INTERNET-DRAFT R. Fernando
Intended Status: Standards track D. Rao
Expires: April 18, 2014 L. Fang
Cisco
M. Napierala
AT&T
N. So
Tata Communications
A. Farrel
Juniper Networks
October 18, 2013
Virtual Topologies for Service Chaining in BGP/IP MPLS VPNs
draft-rfernando-l3vpn-service-chaining-03
Abstract
This document presents techniques built upon BGP/IP MPLS VPN control
plane mechanisms to construct virtual topologies for service
chaining. These virtual service topologies interconnect network zones
and constrain the flow of traffic between these zones via a sequence
of service nodes so that service functions can be applied to the
traffic.
This document also describes approaches enabled by both the routing
control plane and by network orchestration to realize these virtual
service topologies.
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Copyright and License Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Intra-Zone Routing and Traffic Forwarding. . . . . . . . . . . 5
3. Inter-Zone Routing and Traffic Forwarding. . . . . . . . . . . 7
3.1 Traffic Forwarding Operational Flow . . . . . . . . . . . . 8
4. Inter-Zone Model . . . . . . . . . . . . . . . . . . . . . . . 9
4.1 Constructing the Virtual Service Topology . . . . . . . . . 9
4.2 Per-VM Service Chains. . . . . . . . . . . . . . . . . . . . 12
5. Routing Considerations . . . . . . . . . . . . . . . . . . . . 12
5.1 Multiple Service Topologies . . . . . . . . . . . . . . . . 12
5.2 Multipath . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.3 Supporting Redundancy . . . . . . . . . . . . . . . . . . . 12
5.4 Route Aggregation . . . . . . . . . . . . . . . . . . . . . 13
6. Orchestration Driven Approach . . . . . . . . . . . . . . . . . 13
7. Security Considerations. . . . . . . . . . . . . . . . . . . . 13
8. Management Considerations. . . . . . . . . . . . . . . . . . . 13
9. IANA Considerations. . . . . . . . . . . . . . . . . . . . . . 13
10. Acknowledgements. . . . . . . . . . . . . . . . . . . . . . . 14
11. References. . . . . . . . . . . . . . . . . . . . . . . . . . 14
11.1 Normative References . . . . . . . . . . . . . . . . . . . 14
11.2 Informative References . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
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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 supports
certain applications. 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 and
apply services (such as security or load balancing) to the traffic.
But a datagram traveling between hosts in different zones may be
subject to additional services to meet the needs of scaling,
performance, and security for the applications or the networks
themselves.
Networks have achieved division into zones and the imposition of
services through a combination of physical topology constraints and
routing. For example, one can force datagrams to go through a
firewall (FW) by putting the FW in the physical data path from a
source to the destination, or by causing the routed path form source
to destination to go via an W that would not normally be on the path.
Similarly, the datagrams may need to go through a security gateway
for security services, or a Load Balancer (LB) for load balancing
services.
In virtualized data centers, appliances, applications, and network
functions, including IP VPN provider edge (PE) and customer edge (CE)
functions are all commonly virtualized. That is, they exist as
software instances residing in servers or appliances instead of
individual (dedicated) physical devices.
Migrating a network with all its functions and infrastructure
elements to realization in a virtualized data center requires network
overlay mechanisms that provide the ability to create virtual network
topologies that mimic physical networks, and that provide the ability
to constrain the flow of routing and traffic over these virtual
network topologies.
A data center uses 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 might previously have had the source PE-1 and
destination at an Autonomous System Border Router (ASBR), ASBR-1, and
the flow might have needed to be serviced by FW-1 and LB-1. In this
case its path would have been PE-1, FW-1, LB-1, ASBR-1. However, in a
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virtualized data center, the functions of all four nodes could be
provided by virtual nodes that could be placed at arbitrary locations
across the data center. Thus the "virtual service chain" vPE-1,
vFW-1, vLB-1, vASBR-1, that is the sequence of virtual service nodes
that packet must traverse, could be realized by a path between
arbitrary physical locations in the data center.
A data center will likely support multiple tenants. A tenant is a
customer who uses the virtualized data center services. Each tenant
might require different connectedness (i.e., a different virtual
topology) between their zones and applications, and might need the
ability to apply different network policies such that the services
for inter-zone traffic are applied in a specific order according to
the organization objectives of the tenant. Furthermore, a data center
might need multiple virtual topologies per tenant to handle different
types of application traffic.
Additionally, a data center operator may choose to provide services
for multiple tenants on the same virtualized end device, for example,
a server. Such multi-tenant devices must utilize techniques such as
routing isolation to retain separation between tenants' traffic.
To address all of these requirements, the mechanisms devised for use
in a data center need to be flexible enough to accommodate the custom
needs of the tenants and their applications, and at the same time
must be robust enough to satisfy the scale, performance, and high
availability needs that are demanded by the operator of the virtual
network infrastructure that has a very large number of tenants each
with different application types, large networks, multiple services,
and high-volume traffic.
Toward this end, this document introduces the concept of virtual
service topologies and extends IP MPLS VPN control plane mechanisms
to constrain routing and traffic flow over virtual service
topologies.
The creation of these topologies and the setting up of the forwarding
tables to steer traffic over them may be carried out either by
extensions to IP MPLS VPN procedures and functionality at the PEs, or
via a "software defined networking" (SDN) approach. This document
specifies the use of both approaches, but uses the IP MPLS VPN option
to illustrate the various steps involved.
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1.1 Terminology
This document uses the following acronyms and terms.
Terms Meaning
----- --------------------------------------------------
AS Autonomous System
ASBR Autonomous System Border Router
CE Customer Edge
FW Firewall
I2RS Interface to the Routing System
L3VPN Layer Three VPN
LB Load Balancer
NLRI Network Layer Reachability Information [RFC4271]
P Provider backbone router
proxy-arp proxy-Address Resolution Protocol
RR Route Reflector
RT Route Target
SDN Software Defined Network
vCE virtual Customer Edge router
[I-D.fang-l3vpn-virtual-ce]
vFW virtual Firewall
vLB virtual Load Balancer
VM Virtual Machine
vPC virtual Private Cloud
vPE virtual Provider Edge router
[I-D.fang-l3vpn-virtual-pe]
VPN Virtual Private Network
VRF VPN Routing and Forwarding table [RFC4364]
vRR virtual Route Reflector
This document also uses the following general terms:
Service-PE:
A BGP/IP MPLS VPN PE to which a service node in a virtual service
topology is attached. The PE directs incoming traffic from other
PEs or from attached hosts to the service node via an MPLS VPN
label or IP lookup. The PE also forwards traffic from the service
node to the next node in the chain. A Service-PE is a logical
entity and a given PE may be attached to both a service node and
an application host VM.
Service node:
A physical or virtual service appliance/application which inspects
and/or redirects the flow of inter-zone traffic. Examples of
service nodes include FWs, LBs, and deep packet inspectors. The
service node acts as a CE in the VPN network.
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Service chain: A sequence of service nodes that interconnect the
zones containing the source and destination hosts. The service
chain is unidirectional and creates a one way traffic flow between
source zone and destination zone.
Virtual service topology:
A virtual service topology consists of a sequence of service-PEs
and their attached service nodes created in a specific order. A
service topology is constructed via one or more routes that direct
the traffic flow among the PEs that form the service chain.
Service-topology-RT:
A BGP route attribute that identifies the specific service
topology.
Tenant:
A tenant is a higher-level management construct. In the control/
forwarding plane it is the collection of 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 or hosts can communicate
freely within a zone.
2. Intra-Zone Routing and Traffic Forwarding
This section provides a brief overview of how the BGP/IP MPLS VPN
[RFC4364] control plane can be used in a DC network to used to divide
the 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 the tuple <source zone, destination zone,
application>.
The notion of a 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 a
laye-3 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
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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.
It is further assumed that the CE/VMs are associated with network
policies that are activated on an attached PE when a CE/VM is
instantiated. These policies dictate how the network is set up for
the CE/VM including the properties of the CE-PE link, the IP address
of the CE/VM, the zones to which it belongs, QoS policies, etc. There
are many ways to accomplish this step, but a description of such
mechanisms is outside the scope of this document.
When the CE/VM is activated, the attached PE starts to export the
CEs 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.
The classification of VMs into a zone is driven by the communication
and security policy and is independent of the addressing scheme 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 locally attached VMs. If two VMs are in the
same IP subnet, the PE may employ proxy-ARP to assist the VM to
resolve ARP for other VMs in the IP subnet, and may use IP forwarding
to carry traffic between the VMs. When a VM is attached to a remote
PE, IP VPN forwarding is used to tunnel packets to the remote PE.
3. Inter-Zone Routing and Traffic Forwarding
A simple form of inter-zone traffic forwarding can be achieved using
extranets or hub-and-spoke L3VPN configurations [RFC7024]. However,
the ability to enforce constrained traffic flowa through a set of
services is non-existent in extranets and is limited in hub-and-spoke
setups.
Note that the inter-zone services cannot always be assumed to reside
and be in-lined 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. This creates
a situation where services for traffic between zones may be applied
not only at the source-zone PE or the destination-zone PE. Mechanisms
are required that make it easy to direct inter-zone traffic through
the appropriate set of service nodes that might be remote or
virtualized.
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3.1 Traffic Forwarding Operational Flow
Traffic from a source endpoint (a VM/CE) in a source zone reaches an
ingress zone-PE and is associated with a VRF in that zone as
described above. The zone-PE will forward the traffic and direct it
toward the first service-node. If the service-node is attached to the
zone-PE, the zone-PE will forward the packets out of one of its
access interfaces. If the service-node is attached to a different
service-PE, the zone-PE will encapsulate the packets and send them
toward the service-PE. The zone-PE and service PE may be connected
via an intermediate network of devices and the encapsulation causes
the packets to be tunneled across this intermediate network.
The service-PE will receive these encapsulated packets from the
source zone-PE, decapsulate them, and forward them to its attached
service-node. The traffic that comes back to the service-PE from the
service-node must now be forwarded to the next service-node in the
chain. As above, the next service-node may be locally attached or at
a remote service-PE.
At the last service-PE in the chain, the traffic that comes back from
a service-node must be forwarded to the destination in the target
zone. Just as with the service-nodes, the destination may be attached
to the service-PE or reachable via another PE.
As can be seen from this description, a given packet flow needs to be
forwarded differently at each PE depending on whether it is arriving
from a node attached to the PE or from a remote PE, and depending on
whether the traffic is to be routed toward a node attached to the PE
or attached to a remote PE. The next-hop for a flow changes depending
on the relative position within the service chain.
Figure 1 illustrates a virtual service topology, where hosts in Zone
1 are interconnected with hosts in Zone 2 via two service nodes
(Serv-A and Serv-B) attached to two service-PEs (S-PE-A and S-PE-B
respectively).
"""""""""""""""""""""" """"""""""""""""""""""
" +-------+ " +--------+ +--------+ " +-------+ "
" +-----+ | vPE-1 | " | S-PE-A | | S-PE-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. Virtual Service Topology Illustration
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The different forwarding paths can be achieved at any PE as follows.
o Each service node is associated with two VRFs at the service PE to
which it is attached: an in-VRF for traffic toward the service
node, and an out-VRF for traffic from the service node.
o Traffic for the in-VRF arrives from the previous node in the
service chain, and traffic for the out-VRF is destined toward the
next node in the service chain, or toward the destination zone.
o The in-VRF has one or more routes with a next-hop of a local access
interface where the service node is attached. The out-VRF has
routes with a next-hop of the next service node, which may be
situated locally on the service-PE or at a remote PE.
The installation of the forwarding entries to implement the flow
described above may be achieved either via IP VPN mechanisms
described in Sections 4 and 5, or using an SDN approach, as described
in Section 6.
4. Inter-Zone Model
The inter-zone model has the following steps.
4.1 Constructing the Virtual Service Topology
The virtual service topology described in the previous section is
constructed via one or more routes that direct the traffic flow among
the PEs forming the service chain. There should be a route per
service node. The service topologies, and hence the service routes,
are constructed on a per-VPN basis. This service topology is
independent of the routes for the actual destination for a flow,
i.e., the addresses of the VMs present in the various zones. There
can be multiple service topologies for a given VPN.
4.1.1 Reachability to the Service Nodes
Each service node is identified by an IP address that is scoped
within the VPN. The service node is also associated with an in-VRF
and out-VRF at the attached service node.
Reachability to the various service nodes in the service chain occurs
via regular BGP/IP VPN route advertisements.
A service-PE will export a route for each service node attached to
it. Each route will contain the Route-Target configured for the VPN,
and a forwarding label that is associated with the logical in-VRF for
a service node on the service-PE. This label enables the service-PE
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to directly forward incoming traffic from the other PEs to the
service node.
The routes to reach the various service nodes are imported into and
installed in each out-VRF at a service-PE, as well as in the zone VRF
on the ingress zone-PE.
4.1.2 Provisioning the Service Chain
At each PE supporting a given VPN, the sequence of service nodes in a
service chain can be specified in a VPN service route policy.
To create the service chain and give it a unique identity, each PE
may be provisioned with the following tuple for every service chain
that it belongs to:
{Service-topology-RT, Service-node-Sequence}
where Service-node-Sequence is simply an ordered list of the service
node IP addresses that are in the chain.
Every service chain has a single unique service-topology-RT that is
provisioned in all participating PEs.
A PE will also be provisioned with the tables and/or configuration
that support the various zones and the in- and out- VRFs for the
services.
4.1.3 Zone Prefix Next-Hop Resolution
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 VMs in the same
zone.
In addition to the intra-zone RTs, 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 zone-RT, zone prefixes get imported
into the VRFs of the service-PEs that form the service chain
associated to that topology RT. Note that the zone-RT was added to
the relevant VRF's import RT list during the virtual topology
construction phase. These routes may be installed in the in-VRF and
out-VRF at the service-PEs as well as in the ingress zone VRF.
Note that this approach introduces a change in the behavior of the
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service-PEs compared to normal BGP VPN behavior, but does not require
protocol changes to BGP. This modification to PE behavior allows the
automatic and constrained flow of traffic via the service chain.
The PE, based on the presence of the configured Service-topology-RT
in the received zone routes, will perform the following actions:
1. It will ignore the next-hop and VPN label that were advertised in
the NLRI.
2. Instead, it will select the appropriate Service next-hop from the
Service-node sequence associated with the Service-topology-RT.
3. It will further resolve this Service next-hop IP address locally
in the associated VRF, instead of in the global routing table. It
will use the next-hop and label associated with this IP address to
encapsulate traffic toward the next service node.
4. If the importing service-PE is the last 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.
In this way the zone prefixes in the intermediate service-PE hops
recurse over the service chain forcing the traffic destined to them
to flow through the virtual service topology.
Traffic for the zone prefix goes through the service hops created by
the service topology. At each service hop, the service-PE directs the
traffic to the service node. Once the service node is done processing
the traffic, it 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 end-zone or
service-PEs. 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.
There should be one service topology RT per virtual service topology.
There can be multiple virtual service topologies and hence service
topology RTs for a given VPN.
Virtual service topologies are constructed unidirectionally. Traffic
in opposite directions between the same pair of zones will be
supported by two different service topologies and hence two service
topology routes. These two service topologies might or might not be
symmetrical, i.e.m they might or might not traverse the same sequence
of service-PEs/service-nodes in opposite directions.
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As noted above, a service node route can be advertised with a 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 into the service
chain seamlessly by just configuring the service policy
appropriately.
4.2 Per-VM Service Chains
While the service-topology-RT allows an efficient inheritance of the
service chain for all VMs in a zone, there may be a need to create a
distinct service chain for an individual VM. This may be done by
provisioning a separate service-topology RT and service node
sequence. The VM route carries the service-topology RT, and the
destination service-zone is provisioned with this RT as its Service-
Import RT.
5. Routing Considerations
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 of state created by the service topology [RFC4684].
Additional service nodes can be introduced to scale out a particular
service. Each such service would be represented by a virtual IP
address, and multiple service nodes associated with it. Multiple
service-PEs may advertise a route to this address based on the
presence of an attached service node instance, thereby creating
multiple equal cost paths. This technique could be used to
elastically scale out the service nodes with traffic demand.
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 node route: one path goes through the active service
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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-PEs that comprise the service chain.
6. Orchestration Driven Approach
In an orchestration driven approach, there is no need for the zone or
service PEs to determine the appropriate next-hops based on the
specified service node sequence. All the necessary policy
computations are carried out, and the forwarding tables for the
various VRFs at the PEs determined, by the central orchestrator.
The orchestrator communicates with the various PEs (typically virtual
PEs on the end-servers) to populate the forwarding tables.
The protocol used to communicate between the controller/orchestration
and the PE/vPE must be a standard, programmatic interface. The
programmatic interface are currently under definition in the IETF's
Interface to Routing Systems (I2RS) initiative,
[I-D.ietf-i2rs-architecture], [I-D.ietf-i2rs-problem-statement].
7. Security Considerations
To be added.
8. Management Considerations
To be added.
9. IANA Considerations
This proposal does not have any IANA implications.
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10. Acknowledgements
The authors would like to thank the following individuals for their
review and feedback on the proposal: Eric Rosen, Jim Guichard, Paul
Quinn, Peter, Bosch, David Ward, Ashok Ganesan. The option of
configuring an ordered sequence of service nodes via policy is
derived from a suggestion from Eric Rosen.
11. References
11.1 Normative References
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, February 2006.
11.2 Informative References
[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
Protocol 4 (BGP-4)", RFC 4271, January 2006.
[RFC4684] Marques, P., Bonica, R., Fang, L., Martini, L., Raszuk,
R., Patel, K., and J. Guichard, "Constrained Route
Distribution for Border Gateway Protocol/MultiProtocol
Label Switching (BGP/MPLS) Internet Protocol (IP) Virtual
Private Networks (VPNs)", RFC 4684, November 2006.
[RFC7024] Jeng, H., Uttaro, J., Jalil, L., Decraene, B., Rekhter,
Y., and R. Aggarwal, "Virtual Hub-and-Spoke in BGP/MPLS
VPNs", RFC 7024, October 2013.
[I-D.fang-l3vpn-virtual-ce]
L. Fang, et al.,"BGP/MPLS IP VPN Virtual CE",
draft-fang-l3vpn-virtual-ce, work in progress.
[I-D.fang-l3vpn-virtual-pe]
L. Fang, et al., "BGP/MPLS IP VPN Virtual PE",
draft-fang-l3vpn-virtual-pe, work in progress.
[I-D.ietf-i2rs-architecture]
Atlas, A., Halpern, J., Hares, S., Ward, D., and T Nadeau,
"An Architecture for the Interface to the Routing System",
draft-ietf-i2rs-architecture, work in progress.
[I-D.ietf-i2rs-problem-statement]
Atlas, A., Nadeau, T., and D. Ward, "Interface to the
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Fernando, et. al. Expires April 18, 2013 [Page 14]
INTERNET DRAFT Virtual Service Topology October 18, 2013
Authors' Addresses
Dhananjaya Rao
Cisco
170 W Tasman Dr
San Jose, CA
Email: dhrao@cisco.com
Rex Fernando
Cisco
170 W Tasman Dr
San Jose, CA
Email: rex@cisco.com
Luyuan Fang
Cisco
170 W Tasman Dr
San Jose, CA
Email: luyuanf@gmail.com
Maria Napierala
AT&T
200 Laurel Avenue
Middletown, NJ 07748
Email: mnapierala@att.com
Ning So
Tata Communications
Plano, TX 75082, USA
Email: ning.so@tatacommunications.com
Adrian Farrel
Juniper Networks
Email: adrian@olddog.co.uk
Fernando, et. al. Expires April 18, 2013 [Page 15]