Network Working Group Z. Qiang
Internet Draft Ericsson
Intended status: Informational January 22, 2015
Expires: July 2015
Data Plane Handling in NVO3
draft-zu-nvo3-user-plane-signalling-01.txt
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Abstract
This draft discusses the considerations on user plane signaling and
data handling in NVO3 architecture and several related issues which
need to be considered when designing a NVO3 based virtualized data
center network for multiple tenants.
Table of Contents
1. Introduction...................................................3
2. Conventions used in this document..............................3
3. Terminology....................................................3
4. Data Forwarding................................................3
5. STP/RSTP/MSTP..................................................4
6. LACP...........................................................5
7. ARP and Neighbor Discovery.....................................5
8. Routing protocol...............................................6
9. Security Considerations........................................8
10. IANA Considerations...........................................8
11. References....................................................8
11.1. Normative References.....................................8
11.2. Informative References...................................9
12. Acknowledgments..............................................10
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1. Introduction
A high-level overview of a possible architecture for building NVO3
overlay networks has been present in [nvo3-arch]. The corresponding
control plane requirements has documented in [hypervisor-nve-cp] and
[nve-nva-cp-req].
User plane signaling is referring to the Layer 2 Control Protocol
(L2CP) specified in IEEE802.1 and Layer 3 Control Protocol (L3CP)
specified in IETF.
This document is providing some considerations on how the user plane
signaling shall be handled by NVE. And several related issues due to
the user plane signaling handling are discussed.
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].
In this document, these words will appear with that interpretation
only when in ALL CAPS. Lower case uses of these words are not to be
interpreted as carrying RFC-2119 significance.
3. Terminology
This document uses the same terminology as found in the NVO3
Framework document [framework] and [hypervisor-nve-cp].
4. Data Forwarding
In NVO3, a L2 NVE implements Ethernet LAN emulation, an Ethernet
based multipoint service similar to an IETF VPLS [RFC4761] [RFC4762]
or EVPN [EVPN] service. It forwards the multicast and unicast L2
traffic between the TSs. From the Tenant Systems aspect, the NVE is
just like a L2 bridge as specified in IEEE 802.1Q [IEEE 802.1Q].
A L3 NVE provides Virtualized IP forwarding service, similar to IETF
IP VPN, e.g. BGP/MPLS IPVPN [RFC4364]. An L3 NVE provides inter-
subnet layer 3 switching/routing for the TS. The NVE is the first hop
or next hop router to the attached TS.
In NVO3, it is very common to provide both L2 and L3 service to a TS.
In logic view, the TS is attached to a NVE which provides both L2 and
L3 function. In implementation, the L2 NVE function and L3 NVE
function may be collocated. The L2 NVE function provides intra-subnet
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traffic forwarding. The L3 NVE function provides inter-subnet traffic
forwarding.
In NVO3, to avoid flooding issues, the inner-outer address mapping
table is built using the NVA-NVE control signaling [nve-nva-cp-req].
Both L2 and L3 data forwarding are based on the inner-outer address
mapping table lookup (and forwarding policies).
The data forwarding procedure is similar for both L2 NVE and L3 NVE.
Upon receiving a unicast packet from the TS, the NVE performs a
lookup in the inner-outer address mapping table using the received
destination IP/MAC address. If a mapping is found, the received
packet will be encapsulated and forwarded to the destination NVE. If
no mapping is found, the received unknown unicast packet should be
dropped. As an alternative, the inner-outer address mapping table
updating procedure may be triggered using the NVA-NVE control
signaling [nve-nva-cp-req]. However, an attacker may generate large
amount of unknown unicast packets from a compromised VM, which may
result a denial of service (DOS) attacks. Therefore for security
reason, the inner-outer address mapping table updating procedure
shall not be triggered too often. One easy way to avoid this kind
security issue is to implement user plane filtering function.
Discussions: As specified in [nvo3-sec-req], some kind user plane
filtering functions need to be supported in the NVE for security
reason, i.e. the NVE MUST have a frequency limitation on the NVA
query procedure triggered by any received unknown data packets.
5. STP/RSTP/MSTP
For a L2 NVE, the VAP is an emulation of a physical Ethernet port. It
shall have the capability to handle any L2CP.
The Spanning Tree Protocol (STP) is a L2 protocol that ensures a
loop-free topology for any bridged Ethernet local area network. STP
is originally standardized as IEEE 802.1D. It is deprecated as of
802.1d-2004 in favor of Rapid Spanning Tree Protocol (RSTP). The
Multiple Spanning Tree Protocol (MSTP) defines an extension to RSTP
to further develop the usefulness of VLANs.
In NVO3 network, the L2 forwarding / switching function provided by
the NVE is based on the destination MAC address and the inner-outer
address mapping table. There won't be any looping of the L2
connections among the TSes by the NVEs if the NVE inner-outer address
mapping table is configured correctly. Therefor there is no need to
use any L2CP for that purpose among the participated NVEs of a TS.
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However, STP/RSTP/MSTP may be used by the TS, including multi-homing
case.
In NVO3 network, the NVE does not need to propagate any STP messages
to the remote NVEs. But, the NVE may need to learn the Root Bridge
MAC address and Bridge Priority of the root of the Internal Spanning
Tree (IST) of the attached layer 2 segment by listening to the BPDUs.
Discussions: The NVE does not need to forward the L2CP message. But
it may need to participate.
6. LACP
Link Aggregation [IEEE 802.1AXbk-2012] is a mechanism for making
multiple point-to-point links between a pair of devices appear to be
a single logical link between those devices.
A L2 NVE does not have to be involved in the Link Aggregation
procedure. It only needs to encapsulate and forward any Link
Aggregation Control Protocol Data and data packets between the
participated TSs.
Discussions: The NVE does not need to be involved. But it may need to
forward the messages.
7. ARP and Neighbor Discovery
For an L2 service, it is not a must for NVE to support any special
processing of ARP [RFC0826] and IPv6 Neighbor Discovery (ND)
[RFC4861] in NVO3 architecture. The NVE may forward the ARP or ND
messages using the mcast capability. However, as a performance
optimization, an NVE does not need to propagate the ARP or ND
messages. It can intercept ARP or ND requests received from its
attached TSs and respond based on the information configured in the
inner-outer address mapping table.
Discussions: The NVE does not have to forward the ARP or ND messages.
But it may need to response to the received messages based on the
inner-outer address mapping table for performance optimization.
Upon receiving ARP or ND request from a TS, the NVE sends the ARP or
ND response with the requested MAC address back. The NVE may perform
ARP or ND proxy when responding the ARP or ND request. If the NVE
does not have the interested MAC information in the receiving ARP or
ND request, it may query the NVA using the NVA-NVE control signaling
[nve-nva-cp-req]. However, an attacker may generate large amount of
ARP / ND request packets from a compromised VM, which may result a
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denial of service (DOS) attacks. Therefore for security reason, the
inner-outer address mapping table updating procedure shall not be
triggered too often. One easy way to avoid this kind security issue
is to implement user plane signaling filtering function.
Discussions: As specified in [nvo3-sec-req], the NVE shall have some
kind ARP and/or ND filtering functions installed for security reason,
i.e. the NVE MUST have a frequency limitation at sending NVA query
message triggered by the received ARP/ND request messages with
unknown MAC addresses.
In Multi-Homing NVE scenarios, a TS may be reachable via more than
one NVEs. In this case, if ARP / ND proxy is supported at the
participated NVEs of the same network segment where a TS is attached,
all participated NVEs may be aware of the same location of the
traffic's destination. Therefore, all participated NVEs may offer its
own MAC address for the same destination IP address in the ARP / ND
reply message, which could be a racing issue. One NVE may need to be
selected by the NVA at each network segment to avoid racing issue.
Only the selected NVE can response to the ARP / ND request at the
attached network segment.
Discussions: The NVA may need a property way to select one NVE per
network segment of a TS for ARP / ND proxy of given destination IP
addresses to avoid the racing issue.
At VM mobility, a VM may be moved from one layer-2 segment to another
layer-2 segment, assuming IP address preservation is supported. To
optimize the ARP or ND updating procedure, both the source NVE and
the target NVE can have the same MAC address configured at the VAP
where the TS attached.
Discussions: The NVA may need a property way to configure the
participated NVEs with same MAC address on the VAP of the same VN at
each network segment. However, at Multi-Homing NVE scenarios, the NVA
may need a property way to configure the participated NVEs on the VAP
of the same VN at each network segment to avoid duplicated MAC
address issue.
8. Routing protocol
IP routing protocol may be used by the TS for user plane dynamic IP
routing. A routing protocol specifies how routers communicate with
each other, disseminating information that enables them to select
routes between any two nodes on a computer network.
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In NVO3, there are different developments to support layer 3
services: centralized GW function, distributed GW function, or both.
If the layer 3 service is provided by a NVO3 Centralized Gateway
function, the user plane routing function and the NVO3 Centralized
Gateway functions appears as router adjacencies to each other. A
routing protocol may be used between the routers for overlay data
plane. Any user plane routing messages (e.g. routing updates message
from a vR function installed in a VM of the TS) will be handled by
the NVO3 Centralized Gateway function. Once there is a routing rules
installation or updating, the NVO3 Centralized Gateway function may
update its routing distribution polices and forward data packets
accordingly. The user data packet will be forwarded by the attached
NVE to the NVO3 Centralized Gateway function. Then the NVO3
Centralized Gateway function will make the layer 3 routing decision
that either discarding the packet or tunneling it to the destination
NVE where the destination VM attached. In this case, the NVE
functions, both source and destination, only need to support layer 2
functionalities.
If the layer 3 service is provided by the Distributed GW function
embedded in the L3 NVE, this can be an issue for dynamic routing
updates. In tenant view, the Distributed GW function appears as next
hop router to the user plane routing functions, e.g. vR functions
installed in a VM of the TS. The Distributed GW function embedded in
the L3 NVE may need to support one or more routing protocols (e.g.
BGP/OSPF/RIP) to learn any user plane routing rules installation or
updating. This allows a L3 NVE and the attached TS router to learn
the IP routes updates from each other. However, as the user plane
packet forwarding in the L3 NVE is based on the inner-outer address
mapping table configured by NVA using the NVA-NVE control protocol,
any user plane routing updates may trigger the inner-outer address
mapping table updates accordingly, not only in the attached L3 NVE,
but also in the remote participated L3 NVEs. With the NVO3
architecture specified in [nvo3-arch], it is an issue on how this
dynamic updates can be done.
Discussion: Alternatives are:
- Alt A: Disallow the support of dynamic routing function. This is
an easy implementation with missing functionalities.
- Alt B: Using NVE-NVE interaction messages to update the peer L3
NVEs. For instance, the L3NVE may inform the peer NVEs with the
received routing updates information. However, in this case,
should the peer NVE update its inner-outer address mapping table
without NVA's involvements? This may be challenging the NVA's
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centralized control role. And it may also cause some security
violation concerns.
- Alt C: Using the NVA-NVE signaling to update the peer L3 NVEs. In
this case, the L3 NVE shall not forward any routing updates
information to any peer NVEs to avoid flooding. Instead, it shall
always inform the NVA about any routing changes. Then the NVA will
use the NVA-NVE signaling for the inner-outer address mapping
table updating at the peer NVE.
- Alt D: Collocated NVA and GW function. With this alternative, the
TS routing policies (i.e. RIB) is managed by the collocated GW
function. It is assumed that the NVA is synced with the collocated
GW function. The Distributed GW function embedded in the NVE is
installed with the TS IP forwarding policies (i.e. FIB or inner-
outer address mapping table). The TS user plane routing messages
will be terminated at the collocated GW function which is the next
hop router of the user plane routing function. If there is any
user plane routing installing and updating, the collocated GW
function may update the routing policies (i.e. RIB), and the NVA
will notify the distributed GW functions with the updated inner-
outer address mapping table using the NVA-NVE control signaling.
9. Security Considerations
This is a discussion paper which provides inputs for the NVO3
requirement documents and in itself does not introduce any new
security concerns.
10. IANA Considerations
No actions are required from IANA for this informational document.
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2234] Crocker, D. and Overell, P.(Editors), "Augmented BNF for
Syntax Specifications: ABNF", RFC 2234, Internet Mail
Consortium and Demon Internet Ltd., November 1997.
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11.2. Informative References
[overlay-problem-statement] Narten, T., Gray, E., Black, D., Fang,
L., Kreeger, L., and M. Napierala, "Problem Statement:
Overlays for Network Virtualization", draft-ietf-nvo3-
overlay-problem-statement-04 (work in progress), July 31,
2013.
[hypervisor-nve-cp] Li, Y., Yong L., Kreeger, L., Narten, T., and D.
Black, "Hypervisor to NVE Control Plane Requirements",
draft-ietf-nvo3-hpvr2nve-cp-req-00(work in progress), July
1, 2014.
[nvo3-framework] Lasserre, M., Balus, F., Morin, T., Bitar, N., and
Y. Rekhter, "Framework for DC Network Virtualization",
draft-ietf-nvo3-framework-09 (work in progress), July 4,
2014.
[nve-nva-cp-req] Kreeger, L., D. Dutt, T. Narten, D. Black, "Network
Virtualization NVE to NVA Control Protocol Requirements",
draft-ietf-nvo3-nve-nva-cp-req-02 (work in progress), April
24, 2014
[nvo3-arch] D. Black, J. Hudson, L. Kreeger, M. Lasserre, T. Narten,
"An Architecture for Overlay Networks (NVO3)", draft-ietf-
nvo3-arch-01(work in progress), February 14, 2014
[nvo3-sec-req] S.Hartman, D.Zhang, M.Wasserman, Z.Qiang, "Security
Requirements of NVO3", draft-ietf-nvo3-security-
requirements-04 (work in progress), January 12, 2015
[IEEE 802.1Q] "Virtual Bridged Local Area Networks", 2005
[EVPN] Sajassi, A. et al, "BGP MPLS Based Ethernet VPN", draft-
ietf-l2vpn-evpn (work in progress)
[RFC4761] Kompella, K. et al, "Virtual Private LAN Service (VPLS)
Using BGP for auto-discovery and Signaling", RFC4761,
January 2007
[RFC4762] Lasserre, M. et al, "Virtual Private LAN Service (VPLS)
Using Label Distribution Protocol (LDP) Signaling",
RFC4762, January 2007
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[RFC0826] Plummer, D., "Ethernet Address Resolution Protocol: Or
converting network protocol addresses to 48.bit Ethernet
address for transmission on Ethernet hardware", STD 37, RFC
826, November 1982.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, February 2006.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
12. Acknowledgments
Many people have contributed to the development of this document and
many more will probably do so before we are done with it. While we
cannot thank all contributors, some have played an especially
prominent role. The following have provided essential input: Suresh
Krishnan.
Authors' Addresses
Zu Qiang
Ericsson
8400, boul. Decarie
Ville Mont-Royal, QC,
Canada
Email: Zu.Qiang@Ericsson.com
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