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Versions: 00 01 02 03 draft-ietf-bess-evpn-prefix-advertisement

L2VPN Workgroup                                               J. Rabadan
Internet Draft                                             W. Henderickx
                                                         S. Palislamovic
Intended status: Standards Track                          Alcatel-Lucent

J. Drake                                                        F. Balus
Juniper                                                   Nuage Networks

A. Sajassi                                                      A. Isaac
Cisco                                                          Bloomberg


Expires: April 19, 2015                                 October 16, 2014



                    IP Prefix Advertisement in EVPN
            draft-rabadan-l2vpn-evpn-prefix-advertisement-03


Abstract

   EVPN provides a flexible control plane that allows intra-subnet
   connectivity in an IP/MPLS and/or an NVO-based network. In NVO
   networks, there is also a need for a dynamic and efficient inter-
   subnet connectivity across Tenant Systems and End Devices that can be
   physical or virtual and may not support their own routing protocols.
   This document defines a new EVPN route type for the advertisement of
   IP Prefixes and explains some use-case examples where this new route-
   type is used.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt



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   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html

   This Internet-Draft will expire on April 19, 2015.

Copyright Notice

   Copyright (c) 2014 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. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2. Introduction and problem statement  . . . . . . . . . . . . . .  3
     2.1 Inter-subnet connectivity requirements in Data Centers . . .  4
     2.2 The requirement for a new EVPN route type  . . . . . . . . .  6
   3. The BGP EVPN IP Prefix route  . . . . . . . . . . . . . . . . .  7
     3.1 IP Prefix Route encoding . . . . . . . . . . . . . . . . . .  8
   4. Benefits of using the EVPN IP Prefix route  . . . . . . . . . . 10
   5. IP Prefix next-hop use-cases  . . . . . . . . . . . . . . . . . 11
     5.1 TS IP address next-hop use-case  . . . . . . . . . . . . . . 11
     5.2 Floating IP next-hop use-case  . . . . . . . . . . . . . . . 14
     5.3 ESI next-hop ("Bump in the wire") use-case . . . . . . . . . 16
     5.4 IRB forwarding on NVEs for Subnets (IP-VRF-to-IP-VRF)  . . . 18
   6. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . 21
   7. Conventions used in this document . . . . . . . . . . . . . . . 21
   8. Security Considerations . . . . . . . . . . . . . . . . . . . . 22
   9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 22
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
     10.1 Normative References  . . . . . . . . . . . . . . . . . . . 22
     10.2 Informative References  . . . . . . . . . . . . . . . . . . 22
   11. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 22
   12. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 22








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1. Terminology

   GW IP: Gateway IP Address

   IPL: IP address length

   IRB: Integrated Routing and Bridging interface

   ML: MAC address length

   NVE: Network Virtualization Edge

   TS: Tenant System

   VA: Virtual Appliance

   RT-2: EVPN route type 2, i.e. MAC/IP advertisement route

   RT-5: EVPN route type 5, i.e. IP Prefix route

   Overlay next-hop: object used in the IP Prefix route, as described in
   this document. It can be an IP address in the tenant space or an ESI,
   and identifies the next-hop yielded by the IP route lookup at the
   routing context importing the route. An overlay next-hop always needs
   a recursive route resolution on the NVE receiving the IP Prefix
   route, so that the NVE knows to which egress NVE to forward the
   packets.

   Underlay next-hop: IP address sent by BGP along with any EVPN route,
   i.e. BGP next-hop. It identifies the NVE sending the route and it is
   used at the receiving NVE as the VXLAN destination VTEP or NVGRE
   destination end-point.

2. Introduction and problem statement

   Inter-subnet connectivity is required for certain tenants within the
   Data Center. [EVPN-INTERSUBNET] defines some fairly common inter-
   subnet forwarding scenarios where TSes can exchange packets with TSes
   located in remote subnets. In order to meet this requirement,
   [EVPN-INTERSUBNET] describes how MAC/IPs encoded in TS RT-2 routes
   are not only used to populate MAC-VRF and overlay ARP tables, but
   also IP-VRF tables with the encoded TS host routes (/32 or /128). In
   some cases, EVPN may advertise IP Prefixes and therefore provide
   aggregation in the IP-VRF tables, as opposed to program individual
   host routes. This document complements the scenarios described in
   [EVPN-INTERSUBNET] and defines how EVPN may be used to advertise IP
   Prefixes.




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   Section 2.1 describes the inter-subnet connectivity requirements in
   Data Centers. Section 2.2 explains why a new EVPN route type is
   required for IP Prefix advertisements. Once the need for a new EVPN
   route type is justified, sections 3, 4 and 5 will describe this route
   type and how it is used in some specific use cases.

2.1 Inter-subnet connectivity requirements in Data Centers

   [EVPN] is used as the control plane for a Network Virtualization
   Overlay (NVO3) solution in Data Centers (DC), where Network
   Virtualization Edge (NVE) devices can be located in Hypervisors or
   TORs, as described in [EVPN-OVERLAYS].

   If we use the term Tenant System (TS) to designate a physical or
   virtual system identified by MAC and IP addresses, and connected to
   an EVPN instance, the following considerations apply:

   o The Tenant Systems may be Virtual Machines (VMs) that generate
     traffic from their own MAC and IP.

   o The Tenant Systems may be Virtual Appliance entities (VAs) that
     forward traffic to/from IP addresses of different End Devices
     seating behind them.

        o These VAs can be firewalls, load balancers, NAT devices, other
          appliances or virtual gateways with virtual routing instances.

        o These VAs do not have their own routing protocols and hence
          rely on the EVPN NVEs to advertise the routes on their behalf.

        o In all these cases, the VA will forward traffic to the Data
          Center using its own source MAC but the source IP will be the
          one associated to the End Device seating behind or a
          translated IP address (part of a public NAT pool) if the VA is
          performing NAT.

        o Note that the same IP address could exist behind two of these
          TS. One example of this would be certain appliance resiliency
          mechanisms, where a virtual IP or floating IP can be owned by
          one of the two VAs running the resiliency protocol (the master
          VA). VRRP is one particular example of this. Another example
          is multi-homed subnets, i.e. the same subnet is connected to
          two VAs.

        o Although these VAs provide IP connectivity to VMs and subnets
          behind them, they do not always have their own IP interface
          connected to the EVPN NVE, e.g. layer-2 firewalls are examples
          of VAs not supporting IP interfaces.



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   The following figure illustrates some of the examples described
   above.
                       NVE1
                    +-----------+
           TS1(VM)--|(MAC-VRF10)|-----+
             IP1/M1 +-----------+     |               DGW1
                                  +---------+    +-------------+
                                  |         |----|(MAC-VRF10)  |
     SN1---+           NVE2       |         |    |    IRB1\    |
           |        +-----------+ |         |    |     (IP-VRF)|---+
     SN2---TS2(VA)--|(MAC-VRF10)|-|         |    +-------------+  _|_
           | IP2/M2 +-----------+ |  VXLAN/ |                    (   )
     IP4---+  <-+                 |  nvGRE  |         DGW2      ( WAN )
                |                 |         |    +-------------+ (___)
             vIP23 (floating)     |         |----|(MAC-VRF10)  |   |
                |                 +---------+    |    IRB2\    |   |
     SN1---+  <-+      NVE3         |  |  |      |     (IP-VRF)|---+
           | IP3/M3 +-----------+   |  |  |      +-------------+
     SN3---TS3(VA)--|(MAC-VRF10)|---+  |  |
           |        +-----------+      |  |
     IP5---+                           |  |
                                       |  |
                    NVE4               |  |      NVE5            +--SN5
              +---------------------+  |  | +-----------+        |
     IP6------|(MAC-VRF1)           |  |  +-|(MAC-VRF10)|--TS4(VA)--SN6
              |       \             |  |    +-----------+        |
              |    (IP-VRF)         |--+                ESI4     +--SN7
              |       /  \IRB3      |
          |---|(MAC-VRF2)(MAC-VRF10)|
       SN4|   +---------------------+

                    Figure 1 DC inter-subnet use-cases

   Where:

   NVE1, NVE2, NVE3, NVE4, NVE5, DGW1 and DGW2 share the same EVI for a
   particular tenant. EVI-10 is comprised of the collection of MAC-VRF10
   instances defined in all the NVEs. All the hosts connected to EVI-10
   belong to the same IP subnet. The hosts connected to EVI-10 are
   listed below:

        o TS1 is a VM that generates/receives traffic from/to IP1, where
          IP1 belongs to the EVI-10 subnet.

        o TS2 and TS3 are Virtual Appliances (VA) that generate/receive
          traffic from/to the subnets and hosts seating behind them
          (SN1, SN2, SN3, IP4 and IP5). Their IP addresses (IP2 and IP3)
          belong to the EVI-10 subnet and they can also generate/receive



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          traffic. When these VAs receive packets destined to their own
          MAC addresses (M2 and M3) they will route the packets to the
          proper subnet or host. These VAs do not support routing
          protocols to advertise the subnets connected to them and can
          move to a different server and NVE when the Cloud Management
          System decides to do so. These VAs may also support redundancy
          mechanisms for some subnets, similar to VRRP, where a floating
          IP is owned by the master VA and only the master VA forwards
          traffic to a given subnet. E.g.: vIP23 in figure 1 is a
          floating IP that can be owned by TS2 or TS3 depending on who
          the master is. Only the master will forward traffic to SN1.

        o Integrated Routing and Bridging interfaces IRB1, IRB2 and IRB3
          have their own IP addresses that belong to the EVI-10 subnet
          too. These IRB interfaces connect the EVI-10 subnet to Virtual
          Routing and Forwarding (VRF) instances that can route the
          traffic to other connected subnets for the same tenant (within
          the DC or at the other end of the WAN).

        o TS4 is a layer-2 VA that provides connectivity to subnets SN5,
          SN6 and SN7, but does not have an IP address itself in the
          EVI-10. TS4 is connected to a physical port on NVE5 assigned
          to Ethernet Segment Identifier 4.

   All the above DC use cases require inter-subnet forwarding and
   therefore the individual host routes and subnets:

   a) MUST be advertised from the NVEs (since VAs and VMs do not run
      routing protocols) and
   b) MAY be associated to an overlay next-hop that can be a VA IP
      address, a floating IP address or an ESI.

2.2 The requirement for a new EVPN route type

   [EVPN] defines a MAC/IP route (also referred as RT-2) where a MAC
   address can be advertised together with an IP address length (IPL)
   and IP address (IP). While a variable IPL might have been used to
   indicate the presence of an IP prefix in a route type 2, there are
   several specific use cases in which using this route type to deliver
   IP Prefixes is not suitable.

   One example of such use cases is the "floating IP" example described
   in section 2.1. In this example we need to decouple the advertisement
   of the prefixes from the advertisement of the floating IP (vIP23 in
   figure 1) and MAC associated to it, otherwise the solution gets
   highly inefficient and does not scale.

   E.g.: if we are advertising 1k prefixes from M2 (using RT-2) and the



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   floating IP owner changes from M2 to M3, we would need to withdraw 1k
   routes from M2 and re-advertise 1k routes from M3. However if we use
   a separate route type, we can advertise the 1k routes associated to
   the floating IP address (vIP23) and only one RT-2 for advertising the
   ownership of the floating IP, i.e. vIP23 and M2 in the route type 2.
   When the floating IP owner changes from M2 to M3, a single RT-2
   withdraw/update is required to indicate the change. The remote DGW
   will not change any of the 1k prefixes associated to vIP23, but will
   only update the ARP resolution entry for vIP23 (now pointing at M3).

   Other reasons to decouple the IP Prefix advertisement from the MAC/IP
   route are listed below:

        o Clean identification, operation of troubleshooting of IP
          Prefixes, not subject to interpretation and independent of the
          IPL and the IP value. E.g.: a default IP route 0.0.0.0/0 must
          always be easily and clearly distinguished from the absence of
          IP information.

        o MAC address information must not be compared by BGP when
          selecting two IP Prefix routes. If IP Prefixes were to be
          advertised using MAC/IP routes, the MAC information would
          always be present and part of the route key.

        o IP Prefix routes must not be subject to MAC/IP route
          procedures such as MAC mobility or aliasing. Prefixes
          advertised from two different ESIs do not mean mobility; MACs
          advertised from two different ESIs do mean mobility. Similarly
          load balancing for IP prefixes is achieved through IP
          mechanisms such as ECMP, and not through MAC route mechanisms
          such as aliasing.

        o NVEs that do not require processing IP Prefixes must have an
          easy way to identify an update with an IP Prefix and ignore
          it, rather than processing the MAC/IP route to find out only
          later that it carries a Prefix that must be ignored.

   The following sections describe how EVPN is extended with a new route
   type for the advertisement of IP prefixes and how this route is used
   to address the current and future inter-subnet connectivity
   requirements existing in the Data Center.

3. The BGP EVPN IP Prefix route

   The current BGP EVPN NLRI as defined in [EVPN] is shown below:






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    +-----------------------------------+
    |    Route Type (1 octet)           |
    +-----------------------------------+
    |     Length (1 octet)              |
    +-----------------------------------+
    | Route Type specific (variable)    |
    +-----------------------------------+

   Where the route type field can contain one of the following specific
   values:

   + 1 - Ethernet Auto-Discovery (A-D) route

   + 2 - MAC/IP advertisement route

   + 3 - Inclusive Multicast Route

   + 4 - Ethernet Segment Route

   This document defines an additional route type that will be used for
   the advertisement of IP Prefixes:

   + 5 - IP Prefix Route

   The support for this new route type is OPTIONAL.

   Since this new route type is OPTIONAL, an implementation not
   supporting it MUST ignore the route, based on the unknown route type
   value.

   The detailed encoding of this route and associated procedures are
   described in the following sections.


3.1 IP Prefix Route encoding

   An IP Prefix advertisement route NLRI consists of the following
   fields:













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    +---------------------------------------+
    |      RD   (8 octets)                  |
    +---------------------------------------+
    |Ethernet Segment Identifier (10 octets)|
    +---------------------------------------+
    |  Ethernet Tag ID (4 octets)           |
    +---------------------------------------+
    |  IP Prefix Length (1 octet)           |
    +---------------------------------------+
    |  IP Prefix (4 or 16 octets)           |
    +---------------------------------------+
    |  GW IP Address (4 or 16 octets)       |
    +---------------------------------------+
    |  MPLS Label (3 octets)                |
    +---------------------------------------+

   Where:

        o RD, Ethernet Tag ID and MPLS Label fields will be used as
          defined in [EVPN] and [EVPN-OVERLAYS].

        o The Ethernet Segment Identifier will be a non-zero 10-byte
          identifier if the ESI is used as an overlay next-hop. It will
          be zero otherwise.

        o The IP Prefix Length can be set to a value between 0 and 32
          (bits) for ipv4 and between 0 and 128 for ipv6.

        o The IP Prefix will be a 32 or 128-bit field (ipv4 or ipv6).

        o The GW IP (Gateway IP Address) will be a 32 or 128-bit field
          (ipv4 or ipv6), and will encode the overlay IP next-hop for
          the IP Prefixes. The GW IP field can be zero if it is not used
          as an overlay next-hop.

        o The total route length will indicate the type of prefix (ipv4
          or ipv6) and the type of GW IP address (ipv4 or ipv6). Note
          that the IP Prefix + the GW IP should have a length of either
          64 or 256 bits, but never 160 bits (ipv4 and ipv6 mixed values
          are not allowed).

   The Eth-Tag ID, IP Prefix Length and IP Prefix will be part of the
   route key used by BGP to compare routes. The rest of the fields will
   not be part of the route key.

   The route will contain a single overlay next-hop at most, i.e. if the
   ESI field is different from zero, the GW IP field will be zero, and
   vice versa. The following table shows the different inter-subnet use-



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   cases described in this document and the corresponding coding of the
   overlay next-hop in the route type 5 (RT-5). The IP-VRF-to-IP-VRF or
   IRB forwarding on NVEs case is a special use-case, where there is no
   need for overlay next-hop, since the actual next-hop is given by the
   BGP next-hop. When an overlay next-hop is present in the RT-5, the
   receiving NVE will need to perform a recursive route resolution to
   find out to which egress NVE to forward the packets.

   +----------------------------+----------------------------------+
   | Use-case                   | Next-hop in the RT-5 BGP update  |
   +----------------------------+----------------------------------+
   | TS IP address              | GW IP Address                    |
   | Floating IP address        | GW IP Address                    |
   | "Bump in the wire"         | ESI                              |
   | IP-VRF-to-IP-VRF           | BGP next-hop                     |
   +----------------------------+----------------------------------+

4. Benefits of using the EVPN IP Prefix route

   This section clarifies the different functions accomplished by the
   EVPN RT-2 and RT-5 routes, and provides a list of benefits derived
   from using a separate route type for the advertisement of IP Prefixes
   in EVPN.

   [EVPN] describes the content of the BGP EVPN RT-2 specific NLRI, i.e.
   MAC/IP Advertisement Route, where the IP address length (IPL) and IP
   address (IP) of a specific advertised MAC are encoded. The subject of
   the MAC advertisement route is the MAC address (M) and MAC address
   length (ML) encoded in the route. The MAC mobility and other complex
   procedures are defined around that MAC address. The IP address
   information carries the host IP address required for the ARP
   resolution of the MAC according to [EVPN] and the host route to be
   programmed in the IP-VRF [EVPN-INTERSUBNET].

   The BGP EVPN route type 5 defined in this document, i.e. IP Prefix
   Advertisement route, decouples the advertisement of IP prefixes from
   the advertisement of any MAC address related to it. This brings some
   major benefits to NVO-based networks where certain inter-subnet
   forwarding scenarios are required. Some of those benefits are:

   a) Upon receiving a route type 2 or type 5, an egress NVE can easily
      distinguish MACs and IPs from IP Prefixes. E.g. an IP prefix with
      IPL=32 being advertised from two different ingress NVEs (as RT-5)
      can be identified as such and be imported in the designated
      routing context as two ECMP routes, as opposed to two MACs
      competing for the same IP.

   b) Similarly, upon receiving a route, an ingress NVE not supporting



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      processing of IP Prefixes can easily ignore the update, based on
      the route type.

   c) A MAC route includes the ML, M, IPL and IP in the route key that
      is used by BGP to compare routes, whereas for IP Prefix routes,
      only IPL and IP (as well as Ethernet Tag ID) are part of the route
      key. Advertised IP Prefixes are imported into the designated
      routing context, where there is no MAC information associated to
      IP routes. In the example illustrated in figure 1, subnet SN1
      should be advertised by NVE2 and NVE3 and interpreted by DGW1 as
      the same route coming from two different next-hops, regardless of
      the MAC address associated to TS2 or TS3. This is easily
      accomplished in the RT-5 by including only the IP information in
      the route key.

   d) By decoupling the MAC from the IP Prefix advertisement procedures,
      we can leave the IP Prefix advertisements out of the MAC mobility
      procedures defined in [EVPN] for MACs. In addition, this allows us
      to have an indirection mechanism for IP Prefixes advertised from a
      MAC/IP that can move between hypervisors. E.g. if there are 1,000
      prefixes seating behind TS2 (figure 1), NVE2 will advertise all
      those prefixes in RT-5 routes associated to the next-hop IP2.
      Should TS2 move to a different NVE, a single MAC advertisement
      route withdraw for the M2/IP2 route from NVE2 will invalidate the
      1,000 prefixes, as opposed to have to wait for each individual
      prefix to be withdrawn. This may be easily accomplished by using
      IP Prefix routes that are not tied to a MAC address, and use a
      different MAC/IP route to advertise the location and resolution of
      the overlay next-hop to a MAC address.

5. IP Prefix next-hop use-cases

   The IP Prefix route can use a GW IP or an ESI as an overlay next-hop
   as well as no overlay next-hop whatsoever. This section describes
   some use-cases for these next-hop types.

5.1 TS IP address next-hop use-case

   The following figure illustrates an example of inter-subnet
   forwarding for subnets seating behind Virtual Appliances (on TS2 and
   TS3).










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     SN1---+           NVE2                            DGW1
           |        +-----------+ +---------+    +-------------+
     SN2---TS2(VA)--|(MAC-VRF10)|-|         |----|(MAC-VRF10)  |
           | IP2/M2 +-----------+ |         |    |    IRB1\    |
     IP4---+                      |         |    |     (IP-VRF)|---+
                                  |         |    +-------------+  _|_
                                  |  VXLAN/ |                    (   )
                                  |  nvGRE  |         DGW2      ( WAN )
     SN1---+           NVE3       |         |    +-------------+ (___)
           | IP3/M3 +-----------+ |         |----|(MAC-VRF10)  |   |
     SN3---TS3(VA)--|(MAC-VRF10)|-|         |    |    IRB2\    |   |
           |        +-----------+ +---------+    |     (IP-VRF)|---+
     IP5---+                                     +-------------+

                  Figure 2 TS IP address use-case

   An example of inter-subnet forwarding between subnet SN1/24 and a
   subnet seating in the WAN is described below. NVE2, NVE3, DGW1 and
   DGW2 are running BGP EVPN. TS2 and TS3 do not support routing
   protocols, only a static route to forward the traffic to the WAN.

   (1) NVE2 advertises the following BGP routes on behalf of TS2:

        o Route type 2 (MAC/IP route) containing: ML=48, M=M2, IPL=32,
          IP=IP2 and [RFC5512] BGP Encapsulation Extended Community with
          Tunnel-type= VXLAN or NVGRE.

        o Route type 5 (IP Prefix route) containing: IPL=24, IP=SN1,
          ESI=0, GW IP address=IP2 (and BGP Encapsulation Extended
          Community).

   (2) NVE3 advertises the following BGP routes on behalf of TS3:

        o Route type 2 (MAC/IP route) containing: ML=48, M=M3, IPL=32,
          IP=IP3 (and BGP Encapsulation Extended Community).

        o Route type 5 (IP Prefix route) containing: IPL=24, IP=SN1,
          ESI=0, GW IP address=IP3 (and BGP Encapsulation Extended
          Community).

   (3) DGW1 and DGW2 import both received routes based on the
       route-targets:

        o Based on the MAC-VRF10 route-target in DGW1 and DGW2, the
          MAC/IP route is imported and M2 is added to the MAC-VRF10
          along with its corresponding tunnel information. For instance,
          if VXLAN is used, the VTEP will be derived from the MAC/IP
          route BGP next-hop (underlay next-hop) and VNI from the



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          Ethernet Tag or MPLS fields. IP2 - M2 is added to the ARP
          table.

        o Based on the MAC-VRF10 route-target in DGW1 and DGW2, the IP
          Prefix route is also imported and SN1/24 is added to the
          designated routing context with next-hop IP2 pointing at the
          local MAC-VRF10. Should ECMP be enabled in the routing
          context, SN1/24 would also be added to the routing table with
          next-hop IP3.

   (4) When DGW1 receives a packet from the WAN with destination IPx,
       where IPx belongs to SN1/24:

        o A destination IP lookup is performed on the DGW1 IP-VRF
          routing table and next-hop=IP2 is found. Since IP2 is an
          overlay next-hop a recursive route resolution is required for
          IP2.

        o IP2 is resolved to M2 in the ARP table, and M2 is resolved to
          the tunnel information given by the MAC FIB (remote VTEP and
          VNI for the VXLAN case).

        o The IP packet destined to IPx is encapsulated with:

             . Source inner MAC = IRB1 MAC

             . Destination inner MAC = M2

             . Tunnel information provided by the MAC-VRF (VNI, VTEP IPs
               and MACs for the VXLAN case)

   (5) When the packet arrives at NVE2:

        o Based on the tunnel information (VNI for the VXLAN case), the
          MAC-VRF10 context is identified for a MAC lookup.

        o Encapsulation is stripped-off and based on a MAC lookup
          (assuming MAC forwarding on the egress NVE), the packet is
          forwarded to TS2, where it will be properly routed.

   (6) Should TS2 move from NVE2 to NVE3, MAC Mobility procedures will
   be applied to the MAC route IP2/M2, as defined in [EVPN]. Route type
   5 prefixes are not subject to MAC mobility procedures, hence no
   changes in the DGW VRF routing table will occur for TS2 mobility,
   i.e. all the prefixes will still be pointing at IP2 as next-hop.
   There is an indirection for e.g. SN1/24, which still points at
   next-hop IP2 in the routing table, but IP2 will be simply resolved to
   a different tunnel, based on the outcome of the MAC mobility



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   procedures for the MAC/IP route IP2/M2.

   Note that in the opposite direction, TS2 will send traffic based on
   its static-route next-hop information (IRB1 and/or IRB2), and regular
   EVPN procedures will be applied.

5.2 Floating IP next-hop use-case

   Sometimes Tenant Systems (TS) work in active/standby mode where an
   upstream floating IP - owned by the active TS - is used as the
   next-hop to get to some subnets behind. This redundancy mode, already
   introduced in section 2.1 and 2.2, is illustrated in Figure 3.

                       NVE2                           DGW1
                    +-----------+ +---------+    +-------------+
       +---TS2(VA)--|(MAC-VRF10)|-|         |----|(MAC-VRF10)  |
       |     IP2/M2 +-----------+ |         |    |    IRB1\    |
       |      <-+                 |         |    |     (IP-VRF)|---+
       |        |                 |         |    +-------------+  _|_
      SN1    vIP23 (floating)     |  VXLAN/ |                    (   )
       |        |                 |  nvGRE  |         DGW2      ( WAN )
       |      <-+      NVE3       |         |    +-------------+ (___)
       |     IP3/M3 +-----------+ |         |----|(MAC-VRF10)  |   |
       +---TS3(VA)--|(MAC-VRF10)|-|         |    |    IRB2\    |   |
                    +-----------+ +---------+    |     (IP-VRF)|---+
                                                 +-------------+
                  Figure 3 Floating IP next-hop for redundant TS

   In this example, assuming TS2 is the active TS and owns IP23:

   (1) NVE2 advertises the following BGP routes for TS2:

        o Route type 2 (MAC/IP route) containing: ML=48, M=M2, IPL=32,
          IP=IP23 (and BGP Encapsulation Extended Community).

        o Route type 5 (IP Prefix route) containing: IPL=24, IP=SN1,
          ESI=0, GW IP address=IP23 (and BGP Encapsulation Extended
          Community).

   (2) NVE3 advertises the following BGP routes for TS3:

        o Route type 5 (IP Prefix route) containing: IPL=24, IP=SN1,
          ESI=0, GW IP address=IP23 (and BGP Encapsulation Extended
          Community).

   (3) DGW1 and DGW2 import both received routes based on the route-
          target:




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        o M2 is added to the MAC-VRF10 MAC FIB along with its
          corresponding tunnel information. For the VXLAN use case, the
          VTEP will be derived from the MAC/IP route BGP next-hop and
          VNI from the Ethernet Tag or MPLS fields. IP23 - M2 is added
          to the ARP table.

        o SN1/24 is added to the designated routing context in DGW1 and
          DGW2 with next-hop IP23 pointing at the local MAC-VRF10.

   (4) When DGW1 receives a packet from the WAN with destination IPx,
       where IPx belongs to SN1/24:

        o A destination IP lookup is performed on the DGW1 IP-VRF
          routing table and next-hop=IP23 is found. Since IP23 is an
          overlay next-hop, a recursive route resolution for IP23 is
          required.

        o IP23 is resolved to M2 in the ARP table, and M2 is resolved to
          the tunnel information given by the MAC-VRF (remote VTEP and
          VNI for the VXLAN case).

        o The IP packet destined to IPx is encapsulated with:

             . Source inner MAC = IRB1 MAC

             . Destination inner MAC = M2

             . Tunnel information provided by the MAC FIB (VNI, VTEP IPs
               and MACs for the VXLAN case)

   (5) When the packet arrives at NVE2:

        o Based on the tunnel information (VNI for the VXLAN case), the
          MAC-VRF10 context is identified for a MAC lookup.

        o Encapsulation is stripped-off and based on a MAC lookup
          (assuming MAC forwarding on the egress NVE), the packet is
          forwarded to TS2, where it will be properly routed.

   (6) When the redundancy protocol running between TS2 and TS3 appoints
       TS3 as the new active TS for SN1, TS3 will now own the floating
       IP23 and will signal this new ownership (GARP message or
       similar). Upon receiving the new owner's notification, NVE3 will
       issue a route type 2 for M3-IP23. DGW1 and DGW2 will update their
       ARP tables with the new MAC resolving the floating IP. No changes
       are carried out in the VRF routing table.

   In the DGW1/2 BGP RIB, there will be two route type 5 routes for SN1



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   (from NVE2 and NVE3) but only the one with the same BGP next-hop as
   the IP23 RT-2 BGP next-hop will be valid.


5.3 ESI next-hop ("Bump in the wire") use-case

   The following figure illustrates and example of inter-subnet
   forwarding for a subnet route that uses an ESI as an overlay next-
   hop. In this use-case, TS2 and TS3 are layer-2 VA devices without any
   IP address that can be included as an overlay next-hop in the GW IP
   field of the IP Prefix route.

                      NVE2                           DGW1
                  +-----------+ +---------+    +-------------+
     +---TS2(VA)--|(MAC-VRF10)|-|         |----|(MAC-VRF10)  |
     |      ESI23 +-----------+ |         |    |    IRB1\    |
     |        +                 |         |    |     (IP-VRF)|---+
     |        |                 |         |    +-------------+  _|_
    SN1       |                 |  VXLAN/ |                    (   )
     |        |                 |  nvGRE  |         DGW2      ( WAN )
     |        +      NVE3       |         |    +-------------+ (___)
     |      ESI23 +-----------+ |         |----|(MAC-VRF10)  |   |
     +---TS3(VA)--|(MAC-VRF10)|-|         |    |    IRB2\    |   |
                  +-----------+ +---------+    |     (IP-VRF)|---+
                                               +-------------+

                  Figure 5 ESI next-hop use-case

   Since neither TS2 nor TS3 can run any routing protocol and have no IP
   address assigned, an ESI, i.e. ESI23, will be provisioned on the
   attachment ports of NVE2 and NVE3. This model supports VA redundancy
   in a similar way as the one described in section 5.2 for the floating
   IP next-hop use-case, only using the EVPN Ethernet A-D route instead
   of the MAC advertisement route to advertise the location of the
   overlay next-hop. The procedure is explained below:

   (1) NVE2 advertises the following BGP routes for TS2:

        o Route type 1 (Ethernet A-D route for EVI-10) containing:
          ESI=ESI23 and the corresponding tunnel information (Ethernet
          Tag and/or MPLS label), as well as the BGP Encapsulation
          Extended Community. Assuming the ESI is active on NVE2, NVE2
          will advertise this route.

        o Route type 5 (IP Prefix route) containing: IPL=24, IP=SN1,
          ESI=ESI23, GW IP address=0 (and BGP Encapsulation Extended
          Community).




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   (2) NVE3 advertises the following BGP routes for TS3:

        o Route type 1 (Ethernet A-D route for EVI-10) containing:
          ESI=ESI23 and the corresponding tunnel information (Ethernet
          Tag and/or MPLS label), as well as the BGP Encapsulation
          Extended Community. NVE3 will advertise this route assuming
          the ESI is active on NVE2. Note that if the resiliency
          mechanism for TS2 and TS3 is in active-active mode, both NVE2
          and NVE3 will send the A-D route. Otherwise, that is, the
          resiliency is active-standby, only the NVE owning the active
          ESI will advertise the Ethernet A-D route for ESI23.

        o Route type 5 (IP Prefix route) containing: IPL=24, IP=SN1,
          ESI=23, GW IP address=0 (and BGP Encapsulation Extended
          Community).

   (3) DGW1 and DGW2 import the received routes based on the route-
          target:

        o The tunnel information to get to ESI23 is installed in DGW1
          and DGW2. For the VXLAN use case, the VTEP will be derived
          from the Ethernet A-D route BGP next-hop and VNI from the
          Ethernet Tag or MPLS fields (see [EVPN-OVERLAYS]).

        o SN1/24 is added to the designated routing context in DGW1 and
          DGW2 with next-hop ESI23 pointing at the local MAC-VRF10.

   (4) When DGW1 receives a packet from the WAN with destination IPx,
       where IPx belongs to SN1/24:

        o A destination IP lookup is performed on the DGW1 IP-VRF
          routing table and next-hop=ESI23 is found. Since ESI23 is an
          overlay next-hop, a recursive route resolution is required to
          find the egress NVE where ESI23 resides.

        o The IP packet destined to IPx is encapsulated with:

             . Source inner MAC = IRB1 MAC

             . Destination inner MAC = M2 (this MAC will be obtained
               after a lookup in the IP-VRF ARP table or in the MAC-
               VRF10 FDB table associated to ESI23).

             . Tunnel information provided by the Ethernet A-D route for
               ESI23 (VNI, VTEP IP and MACs for the VXLAN case).

   (5) When the packet arrives at NVE2:




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        o Based on the tunnel information (VNI for the VXLAN case), the
          MAC-VRF10 context is identified for a MAC lookup (assuming MAC
          disposition model).

        o Encapsulation is stripped-off and based on a MAC lookup
          (assuming MAC forwarding on the egress NVE), the packet is
          forwarded to TS2, where it will be properly forwarded.

   (6) If the redundancy protocol running between TS2 and TS3 follows an
       active/standby model and there is a failure, appointing TS3 as
       the new active TS for SN1, TS3 will now own the connectivity to
       SN1 and will signal this new ownership. Upon receiving the new
       owner's notification, NVE3 will issue a route type 1 for ESI23,
       whereas NVE2 will withdraw its Ethernet A-D route for ESI23. DGW1
       and DGW2 will update their tunnel information to resolve ESI23.
       No changes are carried out in the IP-VRF routing table.

   In the DGW1/2 BGP RIB, there will be two route type 5 routes for SN1
   (from NVE2 and NVE3) but only the one with the same BGP next-hop as
   the ESI23 route type 1 BGP next-hop will be valid.

5.4 IRB forwarding on NVEs for Subnets (IP-VRF-to-IP-VRF)

   This use-case is similar to the scenario described in "IRB forwarding
   on NVEs for Tenant Systems" in [EVPN-INTERSUBNET], however the new
   requirement here is the advertisement of IP Prefixes as opposed to
   only host routes. In the previous examples, the MAC-VRF instance can
   connect IRB interfaces and any other Tenant Systems connected to it.
   EVPN provides connectivity for:

   a) Traffic destined to the IRB IP interfaces as well as

   b) Traffic destined to IP subnets seating behind the TS, e.g. SN1 or
      SN2.

   In order to provide connectivity for (a) we need MAC/IP routes (RT-2)
   distributing IRB MACs and IPs. Connectivity type (b) is accomplished
   by the exchange of IP Prefix routes (RT-5) for IPs and subnets
   seating behind certain overlay next-hops.

   In some cases, subnets may be advertised in IP Prefix routes without
   any overlay next-hop since the RT-5 itself provides all the
   forwarding information required to send the packets to the egress NVE
   and no recursive route resolution is needed. This use case is
   depicted in the diagram below and we refer to it as the "IRB
   forwarding on NVEs for Subnets" or "IP-VRF-to-IP-VRF" use-case:





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                         NVE1
                +------------+
        IP1-----|(MAC-VRF1)  |                      DGW1
                |      \     |    +---------+ +--------+
                |    (IP-VRF)|----|         |-|(IP-VRF)|----+
                |       /    |    |         | +--------+    |
            |---|(MAC-VRF2)  |    |         |              _|_
            |   +------------+    |         |             (   )
         SN1|                     |  VXLAN/ |            ( WAN )
            |            NVE2     |  nvGRE  |             (___)
            |   +------------+    |         |               |
            |---|(MAC-VRF2)  |    |         |       DGW2    |
                |       \    |    |         | +--------+    |
                |    (IP-VRF)|----|         |-|(IP-VRF)|----+
                |       /    |    +---------+ +--------+
        SN2-----|(MAC-VRF3)  |
                +------------+


         Figure 6 Inter-subnet forwarding on NVEs for Subnets

   In this case, we need to provide connectivity from/to IP hosts in
   SN1, SN2, IP1 and hosts seating at the other end of the WAN. There is
   no need to define IRB interfaces to interconnect the IP-VRF instances
   among the NVEs for the same tenant. This is the reason why we refer
   to this solution as "IP-VRF-to-IP-VRF" solution.

   In this case, the EVPN route type 5 will be used to advertise the IP
   Prefixes, along with the Router's MAC Extended Community as defined
   in [EVPN-INTERSUBNET]. Each NVE/DGW will advertise an RT-5 for each
   of its subnet prefixes with the following fields:

        o RD as per [EVPN].

        o Eth-Tag ID = 0 assuming VLAN-based service.

        o IP address length and IP address, as explained in the previous
          sections.

        o GW IP address=0 and ESI=0, that is, no overlay next-hop is
          required in this use-case, since the BGP next-hop is enough to
          find the egress NVE to forward the packets to.

        o MPLS label or VNID corresponding to the IP-VRF.

   Each RT-5 will be sent with a route-target identifying the tenant
   (IP-VRF) and two BGP extended communities:




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        o The first one is the BGP Encapsulation Extended Community, as
          per [RFC5512], identifying the tunnel type.

        o The second one is the Router's MAC Extended Community as per
          [EVPN-INTERSUBNET] containing the MAC address associated to
          the NVE advertising the route. This MAC address identifies the
          NVE/DGW and MAY be re-used for all the IP-VRFs in the node.
          The ingress NVE will use this MAC address as the inner MAC
          destination address in the packets forwarded to the owner of
          the RT-5.

   Example of prefix advertisement for the ipv4 prefix SN1/24 advertised
   from NVE1:

   (1) NVE1 advertises the following BGP route for SN1:

        o Route type 5 (IP Prefix route) containing: Eth-Tag=0, IPL=24,
          IP=SN1, MPLS Label=10. An [RFC5512] BGP Encapsulation Extended
          Community will be sent, where Tunnel-type= VXLAN or NVGRE. A
          Router's MAC Extended Community will also be sent along with
          the RT-5, where the Router's MAC address value will contain
          the NVE1 MAC.

   (2) DGW1 imports the received route from NVE1 and SN1/24 is added to
       the designated IP-VRF. The next-hop for SN1/24 will be given by
       the route type 5 BGP next-hop (NVE1), which is resolved to a
       tunnel. For instance: if the tunnel is VXLAN based, the BGP next-
       hop will be resolved to a VXLAN tunnel where: destination-VTEP=
       NVE1 IP, VNI=10, inner destination MAC = NVE1 MAC (derived from
       the Router's MAC Extended Community value).

   (3) When DGW1 receives a packet from the WAN with destination IPx,
       where IPx belongs to SN1/24:

        o A destination IP lookup is performed on the DGW1 IP-VRF
          routing table and next-hop= "NVE1 IP" is found. The tunnel
          information to encapsulate the packet will be derived from the
          route type 5 received for SN1.

        o The IP packet destined to IPx is encapsulated with: Source
          inner MAC = DGW1 MAC, Destination inner MAC = NVE1 MAC, Source
          outer IP (source VTEP) = DGW1 IP, Destination outer IP
          (destination VTEP) = NVE1 IP.

   (4) When the packet arrives at NVE1:

        o Based on the tunnel information (VNI for the VXLAN case), the
          routing context is identified for an IP lookup.



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        o An IP lookup is performed in the routing context, where SN1
          turns out to be a local subnet associated to MAC-VRF2. A
          subsequent lookup in the ARP table and the MAC-VRF FIB will
          return the forwarding information for the packet in EVI-2.

6. Conclusions

   A new EVPN route type 5 for the advertisement of IP Prefixes is
   described in this document. This new route type has a differentiated
   role from the RT-2 route and addresses all the Data Center (or NVO-
   based networks in general) inter-subnet connectivity scenarios in
   which an IP Prefix advertisement is required. Using this new RT-5, an
   IP Prefix may be advertised along with an overlay next-hop that can
   be a GW IP address or an ESI, or without an overlay next-hop, in
   which case the BGP next-hop will point at the egress NVE and the MAC
   in the Router's MAC Extended Community will provide the inner MAC
   destination address to be used. As discussed throughout the document,
   the existing EVPN RT-2 does not meet the requirements for all the DC
   use cases, therefore a new EVPN route type is required.

   This new EVPN route type 5 decouples the IP Prefix advertisements
   from the MAC route advertisements in EVPN, hence:

   a) Allows the clean and clear advertisements of ipv4 or ipv6 prefixes
      in an NLRI with no MAC addresses in the route key, so that only IP
      information is used in BGP route comparisons.

   b) Since the route type is different from the MAC/IP advertisement
      route, the advertisement of prefixes will be excluded from all the
      procedures defined for the advertisement of VM MACs, e.g. MAC
      Mobility or aliasing. As a result of that, the current EVPN
      procedures do not need to be modified.

   c) Allows a flexible implementation where the prefix can be linked to
      different types of next-hops: overlay IP address, overlay ESI,
      underlay IP next-hops, etc.

   d) An EVPN implementation not requiring IP Prefixes can simply
      discard them by looking at the route type value. An unknown route
      type MUST be ignored by the receiving NVE/PE.


7. Conventions used in this document

      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].



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8. Security Considerations


9. IANA Considerations


10. References

10.1 Normative References

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


10.2 Informative References

   [EVPN] Sajassi et al., "BGP MPLS Based Ethernet VPN", draft-ietf-
      l2vpn-evpn-11.txt, work in progress, October, 2014

   [EVPN-OVERLAYS] Sajassi-Drake et al., "A Network Virtualization
      Overlay Solution using EVPN", draft-sd-l2vpn-evpn-overlay-03.txt,
      work in progress, June, 2014

   [EVPN-INTERSUBNET] Sajassi et al., "IP Inter-Subnet Forwarding in
      EVPN", draft-sajassi-l2vpn-evpn-inter-subnet-forwarding-05.txt,
      work in progress, October, 2014

11. Acknowledgments

      The authors would like to thank Mukul Katiyar and Senthil
      Sathappan for their valuable feedback and contributions. The
      following people also helped improving this document with their
      feedback: Antoni Przygienda and Thomas Morin.

12. Authors' Addresses

      Jorge Rabadan
      Alcatel-Lucent
      777 E. Middlefield Road
      Mountain View, CA 94043 USA
      Email: jorge.rabadan@alcatel-lucent.com

      Wim Henderickx
      Alcatel-Lucent
      Email: wim.henderickx@alcatel-lucent.com

      Florin Balus



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      Nuage Networks
      Email: florin@nuagenetworks.net

      Aldrin Isaac
      Bloomberg
      Email: aisaac71@bloomberg.net

      Senad Palislamovic
      Alcatel-Lucent
      Email: senad.palislamovic@alcatel-lucent.com

      John E. Drake
      Juniper Networks
      Email: jdrake@juniper.net

      Ali Sajassi
      Cisco
      Email: sajassi@cisco.com

































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