draft-ietf-bess-virtual-subnet-02.txt   draft-ietf-bess-virtual-subnet-03.txt 
Network Working Group X. Xu Network Working Group X. Xu
Internet-Draft Huawei Internet-Draft Huawei
Intended status: Informational R. Raszuk Intended status: Informational R. Raszuk
Expires: April 13, 2016 Mirantis Inc. Expires: May 12, 2016 Mirantis Inc.
C. Jacquenet C. Jacquenet
Orange Orange
T. Boyes T. Boyes
Bloomberg LP Bloomberg LP
B. Fee B. Fee
Extreme Networks Extreme Networks
October 11, 2015 November 9, 2015
Virtual Subnet: A BGP/MPLS IP VPN-based Subnet Extension Solution Virtual Subnet: A BGP/MPLS IP VPN-based Subnet Extension Solution
draft-ietf-bess-virtual-subnet-02 draft-ietf-bess-virtual-subnet-03
Abstract Abstract
This document describes a BGP/MPLS IP VPN-based subnet extension This document describes a BGP/MPLS IP VPN-based subnet extension
solution referred to as Virtual Subnet, which can be used for solution referred to as Virtual Subnet, which can be used for
building Layer3 network virtualization overlays within and/or between building Layer 3 network virtualization overlays within and/or
data centers. between data centers.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 13, 2016. This Internet-Draft will expire on May 12, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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publication of this document. Please review these documents publication of this document. Please review these documents
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include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Solution Description . . . . . . . . . . . . . . . . . . . . 4 3. Solution Description . . . . . . . . . . . . . . . . . . . . 4
3.1. Unicast . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.1. Unicast . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1.1. Intra-subnet Unicast . . . . . . . . . . . . . . . . 5 3.1.1. Intra-subnet Unicast . . . . . . . . . . . . . . . . 4
3.1.2. Inter-subnet Unicast . . . . . . . . . . . . . . . . 6 3.1.2. Inter-subnet Unicast . . . . . . . . . . . . . . . . 5
3.2. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 8 3.2. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 8
3.3. CE Host Discovery . . . . . . . . . . . . . . . . . . . . 9 3.3. Host Discovery . . . . . . . . . . . . . . . . . . . . . 9
3.4. ARP/ND Proxy . . . . . . . . . . . . . . . . . . . . . . 9 3.4. ARP/ND Proxy . . . . . . . . . . . . . . . . . . . . . . 9
3.5. CE Host Mobility . . . . . . . . . . . . . . . . . . . . 9 3.5. Host Mobility . . . . . . . . . . . . . . . . . . . . . . 9
3.6. Forwarding Table Scalability on Data Center Switches . . 10 3.6. Forwarding Table Scalability on Data Center Switches . . 10
3.7. ARP/ND Cache Table Scalability on Default Gateways . . . 10 3.7. ARP/ND Cache Table Scalability on Default Gateways . . . 10
3.8. ARP/ND and Unknown Uncast Flood Avoidance . . . . . . . . 10 3.8. ARP/ND and Unknown Uncast Flood Avoidance . . . . . . . . 10
3.9. Path Optimization . . . . . . . . . . . . . . . . . . . . 10 3.9. Path Optimization . . . . . . . . . . . . . . . . . . . . 10
4. Limitations . . . . . . . . . . . . . . . . . . . . . . . . . 11 4. Limitations . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.1. Non-support of Non-IP Traffic . . . . . . . . . . . . . . 11 4.1. Non-support of Non-IP Traffic . . . . . . . . . . . . . . 11
4.2. Non-support of IP Broadcast and Link-local Multicast . . 11 4.2. Non-support of IP Broadcast and Link-local Multicast . . 11
4.3. TTL and Traceroute . . . . . . . . . . . . . . . . . . . 11 4.3. TTL and Traceroute . . . . . . . . . . . . . . . . . . . 11
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12 7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
8.1. Normative References . . . . . . . . . . . . . . . . . . 12 8.1. Normative References . . . . . . . . . . . . . . . . . . 12
8.2. Informative References . . . . . . . . . . . . . . . . . 13 8.2. Informative References . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction 1. Introduction
For business continuity purpose, Virtual Machine (VM) migration For business continuity purpose, Virtual Machine (VM) migration
across data centers is commonly used in those situations such as data across data centers is commonly used in situations such as data
center maintenance, data center migration, data center consolidation, center maintenance, data center migration, data center consolidation,
data center expansion, and data center disaster avoidance. It's data center expansion, and data center disaster avoidance. It's
generally admitted that IP renumbering of servers (i.e., VMs) after generally admitted that IP renumbering of servers (i.e., VMs) after
the migration is usually complex and costly at the risk of extending the migration is usually complex and costly at the risk of extending
the business downtime during the process of migration. To allow the the business downtime during the process of migration. To allow the
migration of a VM from one data center to another without IP migration of a VM from one data center to another without IP
renumbering, the subnet on which the VM resides needs to be extended renumbering, the subnet on which the VM resides needs to be extended
across these data centers. across these data centers.
To achieve subnet extension across multiple Infrastructure-as- To achieve subnet extension across multiple Infrastructure-as-
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environment, thousands or even tens of thousands of tenants could environment, thousands or even tens of thousands of tenants could
be hosted over a shared network infrastructure. For security and be hosted over a shared network infrastructure. For security and
performance isolation purposes, these tenants need to be isolated performance isolation purposes, these tenants need to be isolated
from one another. from one another.
b. Forwarding Table Scalability: With the development of server b. Forwarding Table Scalability: With the development of server
virtualization technologies, it's not uncommon for a single cloud virtualization technologies, it's not uncommon for a single cloud
data center to contain millions of VMs. This number already data center to contain millions of VMs. This number already
implies a big challenge on the forwarding table scalability of implies a big challenge on the forwarding table scalability of
data center switches. Provided multiple data centers of such data center switches. Provided multiple data centers of such
scale were interconnected at layer2, this challenge would become scale were interconnected at Layer 2, this challenge would become
even worse. even worse.
c. ARP/ND Cache Table Scalability: [RFC6820] notes that the Address c. ARP/ND Cache Table Scalability: [RFC6820] notes that the Address
Resolution Protocol (ARP)/Neighbor Discovery (ND) cache tables Resolution Protocol (ARP)/Neighbor Discovery (ND) cache tables
maintained on default gateways within cloud data centers can maintained on default gateways within cloud data centers can
raise scalability issues. Therefore, it's very useful if the raise scalability issues. Therefore, it's very useful if the
ARP/ND cache table size could be prevented from growing by ARP/ND cache table size could be prevented from growing by
multiples as the number of data centers to be connected multiples as the number of data centers to be connected
increases. increases.
d. ARP/ND and Unknown Unicast Flooding: It's well-known that the d. ARP/ND and Unknown Unicast Flooding: It's well-known that the
flooding of ARP/ND broadcast/multicast and unknown unicast flooding of ARP/ND broadcast/multicast and unknown unicast
traffic within large Layer2 networks would affect the performance traffic within large Layer 2 networks would affect the
of networks and hosts. As multiple data centers with each performance of networks and hosts. As multiple data centers with
containing millions of VMs are interconnected at layer2, the each containing millions of VMs are interconnected at Layer 2,
impact of flooding as mentioned above would become even worse. the impact of flooding as mentioned above would become even
As such, it becomes increasingly important to avoid the flooding worse. As such, it becomes increasingly important to avoid the
of ARP/ND broadcast/multicast and unknown unicast traffic across flooding of ARP/ND broadcast/multicast and unknown unicast
data centers. traffic across data centers.
e. Path Optimization: A subnet usually indicates a location in the e. Path Optimization: A subnet usually indicates a location in the
network. However, when a subnet has been extended across network. However, when a subnet has been extended across
multiple geographically dispersed data center locations, the multiple geographically dispersed data center locations, the
location semantics of such subnet is not retained any longer. As location semantics of such subnet is not retained any longer. As
a result, the traffic from a cloud user (i.e., a VPN user) which a result, the traffic between a specific user and server, in
is destined for a given server located at one data center different data centers, may first be routed through a third data
location of such extended subnet may arrive at another data center. This suboptimal routing would obviously result in an
center location firstly according to the subnet route, and then
be forwarded to the location where the service is actually
located. This suboptimal routing would obviously result in an
unnecessary consumption of the bandwidth resource between data unnecessary consumption of the bandwidth resource between data
centers. Furthermore, in the case where the traditional VPLS centers. Furthermore, in the case where traditional VPLS
technology [RFC4761] [RFC4762] is used for data center technology [RFC4761] [RFC4762] is used for data center
interconnect and default gateways of different data center interconnect, return traffic from a server may be forwarded to a
locations are configured within the same virtual router default gateway located in a different data center due to the
redundancy group, the returning traffic from that server to the configuration in a virtual router redundancy group. This
cloud user may be forwarded at layer2 to a default gateway
located at one of the remote data center premises, rather than
the one placed at the local data center location. This
suboptimal routing would also unnecessarily consume the bandwidth suboptimal routing would also unnecessarily consume the bandwidth
resource between data centers resource between data centers.
This document describes a BGP/MPLS IP VPN-based subnet extension This document describes a BGP/MPLS IP VPN-based subnet extension
solution referred to as Virtual Subnet, which can be used for data solution referred to as Virtual Subnet, which can be used for data
center interconnection while addressing all of the requirements and center interconnection while addressing all of the requirements and
challenges as mentioned above. Here the BGP/MPLS IP VPN means both challenges as mentioned above. Here the BGP/MPLS IP VPN means both
BGP/MPLS IPv4 VPN [RFC4364] and BGP/MPLS IPv6 VPN [RFC4659]. In BGP/MPLS IPv4 VPN [RFC4364] and BGP/MPLS IPv6 VPN [RFC4659]. In
addition, since Virtual Subnet is mainly built on proven technologies addition, since Virtual Subnet is mainly built on proven technologies
such as BGP/MPLS IP VPN and ARP/ND proxy [RFC0925][RFC1027][RFC4389], such as BGP/MPLS IP VPN and ARP/ND proxy [RFC0925][RFC1027][RFC4389],
those service providers offering IaaS public cloud services could those service providers offering IaaS public cloud services could
rely upon their existing BGP/MPLS IP VPN infrastructures and their rely upon their existing BGP/MPLS IP VPN infrastructures and their
corresponding experiences to realize data center interconnection. corresponding experiences to realize data center interconnection.
Although Virtual Subnet is described in this document as an approach Although Virtual Subnet is described in this document as an approach
for data center interconnection, it actually could be used within for data center interconnection, it actually could be used within
data centers as well. data centers as well.
Note that the approach described in this document is not intended to Note that the approach described in this document is not intended to
achieve an exact emulation of L2 connectivity and therefore it can achieve an exact emulation of Layer 2 connectivity and therefore it
only support a restricted L2 connectivity service model with can only support a restricted Layer 2 connectivity service model with
limitations declared in Section 4. As for the discussion about in limitations declared in Section 4. As for the discussion about in
which environment this service model should be suitable, it's outside which environment this service model should be suitable, it's outside
the scope of this document. the scope of this document.
1.1. Requirements Language 1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
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|192.0.2.1/32|127.0.0.1| Direct | |192.0.2.1/32|127.0.0.1| Direct | |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 | |192.0.2.2/32|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 | |192.0.2.3/32| 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 | |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 Figure 1: Intra-subnet Unicast Example
As shown in Figure 1, two CE hosts (i.e., Hosts A and B) belonging to 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 at different data the same subnet (i.e., 192.0.2.0/24) are located at different data
centers (i.e., DC West and DC East) respectively. PE routers (i.e., centers (i.e., DC West and DC East) respectively. PE routers (i.e.,
PE-1 and PE-2) which are used for interconnecting these two data PE-1 and PE-2) which are used for interconnecting these two data
centers create host routes for their own local CE hosts respectively centers create host routes for their own local hosts respectively and
and then advertise them via the BGP/MPLS IP VPN signaling. then advertise them via the BGP/MPLS IP VPN signaling. Meanwhile, an
Meanwhile, ARP proxy is enabled on VRF attachment circuits of these ARP proxy is enabled on VRF attachment circuits of these PE routers.
PE routers.
Now assume host A sends an ARP request for host B before Now assume host A sends an ARP request for host B before
communicating with host B. Upon receiving the ARP request, PE-1 communicating with host B. Upon receiving the ARP request, PE-1
acting as an ARP proxy returns its own MAC address as a response. 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 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, packets towards PE-2 which in turn forwards them to host B. Thus,
hosts A and B can communicate with each other as if they were located hosts A and B can communicate with each other as if they were located
within the same subnet. within the same subnet.
3.1.2. Inter-subnet Unicast 3.1.2. Inter-subnet Unicast
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+------------+---------+--------+ +------------+---------+--------+ +------------+---------+--------+ +------------+---------+--------+
|192.0.2.4/32|192.0.2.4| Direct | |192.0.2.4/32|192.0.2.4| 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 | |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 | | 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) Figure 3: Inter-subnet Unicast Example (2)
As shown in Figure 3, in the case where each data center is deployed As shown in Figure 3, in the case where each data center is deployed
with a default gateway, CE hosts will get ARP responses directly from with a default gateway, hosts will get ARP responses directly from
their local default gateways, rather than from their local PE routers their local default gateways, rather than from their local PE routers
when sending ARP requests for their default gateways. when sending ARP requests for their default gateways.
+------+ +------+
+------+ PE-3 +------+ +------+ PE-3 +------+
+------------------+ | +------+ | +------------------+ +------------------+ | +------+ | +------------------+
|VPN_A:192.0.2.1/24| | | |VPN_A:192.0.2.1/24| |VPN_A:192.0.2.1/24| | | |VPN_A:192.0.2.1/24|
| \ | | | | / | | \ | | | | / |
| +------+ \ ++---+-+ +-+---++/ +------+ | | +------+ \ ++---+-+ +-+---++/ +------+ |
| |Host A+-------+ PE-1 | | PE-2 +------+Host B| | | |Host A+-------+ PE-1 | | PE-2 +------+Host B| |
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+------------+---------+--------+ +------------+---------+--------+ +------------+---------+--------+ +------------+---------+--------+
|192.0.2.3/32| PE-2 | IBGP | |192.0.2.3/32|192.0.2.3| Direct | |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 | |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 | | 0.0.0.0/0 | PE-3 | IBGP | | 0.0.0.0/0 | PE-3 | IBGP |
+------------+---------+--------+ +------------+---------+--------+ +------------+---------+--------+ +------------+---------+--------+
Figure 4: Inter-subnet Unicast Example (3) Figure 4: Inter-subnet Unicast Example (3)
Alternatively, as shown in Figure 4, PE routers themselves could be Alternatively, as shown in Figure 4, PE routers themselves could be
directly configured as default gateways of their locally connected CE directly configured as default gateways of their locally connected
hosts as long as these PE routers have routes for outside networks. hosts as long as these PE routers have routes for outside networks.
3.2. Multicast 3.2. Multicast
To support IP multicast between CE hosts of the same virtual subnet, To support IP multicast between hosts of the same Virtual Subnet,
MVPN technologies [RFC6513] could be directly used without any MVPN technologies [RFC6513] could be directly used without any
change. For example, PE routers attached to a given VPN join a change. For example, PE routers attached to a given VPN join a
default provider multicast distribution tree which is dedicated for default provider multicast distribution tree which is dedicated for
that VPN. Ingress PE routers, upon receiving multicast packets from that VPN. Ingress PE routers, upon receiving multicast packets from
their local CE hosts, forward them towards remote PE routers through their local hosts, forward them towards remote PE routers through the
the corresponding default provider multicast distribution tree. corresponding default provider multicast distribution tree. Note
that here the IP multicast doesn't include link-local multicast.
3.3. CE Host Discovery 3.3. Host Discovery
PE routers SHOULD be able to discover their local CE hosts and keep PE routers should be able to discover their local hosts and keep the
the list of these hosts up to date in a timely manner so as to ensure list of these hosts up to date in a timely manner so as to ensure the
the availability and accuracy of the corresponding host routes availability and accuracy of the corresponding host routes originated
originated from them. PE routers could accomplish local CE host from them. PE routers could accomplish local host discovery by some
discovery by some traditional host discovery mechanisms using ARP or traditional host discovery mechanisms using ARP or ND protocols.
ND protocols. Furthermore, Link Layer Discovery Protocol (LLDP) or
VSI Discovery and Configuration Protocol (VDP), or even interaction
with the data center orchestration system could also be considered as
a means to dynamically discover local CE hosts
3.4. ARP/ND Proxy 3.4. ARP/ND Proxy
Acting as an ARP or ND proxies, a PE routers SHOULD only respond to Acting as an ARP or ND proxies, a PE routers should only respond to
an ARP request or Neighbor Solicitation (NS) message for a target 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 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 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 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 multi-homed scenario where a given VPN site (i.e., a data center) is multi-homed
to more than one PE router via an Ethernet switch or an Ethernet to more than one PE router via an Ethernet switch or an Ethernet
network, Virtual Router Redundancy Protocol (VRRP) [RFC5798] is network, Virtual Router Redundancy Protocol (VRRP) [RFC5798] is
usually enabled on these PE routers. In this case, only the PE usually enabled on these PE routers. In this case, only the PE
router being elected as the VRRP Master is allowed to perform the router being elected as the VRRP Master is allowed to perform the
ARP/ND proxy function. ARP/ND proxy function.
3.5. CE Host Mobility 3.5. Host Mobility
During the VM migration process, the PE router to which the moving VM During the VM migration process, the PE router to which the moving VM
is now attached would create a host route for that CE host upon is now attached would create a host route for that host upon
receiving a notification message of VM attachment (e.g., a gratuitous receiving a notification message of VM attachment (e.g., a gratuitous
ARP or unsolicited NA message). The PE router to which the moving VM ARP or unsolicited NA message). The PE router to which the moving VM
was previously attached would withdraw the corresponding host route was previously attached would withdraw the corresponding host route
when receiving a notification message of VM detachment (e.g., a VDP when receiving a notification message of VM detachment (e.g., a VDP
message about VM detachment). Meanwhile, the latter PE router could message about VM detachment). Meanwhile, the latter PE router could
optionally broadcast a gratuitous ARP or send an unsolicited NA optionally broadcast a gratuitous ARP or send an unsolicited NA
message on behalf of that CE host with source MAC address being one message on behalf of that host with source MAC address being one of
of its own. In this way, the ARP/ND entry of this CE host that moved its own. In this way, the ARP/ND entry of this host that moved and
and which has been cached on any local CE host would be updated which has been cached on any local host would be updated accordingly.
accordingly. In the case where there is no explicit VM detachment In the case where there is no explicit VM detachment notification
notification mechanism, the PE router could also use the following mechanism, the PE router could also use the following trick to
trick to determine the VM detachment event: upon learning a route determine the VM detachment event: upon learning a route update for a
update for a local CE host from a remote PE router for the first local host from a remote PE router for the first time, the PE router
time, the PE router could immediately check whether that local CE could immediately check whether that local host is still attached to
host is still attached to it by some means (e.g., ARP/ND PING and/or it by some means (e.g., ARP/ND PING and/or ICMP PING). It is
ICMP PING). It is important to ensure that the same MAC and IP are important to ensure that the same MAC and IP are associated to the
associated to the default gateway active in each data center, as the default gateway active in each data center, as the VM would most
VM would most likely continue to send packets to the same default likely continue to send packets to the same default gateway address
gateway address after migrated from one data center to another. One after migrated from one data center to another. One possible way to
possible way to achieve this goal is to configure the same VRRP group achieve this goal is to configure the same VRRP group on each
on each location so as to ensure the default gateway active in each location so as to ensure the default gateway active in each data
data center share the same virtual MAC and virtual IP addresses. center share the same virtual MAC and virtual IP addresses.
3.6. Forwarding Table Scalability on Data Center Switches 3.6. Forwarding Table Scalability on Data Center Switches
In a VS environment, the MAC learning domain associated with a given In a Virtual Subnet environment, the MAC learning domain associated
virtual subnet which has been extended across multiple data centers with a given Virtual Subnet which has been extended across multiple
is partitioned into segments and each segment is confined within a data centers is partitioned into segments and each segment is
single data center. Therefore data center switches only need to confined within a single data center. Therefore data center switches
learn local MAC addresses, rather than learning both local and remote only need to learn local MAC addresses, rather than learning both
MAC addresses. local and remote MAC addresses.
3.7. ARP/ND Cache Table Scalability on Default Gateways 3.7. ARP/ND Cache Table Scalability on Default Gateways
When default gateway functions are implemented on PE routers as shown 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 in Figure 4, the ARP/ND cache table on each PE router only needs to
contain ARP/ND entries of local CE hosts As a result, the ARP/ND contain ARP/ND entries of local hosts As a result, the ARP/ND cache
cache table size would not grow as the number of data centers to be table size would not grow as the number of data centers to be
connected increases. connected increases.
3.8. ARP/ND and Unknown Uncast Flood Avoidance 3.8. ARP/ND and Unknown Uncast Flood Avoidance
In VS, the flooding domain associated with a given virtual subnet In VS, the flooding domain associated with a given Virtual Subnet
that has been extended across multiple data centers, is partitioned that has been extended across multiple data centers, is partitioned
into segments and each segment is confined within a single data into segments and each segment is confined within a single data
center. Therefore, the performance impact on networks and servers center. Therefore, the performance impact on networks and servers
imposed by the flooding of ARP/ND broadcast/multicast and unknown imposed by the flooding of ARP/ND broadcast/multicast and unknown
unicast traffic is alleviated. unicast traffic is alleviated.
3.9. Path Optimization 3.9. Path Optimization
Take the scenario shown in Figure 4 as an example, to optimize the Take the scenario shown in Figure 4 as an example, to optimize the
forwarding path for the traffic between cloud users and cloud data forwarding path for the traffic between cloud users and cloud data
centers, PE routers located at cloud data centers (i.e., PE-1 and PE- centers, PE routers located at cloud data centers (i.e., PE-1 and PE-
2), which are also acting as default gateways, propagate host routes 2), which are also acting as default gateways, propagate host routes
for their own local CE hosts respectively to remote PE routers which for their own local hosts respectively to remote PE routers which are
are attached to cloud user sites (i.e., PE-3). As such, the traffic attached to cloud user sites (i.e., PE-3). As such, the traffic from
from cloud user sites to a given server on the virtual subnet which cloud user sites to a given server on the Virtual Subnet which has
has been extended across data centers would be forwarded directly to been extended across data centers would be forwarded directly to the
the data center location where that server resides, since the traffic data center location where that server resides, since the traffic is
is now forwarded according to the host route for that server, rather now forwarded according to the host route for that server, rather
than the subnet route. Furthermore, for the traffic coming from than the subnet route. Furthermore, for the traffic coming from
cloud data centers and forwarded to cloud user sites, each PE router cloud data centers and forwarded to cloud user sites, each PE router
acting as a default gateway would forward the traffic according to acting as a default gateway would forward the traffic according to
the best-match route in the corresponding VRF. As a result, the the best-match route in the corresponding VRF. As a result, the
traffic from data centers to cloud user sites is forwarded along an traffic from data centers to cloud user sites is forwarded along an
optimal path as well. optimal path as well.
4. Limitations 4. Limitations
4.1. Non-support of Non-IP Traffic 4.1. Non-support of Non-IP Traffic
skipping to change at page 11, line 22 skipping to change at page 11, line 20
there may still be a few legacy clustering applications which rely on there may still be a few legacy clustering applications which rely on
non-IP communications (e.g., heartbeat messages between cluster non-IP communications (e.g., heartbeat messages between cluster
nodes). Since Virtual Subnet is strictly based on L3 forwarding, nodes). Since Virtual Subnet is strictly based on L3 forwarding,
those non-IP communications cannot be supported in the Virtual Subnet those non-IP communications cannot be supported in the Virtual Subnet
solution. In order to support those few non-IP traffic (if present) solution. In order to support those few non-IP traffic (if present)
in the environment where the Virtual Subnet solution has been in the environment where the Virtual Subnet solution has been
deployed, the approach following the idea of "route all IP traffic, deployed, the approach following the idea of "route all IP traffic,
bridge non-IP traffic" could be considered. That's to say, all IP bridge non-IP traffic" could be considered. That's to say, all IP
traffic including both intra-subnet and inter-subnet would be traffic including both intra-subnet and inter-subnet would be
processed by the Virtual Subnet process, while the non-IP traffic processed by the Virtual Subnet process, while the non-IP traffic
would be resorted to a particular Layer2 VPN approach. Such unified would be resorted to a particular Layer 2 VPN approach. Such unified
L2/L3 VPN approach requires ingress PE routers to classify the L2/L3 VPN approach requires ingress PE routers to classify the
traffic received from CE hosts before distributing them to the traffic received from hosts before distributing them to the
corresponding L2 or L3 VPN forwarding processes. Note that more and corresponding L2 or L3 VPN forwarding processes. Note that more and
more cluster vendors are offering clustering applications based on more cluster vendors are offering clustering applications based on
Layer 3 interconnection. Layer 3 interconnection.
4.2. Non-support of IP Broadcast and Link-local Multicast 4.2. Non-support of IP Broadcast and Link-local Multicast
As illustrated before, intra-subnet traffic is forwarded at Layer3 in As illustrated before, intra-subnet traffic is forwarded at Layer 3
the Virtual Subnet solution. Therefore, IP broadcast and link-local in the Virtual Subnet solution. Therefore, IP broadcast and link-
multicast traffic cannot be supported by the Virtual Subnet solution. local multicast traffic cannot be supported by the Virtual Subnet
In order to support the IP broadcast and link-local multicast traffic solution. In order to support the IP broadcast and link-local
in the environment where the Virtual Subnet solution has been multicast traffic in the environment where the Virtual Subnet
deployed, the unified L2/L3 overlay approach as described in solution has been deployed, the unified L2/L3 overlay approach as
Section 4.1 could be considered as well. That's to say, the IP described in Section 4.1 could be considered as well. That's to say,
broadcast and link-local multicast would be resorted to the L2VPN the IP broadcast and link-local multicast would be resorted to the
forwarding process while the routable IP traffic would be processed L2VPN forwarding process while the routable IP traffic would be
by the Virtual Subnet process. processed by the Virtual Subnet process.
4.3. TTL and Traceroute 4.3. TTL and Traceroute
As illustrated before, intra-subnet traffic is forwarded at Layer3 in As illustrated before, intra-subnet traffic is forwarded at Layer 3
the Virtual Subnet context. Since it doesn't require any change to in the Virtual Subnet context. Since it doesn't require any change
the TTL handling mechanism of the BGP/MPLS IP VPN, when doing a to the TTL handling mechanism of the BGP/MPLS IP VPN, when doing a
traceroute operation on one CE host for another CE host (assuming traceroute operation on one host for another host (assuming that
that these two hosts are within the same subnet but are attached to these two hosts are within the same subnet but are attached to
different sites), the traceroute output would reflect the fact that different sites), the traceroute output would reflect the fact that
these two hosts belonging to the same subnet are actually connected these two hosts within the same subnet are actually connected via an
via an virtual subnet emulated by ARP proxy, rather than a normal Virtual Subnet, rather than a Layer 2 connection since the PE routers
LAN. In addition, for any other applications which generate intra- to which those two host are connected respectively would be displayed
subnet traffic with TTL set to 1, these applications may not be in the traceroute output. In addition, for any other applications
workable in the Virtual Subnet context, unless special TTL processing which generate intra-subnet traffic with TTL set to 1, these
for such case has been implemented (e.g., if the source and applications may not be workable in the Virtual Subnet context,
destination addresses of a packet whose TTL is set to 1 belong to the unless special TTL processing for such case has been implemented
same extended subnet, neither ingress nor egress PE routers SHOULD (e.g., if the source and destination addresses of a packet whose TTL
decrement the TTL of such packet. Furthermore, the TTL of such is set to 1 belong to the same extended subnet, neither ingress nor
packet SHOULD NOT be copied into the TTL of the transport tunnel and egress PE routers should decrement the TTL of such packet.
vice versa). Furthermore, the TTL of such packet should not be copied into the TTL
of the transport tunnel and vice versa).
5. Acknowledgements 5. Acknowledgements
Thanks to Susan Hares, Yongbing Fan, Dino Farinacci, Himanshu Shah, Thanks to Susan Hares, Yongbing Fan, Dino Farinacci, Himanshu Shah,
Nabil Bitar, Giles Heron, Ronald Bonica, Monique Morrow, Rajiv Asati, Nabil Bitar, Giles Heron, Ronald Bonica, Monique Morrow, Rajiv Asati,
Eric Osborne, Thomas Morin, Martin Vigoureux, Pedro Roque Marque, Joe Eric Osborne, Thomas Morin, Martin Vigoureux, Pedro Roque Marque, Joe
Touch and Wim Henderickx for their valuable comments and suggestions Touch and Wim Henderickx for their valuable comments and suggestions
on this document. Thanks to Loa Andersson for his WG LC review on on this document. Thanks to Loa Andersson for his WG LC review on
this document. this document. Thanks to Alvaro Retana for his AD review on this
document. Thanks to Ronald Bonica for his RtgDir review.
6. IANA Considerations 6. IANA Considerations
There is no requirement for any IANA action. There is no requirement for any IANA action.
7. Security Considerations 7. Security Considerations
This document doesn't introduce additional security risk to BGP/MPLS This document doesn't introduce additional security risk to BGP/MPLS
IP VPN, nor does it provide any additional security feature for BGP/ IP VPN, nor does it provide any additional security feature for BGP/
MPLS IP VPN. MPLS IP VPN.
skipping to change at page 13, line 13 skipping to change at page 13, line 13
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private [RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
2006, <http://www.rfc-editor.org/info/rfc4364>. 2006, <http://www.rfc-editor.org/info/rfc4364>.
[RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery
Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April
2006, <http://www.rfc-editor.org/info/rfc4389>. 2006, <http://www.rfc-editor.org/info/rfc4389>.
8.2. Informative References
[RFC4659] De Clercq, J., Ooms, D., Carugi, M., and F. Le Faucheur, [RFC4659] De Clercq, J., Ooms, D., Carugi, M., and F. Le Faucheur,
"BGP-MPLS IP Virtual Private Network (VPN) Extension for "BGP-MPLS IP Virtual Private Network (VPN) Extension for
IPv6 VPN", RFC 4659, DOI 10.17487/RFC4659, September 2006, IPv6 VPN", RFC 4659, DOI 10.17487/RFC4659, September 2006,
<http://www.rfc-editor.org/info/rfc4659>. <http://www.rfc-editor.org/info/rfc4659>.
[RFC4761] Kompella, K., Ed. and Y. Rekhter, Ed., "Virtual Private [RFC4761] Kompella, K., Ed. and Y. Rekhter, Ed., "Virtual Private
LAN Service (VPLS) Using BGP for Auto-Discovery and LAN Service (VPLS) Using BGP for Auto-Discovery and
Signaling", RFC 4761, DOI 10.17487/RFC4761, January 2007, Signaling", RFC 4761, DOI 10.17487/RFC4761, January 2007,
<http://www.rfc-editor.org/info/rfc4761>. <http://www.rfc-editor.org/info/rfc4761>.
skipping to change at page 13, line 37 skipping to change at page 13, line 39
[RFC5798] Nadas, S., Ed., "Virtual Router Redundancy Protocol (VRRP) [RFC5798] Nadas, S., Ed., "Virtual Router Redundancy Protocol (VRRP)
Version 3 for IPv4 and IPv6", RFC 5798, Version 3 for IPv4 and IPv6", RFC 5798,
DOI 10.17487/RFC5798, March 2010, DOI 10.17487/RFC5798, March 2010,
<http://www.rfc-editor.org/info/rfc5798>. <http://www.rfc-editor.org/info/rfc5798>.
[RFC6513] Rosen, E., Ed. and R. Aggarwal, Ed., "Multicast in MPLS/ [RFC6513] Rosen, E., Ed. and R. Aggarwal, Ed., "Multicast in MPLS/
BGP IP VPNs", RFC 6513, DOI 10.17487/RFC6513, February BGP IP VPNs", RFC 6513, DOI 10.17487/RFC6513, February
2012, <http://www.rfc-editor.org/info/rfc6513>. 2012, <http://www.rfc-editor.org/info/rfc6513>.
8.2. Informative References
[RFC6820] Narten, T., Karir, M., and I. Foo, "Address Resolution [RFC6820] Narten, T., Karir, M., and I. Foo, "Address Resolution
Problems in Large Data Center Networks", RFC 6820, Problems in Large Data Center Networks", RFC 6820,
DOI 10.17487/RFC6820, January 2013, DOI 10.17487/RFC6820, January 2013,
<http://www.rfc-editor.org/info/rfc6820>. <http://www.rfc-editor.org/info/rfc6820>.
Authors' Addresses Authors' Addresses
Xiaohu Xu Xiaohu Xu
Huawei Huawei
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