Internet Engineering Task Force (IETF)
Request for Comments: 7543
Category: Standards Track
ISSN: 2070-1721

H. Jeng
AT&T
L. Jalil
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.

Copyright Notice

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.

   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

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]

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]

MAC - Media Access Control

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

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

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:

AFI [IANA.AFI]

SAFI [IANA.SAFI]

   o  When-to-refresh (IMMEDIATE or DEFERRED)

ORF Type

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)

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:

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

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

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

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

The Match field MUST be equal to PERMIT.

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:

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

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

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

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

Route Type: the type of the selected route

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.

If the ROUTE-REFRESH AFI is equal to IPv4,

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

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

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

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

the Host Address MUST contain exactly 32 bits.

If the ROUTE-REFRESH AFI is equal to IPv6,

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

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

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

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

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]:

1 - Ethernet Autodiscovery Route

2 - MAC/IP Advertisement Route

3 - Inclusive Multicast Route

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,

the value of Minlen MUST be equal to 0;

the value of Maxlen MUST be equal to 0; and

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

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

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

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

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

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.

The following route types can match a CP-ORF:

IPv4-VPN

IPv6-VPN

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:

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

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);

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);

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

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:

Minlen equal to 1

Maxlen equal to 32

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:

1:0.0.0.0/64.

2:192.0.2.0/88

3:192.0.2.0/89

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:

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

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:

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);

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

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.

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:

as a V-hub

as a V-spoke

as neither a V-hub nor a V-spoke

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

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.

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.

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.)

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:

AFI is equal to IPv4 or IPv6, as appropriate

SAFI is equal to "MPLS-labeled VPN address"

When-to-refresh is equal to IMMEDIATE

Action is equal to ADD

Match is equal to PERMIT

ORF Type is equal to CP-ORF

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

CP-ORF Minlen is equal to 1

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

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)

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] 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:

as a DMG

as a Spoke

   o  as neither a DMG nor a Spoke

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

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.

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.

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.

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:

EVPN Route Type is equal to MAC/IP Advertisement Route

MAC address length is equal to 0

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:

AFI is equal to L2VPN

SAFI is equal to BGP EVPN

When-to-refresh is equal to IMMEDIATE

Action is equal to ADD

Match is equal to PERMIT

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

ORF Type is equal to CP-ORF

CP-ORF Sequence is equal to 1

CP-ORF Minlen is equal to 0

CP-ORF Maxlen is equal to 0

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

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

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

The second ORF entry contains the following information:

ORF Type is equal to CP-ORF

CP-ORF Sequence is equal to 2

CP-ORF Minlen is equal to 0

CP-ORF Maxlen is equal to 0

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

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

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

The third ORF entry contains the following information:

ORF Type is equal to CP-ORF

CP-ORF Sequence is equal to 3

CP-ORF Minlen is equal to 0

CP-ORF Maxlen is equal to 0

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

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

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

The fourth ORF entry contains the following information:

ORF Type is equal to CP-ORF

CP-ORF Sequence is equal to 4

CP-ORF Minlen is equal to 0

CP-ORF Maxlen is equal to 0

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

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

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

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

All Ethernet Autodiscovery Routes belonging to RED-EVI

A UMR advertised by DMG1 and belonging to RED-EVI

All Inclusive Multicast Routes belonging to RED-EVI

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:

AFI is equal to L2VPN

SAFI is equal to BGP EVPN

When-to-refresh is equal to IMMEDIATE

Action is equal to ADD

Match is equal to PERMIT

ORF Type is equal to CP-ORF

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

CP-ORF Minlen is equal to 1

CP-ORF Maxlen is equal to 48

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

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

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

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) |
    +------------------------------------------------+---------------+

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:

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.

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>.
   
   [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>.

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:

Yakov Rekhter

Xiaohu Xu

Authors' Addresses

Huajin Jeng
AT&T

EMail:

          hj2387@att.com

Luay Jalil
Verizon

   EMail: luay.jalil@verizon.com
   
   Ron Bonica
   Juniper Networks
   2251 Corporate Park Drive
   Herndon, Virginia  20170
   United States

EMail:

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

EMail:

          keyupate@cisco.com

Lucy Yong
Huawei Technologies
Austin, Texas
United States

   EMail: lucy.yong@huawei.com