Internet Engineering Task Force (IETF) H. Jeng

Internet Engineering Task Force (IETF) H. Jeng
Request for Comments: 7543 AT&T
Category: Standards Track L. Jalil
ISSN: 2070-1721 Verizon
R. Bonica
Juniper Networks
K. Patel
Cisco Systems
L. Yong
Huawei Technologies
May 2015

Covering Prefixes Outbound Route Filter for BGP-4

Abstract

This document defines a new Outbound Route Filter (ORF) type, called
the Covering Prefixes ORF (CP-ORF). CP-ORF is applicable in Virtual
Hub-and-Spoke VPNs. It also is applicable in BGP/MPLS Ethernet VPN
(EVPN) networks.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7543.

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RFC 7543 Covering Prefixes ORF May 2015

Copyright Notice

Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. CP-ORF Encoding . . . . . . . . . . . . . . . . . . . . . . . 4
3. Processing Rules . . . . . . . . . . . . . . . . . . . . . . 7
4. Applicability in Virtual Hub-and-Spoke VPNs . . . . . . . . . 10
4.1. Multicast Considerations . . . . . . . . . . . . . . . . 13
5. Applicability in BGP/MPLS Ethernet VPN (EVPN) . . . . . . . . 13
6. Clean-up . . . . . . . . . . . . . . . . . . . . . . . . . . 17
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
8. Security Considerations . . . . . . . . . . . . . . . . . . . 18
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
9.1. Normative References . . . . . . . . . . . . . . . . . . 18
9.2. Informative References . . . . . . . . . . . . . . . . . 19
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 20
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21

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1. Introduction

A BGP [RFC4271] speaker can send Outbound Route Filters (ORFs)
[RFC5291] to a peer. The peer uses ORFs to filter routing updates
that it sends to the BGP speaker. Using ORF, a BGP speaker can
realize a "route pull" paradigm in which the BGP speaker, on demand,
pulls certain routes from the peer.

This document defines a new ORF-type, called the Covering Prefixes
ORF (CP-ORF). A BGP speaker sends a CP-ORF to a peer in order to
pull routes that cover a specified host address. A prefix covers a
host address if it can be used to forward traffic towards that host
address. Section 3 provides a more complete description of covering
prefix selection criteria.

CP-ORF is applicable in Virtual Hub-and-Spoke VPNs [RFC7024]
[RFC4364]. It also is applicable BGP/MPLS Ethernet VPN (EVPN)
[RFC7432] networks.

1.1. Terminology

This document uses the following terms:

o Address Family Identifier (AFI) - defined in [RFC4760]

o Subsequent Address Family Identifier (SAFI) - defined in [RFC4760]

o Route Target (RT) - defined in [RFC4364]

o VPN-IP Default Route - defined in [RFC7024]

o Virtual Hub (V-hub) - defined in [RFC7024]

o Virtual Spoke (V-spoke) - defined in [RFC7024]

o BGP/MPLS Ethernet VPN (EVPN) - defined in [RFC7432]

o EVPN Instance (EVI) - defined in [RFC7432]

o MAC - Media Access Control

o Unknown MAC Route (UMR) - A regular EVPN MAC/IP Advertisement
route where the MAC Address Length is set to 48 and the MAC
address to 00:00:00:00:00:00

o Default MAC Gateway (DMG) - An EVPN Provider Edge (PE) that
advertises a UMR

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1.2. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].

2. CP-ORF Encoding

RFC 5291 augments the BGP ROUTE-REFRESH message so that it can carry
ORF entries. When the ROUTE-REFRESH message carries ORF entries, it
includes the following fields:

o AFI [IANA.AFI]

o SAFI [IANA.SAFI]

o When-to-refresh (IMMEDIATE or DEFERRED)

o ORF Type

o Length (of ORF entries)

The ROUTE-REFRESH message also contains a list of ORF entries. Each
ORF entry contains the following fields:

o Action (ADD, REMOVE, or REMOVE-ALL)

o Match (PERMIT or DENY)

The ORF entry may also contain Type-specific information. Type-
specific information is present only when the Action is equal to ADD
or REMOVE. It is not present when the Action is equal to REMOVE-ALL.

When the BGP ROUTE-REFRESH message carries CP-ORF entries, the
following conditions MUST be true:

o The ORF Type MUST be equal to CP-ORF (65).

o The AFI MUST be equal to IPv4, IPv6, or Layer 2 VPN (L2VPN).

o If the AFI is equal to IPv4 or IPv6, the SAFI MUST be equal to
MPLS-labeled VPN address.

o If the AFI is equal to L2VPN, the SAFI MUST be equal to BGP EVPN.

o The Match field MUST be equal to PERMIT.

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Figure 1 depicts the encoding of the CP-ORF Type-specific
information.

+--------------------------------+
| Sequence (32 bits) |
+--------------------------------+
| Minlen (8 bits) |
+--------------------------------+
| Maxlen (8 bits) |
+--------------------------------+
| VPN Route Target (64 bits) |
+--------------------------------+
| Import Route Target (64 bits) |
+--------------------------------+
| Route Type (8 bits) |
+--------------------------------+
| Host Address |
| (0, 32, 48, or 128 bits) |
| .... |
+--------------------------------+

Figure 1: CP-ORF Type-Specific Encoding

The CP-ORF recipient uses the following fields to select routes
matching the CP-ORF:

o Sequence: the relative position of a CP-ORF entry among other
CP-ORF entries

o Minlen: the minimum length of the selected route (measured in
bits)

o Maxlen: the maximum length of the selected route (measured in
bits)

o VPN Route Target: the VPN Route Target carried by the selected
route

o Route Type: the type of the selected route

o Host Address: the address covered by the selected route

See Section 3 for details.

The CP-ORF recipient marks routes that match CP-ORF with the Import
Route Target before advertising those routes to the CP-ORF
originator. See Section 3 for details.

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If the ROUTE-REFRESH AFI is equal to IPv4,

o the value of Minlen MUST be less than or equal to 32;

o the value of Maxlen MUST be less than or equal to 32;

o the value of Minlen MUST be less than or equal to the value of
Maxlen;

o the value of Route Type MUST be 0 (i.e., RESERVED); and

o the Host Address MUST contain exactly 32 bits.

If the ROUTE-REFRESH AFI is equal to IPv6,

o the value of Minlen MUST be less than or equal to 128;

o the value of Maxlen MUST be less than or equal to 128;

o the value of Minlen MUST be less than or equal to the value of
Maxlen;

o the value of Route Type MUST be 0 (i.e., RESERVED); and

o the Host Address MUST contain exactly 128 bits.

If the ROUTE-REFRESH AFI is equal to L2VPN, the value of Route Type
MUST be one of the following values taken from the IANA EVPN Registry
[IANA.EVPN]:

o 1 - Ethernet Autodiscovery Route

o 2 - MAC/IP Advertisement Route

o 3 - Inclusive Multicast Route

o 4 - Ethernet Segment

If the ROUTE-REFRESH AFI is equal to L2VPN and the value of Route
Type is equal to Ethernet Autodiscovery Route, Inclusive Multicast
Route, or Ethernet Segment,

o the value of Minlen MUST be equal to 0;

o the value of Maxlen MUST be equal to 0; and

o the Host Address MUST be absent (i.e., contain 0 bits).

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If the ROUTE-REFRESH AFI is equal to L2VPN and the value of Route
Type is equal to MAC/IP Advertisement Route,

o the value of Minlen MUST be less than or equal to 48;

o the value of Maxlen MUST be less than or equal to 48;

o the value of Minlen MUST be less than or equal to the value of
Maxlen; and

o the Host Address MUST contain exactly 48 bits.

3. Processing Rules

According to [RFC4271], every BGP speaker maintains a single Loc-RIB.
For each of its peers, the BGP speaker also maintains an Outbound
Filter and an Adj-RIB-Out. The Outbound Filter defines policy that
determines which Loc-RIB entries are processed into the corresponding
Adj-RIB-Out. Mechanisms such as RT-Constrain [RFC4684] and ORF
[RFC5291] enable a router's peer to influence the Outbound Filter.
Therefore, the Outbound Filter for a given peer is constructed using
a combination of the locally configured policy and the information
received via RT-Constrain and ORF from the peer.

Using this model, we can describe the operations of CP-ORF as
follows:

When a BGP speaker receives a ROUTE-REFRESH message that contains a
CP-ORF and that ROUTE-REFRESH message violates any of the encoding
rules specified in Section 2, the BGP speaker MUST ignore the entire
ROUTE-REFRESH message. It SHOULD also log the event. However, an
implementation MAY apply logging thresholds to avoid excessive
messaging or log file overflow.

Otherwise, the BGP speaker processes each CP-ORF entry as indicated
by the Action field. If the Action is equal to ADD, the BGP speaker
adds the CP-ORF entry to the Outbound Filter associated with the peer
in the position specified by the Sequence field. If the Action is
equal to REMOVE, the BGP speaker removes the CP-ORF entry from the
Outbound Filter. If the Action is equal to REMOVE-ALL, the BGP
speaker removes all CP-ORF entries from the Outbound Filter.

Whenever the BGP speaker applies an Outbound Filter to a route
contained in its Loc-RIB, it evaluates the route in terms of the
CP-ORF entries first. It then evaluates the route in terms of the
remaining non-CP-ORF entries. The rules for the former are described
below. The rules for the latter are outside the scope of this
document.

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The following route types can match a CP-ORF:

o IPv4-VPN

o IPv6-VPN

o L2VPN

In order for an IPv4-VPN route or IPv6-VPN route to match a CP-ORF,
all of the following conditions MUST be true:

o the route carries an RT whose value is the same as the CP-ORF VPN
Route Target;

o the route prefix length is greater than or equal to the CP-ORF
Minlen plus 64 (i.e., the length of a VPN Route Distinguisher);

o the route prefix length is less than or equal to the CP-ORF Maxlen
plus 64 (i.e., the length of a VPN Route Distinguisher);

o ignoring the Route Distinguisher, the leading bits of the route
prefix are identical to the leading bits of the CP-ORF Host
Address, and CP-ORF Minlen defines the number of bits that must be
identical; and

o Loc-RIB does not contain a more specific route that also satisfies
all of the above listed conditions.

The BGP speaker ignores Route Distinguishers when determining whether
a prefix matches a host address. For example, assume that a CP-ORF
carries the following information:

o Minlen equal to 1

o Maxlen equal to 32

o Host Address equal to 192.0.2.1

Assume also that Loc-RIB contains routes for the following IPv4-VPN
prefixes and that all of these routes carry an RT whose value is the
same as the CP-ORF VPN Route Target:

o 1:0.0.0.0/64.

o 2:192.0.2.0/88

o 3:192.0.2.0/89

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Only the prefix 3:192.0.2.0/89 matches the CP-ORF. The prefix
1:0.0.0.0/64 does not match, because its length (64) is less than the
CP-ORF Minlen (1) plus the length of an L3VPN Route Distinguisher
(64). If Loc-RIB did not contain the prefix 3:192.0.2.0/89,
2:192.0.2.0/88 would match the CP-ORF. However, because Loc-RIB also
contains a more specific covering route (3:192.0.2.0/89),
2:192.0.2.0/88 does not match. Only 3:192.0.2.0/89 satisfies all of
the above listed match criteria. Note that the matching algorithm
ignored Route Distinguishers.

In order for an EVPN route to match a CP-ORF, all of the following
conditions MUST be true:

o the EVPN route type is equal to the CP-ORF Route Type; and

o the route carries an RT whose value is equal to the CP-ORF VPN
Route Target.

In addition, if the CP-ORF Route Type is equal to MAC/IP
Advertisement Route, the following conditions also MUST be true:

o the EVPN Route MAC Address Length is greater than or equal to the
CP-ORF Minlen plus 64 (i.e., the length of a VPN Route
Distinguisher);

o the EVPN Route MAC Address Length is less than or equal to the CP-
ORF Maxlen plus 64 (i.e., the length of a VPN Route
Distinguisher); and

o ignoring the Route Distinguisher, the leading bits of the EVPN
Route MAC Address are identical to the leading bits of the CP-ORF
Host Address. CP-ORF Minlen defines the number of bits that must
be identical.

If a route matches the selection criteria of a CP-ORF entry and it
does not violate any subsequent rule specified by the Outbound Filter
(e.g., rules that reflect local policy or rules that are due to
RT-Constrains), the BGP speaker places the route into the Adj-RIB-
Out. In Adj-RIB-Out, the BGP speaker adds the CP-ORF Import Route
Target to the list of RTs that the route already carries. The BGP
speaker also adds a Transitive Opaque Extended Community [RFC4360]
with the sub-type equal to CP-ORF (0x03). As a result of being
placed in Adj-RIB-Out, the route is advertised to the peer associated
with the Adj-RIB-Out.

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Receiving CP-ORF entries with REMOVE or REMOVE-ALL Actions may cause
a route that has previously been installed in a particular Adj-RIB-
Out to be excluded from that Adj-RIB-Out. In this case, as specified
in [RFC4271], "the previously advertised route in that Adj-RIB-Out
MUST be withdrawn from service by means of an UPDATE message".

RFC 5291 states that a BGP speaker should respond to a ROUTE REFRESH
message as follows:

If the When-to-refresh indicates IMMEDIATE, then after processing
all the ORF entries carried in the message the speaker
re-advertises to the peer routes from the Adj-RIB-Out associated
with the peer that have the same AFI/SAFI as what is carried in
the message, and taking into account all the ORF entries for that
AFI/SAFI received from the peer. The speaker MUST re-advertise
all the routes that have been affected by the ORF entries carried
in the message, but MAY also re-advertise the routes that have not
been affected by the ORF entries carried in the message.

When the ROUTE-REFRESH message includes only CP-ORF entries, the BGP
speaker MUST re-advertise routes that have been affected by these
CP-ORF entries. It is RECOMMENDED not to re-advertise the routes
that have not been affected by the CP-ORF entries.

When the ROUTE-REFRESH message includes one or more CP-ORF entries
and one or more ORF entries of a different type, the behavior remains
unchanged from that described in RFC 5291.

4. Applicability in Virtual Hub-and-Spoke VPNs

In a Virtual Hub-and-Spoke environment, VPN sites are attached to PE
routers. For a given VPN, a PE router acts in exactly one of the
following roles:

o as a V-hub

o as a V-spoke

o as neither a V-hub nor a V-spoke

To illustrate CP-ORF operation in conjunction with Virtual Hub-and-
Spoke, assume the following:

o One of the sites in a particular VPN, RED-VPN, is connected to a
PE that acts as neither a V-hub nor a V-spoke for RED-VPN. We
refer to this PE as PE1.

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o Another site in RED-VPN is connected to another PE, and that PE
acts as a V-hub for RED-VPN. We refer to this PE as V-hub1.

o Yet another site in RED-VPN is connected to another PE, and that
PE acts as a V-spoke for RED-VPN. We refer to this PE as
V-spoke1.

All of these PEs advertise RED-VPN routes to a Route Reflector (RR).
They mark these routes with an RT, which we will call RT-RED. In
particular, PE1 advertises a RED-VPN route to a prefix that we will
call P. P covers a host address that we will call H.

For the purpose of illustration, also assume that the PEs and the RRs
use RT-Constrain [RFC4684].

V-hub1 serves the RED-VPN. Therefore, V-hub1 advertises a VPN-IP
default route for the RED-VPN to the RR, carrying the route target
RT-RED-FROM-HUB1.

V-spoke1 establishes a BGP session with the RR, negotiating the
CP-ORF capability as well as the Multiprotocol Extensions capability
[RFC4760]. Upon establishment of the BGP session, the RR does not
advertise any routes to V-spoke1. The RR will not advertise any
routes until it receives either a ROUTE-REFRESH message or a BGP
UPDATE message containing a Route Target Membership Network Layering
Reachability Information (NLRI) [RFC4684].

Immediately after the BGP session is established, V-spoke1 sends the
RR a BGP UPDATE message containing a Route Target Membership NLRI.
The Route Target Membership NLRI specifies RT-RED-FROM-HUB1 as its
RT. In response to the BGP-UPDATE message, the RR advertises the VPN
IP default route for the RED-VPN to V-spoke1. This route carries the
route target RT-RED-FROM-HUB1. V-spoke1 subjects this route to its
import policy and accepts it because it carries the route target
RT-RED-FROM-HUB1.

Now, V-spoke1 begins normal operation, sending all of its RED-VPN
traffic through V-hub1. At some point, V-spoke1 determines that it
might benefit from a more direct route to H. (Note that criteria by
which V-spoke1 determines that it needs a more direct route to H are
beyond the scope of this document.)

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In order to discover a more direct route, V-spoke1 assigns a unique
numeric identifier to H. V-spoke1 then sends a ROUTE-REFRESH message
to the RR, which contains the following information:

o AFI is equal to IPv4 or IPv6, as appropriate

o SAFI is equal to "MPLS-labeled VPN address"

o When-to-refresh is equal to IMMEDIATE

o Action is equal to ADD

o Match is equal to PERMIT

o ORF Type is equal to CP-ORF

o CP-ORF Sequence is equal to the identifier associated with H

o CP-ORF Minlen is equal to 1

o CP-ORF Maxlen is equal to 32 or 128, as appropriate

o CP-ORF VPN Route Target is equal to RT-RED

o CP-ORF Import Route Target is equal to RT-RED-FROM-HUB1

o CP-ORF Route Type is equal to 0 (i.e., undefined)

o CP-ORF Host Address is equal to H

Upon receipt of the ROUTE-REFRESH message, the RR MUST ensure that it
carries all routes belonging to the RED-VPN. In at least one special
case, where all of the RR clients are V-spokes and none of the RR
clients are V-hubs, the RR will lack some or all of the required
RED-VPN routes. So, the RR sends a BGP UPDATE message containing a
Route Target Membership NLRI for VPN-RED to all of its peers. This
causes the peers to advertise VPN-RED routes to the RR if they have
not done so already.

Next, the RR adds the received CP-ORF to the Outbound Filter
associated with V-spoke1. Using the procedures in Section 3, the RR
determines whether any of the routes in its Loc-RIB satisfy the
selection criteria of the newly updated Outbound Filter. If any
routes satisfy the match criteria, they are added to the Adj-RIB-Out
associated with V-spoke1. In Adj-RIB-Out, the RR adds
RT-RED-FROM-HUB1 to the list of RTs that the route already carries.
The RR also adds a Transitive Opaque Extended Community [RFC4360]

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with the sub-type equal to CP-ORF. Finally, RR advertises the newly
added routes to V-spoke1. In this example, the RR advertises P to
V-spoke1 with a next-hop of PE1.

V-spoke1 subjects the advertised routes to its import policy and
accepts them because they carry the route target RT-RED-FROM-HUB1.

V-spoke1 may repeat this process whenever it discovers another flow
that might benefit from a more direct route to its destination.

4.1. Multicast Considerations

When applying Multicast VPN [RFC6513] [RFC6514] procedures, routes
bearing a Transitive Opaque Extended Community [RFC4360] with the
sub-type equal to CP-ORF MUST NOT be used to determine Eligible
Upstream Multicast Hops (UMH).

5. Applicability in BGP/MPLS Ethernet VPN (EVPN)

In an EVPN environment, Customer Edge (CE) devices are attached to PE
routers. A CE can be a host, a router, or a switch. For a given
EVI, a PE router acts in exactly one of the following roles:

o as a DMG

o as a Spoke

o as neither a DMG nor a Spoke

To illustrate CP-ORF operation in the EVPN environment, assume the
following:

o A CE device in a particular EVI, RED-EVI, is connected to a PE
that acts as neither a DMG nor a Spoke for RED-EVI. We refer to
this PE as PE1.

o Another CE device in RED-EVI is connected to another PE, and that
PE acts as a DMG for RED-EVI. We refer to this PE as DMG1.

o Yet another CE device in RED-EVI is connected to another PE, and
that PE acts as a Spoke for RED-EVI. We refer to this PE as
Spoke1.

All of these PEs advertise RED-EVI routes to a RR. They mark these
routes with an RT, which we will call RT-RED. In particular, PE1
advertises a RED-EVI route to a MAC Address that we will call M.

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The RED-EVI VPN Routing and Forwarding tables (VRFs) on all of these
PEs are provisioned to import EVPN routes that carry RT-RED.

Since DMG1 acts as a DMG for RED-EVI, DMG1 advertises a UMR for the
RED-EVI to the RR, carrying the route target RT-RED. The UMR is
characterized as follows:

o EVPN Route Type is equal to MAC/IP Advertisement Route

o MAC address length is equal to 0

o IP address length is equal to 0

Spoke1 establishes a BGP session with the RR, negotiating the CP-ORF
capability as well as the Multiprotocol Extensions capability
[RFC4760]. Upon establishment of the BGP session, the RR does not
advertise any routes to Spoke1. The RR will not advertise any routes
until it receives a ROUTE-REFRESH message.

Immediately after the BGP session is established, Spoke1 sends the RR
a ROUTE REFRESH message containing the following information:

o AFI is equal to L2VPN

o SAFI is equal to BGP EVPN

o When-to-refresh is equal to IMMEDIATE

o Action is equal to ADD

o Match is equal to PERMIT

The ROUTE REFRESH message also contains four ORF entries. The first
ORF entry contains the following information:

o ORF Type is equal to CP-ORF

o CP-ORF Sequence is equal to 1

o CP-ORF Minlen is equal to 0

o CP-ORF Maxlen is equal to 0

o CP-ORF VPN Route Target is equal to RT-RED

o CP-ORF Import Route Target is equal to RT-RED

o CP-ORF Route Type is equal to 1 (Ethernet Autodiscovery Route)

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The second ORF entry contains the following information:

o ORF Type is equal to CP-ORF

o CP-ORF Sequence is equal to 2

o CP-ORF Minlen is equal to 0

o CP-ORF Maxlen is equal to 0

o CP-ORF VPN Route Target is equal to RT-RED

o CP-ORF Import Route Target is equal to RT-RED

o CP-ORF Route Type is equal to 2 (MAC/IP Advertisement Route)

The third ORF entry contains the following information:

o ORF Type is equal to CP-ORF

o CP-ORF Sequence is equal to 3

o CP-ORF Minlen is equal to 0

o CP-ORF Maxlen is equal to 0

o CP-ORF VPN Route Target is equal to RT-RED

o CP-ORF Import Route Target is equal to RT-RED

o CP-ORF Route Type is equal to 3 (Inclusive Multicast Route)

The fourth ORF entry contains the following information:

o ORF Type is equal to CP-ORF

o CP-ORF Sequence is equal to 4

o CP-ORF Minlen is equal to 0

o CP-ORF Maxlen is equal to 0

o CP-ORF VPN Route Target is equal to RT-RED

o CP-ORF Import Route Target is equal to RT-RED

o CP-ORF Route Type is equal to 4 (Ethernet Segment)

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In response to the ROUTE REFRESH message, the RR advertises the
following to V-spoke1:

o All Ethernet Autodiscovery Routes belonging to RED-EVI

o A UMR advertised by DMG1 and belonging to RED-EVI

o All Inclusive Multicast Routes belonging to RED-EVI

o All Ethernet Segment Routes belonging to RED-EVI

All of these routes carry the route target RT-RED. Spoke1 subjects
these routes to its import policy and accepts them because they carry
the route target RT-RED.

Now, Spoke1 begins normal operation, sending all of its RED-VPN
traffic through DMG1. At some point, Spoke1 determines that it might
benefit from a more direct route to M. (Note that criteria by which
Spoke1 determines that it needs a more direct route to M are beyond
the scope of this document.)

In order to discover a more direct route, Spoke1 assigns a unique
numeric identifier to M. V-spoke1 then sends a ROUTE-REFRESH message
to the RR, containing the following information:

o AFI is equal to L2VPN

o SAFI is equal to BGP EVPN

o When-to-refresh is equal to IMMEDIATE

o Action is equal to ADD

o Match is equal to PERMIT

o ORF Type is equal to CP-ORF

o CP-ORF Sequence is equal to the identifier associated with M

o CP-ORF Minlen is equal to 1

o CP-ORF Maxlen is equal to 48

o CP-ORF VPN Route Target is equal to RT-RED

o CP-ORF Import Route Target is equal to RT-RED

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o CP-ORF Route Type is equal to 2 (i.e., MAC/IP Advertisement Route)

o CP-ORF Host Address is equal to M

Next, the RR adds the received CP-ORF to the Outbound Filter
associated with Spoke1. Using the procedures in Section 3, the RR
determines whether any of the routes in its Loc-RIB satisfy the
selection criteria of the newly updated Outbound Filter. If any
routes satisfy the match criteria, they are added to the Adj-RIB-Out
associated with Spoke1. The RR adds a Transitive Opaque Extended
Community [RFC4360] with the sub-type equal to CP-ORF. Note that as
these routes are added to the Adj-RIB-Out, the RR does not change the
list of RTs that the route already carries. Finally, RR advertises
the newly added routes to V-spoke1. In this example, the RR
advertises M to V-spoke1 with a next-hop of PE1.

Spoke1 subjects the advertised routes to its import policy and
accepts them because they carry the route target RT-RED.

Spoke1 may repeat this process whenever it discovers another flow
that might benefit from a more direct route to its destination.

Note that, in general, an EVI may have more than one DMG, in which
case each spoke would receive a UMR from each of them. The spoke
should follow its local route selection procedures to select one of
them as the "best" and use the selected one.

6. Clean-up

Each CP-ORF consumes memory and compute resources on the device that
supports it. Therefore, in order to obtain optimal performance, BGP
speakers periodically evaluate all CP-ORFs that they have originated
and remove unneeded CP-ORFs. The criteria by which a BGP speaker
identifies unneeded CP-ORF entries is a matter of local policy and is
beyond the scope of this document.

7. IANA Considerations

This memo uses code points from the First Come First Served [RFC5226]
range of the following registries:

+------------------------------------------------+---------------+
| Registry | Code Point |
+------------------------------------------------+---------------+
| BGP Outbound Route Filtering (ORF) Types | CP-ORF (65) |
| Transitive Opaque Extended Community Sub-Types | CP-ORF (0x03) |
+------------------------------------------------+---------------+

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IANA has updated the above-mentioned registry entries so that they
reference this memo.

8. Security Considerations

Each CP-ORF consumes memory and compute resources on the device that
supports it. Therefore, a device supporting CP-ORF takes the
following steps to protect itself from oversubscription:

o When negotiating the ORF capability, advertise willingness to
receive the CP-ORF only to known, trusted Internal BGP (iBGP)
peers. See Section 5 of RFC 5291 for negotiation details.

o Enforce a per-peer limit on the number of CP-ORFs that can be
installed at any given time. Ignore all requests to add CP-ORFs
beyond that limit

Security considerations for BGP are presented in [RFC4271] while
further security analysis of BGP is found in [RFC6952].

9. References

9.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.

[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271, January
2006, <http://www.rfc-editor.org/info/rfc4271>.

[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, February 2006,
<http://www.rfc-editor.org/info/rfc4360>.

[RFC4684] Marques, P., Bonica, R., Fang, L., Martini, L., Raszuk,
R., Patel, K., and J. Guichard, "Constrained Route
Distribution for Border Gateway Protocol/MultiProtocol
Label Switching (BGP/MPLS) Internet Protocol (IP) Virtual
Private Networks (VPNs)", RFC 4684, November 2006,
<http://www.rfc-editor.org/info/rfc4684>.

[RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
"Multiprotocol Extensions for BGP-4", RFC 4760, January
2007, <http://www.rfc-editor.org/info/rfc4760>.

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[RFC5291] Chen, E. and Y. Rekhter, "Outbound Route Filtering
Capability for BGP-4", RFC 5291, August 2008,
<http://www.rfc-editor.org/info/rfc5291>.

[RFC6513] Rosen, E., Ed. and R. Aggarwal, Ed., "Multicast in MPLS/
BGP IP VPNs", RFC 6513, February 2012,
<http://www.rfc-editor.org/info/rfc6513>.

[RFC6514] Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP
Encodings and Procedures for Multicast in MPLS/BGP IP
VPNs", RFC 6514, February 2012,
<http://www.rfc-editor.org/info/rfc6514>.

[RFC7024] Jeng, H., Uttaro, J., Jalil, L., Decraene, B., Rekhter,
Y., and R. Aggarwal, "Virtual Hub-and-Spoke in BGP/MPLS
VPNs", RFC 7024, October 2013,
<http://www.rfc-editor.org/info/rfc7024>.

[RFC7432] Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
Ethernet VPN", RFC 7432, February 2015,
<http://www.rfc-editor.org/info/rfc7432>.

9.2. Informative References

[IANA.AFI] IANA, "Address Family Numbers",
<http://www.iana.org/assignments/address-family-numbers>.

[IANA.EVPN] IANA, "Ethernet VPN (EVPN)",
<http://www.iana.org/assignments/evpn>.

[IANA.SAFI] IANA, "Subsequent Address Family Identifiers (SAFI)
Parameters",
<http://www.iana.org/assignments/safi-namespace>.

[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, February 2006,
<http://www.rfc-editor.org/info/rfc4364>.

[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008, <http://www.rfc-editor.org/info/rfc5226>.

[RFC6952] Jethanandani, M., Patel, K., and L. Zheng, "Analysis of
BGP, LDP, PCEP, and MSDP Issues According to the Keying
and Authentication for Routing Protocols (KARP) Design
Guide", RFC 6952, May 2013,
<http://www.rfc-editor.org/info/rfc6952>.

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Acknowledgements

The authors wish to acknowledge Han Nguyen, James Uttaro, and Alvaro
Retana for their comments and contributions.

Contributors

The following individuals contributed to the development of this
document:

o Yakov Rekhter

o Xiaohu Xu

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Authors' Addresses

Huajin Jeng
AT&T

EMail: [email protected]

Luay Jalil
Verizon

EMail: [email protected]

Ron Bonica
Juniper Networks
2251 Corporate Park Drive
Herndon, Virginia 20170
United States

EMail: [email protected]

Keyur Patel
Cisco Systems
170 W. Tasman Drive
San Jose, California 95134
United States

EMail: [email protected]

Lucy Yong
Huawei Technologies
Austin, Texas
United States

EMail: [email protected]

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