draft-ietf-lsvr-applicability-01.txt   draft-ietf-lsvr-applicability-02.txt 
LSVR K. Patel LSVR K. Patel
Internet-Draft Arrcus, Inc. Internet-Draft Arrcus, Inc.
Intended status: Informational A. Lindem Intended status: Informational A. Lindem
Expires: April 25, 2019 Cisco Systems Expires: November 2, 2019 Cisco Systems
S. Zandi S. Zandi
G. Dawra G. Dawra
Linkedin Linkedin
October 22, 2018 May 1, 2019
Usage and Applicability of Link State Vector Routing in Data Centers Usage and Applicability of Link State Vector Routing in Data Centers
draft-ietf-lsvr-applicability-01.txt draft-ietf-lsvr-applicability-02.txt
Abstract Abstract
This document discusses the usage and applicability of Link State This document discusses the usage and applicability of Link State
Vector Routing (LSVR) extensions in the CLOS architecture of Data Vector Routing (LSVR) extensions in data center networks utilizing
Center Networks. The document is intended to provide a simplified CLOS or Fat-Tree topologies. The document is intended to provide a
guide for the deployment of LSVR extensions. simplified guide for the deployment of LSVR extensions.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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 April 25, 2019. This Internet-Draft will expire on November 2, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Recommended Reading . . . . . . . . . . . . . . . . . . . . . 3 3. Recommended Reading . . . . . . . . . . . . . . . . . . . . . 3
4. Common Deployment Scenario . . . . . . . . . . . . . . . . . 3 4. Common Deployment Scenario . . . . . . . . . . . . . . . . . 3
5. Justification for BGP SPF Extension . . . . . . . . . . . . . 4 5. Justification for BGP SPF Extension . . . . . . . . . . . . . 4
6. LSVR Applicability to CLOS Networks . . . . . . . . . . . . . 5 6. LSVR Applicability to CLOS Networks . . . . . . . . . . . . . 5
6.1. Usage of BGP-LS SAFI . . . . . . . . . . . . . . . . . . 5 6.1. Usage of BGP-LS SPF SAFI . . . . . . . . . . . . . . . . 5
6.1.1. Relationship to Other BGP AFI/SAFI Tuples . . . . . . 6 6.1.1. Relationship to Other BGP AFI/SAFI Tuples . . . . . . 6
6.2. Peering Models . . . . . . . . . . . . . . . . . . . . . 6 6.2. Peering Models . . . . . . . . . . . . . . . . . . . . . 6
6.2.1. Sparse Peering Model . . . . . . . . . . . . . . . . 6 6.2.1. Sparse Peering Model . . . . . . . . . . . . . . . . 6
6.2.2. Bi-Connected Graph Heuristic . . . . . . . . . . . . 7 6.2.2. Bi-Connected Graph Heuristic . . . . . . . . . . . . 7
6.3. BGP Peer Discovery . . . . . . . . . . . . . . . . . . . 7 6.3. BGP Spine/Leaf Topology Policy . . . . . . . . . . . . . 7
6.3.1. BGP Peer Discovery Requirements . . . . . . . . . . . 7 6.4. BGP Peer Discovery Requirements . . . . . . . . . . . . . 8
6.3.2. BGP Peer Discovery Alternatives . . . . . . . . . . . 8 6.5. BGP Peer Discovery . . . . . . . . . . . . . . . . . . . 9
6.3.3. Data Center Interconnect (DCI) Applicability . . . . 8 6.5.1. BGP Peer Discovery Alternatives . . . . . . . . . . . 9
6.4. Non-CLOS/FAT Tree Topology Applicability . . . . . . . . 9 6.5.2. Data Center Interconnect (DCI) Applicability . . . . 9
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 6.6. Non-CLOS/FAT Tree Topology Applicability . . . . . . . . 10
8. Security Considerations . . . . . . . . . . . . . . . . . . . 9 7. BGP Policy Applicability . . . . . . . . . . . . . . . . . . 10
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 9. Security Considerations . . . . . . . . . . . . . . . . . . . 10
10.1. Normative References . . . . . . . . . . . . . . . . . . 9 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
10.2. Informative References . . . . . . . . . . . . . . . . . 10 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 11.1. Normative References . . . . . . . . . . . . . . . . . . 11
11.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction 1. Introduction
This document complements [I-D.ietf-lsvr-bgp-spf] by discussing the This document complements [I-D.ietf-lsvr-bgp-spf] by discussing the
applicability of the technology in a simple and fairly common applicability of the technology in a simple and fairly common
deployment scenario, which is described in Section 4. deployment scenario, which is described in Section 4.
After describing the deployment scenario, Section 5 will describe the After describing the deployment scenario, Section 5 will describe the
reasons for BGP modifications for such deployments. reasons for BGP modifications for such deployments.
skipping to change at page 3, line 23 skipping to change at page 3, line 23
3. Recommended Reading 3. Recommended Reading
This document assumes knowledge of existing data center networks and This document assumes knowledge of existing data center networks and
data center network topologies [CLOS]. This document also assumes data center network topologies [CLOS]. This document also assumes
knowledge of data center routing protocols like BGP [RFC4271], BGP- knowledge of data center routing protocols like BGP [RFC4271], BGP-
SPF [I-D.ietf-lsvr-bgp-spf], OSPF [RFC2328], as well as, data center SPF [I-D.ietf-lsvr-bgp-spf], OSPF [RFC2328], as well as, data center
OAM protocols like LLDP [RFC4957] and BFD [RFC5580]. OAM protocols like LLDP [RFC4957] and BFD [RFC5580].
4. Common Deployment Scenario 4. Common Deployment Scenario
Within a Data Center, a common network design to interconnect servers Within a Data Center, servers are commonly interconnected the CLOS
is done using the CLOS topology [CLOS]. The CLOS topology is fully topology [CLOS]. The CLOS topology is fully non-blocking and the
non-blocking and the topology is realized using Equal Cost Multipath topology is realized using Equal Cost Multi-Path (ECMP). In a CLOS
(ECMP). In a CLOS topology, the minimum number of parallel paths topology, the minimum number of parallel paths between two servers is
between two servers is determined by the width of a tier-1 stage as determined by the width of a tier-1 stage as shown in the figure 1.
shown in the figure 1.
The following example illustrates multistage CLOS topology. The following example illustrates multi-stage CLOS topology.
Tier-1 Tier-1
+-----+ +-----+
|NODE | |NODE |
+->| 12 |--+ +->| 12 |--+
| +-----+ | | +-----+ |
Tier-2 | | Tier-2 Tier-2 | | Tier-2
+-----+ | +-----+ | +-----+ +-----+ | +-----+ | +-----+
+------------>|NODE |--+->|NODE |--+--|NODE |-------------+ +------------>|NODE |--+->|NODE |--+--|NODE |-------------+
| +-----| 9 |--+ | 10 | +--| 11 |-----+ | | +-----| 9 |--+ | 10 | +--| 11 |-----+ |
skipping to change at page 4, line 33 skipping to change at page 4, line 33
| 1 | | 2 | | 3 | | 4 | | 5 | | 1 | | 2 | | 3 | | 4 | | 5 |
+-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ +-----+
| | | | | | | | | | | | | | | |
A O B O <- Servers -> Z O O O A O B O <- Servers -> Z O O O
Figure 1: Illustration of the basic CLOS Figure 1: Illustration of the basic CLOS
5. Justification for BGP SPF Extension 5. Justification for BGP SPF Extension
In order to simplify layer-3 routing and operations [RFC7938], many In order to simplify layer-3 routing and operations [RFC7938], many
data centers use BGP as a routing protocol to create an overlay as data centers use BGP as a routing protocol to create both an underlay
well as an underlay network for their CLOS Topologies. However, BGP and overlay network for their CLOS Topologies. However, BGP is a
is a path-vector routing protocol. Since it does not create a fabric path-vector routing protocol. Since it does not create a fabric
topology, it uses hop-by-hop EBGP peering to facilitate hop-by-hop topology, it uses hop-by-hop EBGP peering to facilitate hop-by-hop
routing to create the underlay network and to resolve any overlay routing to create the underlay network and to resolve any overlay
next hops. The hop-by-hop BGP peering paradigm imposes several next hops. The hop-by-hop BGP peering paradigm imposes several
restrictions within a CLOS. It severely prohibits a deployment of restrictions within a CLOS. It severely prohibits a deployment of
Route Reflectors/Route Controllers as the EBGP sessions are congruent Route Reflectors/Route Controllers as the EBGP sessions are congruent
with the data path. The BGP best path algorithm is prefix-based and with the data path. The BGP best-path algorithm is prefix-based and
it prevents announcements of prefixes to other BGP speakers until the it prevents announcements of prefixes to other BGP speakers until the
best path decision process is performed for the prefix at each best-path decision process has been performed for the prefix at each
intermediate hop. These restrictions significantly delay the overall intermediate hop. These restrictions significantly delay the overall
convergence of the underlay network within a CLOS. convergence of the underlay network within a CLOS network.
The LSVR SPF modifications allow BGP to overcome these limitations. The LSVR SPF modifications allow BGP to overcome these limitations.
Furthermore, using the BGP-LS NLRI format [RFC7752] allows the LSVR Furthermore, using the BGP-LS NLRI format [RFC7752] allows the LSVR
data to be advertised for nodes, links, and prefixes in the BGP data to be advertised for nodes, links, and prefixes in the BGP
routing domain and used for SPF computations. routing domain and used for SPF computations.
6. LSVR Applicability to CLOS Networks 6. LSVR Applicability to CLOS Networks
With the BGP SPF extensions [I-D.ietf-lsvr-bgp-spf], the BGP best With the BGP SPF extensions [I-D.ietf-lsvr-bgp-spf], the BGP best-
path computation and route computation are replaced with OSPF-like path computation and route computation are replaced with OSPF-like
algorithms [RFC2328] both to determine whether an BGP-LS NLRI has algorithms [RFC2328] both to determine whether an BGP-LS SPF NLRI has
changed and needs to be re-advertised and to compute the routing changed and needs to be re-advertised and to compute the BGP routes.
table. These modifications will significantly improve convergence of These modifications will significantly improve convergence of the
the underlay while affording the operational benefits of a single underlay while affording the operational benefits of a single routing
routing protocol [RFC7938]. protocol [RFC7938].
Data center controllers typically require visibility to the BGP Data center controllers typically require visibility to the BGP
topology to compute traffic-engineered paths. These controllers topology to compute traffic-engineered paths. These controllers
learn the topology and other relevant information via the BGP-LS learn the topology and other relevant information via the BGP-LS
address family [RFC7752] which is totally independent of the underlay address family [RFC7752] which is totally independent of the underlay
address families (usually IPv4/IPv6 unicast). Furthermore, in address families (usually IPv4/IPv6 unicast). Furthermore, in
traditional BGP underlays, all the BGP routers will need to advertise traditional BGP underlays, all the BGP routers will need to advertise
their BGP-LS information independently. With the BGP SPF extensions, their BGP-LS information independently. With the BGP SPF extensions,
controllers can learn the topology using the same BGP advertisements controllers can learn the topology using the same BGP advertisements
used to compute the underlay routes. Furthermore, these data center used to compute the underlay routes. Furthermore, these data center
controllers can avail the convergence advantages of the BGP SPF controllers can avail the convergence advantages of the BGP SPF
extensions. The placement of controllers can be outside of the extensions. The placement of controllers can be outside of the
forwarding path or within the forwarding path. forwarding path or within the forwarding path.
Alternatively, as each and every router in the BGP SPF domain will Alternatively, as each and every router in the BGP SPF domain will
have a complete view of the topology, the operator can also choose to have a complete view of the topology, the operator can also choose to
configure BGP sessions in hop-by-hop peering model described in configure BGP sessions in hop-by-hop peering model described in
[RFC7938] along with BFD [RFC5580]. In doing so, while the hop-by- [RFC7938] along with BFD [RFC5580]. In doing so, while the hop-by-
hop peering model lacks inherent benefits of the controller-based hop peering model lacks the inherent benefits of the controller-based
model, BGP updates need not be serialized by BGP best path algorithm model, BGP updates need not be serialized by BGP best-path algorithm
in either of these models. This helps overall network convergence. in either of these models. This helps overall network convergence.
6.1. Usage of BGP-LS SAFI 6.1. Usage of BGP-LS SPF SAFI
The BGP SPF extensions [I-D.ietf-lsvr-bgp-spf] define a new BGP-LS The BGP SPF extensions [I-D.ietf-lsvr-bgp-spf] define a new BGP-LS
SAFI for announcement of BGP SPF link-state. The NLRI format and its SPF SAFI for announcement of BGP SPF link-state. The NLRI format and
associated attributes follow the format of BGP-LS for node, link, and its associated attributes follow the format of BGP-LS for node, link,
prefix announcements. Whether the peering model within a CLOS and prefix announcements. Whether the peering model within a CLOS
follows hop-by-hop peering described in [RFC7938] or any controller- follows hop-by-hop peering described in [RFC7938] or any controller-
based or route-reflector peering, an operator can exchange BGP SPF based or route-reflector peering, an operator can exchange BGP SPF
SAFI routes over the BGP peering by simply configuring BGP SPF SAFI SAFI routes over the BGP peering by simply configuring BGP SPF SAFI
between the necessary BGP speakers. between the necessary BGP speakers.
The BGP-LS SPF SAFI can also co-exist with BGP IP Unicast SAFI which The BGP-LS SPF SAFI can also co-exist with BGP IP Unicast SAFI which
could exchange overlapping IP routes. The routes received by these could exchange overlapping IP routes. The routes received by these
SAFIs are evaluated, stored, and announced separately according to SAFIs are evaluated, stored, and announced independently according to
the rules of [RFC4760]. The tie-breaking of route installation is a the rules of [RFC4760]. The tie-breaking of route installation is a
matter of the local policies and preferences of the network operator. matter of the local policies and preferences of the network operator.
Finally, as the BGP SPF peering is done following the procedures Finally, as the BGP SPF peering is done following the procedures
described in [RFC4271], all the existing transport security described in [RFC4271], all the existing transport security
mechanisms including [RFC5925] are available for the BGP-LS SPF SAFI. mechanisms including [RFC5925] are available for the BGP-LS SPF SAFI.
6.1.1. Relationship to Other BGP AFI/SAFI Tuples 6.1.1. Relationship to Other BGP AFI/SAFI Tuples
Normally, the BGP-LS AFI/SAFI is used solely to compute the underlay Normally, the BGP-LS AFI/SAFI is used solely to compute the underlay
and is given preference over other AFI/SAFIs. Other BGP SAFIs, e.g., and is given preference over other AFI/SAFIs. Other BGP SAFIs, e.g.,
IPv6/IPv6 Unicast VPN would use the BGP-SPF computed routes for next IPv6/IPv6 Unicast VPN would use the BGP-SPF computed routes for next
hop resolution. However, if BGP-LS NLRI is also being advertised for hop resolution. However, if BGP-LS NLRI is also being advertised for
controller consumption, there is no need to replicate the Node, Link, controller consumption, there is no need to replicate the Node, Link,
and Prefix NLRI in BGP-NLRI. Rather, additional NLRI attributes can and Prefix NLRI in BGP-NLRI. Rather, additional NLRI attributes can
be advertised in the BGP-LS SPF AFI/SAFI as required. be advertised in the BGP-LS SPF AFI/SAFI as required.
6.2. Peering Models 6.2. Peering Models
As previously stated, BGP SPF can be deployed using the existing As previously stated, BGP SPF can be deployed using the existing
peering model where there is a single hop BGP session on each and peering model where there is a single-hop BGP session on each and
every link in the data center fabric [RFC7938]. This provides for every link in the data center fabric [RFC7938]. This provides for
both the advertisement of routes and the determination of link and both the advertisement of routes and the determination of link and
neighboring switch availability. With BGP SPF, the underlay will neighboring switch availability. With BGP SPF, the underlay will
converge faster due to changes in the decision process which will converge faster due to changes to the decision process that will
allow NLRI changes to be advertised faster after detecting a change. allow NLRI changes to be advertised faster after detecting a change.
6.2.1. Sparse Peering Model 6.2.1. Sparse Peering Model
Alternately, BFD [RFC5580] can be used to swiftly determine the Alternately, BFD [RFC5580] can be used to swiftly determine the
availability of links and the BGP peering model can be significantly availability of links and the BGP peering model can be significantly
sparser than the data center fabric. BGP SPF sessions then only be sparser than the data center fabric. BGP SPF sessions only need to
established with enough peers to provide a bi-connected graph. If be established with enough peers to provide a bi-connected graph. If
IEBGP is used, then the BGP routers at tier N-1 will act as route- IEBGP is used, then the BGP routers at tier N-1 will act as route-
reflectors for the routers at tier N. reflectors for the routers at tier N.
The obvious usage of sparse peering is to avoid parallel sessions The obvious usage of sparse peering is to avoid parallel sessions on
between the same two BGP speakers in the data center fabric. links between the same two BGP speakers in the data center fabric.
However, this use case is not very useful since parallel layer-3 However, this use case is not very useful since parallel layer-3
links between the same two BGP routers are rare in CLOS or Fat-Tree links between the same two BGP routers are rare in CLOS or Fat-Tree
topologies. Two more interesting scenarios are described below. topologies. Two more interesting scenarios are described below.
In current Data Center topologies, there is often a very dense mesh In current data center topologies, there is often a very dense mesh
of links between levels, e.g., leaf and spine, providing 32-way, of links between levels, e.g., leaf and spine, providing 32-way,
64-way, or more Equal-Cost Multi-Path (ECMP) paths. In these 64-way, or more Equal-Cost Multi-Path (ECMP) paths. In these
topologies, it is desirable not to have a BGP session on every link topologies, it is desirable not to have a BGP session on every link
and techniques such as the one described below Section 6.2.2 can be and techniques such as the one described in Section 6.2.2 can be used
used establish sessions on some subset of northbound links. establish sessions on some subset of northbound links.
Alternately, controller-based data center topologies are envisioned Alternately, controller-based data center topologies are envisioned
where BGP speakers within the data center only establish BGP sessions where BGP speakers within the data center only establish BGP sessions
with two or more controllers. In these topologies, fabric nodes with two or more controllers. In these topologies, fabric nodes
below the first tier (using [RFC7938] hierarchy) will establish BGP below the first tier (using [RFC7938] hierarchy) will establish BGP
multi-hop sessions with the controllers. For the multi-hop sessions, multi-hop sessions with the controllers. For the multi-hop sessions,
determining the route to the controllers without depending on BGP determining the route to the controllers without depending on BGP
would need to be through some other means beyond the scope of this would need to be through some other means beyond the scope of this
document. However, the BGP discovery mechanisms Section 6.3 would be document. However, the BGP discovery mechanisms described in
one possibility. Section 6.5 would be one possibility.
6.2.2. Bi-Connected Graph Heuristic 6.2.2. Bi-Connected Graph Heuristic
With this heuristic, discovery of BGP peers is assumed Section 6.3. With this heuristic, discovery of BGP peers is assumed, e.g., as
Additionally, it assumed that the direction of the peering can be described in Section 6.5. Additionally, it assumed that the
ascertained. In the context of a data center fabric, direction is direction of the peering can be ascertained. In the context of a
either northbound (toward the spine), southbound (toward the Top-Of- data center fabric, direction is either northbound (toward the
Rack (TOR) switches) or east-west (same level in hierarchy. The spine), southbound (toward the Top-Of-Rack (TOR) switches) or east-
determination of the direction is beyond the scope of this document. west (same level in hierarchy. The determination of the direction is
However, it would be reasonable to assume a technique where the TOR beyond the scope of this document. However, it would be reasonable
switches can be identified and the number of hops to the TOR is used to assume a technique where the TOR switches can be identified and
to determine the direction. the number of hops to the TOR is used to determine the direction.
In this heuristic, BGP speakers allow passive session establishment In this heuristic, BGP speakers allow passive session establishment
for southbound BGP sessions. For northbound sessions, BGP speakers for southbound BGP sessions. For northbound sessions, BGP speakers
will attempt to maintain two northbound BGP sessions with different will attempt to maintain two northbound BGP sessions with different
switches (in data center fabrics there is normally a single layer-3 switches (in data center fabrics there is normally a single layer-3
connection anyway). For east-west sessions, passive BGP session connection anyway). For east-west sessions, passive BGP session
establishment is allowed. However, BGP speaker will never actively establishment is allowed. However, BGP speaker will never actively
establish an east-west BGP session unless it can't establish two establish an east-west BGP session unless it can't establish two
northbound BGP sessions. northbound BGP sessions.
6.3. BGP Peer Discovery 6.3. BGP Spine/Leaf Topology Policy
6.3.1. BGP Peer Discovery Requirements One of the advantages of using BGP SPF as the underlay protocol is
that BGP policy can be applied at any level. In Spine/Leaf
topologies, it is not necessary to advertise BGP-LS NLRI received by
leaves northbound to the spine nodes at the level above. If a common
AS is used for the spine nodes, This can easily be accomplished with
EBGP and a simple policy to filter advertisements from the leaves to
the spine if the first AS in the AS path is the spine AS.
In the figure below, the leaves would not advertise any NLRI with AS
64512 as the first AS in the AS path.
+--------+ +--------+ +--------+
AS 64512 | | | | | |
for Spine | Spine1 +----+ Spine2 +- ......... -+ SpineN |
Nodes at | | | | | |
this Level +-+-+-+-++ ++-+-+-+-+ +-+-+-+-++
+------+ | | | | | | | | | | |
| +-----|-|-|------+ | | | | | | |
| | +--|-|-|--------+-|-|-----------------+ | | |
| | | | | | +---+ | | | | |
| | | | | | | +--|-|-------------------+ | |
| | | | | | | | | | +------+ +----+
| | | | | | | | | +--------------|----------+ |
| | | | | | | | +-------------+ | | |
| | | | | +----|--|----------------|--|--------+ | |
| | | | +------|--|--------------+ | | | | |
| | | +------+ | | | | | | | |
++--+--++ +-+-+--++ ++-+--+-+ ++-+--+-+
| Leaf1 |~~~~~~| Leaf2 | ........ | LeafX | | LeafY |
+-------+ +-------+ +-------+ +-------+
Figure 2: Spine/Leaf Topology Policy
6.4. BGP Peer Discovery Requirements
The most basic requirement is to be able to discover the address of a The most basic requirement is to be able to discover the address of a
single-hop peer without pre-configuration. This is being single-hop peer without pre-configuration. This is being
accomplished today with using IPv6 Router Advertisements (RA) accomplished today with using IPv6 Router Advertisements (RA)
[RFC4861] and assuming that a BGP sessions is desired with any [RFC4861] and assuming that a BGP sessions is desired with any
discovered peer. Beyond the basic requirement, it is useful to have discovered peer. Beyond the basic requirement, it is useful to have
to following information relating to the BGP session: to following information relating to the BGP session:
o Autonomous System (AS) and BGP Identifier of a potential peer. o Autonomous System (AS) and BGP Identifier of a potential peer.
The latter can be used for debugging and to decrease the The latter can be used for debugging and to decrease the
skipping to change at page 8, line 12 skipping to change at page 9, line 4
authentication, the security capabilities and possibly a key-chain authentication, the security capabilities and possibly a key-chain
[RFC8177] to be used. [RFC8177] to be used.
o Session Policy Identifier - A group number or name used to o Session Policy Identifier - A group number or name used to
associate common session parameters with the peer. For example, associate common session parameters with the peer. For example,
in a data center, BGP sessions with a Top of Rack (ToR) device in a data center, BGP sessions with a Top of Rack (ToR) device
could have parameters than BGP sessions between leaf and spine. could have parameters than BGP sessions between leaf and spine.
In a data center fabric, it is often useful to know whether a peer is In a data center fabric, it is often useful to know whether a peer is
southbound (towards the servers) or northbound (towards the spine or southbound (towards the servers) or northbound (towards the spine or
super-spine) Section 6.2.2. A potential requirement would also be to super-spine), e.g., Section 6.2.2. A potential requirement would be
determine this dynamically. One mechanism, without specifying all to determine this dynamically. One mechanism, without specifying all
the details, might be for the ToRs to be identified when installed the details, might be for the ToRs to be identified when installed
and for the others switches in the fabric to determine their level and for the others switches in the fabric to determine their level
based on the distance from the closest ToR. based on the distance from the closest ToR.
If there are multiple links between BGP speakers or the links between If there are multiple links between BGP speakers or the links between
BGP speakers are unnumbered, it is also useful to be able to BGP speakers are unnumbered, it is also useful to be able to
establish multi-hop sessions using the loopback addresses. This will establish multi-hop sessions using the loopback addresses. This will
often require the discovery protocol to install route(s) toward the often require the discovery protocol to install route(s) toward the
potential peer loopback addresses prior to BGP session establishment. potential peer loopback addresses prior to BGP session establishment.
Finally, a simple BGP discovery protocol could also be used to Finally, a simple BGP discovery protocol could also be used to
establish a multi-hop session with one or more controllers by establish a multi-hop session with one or more controllers by
advertising connectivity to one or more controllers. However, once advertising connectivity to one or more controllers. However, once
the multi-hop session actually traverses multiple nodes, it is the multi-hop session actually traverses multiple nodes, it is
bordering a distance-vector routing protocol and possibly this is not bordering a distance-vector routing protocol and possibly this is not
a good requirement for the discovery protocol. a good requirement for the discovery protocol.
6.3.2. BGP Peer Discovery Alternatives 6.5. BGP Peer Discovery
6.5.1. BGP Peer Discovery Alternatives
While BGP peer discovery is not part of [I-D.ietf-lsvr-bgp-spf], While BGP peer discovery is not part of [I-D.ietf-lsvr-bgp-spf],
there are, at least, three proposals for BGP peer discovery. At there are, at least, three proposals for BGP peer discovery. At
least one of these mechanisms will be adopted and will be applicable least one of these mechanisms will be adopted and will be applicable
to deployments other than the data center. It is strongly to deployments other than the data center. It is strongly
RECOMMENDED that the accepted mechanism be used in conjunction with RECOMMENDED that the accepted mechanism be used in conjunction with
BGP SPF in data centers. The BGP discovery mechanism should BGP SPF in data centers. The BGP discovery mechanism should
discovery both peer addresses and endpoints for BFD discovery. discovery both peer addresses and endpoints for BFD discovery.
Additionally, it would be great if there were a heuristic for Additionally, it would be great if there were a heuristic for
determining whether the peer is at a tier above or below the determining whether the peer is at a tier above or below the
discovering BGP speaker (refer to Section 6.2.2). discovering BGP speaker (refer to Section 6.2.2).
The BGP discovery mechanisms under consideration are The BGP discovery mechanisms under consideration are
[I-D.acee-idr-lldp-peer-discovery], [I-D.acee-idr-lldp-peer-discovery],
[I-D.xu-idr-neighbor-autodiscovery], and [I-D.ymbk-lsvr-lsoe]. [I-D.xu-idr-neighbor-autodiscovery], and [I-D.ietf-lsvr-l3dl].
6.3.3. Data Center Interconnect (DCI) Applicability 6.5.2. Data Center Interconnect (DCI) Applicability
Since BGP SPF is to be used for the routing underlay and DCI gateway Since BGP SPF is to be used for the routing underlay and DCI gateway
boxes typically have direct or very simple connectivity, BGP external boxes typically have direct or very simple connectivity, BGP external
sessions would typically not include the BGP SPF SAFI. sessions would typically not include the BGP SPF SAFI.
6.4. Non-CLOS/FAT Tree Topology Applicability 6.6. Non-CLOS/FAT Tree Topology Applicability
The BGP SPF extensions [I-D.ietf-lsvr-bgp-spf] can be used in other The BGP SPF extensions [I-D.ietf-lsvr-bgp-spf] can be used in other
topologies and avail the inherent convergence improvements. topologies and avail the inherent convergence improvements.
Additionally, sparse peering techniques may be utilized Section 6.2. Additionally, sparse peering techniques may be utilized Section 6.2.
However, determining whether or to establish a BGP session is more However, determining whether or to establish a BGP session is more
complex and the heuristic described in Section 6.2.2 cannot be used. complex and the heuristic described in Section 6.2.2 cannot be used.
In such topologies, other techniques such as those described in In such topologies, other techniques such as those described in
[I-D.li-lsr-dynamic-flooding] may be employed. One potential [I-D.ietf-lsr-dynamic-flooding] may be employed. One potential
deployment would be the underlay for a Service Provider (SP) backbone deployment would be the underlay for a Service Provider (SP) backbone
where usage of a single protocol, i.e., BGP, is desired. where usage of a single protocol, i.e., BGP, is desired.
7. IANA Considerations 7. BGP Policy Applicability
Existing BGP policy including aggregation and prefix filtering may be
used in conjunction with the BGP-LS SPF SAFI. When aggregation
policy is used, BGP-LS SPF prefix NLRI will be originated for the
aggregate prefix and BGP-LS SPF prefix NLRI for components will be
filtered. Additionally, link and node NLRI may be filtered and the
abstracted by the prefix NLRI.
When BGP policy is used with the BGP-LS SPF SAFI, BGP speakers in the
BGP-LS SPF routing domain will not all have the same set of NLRI and
will compute a different BGP local routing table. Consequently, care
must be taken to assure routing is consistent and blackholes or
routing loops do not ensue. However, this is no different than if
tradition BGP routing using the IPv4 and IPv6 address families were
used.
8. IANA Considerations
No IANA updates are requested by this document. No IANA updates are requested by this document.
8. Security Considerations 9. Security Considerations
This document introduces no new security considerations above and This document introduces no new security considerations above and
beyond those already specified in the [RFC4271] and beyond those already specified in the [RFC4271] and
[I-D.ietf-lsvr-bgp-spf]. [I-D.ietf-lsvr-bgp-spf].
9. Acknowledgements 10. Acknowledgements
The authors would like to thank Alvaro Retana and Yan Filyurin for The authors would like to thank Alvaro Retana and Yan Filyurin for
the review and comments. the review and comments.
10. References 11. References
10.1. Normative References 11.1. Normative References
[I-D.ietf-lsvr-bgp-spf] [I-D.ietf-lsvr-bgp-spf]
Patel, K., Lindem, A., Zandi, S., and W. Henderickx, Patel, K., Lindem, A., Zandi, S., and W. Henderickx,
"Shortest Path Routing Extensions for BGP Protocol", "Shortest Path Routing Extensions for BGP Protocol",
draft-ietf-lsvr-bgp-spf-03 (work in progress), September draft-ietf-lsvr-bgp-spf-04 (work in progress), December
2018. 2018.
[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, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, <https://www.rfc- DOI 10.17487/RFC2119, March 1997, <https://www.rfc-
editor.org/info/rfc2119>. editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
10.2. Informative References 11.2. Informative References
[CLOS] "A Study of Non-Blocking Switching Networks", The Bell [CLOS] "A Study of Non-Blocking Switching Networks", The Bell
System Technical Journal, Vol. 32(2), DOI System Technical Journal, Vol. 32(2), DOI
10.1002/j.1538-7305.1953.tb01433.x, March 1953. 10.1002/j.1538-7305.1953.tb01433.x, March 1953.
[I-D.acee-idr-lldp-peer-discovery] [I-D.acee-idr-lldp-peer-discovery]
Lindem, A., Patel, K., Zandi, S., Haas, J., and X. Xu, Lindem, A., Patel, K., Zandi, S., Haas, J., and X. Xu,
"BGP Logical Link Discovery Protocol (LLDP) Peer "BGP Logical Link Discovery Protocol (LLDP) Peer
Discovery", draft-acee-idr-lldp-peer-discovery-03 (work in Discovery", draft-acee-idr-lldp-peer-discovery-04 (work in
progress), June 2018. progress), December 2018.
[I-D.li-lsr-dynamic-flooding] [I-D.ietf-lsr-dynamic-flooding]
Li, T., Psenak, P., Ginsberg, L., Przygienda, T., and D. Li, T., Psenak, P., Ginsberg, L., Przygienda, T., Cooper,
Cooper, "Dynamic Flooding on Dense Graphs", draft-li-lsr- D., Jalil, L., and S. Dontula, "Dynamic Flooding on Dense
dynamic-flooding-01 (work in progress), October 2018. Graphs", draft-ietf-lsr-dynamic-flooding-00 (work in
progress), February 2019.
[I-D.ietf-lsvr-l3dl]
Bush, R., Austein, R., and K. Patel, "Layer 3 Discovery
and Liveness", draft-ietf-lsvr-l3dl-00 (work in progress),
April 2019.
[I-D.xu-idr-neighbor-autodiscovery] [I-D.xu-idr-neighbor-autodiscovery]
Xu, X., Talaulikar, K., Bi, K., Tantsura, J., and N. Xu, X., Talaulikar, K., Bi, K., Tantsura, J., and N.
Triantafillis, "BGP Neighbor Discovery", draft-xu-idr- Triantafillis, "BGP Neighbor Discovery", draft-xu-idr-
neighbor-autodiscovery-10 (work in progress), October neighbor-autodiscovery-11 (work in progress), April 2019.
2018.
[I-D.ymbk-lsvr-lsoe]
Bush, R. and K. Patel, "Link State Over Ethernet", draft-
ymbk-lsvr-lsoe-01 (work in progress), July 2018.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998, <https://www.rfc- DOI 10.17487/RFC2328, April 1998, <https://www.rfc-
editor.org/info/rfc2328>. editor.org/info/rfc2328>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271, Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006, <https://www.rfc- DOI 10.17487/RFC4271, January 2006, <https://www.rfc-
editor.org/info/rfc4271>. editor.org/info/rfc4271>.
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