Network Working Group L. Dunbar
Internet Draft Futurewei
Intended status: Informational B. Sarikaya
Expires: September 25, 2020 Denpel Informatique
B.Khasnabish
Independent
T. Herbert
Intel
S. Dikshit
Aruba-HPE
March 25, 2020
Virtual Machine Mobility Solutions for L2 and L3 Overlay Networks
draft-ietf-nvo3-vmm-08
Abstract
This document describes virtual machine mobility solutions commonly
used in data centers built with overlay-based network. This document
is intended for describing the solutions and the impact of moving
VMs (or applications) from one Rack to another connected by the
Overlay networks.
For layer 2, it is based on using an NVA (Network Virtualization
Authority) - NVE (Network Virtualization Edge) protocol to update
ARP (Address Resolution Protocol) table or neighbor cache entries
after a VM (virtual machine) moves from an Old NVE to a New NVE.
For Layer 3, it is based on address and connection migration after
the move.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. This document may not be modified,
and derivative works of it may not be created, except to publish it
as an RFC and to translate it into languages other than English.
xxx, et al. Expires September 25, 2020 [Page 1]
Internet-Draft VM Mobility Solution March 25, 2020
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/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html
This Internet-Draft will expire on September 24, 2020.
Copyright Notice
Copyright (c) 2020 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
2. Conventions used in this document..............................4
3. Requirements...................................................5
4. Overview of the VM Mobility Solutions..........................6
4.1. VM Migration in Layer 2 Network...........................6
Dunbar, et al. Expires September 25, 2020 [Page 2]
Internet-Draft VM Mobility Solution March 25, 2020
4.2. VM Migration in Layer-3 Network...........................8
4.3. Address and Connection Migration in Task Migration........9
5. Handling Packets in Flight....................................10
6. Moving Local State of VM......................................10
7. Handling of Hot, Warm and Cold VM Mobility....................11
8. Other VM Mobility Options.....................................11
9. VM Lifecycle Management.......................................12
10. Security Considerations......................................12
11. IANA Considerations..........................................12
12. Acknowledgments..............................................12
13. Change Log...................................................13
14. References...................................................13
14.1. Normative References....................................13
14.2. Informative References..................................14
1. Introduction
This document describes the overlay-based data center networks
solutions in supporting multitenancy and VM (Virtual Machine)
mobility. This document is strictly within the DCVPN, as defined
by the NVO3 Framework [RFC 7365]. The intent is to describe Layer
2 and Layer 3 Network behavior when VMs are moved from one NVE to
another. This document assumes that the VMs move is initiated by
VM management system, i.e. planed move. How and when to move VM
are out of the scope of this document. RFC7666 already has the
description of the MIB for VMs controlled by Hypervisor. The
impact of VM mobility on higher layer protocols and applications
is outside its scope.
Many large DCs (Data Centers), especially Cloud DCs, host tasks
(or workloads) for multiple tenants. A tenant can be a department
of one organization or an organization. There are communications
among tasks belonging to one tenant and communications among tasks
belonging to different tenants or with external entities.
Server Virtualization, which is being used in almost all of
today's data centers, enables many VMs to run on a single physical
computer or server sharing the processor/memory/storage. Network
connectivity among VMs is provided by the network virtualization
edge (NVE) [RFC8014]. It is highly desirable [RFC7364] to allow
VMs to be moved dynamically (live, hot, or cold move) from one
server to another for dynamic load balancing or optimized work
distribution.
There are many challenges and requirements related to VM mobility
in large data centers, including dynamic attaching/detaching VMs
to/from Virtual Network Edges (VNEs). In addition, retaining IP
addresses after a move is a key requirement [RFC7364]. Such a
Dunbar, et al. Expires September 25, 2020 [Page 3]
Internet-Draft VM Mobility Solution March 25, 2020
requirement is needed in order to maintain existing transport
connections.
In traditional Layer-3 based networks, retaining IP addresses
after a move is generally not recommended because the frequent
move will cause fragmented IP addresses, which introduces
complexity in IP address management.
In view of many VM mobility schemes that exist today, there is a
desire to document comprehensive VM mobility solutions that cover
both IPv4 and IPv6. The large Data Center networks can be
organized as one large Layer-2 network geographically distributed
in several buildings/cities or Layer-3 networks with large number
of host routes that cannot be aggregated as the result of frequent
moves from one location to another without changing their IP
addresses. The connectivity between Layer 2 boundaries can be
achieved by the network virtualization edge (NVE) functioning as
Layer 3 gateway routing across bridging domain such as in
Warehouse Scale Computers (WSC).
2. Conventions used in this document
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] and [RFC8014].
This document uses the terminology defined in [RFC7364]. In
addition, we make the following definitions:
VM: Virtual Machine
Tasks: Task is a program instantiated or running on a virtual
machine or container. Tasks in virtual machines or
containers can be migrated from one server to another.
We use task, workload and virtual machine
interchangeably in this document.
Hot VM Mobility: A given VM could be moved from one server to
another in running state.
Dunbar, et al. Expires September 25, 2020 [Page 4]
Internet-Draft VM Mobility Solution March 25, 2020
Warm VM Mobility: In case of warm VM mobility, the VM states are
mirrored to the secondary server (or domain) at a
predefined (configurable) regular intervals. This
reduces the overheads and complexity, but this may also
lead to a situation when both servers may not contain
the exact same data (state information)
Cold VM Mobility: A given VM could be moved from one server to
another in stopped or suspended state.
Old NVE: refers to the old NVE where packets were forwarded to
before migration.
New NVE: refers to the new NVE after migration.
Packets in flight: refers to the packets received by the Old NVE
sent by the correspondents that have old ARP or neighbor
cache entry before VM or task migration.
Users of VMs in diskless systems or systems not using
configuration files are called end user clients.
Cloud DC: Third party data centers that host applications,
tasks or workloads owned by different organizations or
tenants.
3. Requirements
This section states requirements on data center network virtual
machine mobility.
Data center network should support both IPv4 and IPv6 VM mobility.
Virtual machine (VM) mobility should not require changing VMs' IP
addresses after the move.
There is "Hot Migration" with transport service continuing, and
"Cold Migration" with transport service restarted, i.e. the task
running is stopped on the Old NVE, moved to the New NVE and the task
is restarted. Not all DCs support "Hot Migration. DCs that only
support Cold Migration should make their customers aware of the
potential service interruption during the Cold Migration.
Dunbar, et al. Expires September 25, 2020 [Page 5]
Internet-Draft VM Mobility Solution March 25, 2020
VM mobility solutions/procedures should minimize triangular routing
except for handling packets in flight.
VM mobility solutions/procedures should not need to use tunneling
except for handling packets in flight.
4. Overview of the VM Mobility Solutions
Layer 2 and Layer 3 mobility solutions are described respectively
in the following sections.
This document assumes that the communication with external
entities are via the NVO3 Gateway as described in RFC8014 (NVO3
Architecture). RFC 8014 (Section 5.3) has the discussion whether a
VM move may result in or cannot result in a change to the network
node providing the NV03 Gateway functionality - if such a change
is not possible, then the path to the external entity may be hair-
pinned to the NVO3 Gateway used prior to the VM move.
4.1. VM Migration in Layer 2 Network
Being able to move VMs dynamically, from one server to another,
makes it possible for dynamic load balancing or work distribution.
Therefore, dynamic VM Mobility is highly desirable for large scale
multi-tenant DCs.
In a Layer-2 based approach, VM moving to another server does not
change its IP address. But this VM is now under a new NVE,
previously communicating NVEs will continue sending their packets
to the Old NVE. To solve this problem, Address Resolution
Protocol (ARP) cache in IPv4 [RFC0826] or neighbor cache in IPv6
[RFC4861] in the NVEs need to be updated promptly. All NVEs need
to change their caches associating the VM Layer-2 or Medium Access
Control (MAC) address with the new NVE's IP address as soon as the
VM is moved. Such a change enables all NVEs to encapsulate the
outgoing MAC frames with the current target NVE IP address. It may
take some time to refresh ARP/ND cache when a VM is moved to a New
NVE. During this period, a tunnel is needed for that Old NVE to
forward packets destined to the VM to the New NVE.
In IPv4, the VM immediately after the move should send a
gratuitous ARP request message containing its IPv4 and Layer 2 MAC
address in its new NVE. This message's destination address is the
broadcast address. Upon receiving this message, both Old and New
NVEs should update the VM's ARP entry in the central directory at
Dunbar, et al. Expires September 25, 2020 [Page 6]
Internet-Draft VM Mobility Solution March 25, 2020
the NVA, to update its mappings to record the IPv4 address & MAC
address of the moving VM along with the new NVE IPv4 address. An
NVE-to-NVA protocol is used for this purpose [RFC8014].
Reverse ARP (RARP) which enables the host to discover its IPv4
address when it boots from a local server [RFC0903], is not used
by VMs if the VM already knows its IPv4 address (most common
scenario). Next, we describe a case where RARP is used.
There are some vendor deployments (diskless systems or systems
without configuration files) wherein the VM's user, i.e. end-user
client askes for the same MAC address upon migration. This can be
achieved by the clients sending RARP request message which carries
the MAC address looking for an IP address allocation. The server,
in this case the new NVE needs to communicate with NVA, just like
in the gratuitous ARP case to ensure that the same IPv4 address is
assigned to the VM. NVA uses the MAC address as the key in the
search of ARP cache to find the IP address and informs this to the
new NVE which in turn sends RARP reply message. This completes IP
address assignment to the migrating VM.
Other NVEs communicating with this VM could have the old ARP
entry. If any VMs in those NVEs need to communicate with the VM
attached to the New NVE, old ARP entries might be used. Thus, the
packets are delivered to the Old NVE. The Old NVE needs to tunnel
these in-flight packets to the New NVE to avoid packets loss.
When an ARP entry for those VMs times out, their corresponding
NVEs should access the NVA for an update.
IPv6 operation is slightly different:
In IPv6, after the move, the VM immediately sends an unsolicited
neighbor advertisement message containing its IPv6 address and
Layer-2 MAC address to its new NVE. This message is sent to the
IPv6 Solicited Node Multicast Address corresponding to the target
address which is the VM's IPv6 address. The NVE receiving this
message should send request to update VM's neighbor cache entry in
the central directory of the NVA. The NVA's neighbor cache entry
should include IPv6 address of the VM, MAC address of the VM and
the NVE IPv6 address. An NVE-to-NVA protocol is used for this
purpose [RFC8014].
Other NVEs communicating with this VM might still use the old
neighbor cache entry. If any VM in those NVEs need to communicate
with the VM attached to the New NVE, it could use the old neighbor
Dunbar, et al. Expires September 25, 2020 [Page 7]
Internet-Draft VM Mobility Solution March 25, 2020
cache entry. Thus, the packets are delivered to the Old NVE. The
Old NVE needs to tunnel these in-flight packets to the New NVE.
When a neighbor cache entry in those VMs times out, their
corresponding NVEs should access the NVA for an update.
4.2. VM Migration in Layer-3 Network
Traditional Layer-3 based data center networks usually have all
hosts (tasks) within one subnet attached to one NVE. By this
design, the NVE becomes the default route for all hosts (tasks)
within the subnet. But this design requires IP address of a host
(task) to change after the move to comply with the prefixes of the
IP address under the new NVE.
A VM migration in Layer 3 Network solution is to allow IP
addresses staying the same after moving to different locations.
The Identifier Locator Addressing or ILA [I-D.herbert-nvo3-ila] is
one of such solutions.
Because broadcasting is not available in Layer-3 based networks,
multicast of neighbor solicitations in IPv6 would need to be
emulated.
Hot VM Migration in Layer 3 involves coordination among many
entities, such as VM management system and NVA. Cold task
migration, which is a common practice in many data centers,
involves the following steps:
- Stop running the task.
- Package the runtime state of the job.
- Send the runtime state of the task to the New NVE where the
task is to run.
- Instantiate the task's state on the new machine.
- Start the tasks for the task continuing from the point at which
it was stopped.
RFC7666 has the more detailed description of the State Machine of
VMs controlled by Hypervisor
Dunbar, et al. Expires September 25, 2020 [Page 8]
Internet-Draft VM Mobility Solution March 25, 2020
4.3. Address and Connection Migration in Task Migration
The term "Task" is referring to an entity (Task) that is
instantiated on a VM or a container, in another word, a Task can
be an "Application" or a "workload" running on a VM or a
Container.
Moving a Task running on a VM attached to one NVE to another VM
attached to a New NVE is same as moving the VM from one NVE to the
New NVE. The VM attached to the New NVE needs to be assigned with
the same address as VM attached to the Old NVE, which is called
Address Migration in this document. Here is an example of the
steps involved in Address Migration:
- Configure IPv4/v6 address on the target VM/NVE.
- Suspend use of the address on the old NVE. This includes
handling established connections. A state may be established
to drop packets or send ICMPv4 or ICMPv6 destination
unreachable message when packets to the migrated address are
received. Referring to the VM State Machine described in
RFC7666.
- Push the new NVE-VM mapping to other NVEs which have the
attached VMs communicating with the VM being moved. All
relevant NVEs will learn the new mapping via their
corresponding NVA.
Connection migration involves reestablishing existing TCP
connections of the task in the new place.
The simplest course of action is to drop all TCP connections to
the VM across a migration. If the migrations are relatively rare
events in a data center, impact is relatively small when TCP
connections are automatically closed in the network stack during a
migration event. If the applications running are known to handle
this gracefully (i.e. reopen dropped connections) then this
approach may be viable.
More involved approach to connection migration entails pausing the
connection, packaging connection state and sending to target,
instantiating connection state in the peer stack, and restarting
the connection. From the time the connection is paused to the
time it is running again in the new stack, packets received for
the connection could be silently dropped. For some period of
time, the old stack will need to keep a record of the migrated
connection. If it receives a packet, it can either silently drop
Dunbar, et al. Expires September 25, 2020 [Page 9]
Internet-Draft VM Mobility Solution March 25, 2020
the packet or forward it to the new location, as described in
Section 5.
5. Handling Packets in Flight
The Old NVE may receive packets from the VM's ongoing
communications. These packets should not be lost; they should be
sent to the New NVE to be delivered to the VM. The steps involved
in handling packets in flight are as follows:
Preparation Step: It takes some time, possibly a few seconds for
a VM to move from its Old NVE to a New NVE. During this period, a
tunnel needs to be established so that the Old NVE can forward
packets to the New NVE. Old NVE gets New NVE address from its NVA
assuming that the NVA gets the notification when a VM is moved
from one NVE to another. It is out of the scope of this document
on which entity manages the VM move and how NVA gets notified of
the move. The Old NVE can store the New NVE address for the VM
with a timer. When the timer expired, the entry for the New NVE
for the VM can be deleted.
Tunnel Establishment - IPv6: Inflight packets are tunneled to the
New NVE using the encapsulation protocol such as VXLAN in IPv6.
Tunnel Establishment - IPv4: Inflight packets are tunneled to the
New NVE using the encapsulation protocol such as VXLAN in IPv4.
Tunneling Packets - IPv6: IPv6 packets received for the migrating
VM are encapsulated in an IPv6 header at the Old NVE. New NVE
decapsulates the packet and sends IPv6 packet to the migrating VM.
Tunneling Packets - IPv4: IPv4 packets received for the migrating
VM are encapsulated in an IPv4 header at the Old NVE. New NVE
decapsulates the packet and sends IPv4 packet to the migrating VM.
Stop Tunneling Packets: When the Timer for storing the New NVE
address for the VM expires. The Timer should be long enough for
all other NVEs that need to communicate with the VM to get their
NVE-VM cache entries updated.
6. Moving Local State of VM
In addition to the VM mobility related signaling (VM Mobility
Registration Request/Reply), the VM state needs to be transferred
to the New NVE. The state includes its memory and file system if
the VM cannot access the memory and the file system after moving
to the New NVE.
Dunbar, et al. Expires September 25, 2020 [Page 10]
Internet-Draft VM Mobility Solution March 25, 2020
The mechanism of transferring VM States and file system is out of
the scope of this document.
7. Handling of Hot, Warm and Cold VM Mobility
Both Cold and Warm VM mobility (or migration) refers to the VM
being completely shut down at the Old NVE before restarted at the
New NVE. Therefore, all transport services to the VM are
restarted.
Upon starting at the New NVE, the VM should send an ARP or
Neighbor Discovery message. Cold VM mobility also allows the Old
NVE and all communicating NVEs to time out ARP/neighbor cache
entries of the VM. It is necessary for the NVA to push the
updated ARP/neighbor cache entry to NVEs or for NVEs to pull the
updated ARP/neighbor cache entry from NVA.
The Cold VM mobility can be facilitated by cold standby entity
receiving scheduled backup information. The cold standby entity
can be a VM or can be other form factors which is beyond the scope
of this document. The cold mobility option can be used for non-
critical applications and services that can tolerate interrupted
TCP connections.
The Warm VM mobility refers the backup entities receive backup
information at more frequent intervals. The duration of the
interval determines the effectiveness (or benefit) of Warm VM
mobility. The larger the duration, the less effective the Warm VM
mobility option becomes.
For Hot VM Mobility, once a VM moves to a New NVE, the VM IP
address does not change and the VM should be able to continue to
receive packets to its address(es). The VM needs to send a
gratuitous Address Resolution message or unsolicited Neighbor
Advertisement message upstream after each move.
8. Other VM Mobility Options
There is also a Hot Standby option in addition to the Hot
Mobility, where there are VMs in both primary and secondary NVEs.
They have identical information and can provide services
simultaneously as in load-share mode of operation. If the VM in
the primary NVE fails, there is no need to actively move the VM to
the secondary NVE because the VM in the secondary NVE already
contain identical information. The Hot Standby option is the
costliest mechanism, and hence this option is utilized only for
mission-critical applications and services. In Hot Standby
Dunbar, et al. Expires September 25, 2020 [Page 11]
Internet-Draft VM Mobility Solution March 25, 2020
option, regarding TCP connections, one option is to start with and
maintain TCP connections to two different VMs at the same time.
The least loaded VM responds first and pickup providing service
while the sender (origin) still continues to receive Ack from the
heavily loaded (secondary) VM and chooses not to use the service
of the secondary responding VM. If the situation (loading
condition of the primary responding VM) changes the secondary
responding VM may start providing service to the sender (origin).
9. VM Lifecycle Management
The VM lifecycle management is a complicated task, which is beyond
the scope of this document. Not only it involves monitoring server
utilization, balanced distribution of workload, etc., but also
needs to manage seamlessly VM migration from one server to
another.
10. Security Considerations
Security threats for the data and control plane for overlay
networks are discussed in [RFC8014]. There are several issues in
a multi-tenant environment that create problems. In Layer-2 based
overlay data center networks, lack of security in VXLAN,
corruption of VNI can lead to delivery to wrong tenant. Also, ARP
in IPv4 and ND in IPv6 are not secure, especially if we accept
gratuitous versions. When these are done over a UDP
encapsulation, like VXLAN, the problem is worse since it is
trivial for a non-trusted entity to spoof UDP packets.
In Layer-3 based overlay data center networks, the problem of
address spoofing may arise. An NVE may have untrusted tasks
attached. This usually happens in cases like the VMs (tasks)
running third party applications. This requires the usage of
stronger security mechanisms.
11. IANA Considerations
This document makes no request to IANA.
12. Acknowledgments
The authors are grateful to Bob Briscoe, David Black, Dave R.
Worley, Qiang Zu, Andrew Malis for helpful comments.
Dunbar, et al. Expires September 25, 2020 [Page 12]
Internet-Draft VM Mobility Solution March 25, 2020
13. Change Log
. submitted version -00 as a working group draft after adoption
. submitted version -01 with these changes: references are updated,
o added packets in flight definition to Section 2
. submitted version -02 with updated address.
. submitted version -03 to fix the nits.
. submitted version -04 in reference to the WG Last call comments.
. Submitted version - 05, 06, 07, and 08 to address IETF LC comments
from TSV area.
14. References
14.1. Normative References
[RFC0826] Plummer, D., "An Ethernet Address Resolution Protocol: Or
Converting Network Protocol Addresses to 48.bit Ethernet
Address for Transmission on Ethernet Hardware", STD 37,
RFC 826, DOI 10.17487/RFC0826, November 1982,
<https://www.rfc-editor.org/info/rfc826>.
[RFC0903] Finlayson, R., Mann, T., Mogul, J., and M. Theimer, "A
Reverse Address Resolution Protocol", STD 38, RFC 903,
DOI 10.17487/RFC0903, June 1984, <https://www.rfc-
editor.org/info/rfc903>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
Dunbar, et al. Expires September 25, 2020 [Page 13]
Internet-Draft VM Mobility Solution March 25, 2020
[RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
DOI 10.17487/RFC2629, June 1999, <https://www.rfc-
editor.org/info/rfc2629>.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007, <https://www.rfc-
editor.org/info/rfc4861>.
[RFC7348] Mahalingam, M., Dutt, D., Duda, K., Agarwal, P.,
Kreeger, L., Sridhar, T., Bursell, M., and C. Wright,
"Virtual eXtensible Local Area Network (VXLAN): A
Framework for Overlaying Virtualized Layer 2 Networks over
Layer 3 Networks", RFC 7348, DOI 10.17487/RFC7348, August
2014, <https://www.rfc-editor.org/info/rfc7348>.
[RFC7364] Narten, T., Ed., Gray, E., Ed., Black, D., Fang, L.,
Kreeger, L., and M. Napierala, "Problem Statement:
Overlays for Network Virtualization", RFC 7364, DOI
10.17487/RFC7364, October 2014, <https://www.rfc-
editor.org/info/rfc7364>.
[RFC7666] H. Asai, et al, "Management Information Base for Virtual
Machines Controlled by a Hypervisor", RFC7666, Oct 2015.
[RFC8014] Black, D., Hudson, J., Kreeger, L., Lasserre, M., and T.
Narten, "An Architecture for Data-Center Network
Virtualization over Layer 3 (NVO3)", RFC 8014, DOI
10.17487/RFC8014, December 2016, <https://www.rfc-
editor.org/info/rfc8014>.
14.2. Informative References
[I-D.herbert-nvo3-ila] Herbert, T. and P. Lapukhov, "Identifier-
locator addressing for IPv6", draft-herbert-nvo3-ila-04
(work in progress), March 2017.
Dunbar, et al. Expires September 25, 2020 [Page 14]
Internet-Draft VM Mobility Solution March 25, 2020
Authors' Addresses
Linda Dunbar
Futurewei
Email: ldunbar@futurewei.com
Behcet Sarikaya
Denpel Informatique
Email: sarikaya@ieee.org
Bhumip Khasnabish
Independent
Email: vumip1@gmail.com
Tom Herbert
Intel
Email: tom@herbertland.com
Saumya Dikshit
Aruba-HPE
Bangalore, India
Email: saumya.dikshit@hpe.com
Dunbar, et al. Expires September 25, 2020 [Page 15]
