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RFC 7814

Virtual Subnet: A BGP/MPLS IP VPN-Based Subnet Extension Solution

Pages: 15
Informational

Top   ToC   RFC7814 - Page 1
Internet Engineering Task Force (IETF)                             X. Xu
Request for Comments: 7814                           Huawei Technologies
Category: Informational                                     C. Jacquenet
ISSN: 2070-1721                                                   Orange
                                                               R. Raszuk
                                                                T. Boyes
                                                            Bloomberg LP
                                                                  B. Fee
                                                        Extreme Networks
                                                              March 2016


   Virtual Subnet: A BGP/MPLS IP VPN-Based Subnet Extension Solution

Abstract

This document describes a BGP/MPLS IP VPN-based subnet extension solution referred to as "Virtual Subnet", which can be used for building Layer 3 network virtualization overlays within and/or between data centers. Status of This Memo This document is not an Internet Standards Track specification; it is published for informational purposes. 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). Not all documents approved by the IESG are a candidate for any level of Internet Standard; see 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/rfc7814.
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Copyright Notice

   Copyright (c) 2016 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 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Solution Description . . . . . . . . . . . . . . . . . . . . 5 3.1. Unicast . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.1.1. Intra-subnet Unicast . . . . . . . . . . . . . . . . 5 3.1.2. Inter-subnet Unicast . . . . . . . . . . . . . . . . 6 3.2. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 8 3.3. Host Discovery . . . . . . . . . . . . . . . . . . . . . 9 3.4. ARP/ND Proxy . . . . . . . . . . . . . . . . . . . . . . 9 3.5. Host Mobility . . . . . . . . . . . . . . . . . . . . . . 9 3.6. Forwarding Table Scalability on Data-Center Switches . . 10 3.7. ARP/ND Cache Table Scalability on Default Gateways . . . 10 3.8. ARP/ND and Unknown Unicast Flood Avoidance . . . . . . . 10 3.9. Path Optimization . . . . . . . . . . . . . . . . . . . . 10 4. Limitations . . . . . . . . . . . . . . . . . . . . . . . . . 11 4.1. Non-support of Non-IP Traffic . . . . . . . . . . . . . . 11 4.2. Non-support of IP Broadcast and Link-Local Multicast . . 11 4.3. TTL and Traceroute . . . . . . . . . . . . . . . . . . . 11 5. Security Considerations . . . . . . . . . . . . . . . . . . . 12 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 6.1. Normative References . . . . . . . . . . . . . . . . . . 12 6.2. Informative References . . . . . . . . . . . . . . . . . 13 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
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1. Introduction

For business continuity purposes, Virtual Machine (VM) migration across data centers is commonly used in situations such as data- center maintenance, migration, consolidation, expansion, or disaster avoidance. The IETF community has recognized that IP renumbering of servers (i.e., VMs) after the migration is usually complex and costly. To allow the migration of a VM from one data center to another without IP renumbering, the subnet on which the VM resides needs to be extended across these data centers. To achieve subnet extension across multiple cloud data centers in a scalable way, the following requirements and challenges must be considered: a. VPN Instance Space Scalability: In a modern cloud data-center environment, thousands or even tens of thousands of tenants could be hosted over a shared network infrastructure. For security and performance isolation purposes, these tenants need to be isolated from one another. b. Forwarding Table Scalability: With the development of server virtualization technologies, it's not uncommon for a single cloud data center to contain millions of VMs. This number already implies a big challenge to the forwarding table scalability of data-center switches. Provided multiple data centers of such scale were interconnected at Layer 2, this challenge would become even worse. c. ARP/ND Cache Table Scalability: [RFC6820] notes that the Address Resolution Protocol (ARP) / Neighbor Discovery (ND) cache tables maintained by default gateways within cloud data centers can raise scalability issues. Therefore, mastering the size of the ARP/ND cache tables is critical as the number of data centers to be connected increases. d. ARP/ND and Unknown Unicast Flooding: It's well-known that the flooding of ARP/ND broadcast/multicast messages as well as unknown unicast traffic within large Layer 2 networks is likely to affect network and host performance. When multiple data centers that each host millions of VMs are interconnected at Layer 2, the impact of such flooding would become even worse. As such, it becomes increasingly important to avoid the flooding of ARP/ND broadcast/multicast as well as unknown unicast traffic across data centers.
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   e.  Path Optimization: A subnet usually indicates a location in the
       network.  However, when a subnet has been extended across
       multiple geographically dispersed data-center locations, the
       location semantics of such a subnet is not retained any longer.
       As a result, traffic exchanged between a specific user and a
       server that would be located in different data centers may first
       be forwarded through a third data center.  This suboptimal
       routing would obviously result in unnecessary consumption of the
       bandwidth resources between data centers.  Furthermore, in the
       case where traditional Virtual Private LAN Service (VPLS)
       technology [RFC4761] [RFC4762] is used for data-center
       interconnect, return traffic from a server may be forwarded to a
       default gateway located in a different data center due to the
       configuration of a virtual router redundancy group.  This
       suboptimal routing would also unnecessarily consume the bandwidth
       resources between data centers.

   This document describes a BGP/MPLS IP VPN-based subnet extension
   solution referred to as "Virtual Subnet", which can be used for data-
   center interconnection while addressing all of the aforementioned
   requirements and challenges.  Here, the BGP/MPLS IP VPN means both
   BGP/MPLS IPv4 VPN [RFC4364] and BGP/MPLS IPv6 VPN [RFC4659].  In
   addition, since Virtual Subnet is built mainly on proven technologies
   such as BGP/MPLS IP VPN and ARP/ND proxy [RFC925] [RFC1027]
   [RFC4389], those service providers that provide Infrastructure as a
   Service (IaaS) cloud services can rely upon their existing BGP/MPLS
   IP VPN infrastructure and take advantage of their BGP/MPLS VPN
   operational experience to interconnect data centers.

   Although Virtual Subnet is described in this document as an approach
   for data-center interconnection, it can be used within data centers
   as well.

   Note that the approach described in this document is not intended to
   achieve an exact emulation of Layer 2 connectivity, and therefore it
   can only support a restricted Layer 2 connectivity service model with
   limitations that are discussed in Section 4.  The discussion about
   where this service model can apply is outside the scope of this
   document.

2. Terminology

This memo makes use of the terms defined in [RFC4364].
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3. Solution Description

3.1. Unicast

3.1.1. Intra-subnet Unicast

+--------------------+ +------------------+ | | +------------------+ |VPN_A:192.0.2.1/24| | | |VPN_A:192.0.2.1/24| | \ | | | | / | | +------+ \ ++---+-+ +-+---++/ +------+ | | |Host A+-----+ PE-1 | | PE-2 +----+Host B| | | +------+\ ++-+-+-+ +-+-+-++ /+------+ | | 192.0.2.2/24 | | | | | | 192.0.2.3/24 | | | | | | | | | | DC West | | | IP/MPLS Backbone | | | DC East | +------------------+ | | | | +------------------+ | +--------------------+ | | | VRF_A : V VRF_A : V +------------+---------+--------+ +------------+---------+--------+ | Prefix |Next hop |Protocol| | Prefix |Next hop |Protocol| +------------+---------+--------+ +------------+---------+--------+ |192.0.2.1/32|127.0.0.1| Direct | |192.0.2.1/32|127.0.0.1| Direct | +------------+---------+--------+ +------------+---------+--------+ |192.0.2.2/32|192.0.2.2| Direct | |192.0.2.2/32| PE-1 | IBGP | +------------+---------+--------+ +------------+---------+--------+ |192.0.2.3/32| PE-2 | IBGP | |192.0.2.3/32|192.0.2.3| Direct | +------------+---------+--------+ +------------+---------+--------+ |192.0.2.0/24|192.0.2.1| Direct | |192.0.2.0/24|192.0.2.1| Direct | +------------+---------+--------+ +------------+---------+--------+ Figure 1: Intra-subnet Unicast Example As shown in Figure 1, two hosts (i.e., Hosts A and B) belonging to the same subnet (i.e., 192.0.2.0/24) are located in different data centers (i.e., DC West and DC East), respectively. PE routers (i.e., PE-1 and PE-2) that are used for interconnecting these two data centers create host routes for their own local hosts respectively and then advertise these routes by means of the BGP/MPLS IP VPN signaling. Meanwhile, an ARP proxy is enabled on Virtual Routing and Forwarding (VRF) attachment circuits of these PE routers. Let's now assume that Host A sends an ARP request for Host B before communicating with Host B. Upon receiving the ARP request, PE-1 acting as an ARP proxy returns its own MAC address as a response. Host A then sends IP packets for Host B to PE-1. PE-1 tunnels such packets towards PE-2, which in turn forwards them to Host B. Thus,
Top   ToC   RFC7814 - Page 6
   Hosts A and B can communicate with each other as if they were located
   within the same subnet.

3.1.2. Inter-subnet Unicast

+--------------------+ +------------------+ | | +------------------+ |VPN_A:192.0.2.1/24| | | |VPN_A:192.0.2.1/24| | \ | | | | / | | +------+ \ ++---+-+ +-+---++/ +------+ | | |Host A+-------+ PE-1 | | PE-2 +-+----+Host B| | | +------+\ ++-+-+-+ +-+-+-++ | /+------+ | | 192.0.2.2/24 | | | | | | | 192.0.2.3/24 | | GW=192.0.2.4 | | | | | | | GW=192.0.2.4 | | | | | | | | | +------+ | | | | | | | | +----+ GW +-- | | | | | | | | /+------+ | | | | | | | | 192.0.2.4/24 | | | | | | | | | | DC West | | | IP/MPLS Backbone | | | DC East | +------------------+ | | | | +------------------+ | +--------------------+ | | | VRF_A : V VRF_A : V +------------+---------+--------+ +------------+---------+--------+ | Prefix |Next hop |Protocol| | Prefix |Next hop |Protocol| +------------+---------+--------+ +------------+---------+--------+ |192.0.2.1/32|127.0.0.1| Direct | |192.0.2.1/32|127.0.0.1| Direct | +------------+---------+--------+ +------------+---------+--------+ |192.0.2.2/32|192.0.2.2| Direct | |192.0.2.2/32| PE-1 | IBGP | +------------+---------+--------+ +------------+---------+--------+ |192.0.2.3/32| PE-2 | IBGP | |192.0.2.3/32|192.0.2.3| Direct | +------------+---------+--------+ +------------+---------+--------+ |192.0.2.4/32| PE-2 | IBGP | |192.0.2.4/32|192.0.2.4| Direct | +------------+---------+--------+ +------------+---------+--------+ |192.0.2.0/24|192.0.2.1| Direct | |192.0.2.0/24|192.0.2.1| Direct | +------------+---------+--------+ +------------+---------+--------+ | 0.0.0.0/0 | PE-2 | IBGP | | 0.0.0.0/0 |192.0.2.4| Static | +------------+---------+--------+ +------------+---------+--------+ Figure 2: Inter-subnet Unicast Example (1) As shown in Figure 2, only one data center (i.e., DC East) is deployed with a default gateway (i.e., GW). PE-2, which is connected to GW, would either be configured with or have learned a default route from GW with the next hop being pointed at GW. Meanwhile, this route is distributed to other PE routers (i.e., PE-1) as per normal operation as described in [RFC4364]. Assume Host A sends an ARP
Top   ToC   RFC7814 - Page 7
   request for its default gateway (i.e., 192.0.2.4) prior to
   communicating with a destination host outside of its subnet.  Upon
   receiving this ARP request, PE-1 acting as an ARP proxy returns its
   own MAC address as a response.  Host A then sends a packet for Host B
   to PE-1.  PE-1 tunnels such a packet towards PE-2 according to the
   default route learned from PE-2, which in turn forwards that packet
   to GW.
                           +--------------------+
    +------------------+   |                    |   +------------------+
    |VPN_A:192.0.2.1/24|   |                    |   |VPN_A:192.0.2.1/24|
    |              \   |   |                    |   |  /               |
    |  +------+     \ ++---+-+                +-+---++/     +------+   |
    |  |Host A+----+--+ PE-1 |                | PE-2 +-+----+Host B|   |
    |  +------+\   |  ++-+-+-+                +-+-+-++ |   /+------+   |
    |  192.0.2.2/24 |  | | |                    | | |  | 192.0.2.3/24  |
    |  GW=192.0.2.4 |  | | |                    | | |  | GW=192.0.2.4  |
    |  +------+    |   | | |                    | | |  |    +------+   |
    |--+ GW-1 +----+   | | |                    | | |  +----+ GW-2 +-- |
    |  +------+\       | | |                    | | |      /+------+   |
    |  192.0.2.4/24    | | |                    | | |    192.0.2.4/24  |
    |                  | | |                    | | |                  |
    |     DC West      | | |  IP/MPLS Backbone  | | |      DC East     |
    +------------------+ | |                    | | +------------------+
                        | +--------------------+ |
                        |                        |
VRF_A :                 V                VRF_A : V
+------------+---------+--------+      +------------+---------+--------+
|   Prefix   |Next hop |Protocol|      |   Prefix   |Next hop |Protocol|
+------------+---------+--------+      +------------+---------+--------+
|192.0.2.1/32|127.0.0.1| Direct |      |192.0.2.1/32|127.0.0.1| Direct |
+------------+---------+--------+      +------------+---------+--------+
|192.0.2.2/32|192.0.2.2| Direct |      |192.0.2.2/32|  PE-1   |  IBGP  |
+------------+---------+--------+      +------------+---------+--------+
|192.0.2.3/32|   PE-2  |  IBGP  |      |192.0.2.3/32|192.0.2.3| Direct |
+------------+---------+--------+      +------------+---------+--------+
|192.0.2.4/32|192.0.2.4| Direct |      |192.0.2.4/32|192.0.2.4| Direct |
+------------+---------+--------+      +------------+---------+--------+
|192.0.2.0/24|192.0.2.1| Direct |      |192.0.2.0/24|192.0.2.1| Direct |
+------------+---------+--------+      +------------+---------+--------+
| 0.0.0.0/0  |192.0.2.4| Static |      | 0.0.0.0/0  |192.0.2.4| Static |
+------------+---------+--------+      +------------+---------+--------+

                Figure 3: Inter-subnet Unicast Example (2)

   As shown in Figure 3, in the case where each data center is deployed
   with a default gateway, hosts will get ARP responses directly from
   their local default gateways, rather than from their local PE routers
   when sending ARP requests for their default gateways.
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                                  +------+
                           +------+ PE-3 +------+
    +------------------+   |      +------+      |   +------------------+
    |VPN_A:192.0.2.1/24|   |                    |   |VPN_A:192.0.2.1/24|
    |              \   |   |                    |   |  /               |
    |  +------+     \ ++---+-+                +-+---++/     +------+   |
    |  |Host A+-------+ PE-1 |                | PE-2 +------+Host B|   |
    |  +------+\      ++-+-+-+                +-+-+-++     /+------+   |
    |  192.0.2.2/24    | | |                    | | |    192.0.2.3/24  |
    |  GW=192.0.2.1    | | |                    | | |    GW=192.0.2.1  |
    |                  | | |                    | | |                  |
    |     DC West      | | |  IP/MPLS Backbone  | | |      DC East     |
    +------------------+ | |                    | | +------------------+
                         | +--------------------+ |
                         |                        |
VRF_A :                  V                VRF_A : V
+------------+---------+--------+      +------------+---------+--------+
|   Prefix   |Next hop |Protocol|      |   Prefix   |Next hop |Protocol|
+------------+---------+--------+      +------------+---------+--------+
|192.0.2.1/32|127.0.0.1| Direct |      |192.0.2.1/32|127.0.0.1| Direct |
+------------+---------+--------+      +------------+---------+--------+
|192.0.2.2/32|192.0.2.2| Direct |      |192.0.2.2/32|  PE-1   |  IBGP  |
+------------+---------+--------+      +------------+---------+--------+
|192.0.2.3/32|   PE-2  |  IBGP  |      |192.0.2.3/32|192.0.2.3| Direct |
+------------+---------+--------+      +------------+---------+--------+
|192.0.2.0/24|192.0.2.1| Direct |      |192.0.2.0/24|192.0.2.1| Direct |
+------------+---------+--------+      +------------+---------+--------+
| 0.0.0.0/0  |   PE-3  |  IBGP  |      | 0.0.0.0/0  |   PE-3  |  IBGP  |
+------------+---------+--------+      +------------+---------+--------+

                Figure 4: Inter-subnet Unicast Example (3)

   Alternatively, as shown in Figure 4, PE routers themselves could be
   configured as default gateways for their locally connected hosts as
   long as these PE routers have routes to reach outside networks.

3.2. Multicast

To support IP multicast between hosts of the same Virtual Subnet, Multicast VPN (MVPN) technologies [RFC6513] could be used without any change. For example, PE routers attached to a given VPN join a default provider multicast distribution tree that is dedicated to that VPN. Ingress PE routers, upon receiving multicast packets from their local hosts, forward them towards remote PE routers through the corresponding default provider multicast distribution tree. Within this context, the IP multicast doesn't include link-local multicast.
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3.3. Host Discovery

PE routers should be able to dynamically discover their local hosts and keep the list of these hosts up-to-date in a timely manner to ensure the availability and accuracy of the corresponding host routes originated from them. PE routers could accomplish local host discovery by some traditional host-discovery mechanisms using ARP or ND protocols.

3.4. ARP/ND Proxy

Acting as an ARP or ND proxy, a PE router should only respond to an ARP request or Neighbor Solicitation (NS) message for a target host when it has a best route for that target host in the associated VRF and the outgoing interface of that best route is different from the one over which the ARP request or NS message is received. In the scenario where a given VPN site (i.e., a data center) is multihomed to more than one PE router via an Ethernet switch or an Ethernet network, the Virtual Router Redundancy Protocol (VRRP) [RFC5798] is usually enabled on these PE routers. In this case, only the PE router being elected as the VRRP Master is allowed to perform the ARP/ND proxy function.

3.5. Host Mobility

During the VM migration process, the PE router to which the moving VM is now attached would create a host route for that host upon receiving a notification message of VM attachment (e.g., a gratuitous ARP or unsolicited NA message). The PE router to which the moving VM was previously attached would withdraw the corresponding host route when noticing the detachment of that VM. Meanwhile, the latter PE router could optionally broadcast a gratuitous ARP or send an unsolicited NA message on behalf of that host with the source MAC address being one of its own. In this way, the ARP/ND entry of this host that moved and that has been cached on any local host would be updated accordingly. In the case where there is no explicit VM detachment notification mechanism, the PE router could also use the following trick to detect the VM detachment: upon learning a route update for a local host from a remote PE router for the first time, the PE router could immediately check whether that local host is still attached to it by some means (e.g., ARP/ND PING and/or ICMP PING). It is important to ensure that the same MAC and IP are associated to the default gateway active in each data center, as the VM would most likely continue to send packets to the same default gateway address after having migrated from one data center to another. One possible way to achieve this goal is to configure the
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   same VRRP group on each location to ensure that the default gateway
   active in each data center shares the same virtual MAC and virtual IP
   addresses.

3.6. Forwarding Table Scalability on Data-Center Switches

In a Virtual Subnet environment, the MAC learning domain associated with a given Virtual Subnet that has been extended across multiple data centers is partitioned into segments, and each segment is confined within a single data center. Therefore, data-center switches only need to learn local MAC addresses, rather than learning both local and remote MAC addresses.

3.7. ARP/ND Cache Table Scalability on Default Gateways

When default gateway functions are implemented on PE routers as shown in Figure 4, the ARP/ND cache table on each PE router only needs to contain ARP/ND entries of local hosts. As a result, the ARP/ND cache table size would not grow as the number of data centers to be connected increases.

3.8. ARP/ND and Unknown Unicast Flood Avoidance

In a Virtual Subnet environment, the flooding domain associated with a given Virtual Subnet that was extended across multiple data centers, is partitioned into segments and each segment is confined within a single data center. Therefore, the performance impact on networks and servers imposed by the flooding of ARP/ND broadcast/ multicast and unknown unicast traffic is minimized.

3.9. Path Optimization

As shown in Figure 4, to optimize the forwarding path for the traffic between cloud users and cloud data centers, PE routers located in cloud data centers (i.e., PE-1 and PE-2), which are also acting as default gateways, propagate host routes for their own local hosts to remote PE routers that are attached to cloud user sites (i.e., PE-3). As such, traffic from cloud user sites to a given server on the Virtual Subnet that has been extended across data centers would be forwarded directly to the data-center location where that server resides, since traffic is now forwarded according to the host route for that server, rather than the subnet route. Furthermore, for traffic coming from cloud data centers and forwarded to cloud user sites, each PE router acting as a default gateway would forward traffic according to the longest-match route in the corresponding VRF. As a result, traffic from data centers to cloud user sites is forwarded along an optimal path as well.
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4. Limitations

4.1. Non-support of Non-IP Traffic

Although most traffic within and across data centers is IP traffic, there may still be a few legacy clustering applications that rely on non-IP communications (e.g., heartbeat messages between cluster nodes). Since Virtual Subnet is strictly based on L3 forwarding, those non-IP communications cannot be supported in the Virtual Subnet solution. In order to support those few non-IP traffic (if present) in the environment where the Virtual Subnet solution has been deployed, the approach following the idea of "route all IP traffic, bridge non-IP traffic" could be considered. In other words, all IP traffic including both intra- and inter-subnet, would be processed according to the Virtual Subnet design, while non-IP traffic would be forwarded according to a particular Layer 2 VPN approach. Such a unified L2/L3 VPN approach requires ingress PE routers to classify packets received from hosts before distributing them to the corresponding L2 or L3 VPN forwarding processes. Note that more and more cluster vendors are offering clustering applications based on Layer 3 interconnection.

4.2. Non-support of IP Broadcast and Link-Local Multicast

As illustrated before, intra-subnet traffic across PE routers is forwarded at Layer 3 in the Virtual Subnet solution. Therefore, IP broadcast and link-local multicast traffic cannot be forwarded across PE routers in the Virtual Subnet solution. In order to support the IP broadcast and link-local multicast traffic in the environment where the Virtual Subnet solution has been deployed, the unified L2/ L3 overlay approach as described in Section 4.1 could be considered as well. That is, IP broadcast and link-local multicast messages would be forwarded at Layer 2 while routable IP traffic would be processed according to the Virtual Subnet design.

4.3. TTL and Traceroute

As mentioned before, intra-subnet traffic is forwarded at Layer 3 in the Virtual Subnet context. Since it doesn't require any change to the Time-To-Live (TTL) handling mechanism of the BGP/MPLS IP VPN, when doing a traceroute operation on one host for another host (assuming that these two hosts are within the same subnet but are attached to different sites), the traceroute output would reflect the fact that these two hosts within the same subnet are actually connected via a Virtual Subnet, rather than a Layer 2 connection since the PE routers to which those two hosts are connected would be displayed in the traceroute output. In addition, for any other applications that generate intra-subnet traffic with TTL set to 1,
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   these applications may not work properly in the Virtual Subnet
   context, unless special TTL processing and loop-prevention mechanisms
   for such context have been implemented.  Details about such special
   TTL processing and loop-prevention mechanisms are outside the scope
   of this document.

5. Security Considerations

Since the BGP/MPLS IP VPN signaling is reused without any change, those security considerations as described in [RFC4364] are applicable to this document. Meanwhile, since security issues associated with the NDP are inherited due to the use of NDP proxy, those security considerations and recommendations as described in [RFC6583] are applicable to this document as well. Inter-data-center traffic often carries highly sensitive information at higher layers that is not directly understood (parsed) within an egress or ingress PE. For example, migrating a VM will often mean moving private keys and other sensitive configuration information. For this reason, inter-data-center traffic should always be protected for both confidentiality and integrity using a strong security mechanism such as IPsec [RFC4301]. In the future, it may be feasible to protect that traffic within the MPLS layer [MPLS-SEC] though at the time of writing, the mechanism for that is not sufficiently mature to recommend. Exactly how such security mechanisms are deployed will vary from case to case, so securing the inter-data- center traffic may or may not involve deploying security mechanisms on the ingress/egress PEs or further "inside" the data centers concerned. Note though that if security is not deployed on the egress/ingress PEs, there is a substantial risk that some sensitive traffic may be sent in the clear and will therefore be vulnerable to pervasive monitoring [RFC7258] or other attacks.

6. References

6.1. Normative References

[RFC925] Postel, J., "Multi-LAN address resolution", RFC 925, DOI 10.17487/RFC0925, October 1984, <http://www.rfc-editor.org/info/rfc925>. [RFC1027] Carl-Mitchell, S. and J. Quarterman, "Using ARP to implement transparent subnet gateways", RFC 1027, DOI 10.17487/RFC1027, October 1987, <http://www.rfc-editor.org/info/rfc1027>.
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   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
              2006, <http://www.rfc-editor.org/info/rfc4364>.

   [RFC4389]  Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery
              Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April
              2006, <http://www.rfc-editor.org/info/rfc4389>.

6.2. Informative References

[MPLS-SEC] Farrel, A. and S. Farrell, "Opportunistic Security in MPLS Networks", Work in Progress, draft-ietf-mpls- opportunistic-encrypt-01, March 2016. [RFC4301] Kent, S. and K. Seo, "Security Architecture for the Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, December 2005, <http://www.rfc-editor.org/info/rfc4301>. [RFC4659] De Clercq, J., Ooms, D., Carugi, M., and F. Le Faucheur, "BGP-MPLS IP Virtual Private Network (VPN) Extension for IPv6 VPN", RFC 4659, DOI 10.17487/RFC4659, September 2006, <http://www.rfc-editor.org/info/rfc4659>. [RFC4761] Kompella, K., Ed. and Y. Rekhter, Ed., "Virtual Private LAN Service (VPLS) Using BGP for Auto-Discovery and Signaling", RFC 4761, DOI 10.17487/RFC4761, January 2007, <http://www.rfc-editor.org/info/rfc4761>. [RFC4762] Lasserre, M., Ed. and V. Kompella, Ed., "Virtual Private LAN Service (VPLS) Using Label Distribution Protocol (LDP) Signaling", RFC 4762, DOI 10.17487/RFC4762, January 2007, <http://www.rfc-editor.org/info/rfc4762>. [RFC5798] Nadas, S., Ed., "Virtual Router Redundancy Protocol (VRRP) Version 3 for IPv4 and IPv6", RFC 5798, DOI 10.17487/RFC5798, March 2010, <http://www.rfc-editor.org/info/rfc5798>. [RFC6513] Rosen, E., Ed. and R. Aggarwal, Ed., "Multicast in MPLS/ BGP IP VPNs", RFC 6513, DOI 10.17487/RFC6513, February 2012, <http://www.rfc-editor.org/info/rfc6513>. [RFC6583] Gashinsky, I., Jaeggli, J., and W. Kumari, "Operational Neighbor Discovery Problems", RFC 6583, DOI 10.17487/RFC6583, March 2012, <http://www.rfc-editor.org/info/rfc6583>.
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   [RFC6820]  Narten, T., Karir, M., and I. Foo, "Address Resolution
              Problems in Large Data Center Networks", RFC 6820,
              DOI 10.17487/RFC6820, January 2013,
              <http://www.rfc-editor.org/info/rfc6820>.

   [RFC7258]  Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
              Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
              2014, <http://www.rfc-editor.org/info/rfc7258>.

Acknowledgements

Thanks to Susan Hares, Yongbing Fan, Dino Farinacci, Himanshu Shah, Nabil Bitar, Giles Heron, Ronald Bonica, Monique Morrow, Rajiv Asati, Eric Osborne, Thomas Morin, Martin Vigoureux, Pedro Roque Marque, Joe Touch, Wim Henderickx, Alia Atlas, and Stephen Farrell for their valuable comments and suggestions on this document. Thanks to Loa Andersson for his WG LC review on this document. Thanks to Alvaro Retana for his AD review on this document. Thanks to Ronald Bonica for his RtgDir review. Thanks to Donald Eastlake 3rd for his Sec-DIR review of this document. Thanks to Jouni Korhonen for the OPS-Dir review of this document. Thanks to Roni Even for the Gen-ART review of this document. Thanks to Sabrina Tanamal for the IANA review of this document.
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Authors' Addresses

Xiaohu Xu Huawei Technologies No.156 Beiqing Rd Beijing 100095 China Email: xuxiaohu@huawei.com Christian Jacquenet Orange 4 rue du Clos Courtel Cesson-Sevigne, 35512 France Email: christian.jacquenet@orange.com Robert Raszuk Bloomberg LP 731 Lexington Avenue New York City, NY 10022 United States Email: robert@raszuk.net Truman Boyes Bloomberg LP Email: tboyes@bloomberg.net Brendan Fee Extreme Networks Email: bfee@extremenetworks.com