Network Working Group P. Marques
Internet-Draft L. Fang
Intended status: Standards Track Cisco Systems
Expires: September 12, 2012 P. Pan
Infinera Corp
A. Shukla
Juniper Networks
M. Napierala
AT&T Labs
March 2012
BGP-signaled end-system IP/VPNs.
draft-marques-l3vpn-end-system-04
Abstract
This document describes how the control plane specified by BGP/MPLS
IP VPNs [RFC4364] can be used to provide a network virtualization
solution for end-systems that meets the requirements of large scale
data-centers.
It specifies how the control and forwarding functions of a Provide
Edge (PE) device described in [RFC4364] can be separated such that
the forwarding function can be implemented in end-systems themselves.
The solution is applicable to any encapsulation that can deliver
packets across an IP network as a tunneled IP datagram plus a 20-bit
label.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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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."
This Internet-Draft will expire on September 12, 2012.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminoloy . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Applicability of BGP IP VPNs . . . . . . . . . . . . . . . . . 5
4. Virtual network end-points . . . . . . . . . . . . . . . . . . 7
5. VPN forwarder . . . . . . . . . . . . . . . . . . . . . . . . 8
6. XMPP signaling protocol . . . . . . . . . . . . . . . . . . . 10
7. Signaling gateway behavior . . . . . . . . . . . . . . . . . . 14
8. Operational Model . . . . . . . . . . . . . . . . . . . . . . 15
9. Security Considerations . . . . . . . . . . . . . . . . . . . 17
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 18
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
11.1. Normative References . . . . . . . . . . . . . . . . . . 18
11.2. Informational References . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction
This document describes the requirements for a network virtualization
solution that satisfies the needs of large scale data-centers. It
then discusses how the BGP IP VPNs [RFC4364] control plane can be
used to provide a solution that meets these requirements. Subsequent
sections provide a detailed discussion of the control and forwarding
plane components.
1.1. Terminoloy
This document makes use of the following terms:
Data-center A logical set of compute, storage and network resources
that may spread over multiple physical facilities. Its geographic
scope is limited by a communication latency requirement.
Typically, it represents an availability zone for applications.
It may be the case that the same physical facilities support
multiple logical data-centers.
Signaling Gateway A software application that implements the control
plane functionality of a BGP IP VPN PE device and a XMPP server
that interacts with VPN forwarders.
Virtual Interface An interface in an end-system that is used by a
virtual machine or by applications. It performs the role of a CE
interface in a BGP IP VPN network.
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VPN Forwarder The forwarding component of a BGP IP VPN PE device.
2. Requirements
The main drivers for network virtualization in data-center solutions
are network based access-control, multi-tenancy support and VM
mobility. Data-centers often have the need to support one or more of
these network functions which have often in the past been implemented
using VLAN [IEEE.802-1Q] technologies.
The prevalence of L2 based implementations in small scale deployments
has created the perception that the network functionality itself
requires L2 transparency and is best served by technologies that
attempt to drive up the scope and scale of L2 broadcast domains.
This document takes the view that the desired functionality requires
a virtualization technology that provides an IP service, with layer 2
topology being irrelevant as long as the service goals are met.
IP-based access control was the first of these functions to be
commonly deployed in data-centers. Its goal is to provide a "closed
user-group" among a set of end-points, often compute resources
dedicated to one application, such that communication within that
group occurs unfettered. This was accomplished by placing all these
end-points on the same IP subnet. At the same time IP-based access
control allows the use of traffic filtering polices to control/
restrict communication between the members of the group and other
groups (inter-subnet communication). These "closed user-groups" are
often used by IT organizations to both segregate applications as well
a separate production, quality-assurance and development environments
which often must be contained in different communication domains.
The term "closed user-group" does not imply that there is no
communication with external groups. Only that the membership in the
group is administratively defined. Each "closed user-group" is a VPN
in the terminology used by BGP IP VPNs. Traditionally this
functionality has been implemented in data-center designs by using a
VLAN between access and aggregation switches and controlling the
VLAN-to-VLAN access control policies at the aggregation switches.
This solution works well in an environment where the I/O bandwidth
between compute resources is considered to be the resource to
optimize for. In this scenario resources associated to a given
application are dedicated to it and kept in physical proximity.
Solutions that optimize for the maximum utilization of fungible
compute and storage resources need a different approach. They
require that the compute resources associated with an application
(and thus a "closed user-group"/VPN) may be located anywhere in the
data-center. And given that this physical spreading of resources
already implies a very significant increase in data-center core
bandwidth requirements, they must also make sure that packets only
traverse the switching infrastructure once.
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If members of a "closed-user group" may be be present anywhere in the
data-center, that implies a different operational environment for a
VLAN based implementation. Either it would have to operate under the
assumption that all switches belong to all VLANs or to be able to
dynamically adjust the topology of each VLAN. The later implies that
the dimension and scope of each broadcast domain is not know
a-priori.
In order to minimize core bandwidth and traffic latency the inter-
subnet traffic exchange policies should be pushed as far as possible
to the edge. The end-systems that source and receive the traffic are
able to implement the virtualization and policy enforcement
functionality while using the optimal path for traffic.
With VLAN [IEEE.802-1Q] an ethernet end-point can only be a member of
a single "closed user group". Ideally a single application end-point
should be able to be a member of multiple "closed user groups". That
is possible with L3 based technologies such as BGP IP VPNs.
Multi-tenant support is an network function that is often combined
with network based access control. Each tenant should be able to
define multiple "closed user-groups", for instance on a per-
application basis, and while "closed user-groups" from multiple
tenants are often not allowed to interact directly, tenants are
typically allowed to use common infrastructure services (e.g.
storage, database services, application-services, etc).
In both of these scenarios, the requirement is to control the IP
traffic crossing multiple subnets (where an IP subnet is a "closed
user group") such that it conforms to the defined traffic policies.
The third requirement to be considered is the need to support "VM
life-migration". This functionality requires a virtual IP topology
by itself even in data-centers where network based access control or
multi-tenancy are not a concern. Life-migration requires virtual
machines to be moved from a physical server A to a physical server B
such that the total migration time does not disrupt its communication
sessions. This implies that transport sessions must answer
keepalives before the user-specified timeout (often a few seconds).
In some cases, the operation may also be constrained by the
application latency requirements which are typically in the sub-
second range. While the main bottleneck in this process is the
process of saving and restoring the VM's modified memory pages, the
connectivity restoration time is critical.
Support for minimizing connectivity interruption and minimum latency
impact would benefit from the ability for the same IP end-point to be
received at the new physical location of the VM (B) as well as the
ability to tunnel traffic from the old location (A) during the
convergence period. It also requires a control plane that can
minimize convergence time and that can decouple the instantiation of
the end-point (i.e. the VM IP address becoming active) from its
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advertisement to the network as the preferred route to that IP
address.
It is important to note that, as with the previous network functions,
we need to consider IP transport sessions with system both in the
same "closed user group" (or subnet) as the VM as well as in
different "closed user groups" (i.e. subnets). Any solution to this
problem must be able to minimize connectivity restoration time across
different IP subnets.
3. Applicability of BGP IP VPNs
BGP IP VPNs [RFC4364] is the industry de-facto standard for providing
"closed user group" functionality in WAN environments. It is used by
service providers in environments where several millions of routes
are present. It supports both isolated VPNs as well as overlapping
VPNs (often referred to as "extranets").
In its traditional usage in Service Provider networks, BGP IP VPN
functionality is implemented in a Provider Edge (PE) device that
combines both BGP signaling as well a VRF-based forwarding functions.
In practice, most PE devices in current use are multi-component
systems with the signaling and forwarding functionality actually
implemented in different processors attached to an internal network.
This document assumes a similar separation of functionality in which
signaling devices implement the control plane functionality of a PE
device and a VPN forwarder (in the hypervisor/host OS or first-hop
switch) implements the forwarding function usually found in a PE
device "line-card".
Operationally, BGP IP VPN technology has several important
characteristics:
It has a high-level of aggregation between customer interfaces and
managed entities (Provider Edge devices).
It defines VPNs as policies, allowing an interface to be a member
of multiple VPNs and allowing for the topology of the virtual
network to be modified by modifying the policy configuration.
It scales horizontally in terms of event propagation. By
increasing the number of signaling devices, implementing the PE
control plane, it is possible to decrease the load on each
signaling device when it comes to propagating events that
originate in a specific location and must be propagated across the
network.
The last point is particularly relevant to the convergence
characteristics required for large scale deployments. BGP's
hierarchical route distribution capabilities allow a deployment to
divide the workload by increasing the number of BGP signaling
gateways.
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As an example consider a topology in which 100 BGP signaling gateways
are deployed in a data-center each serving a subset of the VPN
forwarding elements. The signaling gateways inter-connect to two
top-level BGP Route Reflectors [RFC4456].
If an event (i.e. a VPN route change) needs to be propagated from a
specific machine that activates a VM to 10.000 clients randomly
distributed across a data-center, each of the BGP signaling gateways
must generate 100 updates to its respective downstream clients.
By modifying this topology such that another 100 signaling gateways
are added, then each signaling gateway is now responsible to generate
50 client updates. This example illustrates the linear scaling
properties of BGP: doubling the number of signaling gateways (i.e.
the processing capacity) reduces in half the number of updates
generated by each (i.e. load at each processing node).
The same horizontal scaling techniques can be applied to the Route
Reflector layer in the example above by subsetting the VPN Route
space according to some pre-defined criteria (for instance VPN route
target) and using a pair of Route Reflectors per subset.
In the example above we assumed a dense membership in which all
signaling gateways have local clients that are interested in a
particular event. BGP also optimizes the route distribution for
sparse events. The Route Target Constraint [RFC4684] extension,
builds an optimal distribution tree for message propagation based on
VPN membership. It ensures that only the Signaling Gateways with
local receivers for a particular event do receive it also decreasing
the total load on the upstream BGP speaker.
In the WAN environment, BGP IP VPN control plane scaling is focused
not primarily on route convergence times but on memory footprint of
embedded devices. While memory footprint does not have a similar
linear scaling behavior, memory technology in the data-center is
often at 10x the scale of what is commonly found in WAN environments.
The functionality present in the BGP IP VPN control plane addresses
the requirements specified in the previous section. Specifically, it
supports multiple potentially overlapping "groups", regular or "hub
and spoke" topologies and the scaling characteristics necessary.
The BGP IP VPN control plane supports not only the definition of
"closed user-groups" (VPNs in its terminology) but also the
propagation of inter-VPN traffic policies [RFC5575]. An application
of that mechanism to "end-system" VPN is presented in [I-D.marques-
sdnp-flow-spec].
Note that the signaling protocol itself is rather agnostic of the
encapsulation used on the wire as long as this encapsulation has the
ability to carry a 20 bit label.
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Several data-center deployments use a switching infrastructure that
is only capable of providing an IP unicast service. In order to
support them, implementations of this document should support the
MPLS in GRE [RFC4023] encapsulation. Other encapsulations are
possible, including UDP based encapsulations.
4. Virtual network end-points
This document assumes that end-systems support one or more virtual
network interfaces in addition to a physical interface that is
associated with the data-center switching infrastructure. Virtual
network interfaces can be associated with a VM or they can be used to
provide network connectivity directly to applications in the same way
that a "VPN tunnel" interface is used to provide access between an
end-system (e.g. a laptop) and a remote corporate network.
From an IP address assignment point of view, a virtual network
interface is addressed out of the virtual IP topology and associated
with a "closed user group" or VPN, while the physical interface of
the machine is addressed in the network infrastructure topology. As
a security measure, it is recommended that virtual and infrastructure
topologies never be allowed to exchange traffic directly.
In data-center environments, static IP address allocation is common
since it is desirable to associate a permanent IP address to a VM and
have that IP address remain constant even as the VM migrates.
However dynamic address assignment through DHCP is also possible
assuming that the VPN forwarder implements DHCP relay functionality.
A virtual network interface is connected to a VPN forwarder. This
VPN forwarder MAY be located on the hypervisor or host OS that co-
resides on the same physical machine or it could be located in an
external system, such as the first-hop switch. We refer to this
second system as the external VPN forwarder.
All traffic that ingresses or egresses through this virtual network
interface is routed at the VPN forwarder which acts as the first-hop
router (in the virtual topology). The IP configuration on the client
side of this virtual network interface (e.g. in the guest OS) can
follow one of two models:
point-to-point interface model.
multipoint interface model.
In a point-to-point interface model, the system routing table (e.g.
the guest OS) contains the following routing entires: a host route to
the local IP address, a host route to the first-hop router via the
virtual interface and a default route to the first-hop router. This
is the model typically used in "VPN tunnel" configurations or other
access technologies such as cable deployments or DSL. When this model
is used, the first-hop router IP address is a link-local address that
is the same on all first-hop routers across a specific deployment.
This first-hop IP address should not change when a VM migrates
between different machines.
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In a multi-point interface model, the system routing table (on the
guest OS) contains the following routing entires: a host route to the
local IP address, a subnet route to the local interface and
optionally a default route to an specific router address within that
subnet. In this model, the end-system will issue address resolution
requests for any IP addresses it considers to be directly attached to
the subnet. The VPN forwarder shall answer all address resolution
requests with a virtual MAC address which SHOULD be the same across
all VPN forwarders in a specific deployment. This virtual MAC
address SHALL default to the VRRP [RFC5798] virtual router MAC
address for VRID 1..
When the virtual topology first-hop router resides on the same
physical machine, the host OS is responsible to map the virtual
interface with a VPN specific routing table (without taking L2
addresses into consideration). In this case the mac-addresses known
to the guest OS are not used on the wire.
When the virtual topology first-hop router resides in an external
system (e.g. the first hop-switch) the virtual interface shall be
identified by the combination of the physical interface mac-address
and a 802.1Q VLAN tag. The first-hop switch should use a virtual
router MAC address to answer any address resolution queries.
Whenever an external VPN forwarder is used and resiliency is desired,
the external VPN forwarder should be redundant. It is desirable to
use VRRP as a mechanism to control the flow of traffic between the
end-system and the external VPN forwarder. VRRP already defines the
necessary procedures to elect a single forwarder for a LAN.
This specification uses the VRRP virtual router MAC address as the
default L2 address for the VPN forwarder as a VM may move between
locations where redundancy is and is not present.
While the VRRP Virtual Router MAC will be used resolve any address
resolution request made by the virtual interface client (e.g. the
guest VM) this does not imply that a single default router is elected
per virtual IP subnet. The ingress VPN forwarder will perform an IP
forwarding decision based on the destination IP address of the
(payload) traffic.
VRRP router election is only relevant in selecting the VPN forwarder
associated with a specific machine, when external forwarders are in
use.
5. VPN forwarder
In this solution, the Host OS/Hypervisor in the end-system must
participate in the virtual network service. Given an end-system with
multiple virtual interfaces, these virtual interfaces must be mapped
onto the network by the guest OS such that applications on one
virtual interface are not allowed to impersonate another virtual
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interface.
When VPN forwarder functionality is implemented by the Host OS/
Hypervisor, intermediate systems in the network, be they access,
aggregation or core switches, do not require any knowledge of the
virtual network topology. This can simplify the design an operation
of the data-center switching infrastructure.
When it is not possible or desirable to add the VPN forwarding
functionality to the end-system, it may be implemented by an external
system, typically located as close as possible to the end-system
itself. This could be a top-of-rack or aggregation switch.
Both models, end-system and extern VPN forwarder can co-exist in a
deployment.
In order to implement the BGP IP VPN forwarder functionality a device
MUST implement the following functionality:
Support for multiple "Virtual Routing and Forwarding" (VRF)
tables;
VRF route entries map prefixes in the virtual network topology
to a next-hop containing a infrastructure IP address and a
20-bit label allocated by the destination forwarder. The VRF
table lookup follows the standard IP lookup (best-match)
algorithm.
Associate a end-system virtual interface with a specific VRF
table;
When the first-hop router is the Host OS/hypervisor this
association is performed by an internal mechanism. When the
first-hop router is external this association is performed
using the mac-address of the end-system and a IEEE 802.1Q tag
that identifies the virtual interface within the end-system.
Encapsulate outgoing traffic (end-system to network) according to
the result of the VRF lookup;
Associate incoming packets (network to end-system) to a VRF
according to the 20-bit label contained immediately after the GRE
header;
The VPN forwarder MAY support the ability to associate multiple
virtual interfaces with the same VRF. When that is the case, locally
originated routes, that is IP routes to the local virtual interfaces
SHALL NOT be used to forward outbound traffic (from the virtual
interfaces to the outside) unless a route advertisement has been
received that matches that specific IP prefix and next-hop
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information.
As an example, if a given VRF contains two virtual interfaces,
"veth0" and "veth1", with the addresses 10.0.1.1/32 and 10.0.1.2/32
respectively, the initial forwarding state must be initialized such
that traffic from either of these interfaces does not match the
other's routing table entry. It may for instance match a default
route advertised by a remote system. Traffic received from other VPN
forwarders, however, must be delivered to the correct local
interface. If at a subsequent stage a route is received from the
signaling gateway such that 10.0.1.2/32 has a next-hop with the IP
address of the local host and the correct label, the system may
subsequently install a local routing table entry that delivers
traffic directly to the "veth1" interface.
The 20-bit label which is associated with a virtual-interface is of
local significance only and SHOULD be allocated by the VPN forwarder.
When an external VPN forwarder is used the end-system MUST associate
each virtual interface with a VLAN [IEEE.802-1Q] that is unique on
the end-system. The switching infrastructure MUST be configured such
that multi-destination frames sourced from an end-system are only
delivered to VPN forwarders used by this end-system and not to other
end-systems.
6. XMPP signaling protocol
Signaling Gateways must be made aware of virtual interface creation
and deletion and of when IP addresses are added or removed from these
virtual interfaces.
VPN forwarders must receive VPN route information from which to
populate their forwarding tables. When the VPN forwarder is a
different system than the end-system where the virtual interface
resides, it also needs to receive the interface and IP address events
from the end-system. In this case it is the VPN forwarder that
propagates these to the Signaling Gateway.
When an external VPN forwarder is used, the end-system assigns the
VLAN identifier used for each virtual interface. This information is
conveyed by an optional parameter in the VPN subscription request.
It is not propagated by the VPN forwarder.
In order to exchange this information this specification uses the
XMPP [RFC6120] protocol along with the PubSub Collection Nodes
[pubsub] extension.
Clients (end-systems and external VPN forwarders) establish
persistent XMPP sessions. These sessions MUST use the XMPP Ping
[xmpp-ping] extension in order to detect end-system failures.
A client MAY connect to multiple servers (e.g. VPN-signaling
gateways) for reliability. In this case it SHOULD publish its
information to each of the gateways. It MAY choose to subscribe to
VPN routing information once only from one of the available gateways.
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The information advertised by a client SHOULD be deleted after a
configurable timeout, when the session closes. This timeout should
default to 60 seconds.
+---------+ +--------+
| gateway | ----------- | BGP |
+---------+ +--------+
// \ /
XMPP \ /
// \ /
+------------+ \ /
| end-system | \ /
+------------+ \/
\\ /\
XMPP / \
\\ / \
+---------+ / \ +--------+
| gateway | ----------- | BGP |
+---------+ +--------+
The figure above represents a typical configuration in which an end-
system (implementing the VPN forwarder functionality) is directly
connected to two gateways, which are in turn connected to multiple
BGP spakers which may be other BGP signaling gateways or BGP route
reflectors.
In deployment the number of gateways used will depend on the desired
gateway to VPN forwarder ratio which affects the convergence time of
event propagation.
The XMPP "jid" used by the client shall be a 6-byte value that
uniquely identifies it in the domain. This specification recommends
the use of the MAC address of one of the physical ethernet
interfaces.
Each VPN shall be identified by a 64 ASCII character string.
When external forwarders are used, its control software operates as a
XMPP server processing requests from end-systems and as a client of
one or more Signaling Gateways. The control software relays to the
Signaling Gateways(s) messages it receives from the end-system. VPN
routing information received from the Signaling Gateways(s) SHOULD
NOT be propagated to the end-system.
When a virtual interface is created, for instance as result of a
Virtual Machine being instantiated on a end-system, the host
operating-system software shall generate an XMPP Subscribe message to
its server (the VPN-signaling gateway or external VPN forwarder).
Subscription request from end-system to gateway (local VPN
forwarder):
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The request above, instructs the signaling gateway to start
populating the client's VRF table with any routing information that
is available for this VPN. The XMPP node 'vpn-customer-name' is
assumed to be a collection which is implicitly created by the VPN-
signaling gateway. Creation of a virtual interface may precede any
IP address becoming active on the interface, as it is the case with
VM life migration.
Subscription request from end-system to external VPN forwarder:
vlan-id
When an external VPN forwarder is used the end-system should include
the VLAN identifier it assigned to the virtual interface as a
subscription option.
When a IP address is added to a virtual interface, the end-system
will generate an XMPP Publish request.
Publish request from end-system to gateway:
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to='network-control.domain.org'
id='request1'>
'vpn-ip-address/32''infrastructure-ip-address'
The VPN-signaling gateway will convert the information received in a
the 'publish' request into the corresponding BGP route information
such that:.
It associates the specific request with a local VRF which it
resolves by using a combination of the originator system-id and
the collection 'node' attribute.
It creates a BGP VPN route with a 'Route Distinguisher' (RD) which
contains the the end-system's 'system-id' value and the specified
IP prefix and 'label' as the Network Layer Reachability
Information (NLRI) .
The BGP next-hop address is set to the address of egress VPN
forwarder.
It associates the route with an extended community TDB containing
the version number.
Update notification from gateway to end-system:
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'vpn-ip-address>/32''infrastructure-ip-address'
...
Notifications should be generated whenever a VPN route is added,
modified or deleted.
Note that the Update from the signaling gateway to the end-point does
not contain the system-id of the destination end-point. When
multiple possible routes exist for a given VPN IP address, for
instance because the VM may be in the process of moving location, it
is the responsibility of the gateway to select the best path to
advertise to the end-system.
When routes are withdrawn, the signaling gateway generates both a
"collection disassociate" request as well as a node "delete" request.
In situations where an automated system is controlling the
instantiation of VMs it may be possible to have that system assign a
non-decreasing version number for each instantiation of that
particular VM. In that case, this number, carried in the 'version'
field may be used to help gateways select the most recent
instantiation of a VM during the interval of time where multiple
routes are present.
7. Signaling gateway behavior
BGP Signaling gateways SHALL support the address families: VPN-IPv4
(1, 128), VPN-IPv6 (2, 128) and RT-Constraint (1, 132) [RFC4684].
When a VPN-signaling gateway receives a request to create or modify a
VPN route it SHALL generate a BGP VPN route advertisement with the
corresponding information.
It is assumed that the VPN-signaling gateways contain information
regarding the mapping between end-system the tuple ('system-id',
'vpn-customer-names') and BGP Route Targets used to import and export
information from the associated VRFs. This mapping is known via an
out-of-band mechanism not specified in this document.
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Whenever the Signaling Gateway receives an XMPP subscription request,
it SHALL consult its RT-Constraint Routing Information Base (RIB).
If the Signaling Gateway does not already have locally originated
route that corresponds to the route target being carried in the
request, it SHALL create one and generate the corresponding BGP route
advertisement. This route advertisement should only be withdrawn
when there are no more downstream XMPP clients subscribed to the VPN.
The 32bit route version number defined in the XML schema is
advertised into BGP as a Extended community with type TBD.
Signaling gateways SHOULD automatically assign a BGP route
distinguisher per VPN routing table.
8. Operational Model
In the simplest case, a VPN is a collection of systems that are
allowed to exchange traffic with each other and only with each other.
Since all the forwarding tables in this VPN have the same routing
entires they are often referred to as symmetrical VPNs.
In order to better illustrate the operation of the protocol we
consider a simple example in which "host 1" and "host 2" both contain
a VM that is a member of the same VPN.
Each of these hosts has an XMPP session with a Signaling Gateway, SG1
and SG2 our example, and these Signaling Gateways are part of the
same BGP mesh.
When a virtual interface is created on "host 1", the local XMPP
client generates a XMPP subscription message to its respective
Signaling Gateway. This message contains a VPN identifier that has
been assigned by the VM provisioning system. The Signaling Gateway
maps that identifier to a BGP IP VPN configuration which contains the
list of import and export route targets to be used for that
particular VRF.
Once the VM is operational, "host 1" will publish any IP addresses
that are configured on the respective virtual interface. This will
in turn cause the Signaling Gateway to advertise these to any other
BGP speaker on the network which is connected to an attachement point
of that VPN.
+--------+ +-----------+ +----------+
| host 1 | <===> | signaling | <===> | BGP mesh |
+--------+ | gateway | +----------+
+-----------+
+----------------+-------------+-------+-----------+
| VPN IP address | NEXT-HOP | label | Known via |
+----------------+-------------+-------+-----------+
| 10.1.1.1/32 | 192.168.1.1 | 10000 | XMPP |
| 10.1.1.2/32 | 192.168.2.1 | 20000 | BGP |
+----------------+-------------+-------+-----------+
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VPN Routing table on signaling gateway
The figure above represents the contents of the VRF routing table on
Signaling Gateway 1 after the IPv4 address 10.1.1.1 has been added to
the virtual interface on host 1. It assumes that there is another
attachement point for this VPN with the IPv4 address of 10.1.1.2.
Host 1 has an infrastructure IP address of 192.168.1.1 configured on
its physical interface while host 2 has IP address 192.168.2.1.
The contents of the VRF routing table in the Signaling Gateway are
advertised via XMPP Update notifications sent to host 1. This
information is the used by the host to populate the forwarding table
associated with that VPN.
+--------+ +--------+
VM1 -- veth0 --| host 1 |=== [network] ===| host 2 |-- veth0 -- VM2
+--------+ +--------+
IP pkt ===> GRE encap ===> [IP net] ===> GRE decap ===> IP pkt
[192.168.2.1, 20] map 20 to veth0
+----------------+--------------+-------+
| VPN IP address | Host address | label |
+----------------+--------------+-------+
| 10.1.1.1/32 | localhost | 10000 |
| 10.1.1.2/32 | 192.168.2.1 | 20000 |
+----------------+--------------+-------+
VRF table on host1
When the VM on host 1 generates packets with a destination IP address
of 10.1.1.2 these are routed by the VPN forwarder implemented in the
Host OS. The packets are encapsulated with a GRE header that
contains a 20-bit label assigned by host 2.
When the VM on host 1 sends packets on the virtual interface it is
using the Virtual Router MAC address as the destination MAC. When
host 2 delivers packets to the remote VM it sets the Virtual Router
MAC address as the source MAC address. This MAC address is not
present on the GRE encapsulated packet.
BGP/XMPP Signaling Gateways are software applications the implement
both the BGP IP VPN PE control plane as well as XMPP server
functionality. These application are not in the forwarding plane and
do not need to be co-located with a network device.
Network devices MAY have direct BGP sessions to the Signaling
Gateways. For instance, a router or security appliance that supports
BGP/MPLS IP VPNs over GRE may use its existing functionality to
inter-operate directly with a collection of Virtual Machines.
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Signaling Gateways implement the VRF import policy and export policy
functionality that is associated with PE routers in standard BGP IP/
VPN deployments. VPN forwarders receive forwarding information after
policy and route selection is applied. These are unqualified routes
in a specific VRF rather than VPN routing information qualified by a
Route Distinguisher and with a set of Route Targets.
A symmetrical VPN uses a vrf import and vrf export polices that
contain a single route target, where the route target used for both
import and export is the same.
Different VPN topologies can be created by manipulating the vrf
import and export configuration including "hub-and-spoke" topologies
or overlapping VPNs.
An example of a hub-and-spoke VPN configuration is one where all the
traffic from VMs must be redirected though a middle-box (on a VM) for
inspection. Assuming that the VMs of a particular user are
configured to be in the VPN "tenant1". At an initial stage this
"tenant1" VPN is symmetrical and uses a single Route Target in both
its import and export policies. The middle-box functionality can be
incrementally deployed by defining a new VPN, "tenant1-hub", and an
associated Route Target. Accompanied with a change in the Signaling
Gateway configuration such that VPN "tenant1" only imports routes
with the Route Target associated with the hub. The "hub" VPN is
assumed to advertise a prefix that covers all the VMs IP addresses.
The "hub" VPN imports the VMs routes in order for it to be able to
generate the XMPP updates to the "hub" end-system. This information
is required for the return traffic from the hub to the spokes (the
standard VMs). In such a scenario a single interface can connect the
middle-box to the VMs in a given VPN which appear logically as
downstream from it. Such a middle-box would often require
connectivity to multiple VPNs, such as for instance an "outside" VPN
which provides external connectivity to one or more "inside" VPNs.
The functionality defined in this document in which the BGP IP VPN PE
functionality is split into its control (Signaling Gateway) and
forwarding (VPN forwarder) components is fully interoperable with
existing BGP IP VPN PEs.
This makes it possible to reuse existing systems. For example, at
the edge of a data-center facility it may be desirable to use an
existing router or appliance that aggregates IP VPN routing
information and/or provides IP based services such as stateful packet
inspection.
Such a system can be configured, based on existing functionality, to
suppress more specific routes than a specified aggregate while
advertising the aggregate with a BGP NEXT_HOP containing the PE's IP
address and a locally assigned label corresponding to a VRF where the
more specific routes are present.
9. Security Considerations
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The signaling protocol defines the access control policies for each
virtual interface and any VM associated with it. It is important to
secure the end-system access to signaling gateways and the BGP
infrastructure itself.
The XMPP session between end-systems and the XMPP gateways MUST use
mutual authentication. One possible strategy is to distribute pre-
signed certificates to end-systems which are presented as proof of
authorization to the signaling gateway.
BGP sessions MUST be authenticated using a shared secret. This
document recommends that BGP speaking systems filter traffic on port
179 such that only IP addresses which are known to participate in the
BGP signaling protocol are allowed.
10. Acknowledgements
Yakov Rekhter has contributed to this document by providing detailed
feedback and suggestions. The authors would also like to thank
Thomas Morin for his comments.
11. References
11.1. Normative References
[RFC4023] Worster, T., Rekhter, Y. and E. Rosen, "Encapsulating MPLS
in IP or Generic Routing Encapsulation (GRE)", RFC 4023,
March 2005.
[RFC4271] Rekhter, Y., Li, T. and S. Hares, "A Border Gateway
Protocol 4 (BGP-4)", RFC 4271, January 2006.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, February 2006.
[RFC4456] Bates, T., Chen, E. and R. Chandra, "BGP Route Reflection:
An Alternative to Full Mesh Internal BGP (IBGP)", RFC
4456, April 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.
[RFC5575] Marques, P., Sheth, N., Raszuk, R., Greene, B., Mauch, J.
and D. McPherson, "Dissemination of Flow Specification
Rules", RFC 5575, August 2009.
[RFC5798] Nadas, S., "Virtual Router Redundancy Protocol (VRRP)
Version 3 for IPv4 and IPv6", RFC 5798, March 2010.
[RFC6120] Saint-Andre, P., "Extensible Messaging and Presence
Protocol (XMPP): Core", RFC 6120, March 2011.
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[xmpp-ping]
"XMPP Ping", XEP 0199, June 2009.
[pubsub] "PubSub Collection Nodes", XEP 0248, September 2010.
11.2. Informational References
[I-D.marques-sdnp-flow-spec]
Marques, P, Fang, L, Pan, P and A Shukla, "Traffic
classification, filtering and redirection for end-system
IP VPNs.", Internet-Draft draft-marques-sdnp-flow-spec-00,
October 2011.
[IEEE.802-1Q]
Institute of Electrical and Electronics Engineers, "Local
and Metropolitan Area Networks: Virtual Bridged Local Area
Networks", IEEE Std 802.1Q-2005, May 2006.
Authors' Addresses
Pedro Marques
Email: pedro.r.marques@gmail.com
Luyuan Fang
Cisco Systems
111 Wood Avenue South
Iselin, NJ 08830
Email: lufang@cisco.com
Ping Pan
Infinera Corp
140 Caspian Ct.
Sunnyvale, CA 94089
Email: ppan@infinera.com
Amit Shukla
Juniper Networks
1194 N. Mathilda Av.
Sunnyvale, CA 94089
Email: amit@juniper.net
Maria Napierala
AT&T Labs
200 Laurel Avenue
Middletown, NJ 07748
Email: mnapierala@att.com
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