Internet DRAFT - draft-rfernando-virt-topo-bgp-vpn
draft-rfernando-virt-topo-bgp-vpn
INTERNET-DRAFT R. Fernando
Intended Status: Informational D. Rao
Expires: April 25, 2013 L. Fang
Cisco
October 22, 2012
Virtual Service Topologies in BGP VPNs
draft-rfernando-virt-topo-bgp-vpn-01
Abstract
This document presents techniques that build on MPLS/VPN control
plane mechanisms to construct virtual service topologies in data
centers. These virtual service topologies interconnect network zones
and help to constrain the flow of traffic that go between zones so
that interesting services can be applied to them.
The techniques suggested are required to create a rich overlay
network that mimics topology and routing functions of physical
networks. Steps to create a virtual service topology and the ability
to constrain routing and traffic to flow in this topology are
outlined in this document.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as
Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/1id-abstracts.html
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html
Fernando, et. al. Expires April 25, 2013 [Page 1]
INTERNET DRAFT Virtual Service Topology October 22, 2012
Copyright and License Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
2 Intra-Zone Routing and Traffic Forwarding . . . . . . . . . . . 3
3 Inter-Zone Routing and Traffic Forwarding . . . . . . . . . . . 4
4 Proposed Inter-Zone Model . . . . . . . . . . . . . . . . . . . 5
4.1 Constructing the Virtual Service Topology . . . . . . . . . 5
4.2 Inter-zone Routing and Service Chaining . . . . . . . . . . 7
5 Routing Considerations . . . . . . . . . . . . . . . . . . . . 8
5.1 Multiple service topologies . . . . . . . . . . . . . . . . 8
5.2 Multipath . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.3 Supporting redundancy . . . . . . . . . . . . . . . . . . . 9
5.4 Route Aggregation . . . . . . . . . . . . . . . . . . . . . 9
6 Security Considerations . . . . . . . . . . . . . . . . . . . . 10
7 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 10
8 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
9 References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.1 Normative References . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
Fernando, et. al. Expires April 25, 2013 [Page 2]
INTERNET DRAFT Virtual Service Topology October 22, 2012
1 Introduction
Network topologies and routing in the enterprise, data center and
campus networks reflect the needs of the organization in terms of
performance, scale, security and availability. For scale and security
reasons, networks are composed of multiple small domains or zones
each serving one or more logical functions of the organization.
Hosts within a zone can freely communicate with one another but
traffic between hosts in different zones is subjected to additional
services that help in scaling and securing the end applications.
Traditional networks achieve this using a combination of physical
topology constraints and routing.
Porting a traditional network with all its functions and
infrastructure elements to a virtualized data center 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.
Furthermore, data centers might need multiple virtual topologies per
tenant to handle different types of application 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 manner specific to
their organizational objectives. Therefore, the mechanisms devised
should be flexible to accommodate the custom needs of a tenant and
their applications at the same time 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 Intra-Zone Routing and Traffic Forwarding
This section provides a brief overview of how L3VPNs [RFC4364] can be
used in data center networks to create a single zone to host customer
Fernando, et. al. Expires April 25, 2013 [Page 3]
INTERNET DRAFT Virtual Service Topology October 22, 2012
applications. The subsequent sections in the document builds on this
base model to create richer topologies by interconnecting these zones
and enforcing services for inter-zone traffic.
In a DC, servers host virtual machines where end applications reside.
A collection of VMs that can communicate freely form a zone.
The notions of L3VPN when applied to the virtual data center works in
the following manner.
The VM that runs the applications that is the CE. A CE/VM belongs to
a zone. As in traditional L3VPN, 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).
The PE helps create the zone that the CE belongs to by placing the
CE-PE link in a VRF corresponding to that zone. Intra-zone
connectivity is achieved by designating an RT per zone (zone-RT) that
is applied on all PE VRFs that terminate the CE/VMs that belong to
the zone.
It is further assumed that the CE/VM's are associated with network
policies that get 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 achieve this step, a description of which is outside
the scope of this proposal.
When the CE/VM gets activated the attached PE starts exporting its IP
address with the corresponding zone-RT. This creates a full mesh
connectivity between the newly active VM and the rest of the VMs in
the zone.
Note that the IP address mask of the CE/VM need not necessarily be a
/32. 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 and use L3VPN style
forwarding to carry traffic between the VMs.
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. However, the ability
Fernando, et. al. Expires April 25, 2013 [Page 4]
INTERNET DRAFT Virtual Service Topology October 22, 2012
to enforce constrained traffic flow 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 inlined 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 not be
applied 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 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 are CE's attached to a
service-PE.
A service-PE is a normal L3VPN 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-
PE's.
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 service PE closest to the source zone is
the source service-PE and the service PE closest to the destination
zone is called the destination service-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.
Fernando, et. al. Expires April 25, 2013 [Page 5]
INTERNET DRAFT Virtual Service Topology October 22, 2012
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 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
service-PE's.
The three service RT's (import, export and topology) 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
toplogy. There can be multiple virtual service topologies and hence
service topology routes for a given VPN.
Fernando, et. al. Expires April 25, 2013 [Page 6]
INTERNET DRAFT Virtual Service Topology October 22, 2012
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.
In addition to the intra-zone RT's, zone prefixes are also tagged
with the set of service-topology-RT's that they belong to at the
point of origination.
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.
Fernando, et. al. Expires April 25, 2013 [Page 7]
INTERNET DRAFT Virtual Service Topology October 22, 2012
o 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.
o 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
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.
Fernando, et. al. Expires April 25, 2013 [Page 8]
INTERNET DRAFT Virtual Service Topology October 22, 2012
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.
Fernando, et. al. Expires April 25, 2013 [Page 9]
INTERNET DRAFT Virtual Service Topology October 22, 2012
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: Paul Quinn, David Ward, Ashok
Ganesan, Peter Bosch.
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
Email: dhrao@cisco.com
Rex Fernando
Cisco
170 W Tasman Dr
San Jose, CA
Fernando, et. al. Expires April 25, 2013 [Page 10]
INTERNET DRAFT Virtual Service Topology October 22, 2012
Email: rex@cisco.com
Luyuan Fang
Cisco
170 W Tasman Dr
San Jose, CA
Email: lufang@cisco.com
Fernando, et. al. Expires April 25, 2013 [Page 11]
