL) provides an Policy Specification Language (RPSL)" [RFC2622] provides a
comprehensive grammar for describing interconnection relationships, comprehensive grammar for describing interconnection relationships,
and several toolsets exist which can be used to translate RPSL policy and several toolsets exist that can be used to translate RPSL policy
description into route server configurations. description into route server configurations.
4.6.3. Client-accessible Databases 4.6.3. Client-Accessible Databases
Should the route server operator not wish to use either BGP community Should the route server operator not wish to use either BGP
tags or the public IRRDBs for implementing client export policies, Communities or the public IRRDBs for implementing client export
they may implement their own routing policy database system for policies, they may implement their own routing policy database system
managing their clients' requirements. A database of this form SHOULD for managing their clients' requirements. A database of this form
allow a route server client operator to update their routing policy SHOULD allow a route server client operator to update their routing
and provide a mechanism for allowing the client to specify whether policy and provide a mechanism for allowing the client to specify
they wish to exchange all their prefixes with any other route server whether they wish to exchange all their prefixes with any other route
client. Optionally, the implementation may allow a client to specify server client. Optionally, the implementation may allow a client to
unique routing policies for individual prefixes over which they have specify unique routing policies for individual prefixes over which
routing policy control. they have routing policy control.
4.7. Layer 2 Reachability Problems 4.7. Layer 2 Reachability Problems
Layer 2 reachability problems on an IXP can cause serious operational Layer 2 reachability problems on an IXP can cause serious operational
problems for IXP participants which depend on route servers for problems for IXP participants that depend on route servers for
interconnection. Ethernet switch forwarding bugs have occasionally interconnection. Ethernet switch forwarding bugs have occasionally
been observed to cause non-transitive reachability. For example, been observed to cause non-transitive reachability. For example,
given a route server and two IXP participants, A and B, if the two given a route server and two IXP participants, A and B, if the two
participants can reach the route server but cannot reach each other, participants can reach the route server but cannot reach each other,
then traffic between the participants may be dropped until such time then traffic between the participants may be dropped until such time
as the layer 2 forwarding problem is resolved. This situation does as the Layer 2 forwarding problem is resolved. This situation does
not tend to occur in bilateral interconnection arrangements, as the not tend to occur in bilateral interconnection arrangements, as the
routing control path between the two hosts is usually (but not routing control path between the two hosts is usually (but not
always, due to IXP inter-switch connectivity load balancing always, due to IXP inter-switch connectivity load-balancing
algorithms) the same as the data path between them. algorithms) the same as the data path between them.
Problems of this form can be partially mitigated by using [RFC5881] Problems of this form can be partially mitigated by using
bidirectional forwarding detection. However, as this is a bilateral Bidirectional Forwarding Detection (BFD) [RFC5881]. However, as this
protocol configured between routers, and as there is currently no is a bilateral protocol configured between routers, and as there is
protocol to automatically configure BFD sessions between route server currently no protocol to automatically configure BFD sessions between
clients, BFD does not currently provide an optimal means of handling route server clients, BFD does not currently provide an optimal means
the problem. Even if automatic BFD session configuration were of handling the problem. Even if automatic BFD session configuration
possible, practical problems would remain. If two IXP route server were possible, practical problems would remain. If two IXP route
clients were configured to run BFD between each other and the server clients were configured to run BFD between each other and the
protocol detected a non-transitive loss of reachability between them, protocol detected a non-transitive loss of reachability between them,
each of those routers would internally mark the other's prefixes as each of those routers would internally mark the other's prefixes as
unreachable via the BGP path announced by the route server. As the unreachable via the BGP path announced by the route server. As the
route server only propagates a single best path to each client, this route server only propagates a single best path to each client, this
could cause either sub-optimal routing or complete connectivity loss could cause either sub-optimal routing or complete connectivity loss
if there were no alternative paths learned from other BGP sessions. if there were no alternative paths learned from other BGP sessions.
4.8. BGP NEXT_HOP Hijacking 4.8. BGP NEXT_HOP Hijacking
Section 5.1.3(2) of [RFC4271] allows eBGP speakers to change the Item 2 in Section 5.1.3 of [RFC4271] allows EBGP speakers to change
NEXT_HOP address of a received BGP route to be a different internet the NEXT_HOP address of a received BGP route to be a different
address on the same subnet. This is the mechanism which allows route Internet address on the same subnet. This is the mechanism that
servers to operate on a shared layer 2 IXP network. However, the allows route servers to operate on a shared Layer 2 IXP network.
mechanism can be abused by route server clients to redirect traffic However, the mechanism can be abused by route server clients to
for their prefixes to other IXP participant routers. redirect traffic for their prefixes to other IXP participant routers.
____ ____
/ \ / \
| AS99 | | AS99 |
\____/ \____/
/ \ / \
/ \ / \
__/ \__ __/ \__
/ \ / \ / \ / \
..| AS1 |..| AS2 |.. ..| AS1 |..| AS2 |..
: \___/ \___/ : : \___/ \___/ :
: \ / : : \ / :
: \ / : : \ / :
: \__/ : : \__/ :
: IXP / \ : : IXP / \ :
: | RS | : : | RS | :
: \____/ : : \____/ :
: : : :
.................... ....................
Figure 3: BGP NEXT_HOP Hijacking using a Route Server Figure 3: BGP NEXT_HOP Hijacking Using a Route Server
For example in Figure 3, if AS1 and AS2 both announce BGP routes for For example, in Figure 3, if AS1 and AS2 both announce BGP routes for
AS99 to the route server, AS1 could set the NEXT_HOP address for AS99 to the route server, AS1 could set the NEXT_HOP address for
AS99's routes to be the address of AS2's router, thereby diverting AS99's routes to be the address of AS2's router, thereby diverting
traffic for AS99 via AS2. This may override the routing policies of traffic for AS99 via AS2. This may override the routing policies of
AS99 and AS2. AS99 and AS2.
Worse still, if the route server operator does not use inbound prefix Worse still, if the route server operator does not use inbound prefix
filtering, AS1 could announce any arbitrary prefix to the route filtering, AS1 could announce any arbitrary prefix to the route
server with a NEXT_HOP address of any other IXP participant. This server with a NEXT_HOP address of any other IXP participant. This
could be used as a denial of service mechanism against either the could be used as a denial-of-service mechanism against either the
users of the address space being announced by illicitly diverting users of the address space being announced by illicitly diverting
their traffic, or the other IXP participant by overloading their their traffic or the other IXP participant by overloading their
network with traffic which would not normally be sent there. network with traffic that would not normally be sent there.
This problem is not specific to route servers and it can also be This problem is not specific to route servers, and it can also be
implemented using bilateral BGP sessions. However, the potential implemented using bilateral BGP sessions. However, the potential
damage is amplified by route servers because a single BGP session can damage is amplified by route servers because a single BGP session can
be used to affect many networks simultaneously. be used to affect many networks simultaneously.
Because route server clients cannot easily implement next-hop policy Because route server clients cannot easily implement next-hop policy
checks against route server BGP sessions, route server operators checks against route server BGP sessions, route server operators
SHOULD check that the BGP NEXT_HOP attribute for BGP routes received SHOULD check that the BGP NEXT_HOP attribute for BGP routes received
from a route server client matches the interface address of the from a route server client matches the interface address of the
client. If the route server receives an BGP route where these client. If the route server receives a BGP route where these
addresses are different and where the announcing route server client addresses are different and where the announcing route server client
is in a different autonomous system to the route server client which is in a different AS to the route server client that uses the next-
uses the next hop address, the BGP route SHOULD be dropped. hop address, the BGP route SHOULD be dropped. Permitting next-hop
rewriting for the same AS allows an organization with multiple
connections into an IXP configured with different IP addresses to
direct traffic off the IXP infrastructure through any of their
connections for traffic engineering or other purposes.
Permitting next-hop rewriting for the same autonomous system allows 4.9. BGP Operations and Security
an organisation with multiple connections into an IXP configured with
different IP addresses to direct traffic off the IXP infrastructure BGP route servers SHOULD be configured and operated in compliance
through any of their connections for traffic engineering or other with [RFC7454] with the exception of Section 11, "BGP Community
purposes. Scrubbing", which may not necessarily apply on a route server,
depending on the route server operator policy.
5. Security Considerations 5. Security Considerations
On route server installations which do not employ path hiding On route server installations that do not employ path-hiding
mitigation techniques, the path hiding problem outlined in mitigation techniques, the path-hiding problem outlined in
Section 4.1 could be used by an IXP participant to prevent the route Section 4.1 could be used by an IXP participant to prevent the route
server from sending any BGP routes for a particular prefix to other server from sending any BGP routes for a particular prefix to other
route server clients, even if there were a valid path to that route server clients, even if there was a valid path to that
destination via another route server client. destination via another route server client.
If the route server operator does not implement prefix leakage If the route server operator does not implement prefix leakage
mitigation as described in Section 4.3, it is trivial for route mitigation as described in Section 4.3, it is trivial for route
server clients to implement denial of service attacks against server clients to implement denial-of-service attacks against
arbitrary Internet networks by leaking BGP routes to a route server. arbitrary Internet networks by leaking BGP routes to a route server.
Route server installations SHOULD be secured against BGP NEXT_HOP Route server installations SHOULD be secured against BGP NEXT_HOP
hijacking, as described in Section 4.8. hijacking, as described in Section 4.8.
6. IANA Considerations 6. References
There are no IANA considerations.
7. Acknowledgments
The authors would like to thank Chris Hall, Ryan Bickhart, Steven
Bakker and Eduardo Ascenco Reis for their valuable input.
8. References
8.1. Normative References
[I-D.ietf-idr-ix-bgp-route-server] 6.1. Normative References
Jasinska, E., Hilliard, N., Raszuk, R., and N. Bakker,
"Internet Exchange Route Server", draft-ietf-idr-ix-bgp-
route-server-06 (work in progress), December 2014.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
8.2. Informative References [RFC7947] Jasinska, E., Hilliard, N., Raszuk, R., and N. Bakker,
"Internet Exchange BGP Route Server", RFC 7947,
DOI 10.17487/RFC7947, September 2016,
<http://www.rfc-editor.org/info/rfc7947>.
[RFC1997] Chandrasekeran, R., Traina, P., and T. Li, "BGP 6.2. Informative References
Communities Attribute", RFC 1997, August 1996.
[RFC1997] Chandra, R., Traina, P., and T. Li, "BGP Communities
Attribute", RFC 1997, DOI 10.17487/RFC1997, August 1996,
<http://www.rfc-editor.org/info/rfc1997>.
[RFC2622] Alaettinoglu, C., Villamizar, C., Gerich, E., Kessens, D., [RFC2622] Alaettinoglu, C., Villamizar, C., Gerich, E., Kessens, D.,
Meyer, D., Bates, T., Karrenberg, D., and M. Terpstra, Meyer, D., Bates, T., Karrenberg, D., and M. Terpstra,
"Routing Policy Specification Language (RPSL)", RFC 2622, "Routing Policy Specification Language (RPSL)", RFC 2622,
June 1999. DOI 10.17487/RFC2622, June 1999,
<http://www.rfc-editor.org/info/rfc2622>.
[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Protocol 4 (BGP-4)", RFC 4271, January 2006. Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<http://www.rfc-editor.org/info/rfc4271>.
[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended [RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, February 2006. Communities Attribute", RFC 4360, DOI 10.17487/RFC4360,
February 2006, <http://www.rfc-editor.org/info/rfc4360>.
[RFC4456] Bates, T., Chen, E., and R. Chandra, "BGP Route [RFC4456] Bates, T., Chen, E., and R. Chandra, "BGP Route
Reflection: An Alternative to Full Mesh Internal BGP Reflection: An Alternative to Full Mesh Internal BGP
(IBGP)", RFC 4456, April 2006. (IBGP)", RFC 4456, DOI 10.17487/RFC4456, April 2006,
<http://www.rfc-editor.org/info/rfc4456>.
[RFC4893] Vohra, Q. and E. Chen, "BGP Support for Four-octet AS
Number Space", RFC 4893, May 2007.
[RFC5291] Chen, E. and Y. Rekhter, "Outbound Route Filtering [RFC5291] Chen, E. and Y. Rekhter, "Outbound Route Filtering
Capability for BGP-4", RFC 5291, August 2008. Capability for BGP-4", RFC 5291, DOI 10.17487/RFC5291,
August 2008, <http://www.rfc-editor.org/info/rfc5291>.
[RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection [RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881, June (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881,
2010. DOI 10.17487/RFC5881, June 2010,
<http://www.rfc-editor.org/info/rfc5881>.
[RFC6793] Vohra, Q. and E. Chen, "BGP Support for Four-Octet
Autonomous System (AS) Number Space", RFC 6793,
DOI 10.17487/RFC6793, December 2012,
<http://www.rfc-editor.org/info/rfc6793>.
[RFC7454] Durand, J., Pepelnjak, I., and G. Doering, "BGP Operations
and Security", BCP 194, RFC 7454, DOI 10.17487/RFC7454,
February 2015, <http://www.rfc-editor.org/info/rfc7454>.
[RS-ARCH] Govindan, R., Alaettinoglu, C., Varadhan, K., and D. [RS-ARCH] Govindan, R., Alaettinoglu, C., Varadhan, K., and D.
Estrin, "A Route Server Architecture for Inter-Domain Estrin, "A Route Server Architecture for Inter-Domain
Routing", 1995, Routing", 1995,
<http://www.cs.usc.edu/assets/003/83191.pdf>. <http://www.cs.usc.edu/assets/003/83191.pdf>.
Acknowledgments
The authors would like to thank Chris Hall, Ryan Bickhart, Steven
Bakker, and Eduardo Ascenco Reis for their valuable input.
Authors' Addresses Authors' Addresses
Nick Hilliard Nick Hilliard
INEX INEX
4027 Kingswood Road 4027 Kingswood Road
Dublin 24 Dublin 24
IE Ireland
Email: nick@inex.ie Email: nick@inex.ie
Elisa Jasinska Elisa Jasinska
BigWave IT BigWave IT
ul. Skawinska 27/7 ul. Skawinska 27/7
Krakow, MP 31-066 Krakow, MP 31-066
Poland Poland
Email: elisa@bigwaveit.org Email: elisa@bigwaveit.org
Robert Raszuk Robert Raszuk
Mirantis Inc. Bloomberg LP
615 National Ave. #100 731 Lexington Ave.
Mt View, CA 94043 New York, NY 10022
USA United States of America
Email: robert@raszuk.net Email: robert@raszuk.net
Niels Bakker Niels Bakker
Akamai Technologies B.V. Akamai Technologies B.V.
Kingsfordweg 151 Kingsfordweg 151
Amsterdam 1043 GR Amsterdam 1043 GR
NL Netherlands
Email: nbakker@akamai.com Email: nbakker@akamai.com
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