draft-ietf-rtgwg-bgp-routing-large-dc-03.txt   draft-ietf-rtgwg-bgp-routing-large-dc-04.txt 
Routing Area Working Group P. Lapukhov Routing Area Working Group P. Lapukhov
Internet-Draft Facebook Internet-Draft Facebook
Intended status: Informational A. Premji Intended status: Informational A. Premji
Expires: December 17, 2015 Arista Networks Expires: January 22, 2016 Arista Networks
J. Mitchell, Ed. J. Mitchell, Ed.
Google July 21, 2015
June 15, 2015
Use of BGP for routing in large-scale data centers Use of BGP for routing in large-scale data centers
draft-ietf-rtgwg-bgp-routing-large-dc-03 draft-ietf-rtgwg-bgp-routing-large-dc-04
Abstract Abstract
Some network operators build and operate data centers that support Some network operators build and operate data centers that support
over one hundred thousand servers. In this document, such data over one hundred thousand servers. In this document, such data
centers are referred to as "large-scale" to differentiate them from centers are referred to as "large-scale" to differentiate them from
smaller infrastructures. Environments of this scale have a unique smaller infrastructures. Environments of this scale have a unique
set of network requirements with an emphasis on operational set of network requirements with an emphasis on operational
simplicity and network stability. This document summarizes simplicity and network stability. This document summarizes
operational experience in designing and operating large-scale data operational experience in designing and operating large-scale data
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 17, 2015. This Internet-Draft will expire on January 22, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Network Design Requirements . . . . . . . . . . . . . . . . . 4 2. Network Design Requirements . . . . . . . . . . . . . . . . . 4
2.1. Bandwidth and Traffic Patterns . . . . . . . . . . . . . 4 2.1. Bandwidth and Traffic Patterns . . . . . . . . . . . . . 4
2.2. CAPEX Minimization . . . . . . . . . . . . . . . . . . . 4 2.2. CAPEX Minimization . . . . . . . . . . . . . . . . . . . 4
2.3. OPEX Minimization . . . . . . . . . . . . . . . . . . . . 5 2.3. OPEX Minimization . . . . . . . . . . . . . . . . . . . . 5
2.4. Traffic Engineering . . . . . . . . . . . . . . . . . . . 5 2.4. Traffic Engineering . . . . . . . . . . . . . . . . . . . 5
2.5. Summarized Requirements . . . . . . . . . . . . . . . . . 6 2.5. Summarized Requirements . . . . . . . . . . . . . . . . . 5
3. Data Center Topologies Overview . . . . . . . . . . . . . . . 6 3. Data Center Topologies Overview . . . . . . . . . . . . . . . 6
3.1. Traditional DC Topology . . . . . . . . . . . . . . . . . 6 3.1. Traditional DC Topology . . . . . . . . . . . . . . . . . 6
3.2. Clos Network topology . . . . . . . . . . . . . . . . . . 7 3.2. Clos Network topology . . . . . . . . . . . . . . . . . . 7
3.2.1. Overview . . . . . . . . . . . . . . . . . . . . . . 7 3.2.1. Overview . . . . . . . . . . . . . . . . . . . . . . 7
3.2.2. Clos Topology Properties . . . . . . . . . . . . . . 8 3.2.2. Clos Topology Properties . . . . . . . . . . . . . . 8
3.2.3. Scaling the Clos topology . . . . . . . . . . . . . . 9 3.2.3. Scaling the Clos topology . . . . . . . . . . . . . . 9
3.2.4. Managing the Size of Clos Topology Tiers . . . . . . 10 3.2.4. Managing the Size of Clos Topology Tiers . . . . . . 10
4. Data Center Routing Overview . . . . . . . . . . . . . . . . 11 4. Data Center Routing Overview . . . . . . . . . . . . . . . . 11
4.1. Layer 2 Only Designs . . . . . . . . . . . . . . . . . . 11 4.1. Layer 2 Only Designs . . . . . . . . . . . . . . . . . . 11
4.2. Hybrid L2/L3 Designs . . . . . . . . . . . . . . . . . . 12 4.2. Hybrid L2/L3 Designs . . . . . . . . . . . . . . . . . . 12
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7.4. Failure Impact Scope . . . . . . . . . . . . . . . . . . 24 7.4. Failure Impact Scope . . . . . . . . . . . . . . . . . . 24
7.5. Routing Micro-Loops . . . . . . . . . . . . . . . . . . . 25 7.5. Routing Micro-Loops . . . . . . . . . . . . . . . . . . . 25
8. Additional Options for Design . . . . . . . . . . . . . . . . 26 8. Additional Options for Design . . . . . . . . . . . . . . . . 26
8.1. Third-party Route Injection . . . . . . . . . . . . . . . 26 8.1. Third-party Route Injection . . . . . . . . . . . . . . . 26
8.2. Route Summarization within Clos Topology . . . . . . . . 26 8.2. Route Summarization within Clos Topology . . . . . . . . 26
8.2.1. Collapsing Tier-1 Devices Layer . . . . . . . . . . . 27 8.2.1. Collapsing Tier-1 Devices Layer . . . . . . . . . . . 27
8.2.2. Simple Virtual Aggregation . . . . . . . . . . . . . 28 8.2.2. Simple Virtual Aggregation . . . . . . . . . . . . . 28
8.3. ICMP Unreachable Message Masquerading . . . . . . . . . . 29 8.3. ICMP Unreachable Message Masquerading . . . . . . . . . . 29
9. Security Considerations . . . . . . . . . . . . . . . . . . . 29 9. Security Considerations . . . . . . . . . . . . . . . . . . . 29
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 29 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 30
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 30 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 30
12.1. Normative References . . . . . . . . . . . . . . . . . . 30 12.1. Normative References . . . . . . . . . . . . . . . . . . 30
12.2. Informative References . . . . . . . . . . . . . . . . . 30 12.2. Informative References . . . . . . . . . . . . . . . . . 30
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 33 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 33
1. Introduction 1. Introduction
This document describes a practical routing design that can be used This document describes a practical routing design that can be used
in a large-scale data center ("DC") design. Such data centers, also in a large-scale data center ("DC") design. Such data centers, also
known as hyper-scale or warehouse-scale data centers, have a unique known as hyper-scale or warehouse-scale data centers, have a unique
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accommodate networks of this scale, operators are revisiting accommodate networks of this scale, operators are revisiting
networking designs and platforms to address this need. networking designs and platforms to address this need.
The design presented in this document is based on operational The design presented in this document is based on operational
experience with data centers built to support large-scale distributed experience with data centers built to support large-scale distributed
software infrastructure, such as a Web search engine. The primary software infrastructure, such as a Web search engine. The primary
requirements in such an environment are operational simplicity and requirements in such an environment are operational simplicity and
network stability so that a small group of people can effectively network stability so that a small group of people can effectively
support a significantly sized network. support a significantly sized network.
After experimentation and extensive testing, Microsoft chose to use After experimentation and extensive testing, the authors and their
an end-to-end routed network infrastructure with External BGP (EBGP) colleagues chose to use an end-to-end routed network infrastructure
[RFC4271] as the only routing protocol for some of its DC with External BGP (EBGP) [RFC4271] as the only routing protocol for
deployments. This is in contrast with more traditional DC designs, some of its DC deployments. This is in contrast with more
which may use simple tree topologies and rely on extending Layer 2 traditional DC designs, which may use simple tree topologies and rely
domains across multiple network devices. This document elaborates on on extending Layer 2 domains across multiple network devices. This
the requirements that led to this design choice and presents details document elaborates on the requirements that led to this design
of the EBGP routing design as well as explores ideas for further choice and presents details of the EBGP routing design as well as
enhancements. explores ideas for further enhancements.
This document first presents an overview of network design This document first presents an overview of network design
requirements and considerations for large-scale data centers. Then requirements and considerations for large-scale data centers. Then
traditional hierarchical data center network topologies are traditional hierarchical data center network topologies are
contrasted with Clos networks [CLOS1953] that are horizontally scaled contrasted with Clos networks [CLOS1953] that are horizontally scaled
out. This is followed by arguments for selecting EBGP with a Clos out. This is followed by arguments for selecting EBGP with a Clos
topology as the most appropriate routing protocol to meet the topology as the most appropriate routing protocol to meet the
requirements and the proposed design is described in detail. requirements and the proposed design is described in detail.
Finally, the document reviews some additional considerations and Finally, the document reviews some additional considerations and
design options. design options.
2. Network Design Requirements 2. Network Design Requirements
This section describes and summarizes network design requirements for This section describes and summarizes network design requirements for
large-scale data centers. large-scale data centers.
2.1. Bandwidth and Traffic Patterns 2.1. Bandwidth and Traffic Patterns
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o REQ2: Define a narrow set of software features/protocols supported o REQ2: Define a narrow set of software features/protocols supported
by a multitude of networking equipment vendors. by a multitude of networking equipment vendors.
o REQ3: Choose a routing protocol that has a simple implementation o REQ3: Choose a routing protocol that has a simple implementation
in terms of programming code complexity and ease of operational in terms of programming code complexity and ease of operational
support. support.
o REQ4: Minimize the failure domain of equipment or protocol issues o REQ4: Minimize the failure domain of equipment or protocol issues
as much as possible. as much as possible.
o REQ5: Allow for traffic engineering, preferably via explicit o REQ5: Allow for some traffic engineering, preferably via explicit
control of the routing prefix next-hop using built-in protocol control of the routing prefix next-hop using built-in protocol
mechanics. mechanics.
3. Data Center Topologies Overview 3. Data Center Topologies Overview
This section provides an overview of two general types of data center This section provides an overview of two general types of data center
designs - hierarchical (also known as tree based) and Clos based designs - hierarchical (also known as tree based) and Clos based
network designs. network designs.
3.1. Traditional DC Topology 3.1. Traditional DC Topology
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presence of an IGP for next-hop resolution. presence of an IGP for next-hop resolution.
o BGP is perceived to require significant configuration overhead and o BGP is perceived to require significant configuration overhead and
does not support neighbor auto-discovery. does not support neighbor auto-discovery.
This document discusses some of these perceptions, especially as This document discusses some of these perceptions, especially as
applicable to the proposed design, and highlights some of the applicable to the proposed design, and highlights some of the
advantages of using the protocol such as: advantages of using the protocol such as:
o BGP has less complexity in parts of its protocol design - internal o BGP has less complexity in parts of its protocol design - internal
data structures and state machine are simple when compared to most data structures and state machine are simpler as compared to most
link-state IGP such as OSPF. For example, instead of implementing link-state IGPs such as OSPF. For example, instead of
adjacency formation, adjacency maintenance and/or flow-control, implementing adjacency formation, adjacency maintenance and/or
BGP simply relies on TCP as the underlying transport. This flow-control, BGP simply relies on TCP as the underlying
fulfills REQ2 and REQ3. transport. This fulfills REQ2 and REQ3.
o BGP information flooding overhead is less when compared to link- o BGP information flooding overhead is less when compared to link-
state IGPs. Since every BGP router calculates and propagates only state IGPs. Since every BGP router calculates and propagates only
the best-path selected, a network failure is masked as soon as the the best-path selected, a network failure is masked as soon as the
BGP speaker finds an alternate path, which exists when highly BGP speaker finds an alternate path, which exists when highly
symmetric topologies, such as Clos, are coupled with EBGP only symmetric topologies, such as Clos, are coupled with EBGP only
design. In contrast, the event propagation scope of a link-state design. In contrast, the event propagation scope of a link-state
IGP is an entire area, regardless of the failure type. This meets IGP is an entire area, regardless of the failure type. This meets
REQ3 and REQ4. It is worth mentioning that all widely deployed REQ3 and REQ4. It is worth mentioning that all widely deployed
link-state IGPs also feature periodic refreshes of routing link-state IGPs also feature periodic refreshes of routing
information, while BGP does not expire routing state, even if this information, while BGP does not expire routing state, even if this
rarely causes significant impact to modern router control planes. rarely causes significant impact to modern router control planes.
o BGP supports third-party (recursively resolved) next-hops. This o BGP supports third-party (recursively resolved) next-hops. This
allows for manipulating multipath to be non-ECMP based or allows for manipulating multipath to be non-ECMP based or
forwarding based on application-defined forwarding paths, through forwarding based on application-defined paths, through
establishment of a peering session with an application establishment of a peering session with an application
"controller" which can inject routing information into the system, "controller" which can inject routing information into the system,
satisfying REQ5. OSPF provides similar functionality using satisfying REQ5. OSPF provides similar functionality using
concepts such as "Forwarding Address", but with more difficulty in concepts such as "Forwarding Address", but with more difficulty in
implementation and lack of protocol simplicity. implementation and far less control of information propagation
scope.
o Using a well-defined ASN allocation scheme and standard AS_PATH o Using a well-defined ASN allocation scheme and standard AS_PATH
loop detection, "BGP path hunting" (see [JAKMA2008]) can be loop detection, "BGP path hunting" (see [JAKMA2008]) can be
controlled and complex unwanted paths will be ignored. See controlled and complex unwanted paths will be ignored. See
Section 5.2 for an example of a working ASN allocation scheme. In Section 5.2 for an example of a working ASN allocation scheme. In
a link-state IGP accomplishing the same goal would require multi- a link-state IGP accomplishing the same goal would require multi-
(instance/topology/processes) support, typically not available in (instance/topology/processes) support, typically not available in
all DC devices and quite complex to configure and troubleshoot. all DC devices and quite complex to configure and troubleshoot.
Using a traditional single flooding domain, which most DC designs Using a traditional single flooding domain, which most DC designs
utilize, under certain failure conditions may pick up unwanted utilize, under certain failure conditions may pick up unwanted
lengthy paths, e.g. traversing multiple Tier-2 devices. lengthy paths, e.g. traversing multiple Tier-2 devices.
o EBGP configuration that is implemented with minimal routing policy o EBGP configuration that is implemented with minimal routing policy
is easier to troubleshoot for network reachability issues. In is easier to troubleshoot for network reachability issues. In
most implementations, it is straightforward to view contents of most implementations, it is straightforward to view contents of
BGP Loc-RIB and compare it to the router's RIB. Also in most BGP Loc-RIB and compare it to the router's RIB. Also, in most
implementations an operator can view every BGP neighbors Adj-RIB- implementations an operator can view every BGP neighbors Adj-RIB-
In and Adj-RIB-Out structures and therefore incoming and outgoing In and Adj-RIB-Out structures and therefore incoming and outgoing
NRLI information can be easily correlated on both sides of a BGP NRLI information can be easily correlated on both sides of a BGP
session. Thus, BGP satisfies REQ3. session. Thus, BGP satisfies REQ3.
5.2. EBGP Configuration for Clos topology 5.2. EBGP Configuration for Clos topology
Clos topologies that have more than 5 stages are very uncommon due to Clos topologies that have more than 5 stages are very uncommon due to
the large numbers of interconnects required by such a design. the large numbers of interconnects required by such a design.
Therefore, the examples below are made with reference to the 5-stage Therefore, the examples below are made with reference to the 5-stage
Clos topology (5 stages in unfolded state). Clos topology (in unfolded state).
5.2.1. EBGP Configuration Guidelines and Example ASN Scheme 5.2.1. EBGP Configuration Guidelines and Example ASN Scheme
The diagram below illustrates an example ASN allocation scheme. The The diagram below illustrates an example ASN allocation scheme. The
following is a list of guidelines that can be used: following is a list of guidelines that can be used:
o EBGP single-hop sessions are established over direct point-to- o EBGP single-hop sessions are established over direct point-to-
point links interconnecting the network nodes, no multi-hop or point links interconnecting the network nodes, no multi-hop or
loopback sessions are used even in the case of multiple links loopback sessions are used even in the case of multiple links
between the same pair of nodes. between the same pair of nodes.
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A Clos topology features a large number of point-to-point links and A Clos topology features a large number of point-to-point links and
associated prefixes. Advertising all of these routes into BGP may associated prefixes. Advertising all of these routes into BGP may
create FIB overload conditions in the network devices. Advertising create FIB overload conditions in the network devices. Advertising
these links also puts additional path computation stress on the BGP these links also puts additional path computation stress on the BGP
control plane for little benefit. There are two possible solutions: control plane for little benefit. There are two possible solutions:
o Do not advertise any of the point-to-point links into BGP. Since o Do not advertise any of the point-to-point links into BGP. Since
the EBGP-based design changes the next-hop address at every the EBGP-based design changes the next-hop address at every
device, distant networks will automatically be reachable via the device, distant networks will automatically be reachable via the
advertising EBGP peer and do not require reachability to these advertising EBGP peer and do not require reachability to these
prefixes. However, this may complicate operational prefixes. However, this may complicate operations or monitoring:
troubleshooting or monitoring systems if the addresses are not e.g. using the popular "traceroute" tool will display IP addresses
reachable: e.g. using the popular "traceroute" tool will display that are not reachable.
IP addresses that are not reachable.
o Advertise point-to-point links, but summarize them on every o Advertise point-to-point links, but summarize them on every
device. This requires an address allocation scheme such as device. This requires an address allocation scheme such as
allocating a consecutive block of IP addresses per Tier-1 and allocating a consecutive block of IP addresses per Tier-1 and
Tier-2 device to be used for point-to-point interface addressing Tier-2 device to be used for point-to-point interface addressing
to the lower layers (Tier-2 uplinks will be numbered out of Tier-1 to the lower layers (Tier-2 uplinks will be numbered out of Tier-1
addressing and so forth). addressing and so forth).
Server subnets on Tier-3 devices must be announced into BGP without Server subnets on Tier-3 devices must be announced into BGP without
using route summarization on Tier-2 and Tier-1 devices. Summarizing using route summarization on Tier-2 and Tier-1 devices. Summarizing
subnets in a Clos topology results in route black-holing under a subnets in a Clos topology results in route black-holing under a
single link failure (e.g. between Tier-2 and Tier-3 devices) and single link failure (e.g. between Tier-2 and Tier-3 devices) and
hence must be avoided. The use of peer links within the same tier to hence must be avoided. The use of peer links within the same tier to
resolve the black-holing problem by providing "bypass paths" is resolve the black-holing problem by providing "bypass paths" is
undesirable due to O(N^2) complexity of the peering mesh and waste of undesirable due to O(N^2) complexity of the peering mesh and waste of
ports on the devices. An alternative to the full-mesh of peer-links ports on the devices. An alternative to the full-mesh of peer-links
would be using a simpler bypass topology, e.g. a "ring" as described would be using a simpler bypass topology, e.g. a "ring" as described
in [FB4POST], but such a topology adds extra hops and has very in [FB4POST], but such a topology adds extra hops and has very
limited bisection bandwidth, in addition requiring special tweaks to limited bisection bandwidth, in addition requiring special tweaks to
make BGP routing work - such as possibly splitting every device into make BGP routing work - such as possibly splitting every device into
an ASN on its own. In Section 8.2 another, less intrusive, method an ASN on its own. The section Section 8.2 introduces another, less
for performing a limited form route summarization in Clos networks intrusive, method for performing a limited form route summarization
and the associated trade-offs are described. in Clos networks and the discusses the associated trade-offs.
5.2.4. External Connectivity 5.2.4. External Connectivity
A dedicated cluster (or clusters) in the Clos topology could be used A dedicated cluster (or clusters) in the Clos topology could be used
for the purpose of connecting to the Wide Area Network (WAN) edge for the purpose of connecting to the Wide Area Network (WAN) edge
devices, or WAN Routers. Tier-3 devices in such cluster would be devices, or WAN Routers. Tier-3 devices in such cluster would be
replaced with WAN routers, and EBGP peering would be used again, replaced with WAN routers, and EBGP peering would be used again,
though WAN routers are likely to belong to a public ASN if Internet though WAN routers are likely to belong to a public ASN if Internet
connectivity is required in the design. The Tier-2 devices in such a connectivity is required in the design. The Tier-2 devices in such a
dedicated cluster will be referred to as "Border Routers" in this dedicated cluster will be referred to as "Border Routers" in this
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vendor's document [REMOVE-PRIVATE-AS]. vendor's document [REMOVE-PRIVATE-AS].
o Originate a default route to the data center devices. This is the o Originate a default route to the data center devices. This is the
only place where default route can be originated, as route only place where default route can be originated, as route
summarization is risky for the "scale-out" topology. summarization is risky for the "scale-out" topology.
Alternatively, Border Routers may simply relay the default route Alternatively, Border Routers may simply relay the default route
learned from WAN routers. Advertising the default route from learned from WAN routers. Advertising the default route from
Border Routers requires that all Border Routers be fully connected Border Routers requires that all Border Routers be fully connected
to the WAN Routers upstream, to provide resistance to a single- to the WAN Routers upstream, to provide resistance to a single-
link failure causing the black-holing of traffic. To prevent link failure causing the black-holing of traffic. To prevent
chance of operator or implementation error that may impact EBGP black-holing in the situation when all of the EBGP sessions to the
sessions to the WAN routers simultaneously (although these WAN routers fail simultaneously on a given device it is more
scenarios are not planned for by many operators since they desirable to take the "relaying" approach rather than introducing
represents a multiple failure) it is more desirable to take this the default route via complicated conditional route origination
approach rather than introducing the default route via complicated schemes provided by some implementations [CONDITIONALROUTE].
conditional route origination schemes provided by some
implementations [CONDITIONALROUTE].
5.2.5. Route Summarization at the Edge 5.2.5. Route Summarization at the Edge
It is often desirable to summarize network reachability information It is often desirable to summarize network reachability information
prior to advertising it to the WAN network due to high amount of IP prior to advertising it to the WAN network due to high amount of IP
prefixes originated from within the data center in a fully routed prefixes originated from within the data center in a fully routed
network design. For example, a network with 2000 Tier-3 devices will network design. For example, a network with 2000 Tier-3 devices will
have at least 2000 servers subnets advertised into BGP, along with have at least 2000 servers subnets advertised into BGP, along with
the infrastructure or other prefixes. However, as discussed before, the infrastructure or other prefixes. However, as discussed before,
the proposed network design does not allow for route summarization the proposed network design does not allow for route summarization
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increases the risk of flow polarization, as less entropy will be increases the risk of flow polarization, as less entropy will be
available to the second stage of ECMP. available to the second stage of ECMP.
Most BGP implementations declare paths to be equal from ECMP Most BGP implementations declare paths to be equal from ECMP
perspective if they match up to and including step (e) perspective if they match up to and including step (e)
Section 9.1.2.2 of [RFC4271]. In the proposed network design there Section 9.1.2.2 of [RFC4271]. In the proposed network design there
is no underlying IGP, so all IGP costs are assumed to be zero or is no underlying IGP, so all IGP costs are assumed to be zero or
otherwise the same value across all paths and policies may be applied otherwise the same value across all paths and policies may be applied
as necessary to equalize BGP attributes that vary in vendor defaults, as necessary to equalize BGP attributes that vary in vendor defaults,
such as MED and origin code. For historical reasons it is also such as MED and origin code. For historical reasons it is also
useful to not use 0 as the equalized MED value, this and some other useful to not use 0 as the equalized MED value; this and some other
useful BGP information is available in [RFC4277] . Routing loops are useful BGP information is available in [RFC4277] . Routing loops are
unlikely due to the BGP best-path selection process which prefers unlikely due to the BGP best-path selection process which prefers
shorter AS_PATH length, and longer paths through the Tier-1 devices shorter AS_PATH length, and longer paths through the Tier-1 devices
which don't allow their own ASN in the path and have the same ASN are which don't allow their own ASN in the path and have the same ASN are
also not possible. also not possible.
6.2. BGP ECMP over Multiple ASNs 6.2. BGP ECMP over Multiple ASNs
For application load balancing purposes it is desirable to have the For application load balancing purposes it is desirable to have the
same prefix advertised from multiple Tier-3 devices. From the same prefix advertised from multiple Tier-3 devices. From the
perspective of other devices, such a prefix would have BGP paths with perspective of other devices, such a prefix would have BGP paths with
different AS_PATH attribute values, while having the same AS_PATH different AS_PATH attribute values, while having the same AS_PATH
attribute lengths. Therefore, BGP implementations must support load attribute lengths. Therefore, BGP implementations must support load
sharing over above-mentioned paths. This feature is sometimes known sharing over above-mentioned paths. This feature is sometimes known
as "multipath relax" and effectively allows for ECMP to be done as "multipath relax" and effectively allows for ECMP to be done
across different neighboring ASNs if all other attributes are equal across different neighboring ASNs if all other attributes are equal
as described in the previous section. as described in the previous section.
6.3. Weighted ECMP 6.3. Weighted ECMP
It may be desirable for the network devices to implement weighted It may be desirable for the network devices to implement "weighted"
ECMP, to be able to send more traffic over some paths in ECMP fan- ECMP, to be able to send more traffic over some paths in ECMP fan-
out. This could be helpful to compensate for failures in the network out. This could be helpful to compensate for failures in the network
and send more traffic over paths that have more capacity. The and send more traffic over paths that have more capacity. The
prefixes that require weighted ECMP would have to be injected using prefixes that require weighted ECMP would have to be injected using
remote BGP speaker (central agent) over a multihop session as remote BGP speaker (central agent) over a multihop session as
described further in Section 8.1. If support in implementations is described further in Section 8.1. If support in implementations is
available, weight-distribution for multiple BGP paths could be available, weight-distribution for multiple BGP paths could be
signaled using the technique described in signaled using the technique described in
[I-D.ietf-idr-link-bandwidth]. [I-D.ietf-idr-link-bandwidth].
skipping to change at page 22, line 18 skipping to change at page 22, line 18
consistent (see [CONS-HASH]), to minimizing the impact on flow to consistent (see [CONS-HASH]), to minimizing the impact on flow to
next-hop affinity changes when a next-hop is added or removed to ECMP next-hop affinity changes when a next-hop is added or removed to ECMP
group. This could be used if the network device is used as a load group. This could be used if the network device is used as a load
balancer, mapping flows toward multiple destinations - in this case, balancer, mapping flows toward multiple destinations - in this case,
losing or adding a destination will not have detrimental effect of losing or adding a destination will not have detrimental effect of
currently established flows. One particular recommendation on currently established flows. One particular recommendation on
implementing consistent hashing is provided in [RFC2992], though implementing consistent hashing is provided in [RFC2992], though
other implementations are possible. This functionality could be other implementations are possible. This functionality could be
naturally combined with weighted ECMP, with the impact of the next- naturally combined with weighted ECMP, with the impact of the next-
hop changes being proportional to the weight of the given next-hop. hop changes being proportional to the weight of the given next-hop.
Notice that the usual downside of consistent hashing is increased The downside of consistent hashing is increased load on hardware
load on hardware resource utilization, as typically more space is resource utilization, as typically more space is required to
required to implement a consistent-hashing region. implement a consistent-hashing region.
7. Routing Convergence Properties 7. Routing Convergence Properties
This section reviews routing convergence properties in the proposed This section reviews routing convergence properties in the proposed
design. A case is made that sub-second convergence is achievable if design. A case is made that sub-second convergence is achievable if
the implementation supports fast EBGP peering session deactivation the implementation supports fast EBGP peering session deactivation
and timely RIB and FIB update upon failure of the associated link. and timely RIB and FIB update upon failure of the associated link.
7.1. Fault Detection Timing 7.1. Fault Detection Timing
BGP typically relies on an IGP to route around link/node failures BGP typically relies on an IGP to route around link/node failures
inside an AS, and implements either a polling based or an event- inside an AS, and implements either a polling based or an event-
driven mechanism to obtain updates on IGP state changes. The driven mechanism to obtain updates on IGP state changes. The
proposed routing design does not use an IGP, so the only mechanisms proposed routing design does not use an IGP, so the remaining
that could be used for fault detection are BGP keep-alive process (or mechanisms that could be used for fault detection are BGP keep-alive
any other type of keep-alive mechanism) and link-failure triggers. process (or any other type of keep-alive mechanism) and link-failure
triggers.
Relying solely on BGP keep-alive packets may result in high Relying solely on BGP keep-alive packets may result in high
convergence delays, in the order of multiple seconds (on many BGP convergence delays, in the order of multiple seconds (on many BGP
implementations the minimum configurable BGP hold timer value is implementations the minimum configurable BGP hold timer value is
three seconds). However, many BGP implementations can shut down three seconds). However, many BGP implementations can shut down
local EBGP peering sessions in response to the "link down" event for local EBGP peering sessions in response to the "link down" event for
the outgoing interface used for BGP peering. This feature is the outgoing interface used for BGP peering. This feature is
sometimes called as "fast fallover". Since links in modern data sometimes called as "fast fallover". Since links in modern data
centers are often point-to-point fiber connections, a physical centers are predominantly point-to-point fiber connections, a
interface failure is often detected in milliseconds and subsequently physical interface failure is often detected in milliseconds and
triggers a BGP re-convergence. subsequently triggers a BGP re-convergence.
Ethernet technologies may support failure signaling or detection Ethernet technologies may support failure signaling or detection
standards such as Connectivity Fault Management (CFM) as described in standards such as Connectivity Fault Management (CFM) as described in
[IEEE8021Q], which may make failure detection more robust. [IEEE8021Q], which may make failure detection more robust.
Alternatively, some platforms may support Bidirectional Forwarding Alternatively, some platforms may support Bidirectional Forwarding
Detection (BFD) [RFC5880] to allow for sub-second failure detection Detection (BFD) [RFC5880] to allow for sub-second failure detection
and fault signaling to the BGP process. However, use of either of and fault signaling to the BGP process. However, use of either of
these presents additional requirements to vendor software and these presents additional requirements to vendor software and
possibly hardware, and may contradict REQ1. Until recently with possibly hardware, and may contradict REQ1. Until recently with
[RFC7130], BFD also did not allow detection of a single member link [RFC7130], BFD also did not allow detection of a single member link
failure on a LAG, which would limit's it's usefulness in some failure on a LAG, which would have limited it's usefulness in some
designs. designs.
7.2. Event Propagation Timing 7.2. Event Propagation Timing
In this design the impact of BGP Minimum Route Advertisement Interval In the proposed design the impact of BGP Minimum Route Advertisement
(MRAI) timer (See section 9.2.1.1 of [RFC4271]) should be considered. Interval (MRAI) timer (See section 9.2.1.1 of [RFC4271]) should be
Per the standard it is required for BGP implementations to space out considered. Per the standard it is required for BGP implementations
consecutive BGP UPDATE messages by at least MRAI seconds, which is to space out consecutive BGP UPDATE messages by at least MRAI
often a configurable value. The initial BGP UPDATE messages after an seconds, which is often a configurable value. The initial BGP UPDATE
event carrying withdrawn routes are commonly not affected by this messages after an event carrying withdrawn routes are commonly not
timer. The MRAI timer may present significant convergence delays affected by this timer. The MRAI timer may present significant
when a BGP speaker "waits" for the new path to be learned from its convergence delays when a BGP speaker "waits" for the new path to be
peers and has no local backup path information. learned from its peers and has no local backup path information.
In a Clos topology each EBGP speaker has either one path or N paths In a Clos topology each EBGP speaker has either one path or N paths
for the same prefix, where N is a significantly large number, e.g. for the same prefix, where N is a significantly large number, e.g.
N=32 (the ECMP fan-out). Therefore, if a path fails there is either N=32 (the ECMP fan-out). Therefore, if a path fails there is either
no backup path at all, or the backup is readily available in BGP Loc- no backup path at all (e.g. from perspective of a Tier-2 switch
RIB. In the former case, the BGP withdrawal announcement will losing link to a Tier-3 device), or the backup is readily available
propagate un-delayed and trigger re-convergence on affected devices. in BGP Loc-RIB (e.g. from perspective of a Tier-2 device losing link
In the latter case, the best-path will be re-evaluated and the local to a Tier-1 switch). In the former case, the BGP withdrawal
ECMP group corresponding to the new next-hop set changed. If the BGP announcement will propagate un-delayed and trigger re-convergence on
path was the best-path selected previously, an "implicit withdraw" affected devices. In the latter case, the best-path will be re-
will be sent via a BGP UPDATE message as described as option b in evaluated and the local ECMP group corresponding to the new next-hop
Section 3.1 of [RFC4271] due to the BGP AS_PATH attribute changing. set changed. If the BGP path was the best-path selected previously,
an "implicit withdraw" will be sent via a BGP UPDATE message as
described as Option b in Section 3.1 of [RFC4271] due to the BGP
AS_PATH attribute changing.
7.3. Impact of Clos Topology Fan-outs 7.3. Impact of Clos Topology Fan-outs
Clos topology has large fan-outs, which may impact the "Up->Down" Clos topology has large fan-outs, which may impact the "Up->Down"
convergence in some cases, as described in this section. In a convergence in some cases, as described in this section. In a
situation when a link between Tier-3 and Tier-2 device fails, the situation when a link between Tier-3 and Tier-2 device fails, the
Tier-2 device will send BGP WITHDRAW message to all upstream Tier-1 Tier-2 device will send BGP UPDATE messages to all upstream Tier-1
devices, and Tier-1 devices will relay this message to all downstream devices, withdrawing the affected prefixes. The Tier-1 devices, in
Tier-2 devices (except for the originator). Tier-2 devices other turn, will relay those messages to all downstream Tier-2 devices
than the one originating the WITHDRAW should then wait for ALL (except for the originator). Tier-2 devices other than the one
adjacent Tier-1 devices to send a WITHDRAW message before it removes originating the UPDATE should then wait for ALL upstream Tier-1
the affected prefixes and sends corresponding WITHDRAW downstream to devices to send an UPDATE message before removing the affected
connected Tier-3 devices. If the original Tier-2 device or the prefixes and sending corresponding UPDATE downstream to connected
relaying Tier-1 devices introduce some delay into their Tier-3 devices. If the original Tier-2 device or the relaying Tier-1
announcements, the result could be WITHDRAW message "dispersion", devices introduce some delay into their UPDATE message announcements,
that could be as long as multiple seconds. In order to avoid such the result could be UPDATE message "dispersion", that could be as
behavior, BGP implementations must support "update groups". The long as multiple seconds. In order to avoid such a behavior, BGP
"update group" is defined as a collection of neighbors sharing the implementations must support "update groups". The "update group" is
same outbound policy - the local speaker will send BGP updates to the defined as a collection of neighbors sharing the same outbound policy
members of the group synchronously. - the local speaker will send BGP updates to the members of the group
synchronously.
The impact of such "dispersion" grows with the size of topology fan- The impact of such "dispersion" grows with the size of topology fan-
out and could also grow under network convergence churn. Some out and could also grow under network convergence churn. Some
operators may be tempted to introduce "route flap dampening" type operators may be tempted to introduce "route flap dampening" type
features that vendors include to reduce the control plane impact of features that vendors include to reduce the control plane impact of
rapidly flapping prefixes, however due to issues described with false rapidly flapping prefixes. However, due to issues described with
positives in these implementations especially under such "dispersion" false positives in these implementations especially under such
events, it is not recommended to turn this feature on in this design. "dispersion" events, it is not recommended to turn this feature on in
More background and issues with "route flap dampening" and possible this design. More background and issues with "route flap dampening"
implementation changes that could change this are well described in and possible implementation changes that could affect this are well
[RFC7196]. described in [RFC7196].
7.4. Failure Impact Scope 7.4. Failure Impact Scope
A network is declared to converge in response to a failure once all A network is declared to converge in response to a failure once all
devices within the failure impact scope are notified of the event and devices within the failure impact scope are notified of the event and
have re-calculated their RIB's and consequently updated their FIB's. have re-calculated their RIB's and consequently updated their FIB's.
Larger failure impact scope typically means slower convergence since Larger failure impact scope typically means slower convergence since
more devices have to be notified, and additionally results in a less more devices have to be notified, and additionally results in a less
stable network. In this section we describe BGP's advantages over stable network. In this section we describe BGP's advantages over
link-state routing protocols in reducing failure impact scope for a link-state routing protocols in reducing failure impact scope for a
skipping to change at page 25, line 22 skipping to change at page 25, line 26
Even though in case of such failures multiple IP prefixes will have Even though in case of such failures multiple IP prefixes will have
to be reprogrammed in the FIB, it is worth noting that ALL of these to be reprogrammed in the FIB, it is worth noting that ALL of these
prefixes share a single ECMP group on Tier-2 device. Therefore, in prefixes share a single ECMP group on Tier-2 device. Therefore, in
the case of implementations with a hierarchical FIB, only a single the case of implementations with a hierarchical FIB, only a single
change has to be made to the FIB. Hierarchical FIB here means FIB change has to be made to the FIB. Hierarchical FIB here means FIB
structure where the next-hop forwarding information is stored structure where the next-hop forwarding information is stored
separately from the prefix lookup table, and the latter only store separately from the prefix lookup table, and the latter only store
pointers to the respective forwarding information. pointers to the respective forwarding information.
Even though BGP offers some failure scope reduction, reduction of the Even though BGP offers reduced failure scope for some cases, further
fault domain using summarization is not always possible with the reduction of the fault domain using summarization is not always
proposed design, since using this technique may create routing black- possible with the proposed design, since using this technique may
holes as mentioned previously. Therefore, the worst control plane create routing black-holes as mentioned previously. Therefore, the
failure impact scope is the network as a whole, for instance in a worst control plane failure impact scope is the network as a whole,
case of a link failure between Tier-2 and Tier-3 devices. The amount for instance in a case of a link failure between Tier-2 and Tier-3
of impacted prefixes in this case would be much less than in the case devices. The amount of impacted prefixes in this case would be much
of a failure in the upper layers of a Clos network topology. The less than in the case of a failure in the upper layers of a Clos
property of having such large failure scope is not a result of network topology. The property of having such large failure scope is
choosing EBGP in the design but rather a result of using the "scale- not a result of choosing EBGP in the design but rather a result of
out" Clos topology. using the "scale-out" Clos topology.
7.5. Routing Micro-Loops 7.5. Routing Micro-Loops
When a downstream device, e.g. Tier-2 device, loses all paths for a When a downstream device, e.g. Tier-2 device, loses all paths for a
prefix, it normally has the default route pointing toward the prefix, it normally has the default route pointing toward the
upstream device, in this case the Tier-1 device. As a result, it is upstream device, in this case the Tier-1 device. As a result, it is
possible to get in the situation when Tier-2 switch loses a prefix, possible to get in the situation when Tier-2 switch loses a prefix,
but Tier-1 switch still has the path pointing to the Tier-2 device, but Tier-1 switch still has the path pointing to the Tier-2 device,
which results in transient micro-loop, since Tier-1 switch will keep which results in transient micro-loop, since Tier-1 switch will keep
passing packets to the affected prefix back to Tier-2 device, and passing packets to the affected prefix back to Tier-2 device, and
Tier-2 will bounce it back again using the default route. This Tier-2 will bounce it back again using the default route. This
micro-loop will last for the duration of time it takes the upstream micro-loop will last for the duration of time it takes the upstream
device to fully update its forwarding tables. device to fully update its forwarding tables.
To minimize impact of the micro-loops, Tier-2 and Tier-1 switches can To minimize impact of the micro-loops, Tier-2 and Tier-1 switches can
be configured with static "discard" or "null" routes that will be be configured with static "discard" or "null" routes that will be
more specific than the default route for specific prefixes missing more specific than the default route for prefixes missing during
during network convergence. For Tier-2 switches, the discard route network convergence. For Tier-2 switches, the discard route should
should be a summary route, covering all server subnets of the be a summary route, covering all server subnets of the underlying
underlying Tier-3 devices. For Tier-1 devices, the discard route Tier-3 devices. For Tier-1 devices, the discard route should be a
should be a summary covering the server IP address subnet allocated summary covering the server IP address subnet allocated for the whole
for the whole data center. Those discard routes will only take data center. Those discard routes will only take precedence for the
precedence for the duration of network convergence, until the device duration of network convergence, until the device learns a more
learns a more specific prefix via a new path. specific prefix via a new path.
8. Additional Options for Design 8. Additional Options for Design
8.1. Third-party Route Injection 8.1. Third-party Route Injection
BGP allows for a "third-party", i.e. directly attached, BGP speaker BGP allows for a "third-party", i.e. directly attached, BGP speaker
to inject routes anywhere in the network topology, meeting REQ5. to inject routes anywhere in the network topology, meeting REQ5.
This can be achieved by peering via a multihop BGP session with some This can be achieved by peering via a multihop BGP session with some
or even all devices in the topology. Furthermore, BGP diverse path or even all devices in the topology. Furthermore, BGP diverse path
distribution [RFC6774] could be used to inject multiple BGP next hops distribution [RFC6774] could be used to inject multiple BGP next hops
for the same prefix to facilitate load balancing, or using the BGP for the same prefix to facilitate load balancing, or using the BGP
ADD-PATH capability [I-D.ietf-idr-add-paths] if supported by the ADD-PATH capability [I-D.ietf-idr-add-paths] if supported by the
implementation. Unfortunately, in many implementations ADD-PATH has implementation. Unfortunately, in many implementations ADD-PATH has
been found to only support IBGP properly due to the use cases it was been found to only support IBGP properly due to the use cases it was
originally optimized for, which limits the "third-party" peering to originally optimized for, which limits the "third-party" peering to
iBGP only, if the feature is used. iBGP only, if the feature is used.
To implement route injection in the proposed design a third-party BGP To implement route injection in the proposed design, a third-party
speaker may peer with Tier-3 and Tier-1 switches, injecting the same BGP speaker may peer with Tier-3 and Tier-1 switches, injecting the
prefix, but using a special set of BGP next-hops for Tier-1 devices. same prefix, but using a special set of BGP next-hops for Tier-1
Those next-hops are assumed to resolve recursively via BGP, and could devices. Those next-hops are assumed to resolve recursively via BGP,
be, for example, IP addresses on Tier-3 devices. The resulting and could be, for example, IP addresses on Tier-3 devices. The
forwarding table programming could provide desired traffic proportion resulting forwarding table programming could provide desired traffic
distribution among different clusters. proportion distribution among different clusters.
8.2. Route Summarization within Clos Topology 8.2. Route Summarization within Clos Topology
As mentioned previously, route summarization is not possible within As mentioned previously, route summarization is not possible within
the proposed Clos topology since it makes the network susceptible to the proposed Clos topology since it makes the network susceptible to
route black-holing under single link failures. The main problem is route black-holing under single link failures. The main problem is
the limited number of parallel paths between network elements, e.g. the limited number of redundant paths between network elements, e.g.
there is only a single path between any pair of Tier-1 and Tier-3 there is only a single path between any pair of Tier-1 and Tier-3
devices. However, some operators may find route aggregation devices. However, some operators may find route aggregation
desirable to improve control plane stability. desirable to improve control plane stability.
If planning on using any technique to summarize within the topology If planning on using any technique to summarize within the topology
modeling of the routing behavior and potential for black-holing modeling of the routing behavior and potential for black-holing
should be done not only for single or multiple link failures, but should be done not only for single or multiple link failures, but
also fiber pathway failures or optical domain failures if the also fiber pathway failures or optical domain failures if the
topology extends beyond a physical location. Simple modeling can be topology extends beyond a physical location. Simple modeling can be
done by checking the reachability on devices doing summarization done by checking the reachability on devices doing summarization
skipping to change at page 27, line 48 skipping to change at page 28, line 4
| A | | B | Tier-3 Tier-3 | | | | | A | | B | Tier-3 Tier-3 | | | |
+-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+
| | | | | | | | | | | | | | | |
O O O O <- Servers -> O O O O O O O O <- Servers -> O O O O
Figure 6: 5-Stage Clos topology Figure 6: 5-Stage Clos topology
Having this design in place, Tier-2 devices may be configured to Having this design in place, Tier-2 devices may be configured to
advertise only a default route down to Tier-3 devices. If a link advertise only a default route down to Tier-3 devices. If a link
between Tier-2 and Tier-3 fails, the traffic will be re-routed via between Tier-2 and Tier-3 fails, the traffic will be re-routed via
the second available path known to a Tier-2 switch. It is not the second available path known to a Tier-2 switch. It is still not
possible to advertise a summary route covering prefixes for a single possible to advertise a summary route covering prefixes for a single
cluster from Tier-2 devices since each of them has only a single path cluster from Tier-2 devices since each of them has only a single path
down to this prefix. It would require dual-homed servers to down to this prefix. It would require dual-homed servers to
accomplish that. Also note that this design is only resilient to accomplish that. Also note that this design is only resilient to
single link failure. It is possible for a double link failure to single link failure. It is possible for a double link failure to
isolate a Tier-2 device from all paths toward a specific Tier-3 isolate a Tier-2 device from all paths toward a specific Tier-3
device, thus causing a routing black-hole. device, thus causing a routing black-hole.
A result of the proposed topology modification would be reduction of A result of the proposed topology modification would be reduction of
Tier-1 devices port capacity. This limits the maximum number of Tier-1 devices port capacity. This limits the maximum number of
skipping to change at page 29, line 33 skipping to change at page 29, line 38
Another option is to make the network device perform IP address Another option is to make the network device perform IP address
masquerading, that is rewriting the source IP addresses of the masquerading, that is rewriting the source IP addresses of the
appropriate ICMP messages sent off of the device with the "primary" appropriate ICMP messages sent off of the device with the "primary"
IP address of the device. Specifically, the ICMP Destination IP address of the device. Specifically, the ICMP Destination
Unreachable Message (type 3) codes 3 (port unreachable) and ICMP Time Unreachable Message (type 3) codes 3 (port unreachable) and ICMP Time
Exceeded (type 11) code 0, which are involved in proper working of Exceeded (type 11) code 0, which are involved in proper working of
the "traceroute" tool. With this modification, the "traceroute" the "traceroute" tool. With this modification, the "traceroute"
probes sent to the devices will always be sent back with the probes sent to the devices will always be sent back with the
"primary" IP address as the source, allowing the operator to discover "primary" IP address as the source, allowing the operator to discover
the "reachable" IP address of the box. the "reachable" IP address of the box. This has the downside of
hiding the address of the "entry point" into the device.
9. Security Considerations 9. Security Considerations
The design does not introduce any additional security concerns. The design does not introduce any additional security concerns.
General BGP security considerations are discussed in [RFC4271] and General BGP security considerations are discussed in [RFC4271] and
[RFC4272]. Furthermore, the Generalized TTL Security Mechanism [RFC4272]. Furthermore, the Generalized TTL Security Mechanism
[RFC5082] could be used to reduce the risk of BGP session spoofing. [RFC5082] could be used to reduce the risk of BGP session spoofing.
10. IANA Considerations 10. IANA Considerations
skipping to change at page 30, line 11 skipping to change at page 30, line 19
of whom were George Chen, Parantap Lahiri, Dave Maltz, Edet Nkposong, of whom were George Chen, Parantap Lahiri, Dave Maltz, Edet Nkposong,
Robert Toomey, and Lihua Yuan. Authors would also like to thank Robert Toomey, and Lihua Yuan. Authors would also like to thank
Linda Dunbar, Susan Hares, Danny McPherson, Russ White and Robert Linda Dunbar, Susan Hares, Danny McPherson, Russ White and Robert
Raszuk for reviewing the document and providing valuable feedback and Raszuk for reviewing the document and providing valuable feedback and
Mary Mitchell for grammar and style suggestions. Mary Mitchell for grammar and style suggestions.
12. References 12. References
12.1. Normative References 12.1. Normative References
[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>.
[RFC6996] Mitchell, J., "Autonomous System (AS) Reservation for [RFC6996] Mitchell, J., "Autonomous System (AS) Reservation for
Private Use", BCP 6, RFC 6996, July 2013. Private Use", BCP 6, RFC 6996, DOI 10.17487/RFC6996, July
2013, <http://www.rfc-editor.org/info/rfc6996>.
12.2. Informative References 12.2. Informative References
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998. [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998,
<http://www.rfc-editor.org/info/rfc2328>.
[RFC2992] Hopps, C., "Analysis of an Equal-Cost Multi-Path [RFC2992] Hopps, C., "Analysis of an Equal-Cost Multi-Path
Algorithm", RFC 2992, November 2000. Algorithm", RFC 2992, DOI 10.17487/RFC2992, November 2000,
<http://www.rfc-editor.org/info/rfc2992>.
[RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis", RFC [RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis",
4272, January 2006. RFC 4272, DOI 10.17487/RFC4272, January 2006,
<http://www.rfc-editor.org/info/rfc4272>.
[RFC4277] McPherson, D. and K. Patel, "Experience with the BGP-4 [RFC4277] McPherson, D. and K. Patel, "Experience with the BGP-4
Protocol", RFC 4277, January 2006. Protocol", RFC 4277, DOI 10.17487/RFC4277, January 2006,
<http://www.rfc-editor.org/info/rfc4277>.
[RFC4786] Abley, J. and K. Lindqvist, "Operation of Anycast [RFC4786] Abley, J. and K. Lindqvist, "Operation of Anycast
Services", BCP 126, RFC 4786, December 2006. Services", BCP 126, RFC 4786, DOI 10.17487/RFC4786,
December 2006, <http://www.rfc-editor.org/info/rfc4786>.
[RFC5082] Gill, V., Heasley, J., Meyer, D., Savola, P., and C. [RFC5082] Gill, V., Heasley, J., Meyer, D., Savola, P., Ed., and C.
Pignataro, "The Generalized TTL Security Mechanism Pignataro, "The Generalized TTL Security Mechanism
(GTSM)", RFC 5082, October 2007. (GTSM)", RFC 5082, DOI 10.17487/RFC5082, October 2007,
<http://www.rfc-editor.org/info/rfc5082>.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, June 2010. (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
<http://www.rfc-editor.org/info/rfc5880>.
[RFC6325] Perlman, R., Eastlake, D., Dutt, D., Gai, S., and A. [RFC6325] Perlman, R., Eastlake 3rd, D., Dutt, D., Gai, S., and A.
Ghanwani, "Routing Bridges (RBridges): Base Protocol Ghanwani, "Routing Bridges (RBridges): Base Protocol
Specification", RFC 6325, July 2011. Specification", RFC 6325, DOI 10.17487/RFC6325, July 2011,
<http://www.rfc-editor.org/info/rfc6325>.
[RFC6769] Raszuk, R., Heitz, J., Lo, A., Zhang, L., and X. Xu, [RFC6769] Raszuk, R., Heitz, J., Lo, A., Zhang, L., and X. Xu,
"Simple Virtual Aggregation (S-VA)", RFC 6769, October "Simple Virtual Aggregation (S-VA)", RFC 6769,
2012. DOI 10.17487/RFC6769, October 2012,
<http://www.rfc-editor.org/info/rfc6769>.
[RFC6774] Raszuk, R., Fernando, R., Patel, K., McPherson, D., and K. [RFC6774] Raszuk, R., Ed., Fernando, R., Patel, K., McPherson, D.,
Kumaki, "Distribution of Diverse BGP Paths", RFC 6774, and K. Kumaki, "Distribution of Diverse BGP Paths",
November 2012. RFC 6774, DOI 10.17487/RFC6774, November 2012,
<http://www.rfc-editor.org/info/rfc6774>.
[RFC6793] Vohra, Q. and E. Chen, "BGP Support for Four-Octet [RFC6793] Vohra, Q. and E. Chen, "BGP Support for Four-Octet
Autonomous System (AS) Number Space", RFC 6793, December Autonomous System (AS) Number Space", RFC 6793,
2012. DOI 10.17487/RFC6793, December 2012,
<http://www.rfc-editor.org/info/rfc6793>.
[RFC7130] Bhatia, M., Chen, M., Boutros, S., Binderberger, M., and [RFC7130] Bhatia, M., Ed., Chen, M., Ed., Boutros, S., Ed.,
J. Haas, "Bidirectional Forwarding Detection (BFD) on Link Binderberger, M., Ed., and J. Haas, Ed., "Bidirectional
Aggregation Group (LAG) Interfaces", RFC 7130, February Forwarding Detection (BFD) on Link Aggregation Group (LAG)
2014. Interfaces", RFC 7130, DOI 10.17487/RFC7130, February
2014, <http://www.rfc-editor.org/info/rfc7130>.
[RFC7196] Pelsser, C., Bush, R., Patel, K., Mohapatra, P., and O. [RFC7196] Pelsser, C., Bush, R., Patel, K., Mohapatra, P., and O.
Maennel, "Making Route Flap Damping Usable", RFC 7196, May Maennel, "Making Route Flap Damping Usable", RFC 7196,
2014. DOI 10.17487/RFC7196, May 2014,
<http://www.rfc-editor.org/info/rfc7196>.
[I-D.ietf-idr-add-paths] [I-D.ietf-idr-add-paths]
Walton, D., Retana, A., Chen, E., and J. Scudder, Walton, D., Retana, A., Chen, E., and J. Scudder,
"Advertisement of Multiple Paths in BGP", draft-ietf-idr- "Advertisement of Multiple Paths in BGP", draft-ietf-idr-
add-paths-10 (work in progress), October 2014. add-paths-10 (work in progress), October 2014.
[I-D.ietf-idr-link-bandwidth] [I-D.ietf-idr-link-bandwidth]
Mohapatra, P. and R. Fernando, "BGP Link Bandwidth Mohapatra, P. and R. Fernando, "BGP Link Bandwidth
Extended Community", draft-ietf-idr-link-bandwidth-06 Extended Community", draft-ietf-idr-link-bandwidth-06
(work in progress), January 2013. (work in progress), January 2013.
[CLOS1953] [CLOS1953]
Clos, C., "A Study of Non-Blocking Switching Networks: Clos, C., "A Study of Non-Blocking Switching Networks:
Bell System Technical Journal Vol. 32(2)", March 1953. Bell System Technical Journal Vol. 32(2)", March 1953.
[HADOOP] Apache, , "Apache HaDoop", June 2015, [HADOOP] Apache, , "Apache HaDoop", July 2015,
<https://hadoop.apache.org/>. <https://hadoop.apache.org/>.
[GREENBERG2009] [GREENBERG2009]
Greenberg, A., Hamilton, J., and D. Maltz, "The Cost of a Greenberg, A., Hamilton, J., and D. Maltz, "The Cost of a
Cloud: Research Problems in Data Center Networks", January Cloud: Research Problems in Data Center Networks", January
2009. 2009.
[IEEE8021D-1990] [IEEE8021D-1990]
IEEE 802.1D, , "IEEE Standard for Local and Metropolitan IEEE 802.1D, , "IEEE Standard for Local and Metropolitan
Area Networks--Media access control (MAC) Bridges", May Area Networks--Media access control (MAC) Bridges", May
skipping to change at page 32, line 19 skipping to change at page 32, line 46
[INTERCON] [INTERCON]
Dally, W. and B. Towles, "Principles and Practices of Dally, W. and B. Towles, "Principles and Practices of
Interconnection Networks", ISBN 978-0122007514, January Interconnection Networks", ISBN 978-0122007514, January
2004. 2004.
[ALFARES2008] [ALFARES2008]
Al-Fares, M., Loukissas, A., and A. Vahdat, "A Scalable, Al-Fares, M., Loukissas, A., and A. Vahdat, "A Scalable,
Commodity Data Center Network Architecture", August 2008. Commodity Data Center Network Architecture", August 2008.
[IANA.AS] IANA, , "Autonomous System (AS) Numbers", June 2015, [IANA.AS] IANA, , "Autonomous System (AS) Numbers", July 2015,
<http://www.iana.org/assignments/as-numbers/>. <http://www.iana.org/assignments/as-numbers/>.
[IEEE8023AD] [IEEE8023AD]
IEEE 802.3ad, , "IEEE Standard for Link aggregation for IEEE 802.3ad, , "IEEE Standard for Link aggregation for
parallel links", October 2000. parallel links", October 2000.
[ALLOWASIN] [ALLOWASIN]
Cisco Systems, , "Allowas-in Feature in BGP Configuration Cisco Systems, , "Allowas-in Feature in BGP Configuration
Example", February 2015, Example", February 2015,
<http://www.cisco.com/c/en/us/support/docs/ip/border- <http://www.cisco.com/c/en/us/support/docs/ip/border-
skipping to change at page 33, line 29 skipping to change at page 34, line 14
Ariff Premji Ariff Premji
Arista Networks Arista Networks
5453 Great America Parkway 5453 Great America Parkway
Santa Clara, CA 95054 Santa Clara, CA 95054
US US
Email: ariff@arista.com Email: ariff@arista.com
URI: http://arista.com/ URI: http://arista.com/
Jon Mitchell (editor) Jon Mitchell (editor)
Google
1600 Amphitheatre Parkway
Mountain View, CA 94043
US
Email: jrmitche@puck.nether.net Email: jrmitche@puck.nether.net
 End of changes. 54 change blocks. 
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