Virtual Topologies for Service Chaining in BGP IP VPNs
draft-rfernando-l3vpn-service-chaining-00

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Document Type Active Internet-Draft (individual)
Authors Rex Fernando  , Dhananjaya Rao  , Luyuan Fang  , Maria Napierala  , Nabil Bitar  , Ning So 
Last updated 2013-02-18
Replaced by draft-rfernando-bess-service-chaining
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INTERNET-DRAFT                                               R. Fernando
Intended Status: Standards track                                  D. Rao
Expires: August 18, 2013                                         L. Fang
                                                                   Cisco
                                                            M. Napierala
                                                                    AT&T
                                                                N. Bitar
                                                                 Verizon
                                                                   N. So
                                                     Tata Communications

                                                       February 18, 2013

         Virtual Topologies for Service Chaining in BGP IP VPNs
               draft-rfernando-l3vpn-service-chaining-00

Abstract

   This document presents the techniques built upon BGP/MPLS IP VPN
   control plane mechanisms to construct virtual service topologies for
   service chaining. These virtual service topologies allow a sequence
   of service nodes to be visited across multiple zones in a data center
   to form a service chain. The method uses service topology specific
   Route Targets (RTs) in addition to general purpose RTs. 

Status of this Memo

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

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Copyright and License Notice

   Copyright (c) 2013 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
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   described in the Simplified BSD License.

Table of Contents

   1  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1  Terminology . . . . . . . . . . . . . . . . . . . . . . . .  4
   2  Intra-Zone Routing and Traffic Forwarding . . . . . . . . . . .  6
   3  Inter-Zone Routing and Traffic Forwarding . . . . . . . . . . .  7
   4  Proposed Inter-Zone Model . . . . . . . . . . . . . . . . . . .  8
     4.1  Constructing the Virtual Service Topology . . . . . . . . .  8
     4.2  Inter-zone Routing and Service Chaining . . . . . . . . . . 10
   5  Routing Considerations  . . . . . . . . . . . . . . . . . . . . 11
     5.1  Multiple service topologies . . . . . . . . . . . . . . . . 12
     5.2  Multipath . . . . . . . . . . . . . . . . . . . . . . . . . 12
     5.3  Supporting redundancy . . . . . . . . . . . . . . . . . . . 12
     5.4  Route Aggregation . . . . . . . . . . . . . . . . . . . . . 12
   6  Security Considerations . . . . . . . . . . . . . . . . . . . . 13
   7  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 13
   8  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 13
   9  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     9.1  Normative References  . . . . . . . . . . . . . . . . . . . 13
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13

 

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1  Introduction

   Network topologies and routing design in enterprise, Data Center, and
   campus networks typically reflect the needs of the organization in
   terms of performance, scale, security and availability. For scale and
   security reasons, these networks may be composed of multiple small
   domains or zones each serving one or more functions of the
   organization.

   A network zone is a logical grouping of physical assets that support
   certain applications or a subset thereof. Hosts can communicate
   freely within a zone, that is, a datagram traveling between two hosts
   in the same zone is not routed through any servers that examine the
   datagram payload, but a datagram traveling between hosts in different
   zones is subject to additional services to meet the needs of scaling,
   performance, and security for specific applications. Example of such
   services can be a security gateway or a load-balancer. 

   Traditional networks achieve this by using a combination of physical
   topology constraints and routing. For example, one can force
   datagrams going through a FireWall (FW) by putting the firewall in
   the data path from a source to a destination. In some other cases,
   the datagrams needs to go through a security gateway for security
   service, and a Load Balancer (LB) for load balancing service. 

   In the modern virtualized Data Centers, appliances, applications, and
   network functions are virtualized, they are software instances
   residing in servers or appliances instead of individual physical
   devices.

   Porting a traditional network with all its functions and
   infrastructure elements to a virtualized DC requires network overlay
   mechanisms that provide the ability to create virtual network
   topologies that mimic physical networks and the ability to constrain
   the flow of routing and traffic over these virtual network
   topologies.

   A Data Center needs a virtual topology in which the servers are in
   the "virtual" data path, rather than in the physical data path. For
   example, a traffic flow in the traditional network has the resource
   as Provider Edge (PE) 1, and destination as Autonomous System Border
   Router (ASBR) 1, the flow must be serviced by FW1 and LB2, its path
   would be PE1 -> FW1 -> LB1 -> ASBR1. In a virtualized DC, the virtual
   topology for this path may be vPE1 -> vFW1 -> vLB1 -> ASBR1, assume
   PE1, FW1 and LB1 are virtual nodes. This sequence represents an
   example of virtual service chain. The nodes in the chain may be
   placed at arbitrary physical locations.

 

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   Furthermore, data centers might need multiple virtual topologies per
   tenant to handle different types of application traffic. A tenant is
   a customer who uses the virtualized data center services. The term
   Multi-tenant means virtualized single end device, for example, a
   server, supports multiple tenants which requires routing isolation
   among the tenants' traffic. Each tenant might dictate a different
   topology of connectedness between their zones and applications and
   might need the ability to apply network policies and services for
   inter-zone traffic in specific order to the organization objectives
   of the tenant. Therefore, the mechanisms devised should be flexible
   to accommodate the custom needs of a tenant and their applications at
   the same time MUST be robust enough to satisfy the scale, performance
   and HA needs that they demand from the virtual network
   infrastructure.

   Towards this end, this document introduces the concept of virtual
   service topologies and extends MPLS/VPN control plane mechanisms to
   constrain routing and traffic flow over virtual service topologies.

1.1  Terminology

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

   2. Suggested text under terminology in 1.1 (after the key word
   paragraph)

   Terms            description
   -----            ---------------------------

   AS                Autonomous System 
   ASBR              Autonomous System Border Router
   BGP               Border Gateway Protocol
   CE                Customer Edge
   ED                End device: where Guest OS, Host OS/Hypervisor, 
                     applications, VMs, and virtual router may reside
   Forwarder         L3VPN forwarding function
   FW                FireWall
   GRE               Generic Routing Encapsulation
   Hypervisor        Virtual Machine Manager running on each end device  
   I2RS              Interface to Routing System
   LB                Load Balancer
   LTE               Long Term Evolution
   MP-BGP            Multi-Protocol Border Gateway Protocol
   PCEF              Policy Charging and Enforcement Function
   P                 Provider backbone router
   proxy-arp         proxy-Address Resolution Protocol
 

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   QoS               Quality of Service
   RR                Route Reflector
   RT                Route Target
   RTC               RT Constraint
   SDN               Software Defined Network
   ToR               Top-of-Rack switch
   VI                Virtual Interface
   vCE               virtual Customer Router
   vFW               virtual FireWall
   vLB               virtual Load Balancer
   VM                Virtual Machine
   vPC               virtual Private Cloud
   vPE               virtual Provider Edge
   VPN               Virtual Private Network
   vRR               virtual Route Reflector1.2 Scope of the document
   WAN               Wide Area Network

   General terminologies:

   Service-PE: A BGP IP-VPN PE to which a service node in a virtual
   service topology is attached. The PE directs incoming traffic from
   other PEs to the service node via an MPLS VPN label or IP lookup; and
   forwards traffic from the service node to the next node in the chain.
   A Service-PE is a logical entity, in that a given PE may be attached
   to both a service node and an application VM.

   Service node:  A physical or virtual service appliance/application
   which inspects and/or redirects the flow of inter-zone traffic.
   Examples of service CEs: Firewalls, load-balancers, deep packet
   inspectors. The Service node acts as a CE in the VPN network. 

   Service Chain: A sequence of service-PE's and the corresponding
   service nodes created in a specific order. The service chain is
   unidirectional and creates a one way traffic flow between source
   Service-PE in the source zone and Destination Service-PE in the
   destination zone. 

   Service topology route: A topology service route is a route that is
   used to direct the traffic flow along the service topology. There
   should be one such route per service topology. The service topology -
   and hence the service route - is constructed on a per-VPN basis. This
   service topology is independent of the routes for the actual
   addresses of the VMs present in the various zones. There can be
   multiple service topologies for a given VPN. Topologies are
   constructed unidirectonally. Between the same pair of zones, traffic
   in opposite directions will be supported by two service topologies.

   Source Service-PE: The service-PE closest to the source zone.
 

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   Destination Service-PE: The service PE closest to the destination
   zone.

   Service-import-RT: A RT allows the routes to be imported into a
   Service-VRF. The route which is imported through service-import-RT
   MUST be re-originated with the corresponding service-export-RT.

   Service-export-RT: A RT allows the routes to be exported from a
   Service-VRF.

   Service-topology-RT: identifies the specific service topology.

   Tenant. A tenant is a higher-level management construct. In the
   control/forwarding plane, it is the various virtual networks that get
   instantiated. A tenant may have more than one virtual network or VPN.

   Zone: A logical grouping of physical assets that supports certain
   applications or a subset thereof. VMs can communicate freely within a
   zone.

2  Intra-Zone Routing and Traffic Forwarding

   This section provides a brief overview of how BGP/MPLS IP VPNs
   [RFC4364] control plane can be used in DC networks to used to divide
   a DC network into a number of zones. The subsequent sections in the
   document build on this base model to create inter-zone service
   topologies by interconnecting these zones and forcing inter-zone
   traffic to travel through a sequence of servers where the sequence of
   servers depends on <source zone, destination zone, application>.

   The notion of BGP IP VPN when applied to the virtual Data Center
   works in the following manner. 

   The VM that runs the applications in the server is treated as a CE
   attached to the VPN. A CE/VM belongs to a zone. The PE is the first
   hop router from the CE/VM and the PE-CE link is single hop from an L3
   perspective. Any of the available physical, logical or tunneling
   technologies can be used to create this "direct" link between the
   CE/VM and its attached PE(s).

   If a PE attaches to one or more CEs of a certain zone, the PE must
   have exactly one VRF for that zone, and the PE-CE links to those CEs
   must all be associated with that VRF. Intra-zone connectivity between
   CE/VMs that attach to different PEs is achieved by designating an RT
   per zone (zone-RT) that is both an import RT and an export RT of all
   PE VRFs that terminate the CE/VMs that belong to the zone. A VM may
   have multiple virtual interfaces that attach to different zones.
 

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   It is further assumed that the CE/VM's are associated with network
   policies that become activated on an attached PE when a CE/VM becomes
   alive. These policies dictate how networking should be set up for the
   CE/VM including the properties of the CE-PE link, the IP address of
   the CE/VM, the zone(s) that it belongs to, QoS policies etc. There
   are many ways to accomplish this step, a description of which is
   outside the scope of this document.

   When the CE/VM is activated, the attached PE starts exporting its IP
   address with the corresponding zone-RT. This allows unrestricted any-
   to-any communication between the newly active VM and the rest of the
   VMs in the zone.

   Note that the IP address mask of the CE/VM that the PE advertises
   along with the CE's address need not necessarily be a /32 for IPv4,
   and /128 for IPv6. This is the case when the CE/VM's in a zone belong
   to a single IP subnet. The PE, in this case, would use proxy-arp to
   resolve ARP's for remote destinations in the IP subnet.

   Alternatively, there may be a pool of dedicated service appliances
   which support multiple contexts.

   The classification of VMs into a zone is driven by the communication
   and security policy and is independent of the addressing for the VMs.
   The VMs in a zone may be in the same or different IP subnets with
   user-defined mask-lengths. The PE advertises /32 routes to advertise
   reachability to a locally attached VM. If two VMs are in the same IP
   subnet, the PE employs proxy-ARP to assist the VM resolve ARP for
   other VMs in the IP subnet, and uses IP forwarding to carry traffic
   between the VMs. When a VM is remotely attached to another PE, BGP
   IP-VPN forwarding is used.

3  Inter-Zone Routing and Traffic Forwarding

   A simple form of inter-zone traffic forwarding can be achieved using
   extranets BGP IP VPN configurations. However, extranet procedures do
   not by themselves provide the ability to force inter-zone traffic
   flows through a set of servers.

   Note that the inter-zone services cannot always be assumed to reside
   on a PE. There is a need to virtualize the services themselves so
   that they can be implemented on commodity hardware and scaled out
   'elastically' when traffic demands increase. Alternatively, there may
   be a pool of dedicated service appliances which support multiple
   contexts and hence multiple tenants, that are attached to different
   PEs distributed across the DC.This creates a situation where services
   for traffic between zones may not be applied only at the source-zone
   PE or the destination-zone PE. Mechanisms are required that make it
 

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   easy to direct inter-zone traffic through the appropriate set of
   service nodes that might be remote and virtualized.

   A service node for the purposes of this proposal is a physical or
   virtual service appliance that inspects and/or impacts the flow of
   inter-zone traffic. Firewalls, load-balancers, deep packet inspectors
   are examples of service nodes. Service nodes modeled as CEs, either
   they are reside on a PE, or they are then attached to a service-PE.

   A service-PE is a normal BGP IP VPN PE that recognizes and directs
   the appropriate traffic flows to its attached service nodes through
   VPN label lookup. Service nodes may be integrated or attached to
   service-PEs.

   A sequence of service-PE's and the corresponding service nodes create
   a service chain for inter-zone traffic. The service chain is
   unidirectional and creates a one way traffic flow between source zone
   and destination zone. The first service PE in the path is called as
   the source service-PE and the last service PE in the path is called
   the destination service-PE, there can be arbitrary numbers of
   service-PE between the source service-PE and the destination service-
   PE. An example of a service chain may look like this: ingress-PE -->
   source-service-PE --> other-service-PE --> destination-service-PE -->
   egress-PE.

4  Proposed Inter-Zone Model

   The proposed model has two steps to it. 

4.1  Constructing the Virtual Service Topology 

   The first step involves creating the virtual service topology that
   ties two or more zones through one or more service nodes.

   This is done by originating a service topology route that creates the
   route resolution state for the zone prefixes in a set of service-PEs.
   The service topology route is originated in the destination service-
   PE. It then propagates through the series of service-PE's from the
   destination service-PE to the source service-PE.

 

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   """"""""""""""""""""""                         """"""""""""""""""""""
   "          +-------+ " +--------+   +--------+ " +-------+          "
   " +-----+  | vPE-1 | " |ServPE-A|   |ServPE-B| " | vPE-2 |  +-----+ "
   " |VM/CE|--|       |---|        |---|        |---|       |--|VM/CE| "
   " +-----+  |(VRF-1)| " |(VRF-A) |   |(VRF-B) | " |(VRF-2)|  +-----+ "
   "          +-------+ " +--------+   +--------+ " +-------+          "
   "                    "      |            |     "                    "
   "     Zone 1         " +--------+   +--------+ "       Zone 2       "
   """""""""""""""""""""" | Serv-A |   | Serv-B | """"""""""""""""""""""
                          +--------+   +--------+ 

                 Figure 1. Construct of Service Chain Topology  

   A modification is proposed to the service-PE behavior to allow the
   automatic and constrained propagation of service topology routes
   through the service-PE's that form the service chain. A service-PE in
   a given service chain is provisioned to accept the service topology
   route and re-originate it such that the upstream service-PE imports
   it and so on. The sequential import and export of the service
   topology route along the service chain is controlled by RTs
   provisioned appropriately at each service-PE.

   To create the service chain and give it a unique identity, each
   service-PE is provisioned with three service RT's per VRF for every
   service chain that it belongs to: {service-import-RT, service-export-
   RT, service-topology-RT}.

   A service-import-RT acts exactly as a regular import RT importing any
   route that carries that RT into the service-VRF. Additionally, any
   route that was imported using the service-import-RT MUST be
   automatically re-originated with the corresponding service-export-RT.

   The next-hop of the re-originated route points to the service node
   attached to the service-PE. The VPN label carried in the re-
   originated route directs all traffic received by the service-PE to
   the service node.

   The service-export-RT of a downstream service-PE MUST be equal to the
   service-import-RT of the immediate upstream service-PE. The service
   topology route MUST be originated in the destination service-PE
   carrying its service-export-RT. The flow of the service topology
   route creates both the service chain as well as the route resolution
   state for the zone prefixes.

   Finally, the presence of the service topology route in a service-PE
   triggers the addition of the service-topology-RT to the regular
   import RT's of the service-VRF. Every service chain has a single
   unique service-topology-RT that's provisioned in all participating
 

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   service-PE's.

   The three service RT's (import, export and topology) are special RTs
   which should not be reused for other purposes within the network. The
   service RT's that establish the chain and give it its identity can be
   pre-provisioned or activated due to the appearance of a attached
   virtual service node. The provisioning system is assumed to have the
   intelligence to create loop-free virtual service topologies.

   There should be one service topology route per virtual service
   topology. There can be multiple virtual service topologies and hence
   service topology routes for a given VPN.

   Virtual service topologies are constructed unidirectionally. Between
   the same pair of zones, traffic in opposite directions will be
   supported by two service topologies and hence two service topology
   routes. These two service topologies might or might not be
   symmetrical, i.e. they might or might not traverse the same service-
   PE's/service-nodes in opposite directions.

   As noted above, a service topology route can be advertised with a
   per-next-hop label that directs incoming traffic to the attached
   service node. Alternatively, an aggregate label may be used for the
   service route and an IP route lookup done at the service-PE to send
   traffic to the service node.

   Note that a new service node could be inserted seamlessly by just
   configuring the three service RT's in the attached service-PE. This
   technique could be used to elastically scale out the service nodes
   with traffic demand.

   The distribution of the service topology route itself can be
   controlled by RT constrains [RFC4684] to only the interesting
   service-PE's.

   Finally, note that the service topology route is independent of the
   zone prefixes which are the actual addresses of the VMs present in
   the various zones. The zone prefixes use the service topology route
   to resolve their next-hop.

4.2  Inter-zone Routing and Service Chaining

   Routes representing hosts or VMs from a zone are called zone
   prefixes. A zone prefix will have its regular zone RTs attached when
   it is originated. This will be used by PEs in the same zone to import
   these prefixes to enable direct communication between VM's of the
   same zone.
 

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   In addition to the intra-zone RT's, zone prefixes are also tagged at
   the point of origination with the set of service-topology-RTs to
   which they belong.

   Since they are tagged with the service-topology-RT, zone prefixes get
   imported into the appropriate service-VRF's of particular service-
   PE's that form the service chain associated to that topology RT. Note
   that the topology RT was added to the relevant service-VRF's import
   RT list during the virtual topology construction phase.

   Once the zone prefixes are imported into the service-PE, their next-
   hops are resolved as follows. 

   - If the importing service-PE is the destination service-PE, it uses
   the next hop that came with the zone prefix for route resolution. It
   also uses the VPN label that came with the prefix.

   - If the importing service-PE is not the destination service-PE, it
   rewrites the received next-hop of the zone prefix with the service
   topology route.

   In an MPLS VPN, the zone prefixes come with VPN labels. The labels
   also must be ignored when in the intermediate service-PEs. Instead,
   the zone prefix gets resolved via the service topology route and uses
   the associated service route's VPN label.

   This way the zone prefixes in the intermediate service-PE hops
   recurse over the service topology route forcing the traffic destined
   to them flow through the virtual service topology.

   Traffic for the zone prefix goes through the service hops created by
   the service topology route. At each service hop, the service-PE
   directs the traffic to the service node. Once the service node is
   done processing the traffic, it then sends it back to the service-PE
   which forwards the traffic to the next service-PE and so on.

   A significant benefit of this next-hop indirection is to avoid
   redundant advertisement of zone prefixes from the service-PE's. Also,
   when the virtual service topology is changed (due to addition or
   removal of service-PEs), there should be no change to the zone
   prefix's import/export RT configuration.

   Note that this proposal introduces a change in the behavior of the
   service-PE's but does not require protocol changes to BGP. 

5  Routing Considerations
 

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5.1  Multiple service topologies

   A service-PE can support multiple distinct service topologies for a
   VPN.

5.2  Multipath

   One could use all tools available in BGP to constrain the propagation
   and resolution state created by the service topology route. A service
   topology route can have multiple equal cost paths, for inter-zone
   traffic to get load-balanced over. 

5.3  Supporting redundancy

   For stateful services an active-standby mechanism could be used at
   the service level. In this case, the inter-zone traffic should prefer
   the active service node over the standby service node.

   At a routing level, this is achieved by setting up two paths for the
   same service topology route - one path goes through the active
   service node and the other through the standby service node. The
   active service path can then be made to win over the standby service
   path by appropriately setting the BGP path attributes of the service
   topology route such that the active path succeeds in path selection.
   This forces all inter-zone traffic through the active service node.

5.4  Route Aggregation

   Instead of the actual zone prefixes being imported and used at
   various points along the chain, the zone prefixes may be aggregated
   at the destination service-PE and the aggregate zone prefix used in
   the service chain between zones. In such a case, it is the aggregate
   zone prefix that carries the service-topology-RT and gets imported in
   the service-PE's that comprise the service chain.

 

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6  Security Considerations

   This proposal does not change the security model of MPLS/VPN BGP.

7  IANA Considerations

   This proposal does not have any IANA implications.

8  Acknowledgements

   The authors would like to thank the following individuals for their
   review and feedback on the proposal: Eric Rosen, Jim Guichard, Paul
   Quinn, David Ward, Ashok Ganesan.

9  References

9.1  Normative References

   [RFC4364] Rosen, E., "BGP/MPLS IP Virtual Private Networks (VPNs)",
              RFC4364.

   [RFC4684] Marques, P., "Constrained Route Distribution for Border
              Gateway Protocol/Multiprotocol Label Switching (BGP/MPLS)
              Internet Protocol (IP) Virtual Private Networks (VPNs)

Authors' Addresses

              Dhananjaya Rao
              Cisco
              170 W Tasman Dr
              San Jose, CA
              US
              Email: dhrao@cisco.com

              Rex Fernando
              Cisco 
              170 W Tasman Dr
              San Jose, CA
              US
              Email: rex@cisco.com
 

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              Luyuan Fang
              Cisco
              170 W Tasman Dr
              San Jose, CA
              US
              Email: lufang@cisco.com

              Maria Napierala 
              AT&T
              200 Laurel Avenue 
              Middletown, NJ 07748
              US
              Email: mnapierala@att.com 

              Nabil Bitar
              Verizon
              40 Sylvan Road
              Waltham, MA 02145
              US
              Email: nabil.bitar@verizon.com

              Ning So
              Tata Communications
              Plano, TX 75082, USA
              Email: ning.so@tatacommunications.com

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