Layer 2 Gateway (L2GW)
draft-xia-nvo3-l2gw-00
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| Last updated | 2014-02-13 | ||
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draft-xia-nvo3-l2gw-00
Network working group L. Xia
Internet Draft L. Yong
Category: Standard Track Huawei
Expires: September 2014 February 14, 2014
Layer 2 Gateway (L2GW)
draft-xia-nvo3-l2gw-00
Abstract
Layer 2 Gateway (L2GW) is used for interconnecting layer 2 overlay
network [NVO3FRWK] with layer 2 bridge networks [IEEE802.1Q] to form
one layer 2 virtual network. This draft discusses which Layer 2
Control Protocol (L2CP) specified in IEEE802.1 should be supported
by the layer 2 overlay network and which not, and specifies how L2GW
should deal with L2CP frames.
Status of this Memo
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This Internet-Draft will expire on September 14, 2014.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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.
Table of Contents
1. Introduction ................................................ 3
1.1. Conventions used in this document ...................... 4
1.2. Terminology ............................................ 4
2. L2GW Reference Model......................................... 4
3. L2CP Review and Applicability to L2 Overlay Network.......... 5
3.1. STP/RSTP/MSTP .......................................... 7
3.2. PAUSE .................................................. 7
3.3. LACP/LAMP .............................................. 7
3.4. Link OAM ............................................... 8
3.5. Port Authentication .................................... 9
3.6. E-LMI .................................................. 9
3.7. LLDP ................................................... 9
3.8. PTP Peer Delay ........................................ 10
3.9. ESMC .................................................. 10
3.10. GARP/MRP Block........................................ 10
4. L2CP Process in L2GW........................................ 10
4.1. L2CP Frames Filtered (Peered or Discarded) in L2GW .... 11
4.2. L2CP Frames Passed through L2GW ....................... 11
5. Other Interworking Cases ................................... 12
6. Security Considerations .................................... 12
7. IANA Considerations ........................................ 12
8. References ................................................. 12
8.1. Normative References .................................. 12
8.2. Informative References ................................ 13
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1. Introduction
Cloud computing and network virtualization is evolving to the
direction of virtualized networks in overlay, which aims fast and
easy to create tenant networks, support tenant system mobility, and
bring the manageability of all virtualized resources in DC.
Layer 2 (L2) overlay network in NVO3 means an L2 overlay network
interconnecting tenant systems, where any pair of Network
Virtualization Edges (NVE) are connected by IP tunnels. As a result,
it forms a full mesh topology of overlay network, i.e. only one hop
between any pair of NVEs. L2 bridge network in this draft is the
network specified in IEEE 802.1Q [IEEE 802.1Q] which are widely
deployed in DCs. L2 overlay network is used to refer the L2 network
specified in NVO3.
During DC network migration, it's very common that L2 overlay
network may be mix used with L2 bridge network in a DC, and the
communication between them is required. In another use case, using
L2 bridge network to connect non-virtualized devices in DC are
mature and well deployed method in DC; these non-virtualized devices
are necessary for some applications such as BIG data and are
required to communicate with virtualized resources.
To interconnect an L2 overlay network with an L2 bridge network,
gateway functions are needed on the device(s)/system(s) connecting
two networks. This device is referred as to Layer 2 Gateway (L2GW)
in this draft. L2GW processes the encapsulation translation of
packets between overlay technologies (e.g., VxLAN [VXLAN], NVGRE
[NVGRE]) and the technologies specified in IEEE 802.1Q; it also
deals with Layer 2 Control Protocol (L2CP) frames from the bridge
network.
L2CP frames are defined by IEEE802.1 to be used for L2 network
control, e.g., STP, LACP, etc. An L2CP is identified by one of the
following MAC destination addresses:
o 01-80-C2-00-00-00 through 01-80-C2-00-00-0F: Bridge Block of
protocols
o 01-80-C2-00-00-20 through 01-80-C2-00-00-2F: GARP/MRP Block of
protocols
All L2CPs are supported in a L2 bridge network, every 802.1Q bridge
performs corresponding action, i.e., peer (to be processed by local
protocol entity), discard, pass, based on L2CP frame's MAC
destination address (DA) and protocol identifier (Ethertype or LLC
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Address). For L2 overlay VN, most of L2CPs are unnecessary because
L2 overlay VN has its own control plane functions to support needed
L2 communication such as transport over a tunnel or OAM. It is very
useful to document how these service frames should be handled at
L2GW to ensure that two networks can interwork.
This draft discusses which L2CP should be supported by L2 overlay
network and which not, and specifies how L2GW should deal with L2CP
frames.
1.1. 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].
1.2. Terminology
This document uses the terms defined in NVO3 framework [NVO3FRWK]
and architecture [NVO3ARCH] documents.
2. L2GW Reference Model
The following diagram shows a reference model where L2GW provides an
interconnection between L2 overlay network and L2 bridge network.
......... .........
+---+ ... .... . +------+
TSs-+NVE| +---------+ +-+Server|
+---+ L2 Overlay | | L2 Bridge . +------+
. Network | L2GW | Network .
. | | . +------+
..+---+ +---------+ +-+Server|
TSs-+NVE| ... .... ... +------+
+---+......... ........
Figure 1: L2GW Reference Model
L2GW can reside on access switch providing direct connection with
physical server, or reside on core switch or edge router providing
connection with L2 bridge network.
Note that this draft only addresses the case that L2GW and L2 NVE
are co-located at the edge device between two L2 networks, where
L2GW can deal with the interworking work. Other cases are not yet
covered in this draft.
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3. L2CP Review and Applicability to L2 Overlay Network
L2CP protocols defined in IEEE 802.1 are listed in Table 1:
+------------------+----------+----------+---------------------+
|MAC DA |Assignment| Protocol | L2CP Action |
| | | Type +----------+----------+
| | | |VLAN-based|PORT-based|
| | | | L2 | L2 |
| | | | services | services |
+------------------+----------+----------+----------+----------+
|01-80-C2-00-00-00 |Nearest |STP/RSTP/M|Filter |Pass |
| |Customer |STP, | | |
| |Bridge |LACP/LAMP | | |
+------------------+----------+----------+----------+----------+
|01-80-C2-00-00-01 |IEEE MAC |PAUSE |Filter |Filter |
| |Specific | | | |
| |Control | | | |
| |Protocols | | | |
+------------------+----------+----------+----------+----------+
|01-80-C2-00-00-02 |IEEE 802 |LACP/LAMP,|Filter |Filter |
| |Slow |Link OAM, | | |
| |Protocols |ESMC | | |
+------------------+----------+----------+----------+----------+
|01-80-C2-00-00-03 |Nearest |Port |Filter |Filter |
| |non-TPRM |Authentica| | |
| |Bridge |tion, | | |
| | |LACP/LAMP | | |
+------------------+----------+----------+----------+----------+
|01-80-C2-00-00-04 |IEEE MAC | |Filter |Filter |
| |Specific | | | |
| |Control | | | |
| |Protocols | | | |
+------------------+----------+----------+----------+----------+
|01-80-C2-00-00-05 |Reserved | |Filter |Filter |
| |for Future| | | |
|01-80-C2-00-00-06 |Standardiz| | | |
| |ation | | | |
|01-80-C2-00-00-09 | | | | |
| | | | | |
|01-80-C2-00-00-0A | | | | |
+------------------+----------+----------+----------+----------+
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|01-80-C2-00-00-07 |MEF ELMI |E-LMI |Filter |Filter |
+------------------+----------+----------+----------+----------+
|01-80-C2-00-00-08 |Provide | |Filter |Filter |
| |Bridge | | | |
| |Group | | | |
+------------------+----------+----------+----------+----------+
|01-80-C2-00-00-0B |Reserved | |Filter |Pass |
| |for Future| | | |
|01-80-C2-00-00-0C |Standardiz| | | |
| |ation | | | |
+------------------+----------+----------+----------+----------+
|01-80-C2-00-00-0D |Provider | |Filter |Pass |
| |Bridge | | | |
| |MVRP | | | |
+------------------+----------+----------+----------+----------+
|01-80-C2-00-00-0E |Nearest |LLDP, PTP |Filter |Filter |
| |Bridge, |Peer Delay| | |
| |Individual| | | |
| |LAN Scope | | | |
+------------------+----------+----------+----------+----------+
|01-80-C2-00-00-20 | |GARP/MRP |Pass |Pass |
| | |Block | | |
| through | | | | |
| | | | | |
|01-80-C2-00-00-2F | | | | |
+------------------+----------+----------+----------+----------+
Table 1 L2CP protocols specification
Note:
Different L2CP protocols can use the same MAC DA in above block of
32 addresses, but be differentiated by protocol identifier. MAC DA
determines the intended recipient device for the frame;
Filter represent the L2CP action of peer or discard;
Based on whether L2 interface is VLAN-aware, L2 services can
divided into two categories: VLAN-based L2 services, PORT-based L2
services. L2CP action (peer, discard, pass) for these two L2
services is also different;
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Whether the L2CP frames are peered or discarded is further
determined by the configuration of L2 interface.
Further analysis about whether a L2CP protocol is necessary and how
it is processed in NVO3 supported L2 VN, is provided in the
following sub sections.
3.1. STP/RSTP/MSTP
The Spanning Tree Protocol (STP) is a L2 protocol that ensures a
loop-free topology for any bridged Ethernet local area network. The
basic function of STP is to prevent bridge loops and the broadcast
storm that results from them. Rapid spanning Tree Protocol (RSTP)
and Multiple Spanning Tree Protocol (MSTP) are all the enhanced xSTP
protocols.
L2 overlay network does not need xSTP protocols to prevent bridge
loops because it has its own mechanism for it, i.e., NVA, control
plane mechanisms, full mesh + split horizon, etc. So, the process of
xSTP frames in L2 VN is:
Be in line with L2CP protocols' specification of Table 1 from IEEE
in the L2 sub-networks attached to L2 NVEs;
xSTP frames are filtered in L2 NVEs and should not go into L2
overlay network.
3.2. PAUSE
[IEEE 802.3-2005] has specified a L2 flow control mechanism through
using the PAUSE frame. This frame uses L2CP MAC DA of 01-80-C2-00-
00-01 to be sent to the node at the other end of the link for
informing it to halt the frame transmission for a specified period
of time.
When L2 NVE is co-located in Hypervisor, PAUSE frame is not
necessary in one device. When they are separated, PAUSE frame is
only used in layer 2 network between L2 NVE and Hypervisor, there is
no need to overlay PAUSE frame between L2 NVEs.
3.3. LACP/LAMP
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. Link Aggregation
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Control Protocol (LACP) and Link Marker Control Protocol (LAMP)
operate between exactly two peer devices for the purpose of creating,
verifying, and monitoring the logical link created by aggregating
individual links. Specific L2CP frames, known as Link Aggregation
Control Protocol Data Units (LACPDUs), are exchanged between the
peer devices on each individual link in the aggregation. The
protocol identifier used by LACP is an Ethertype with a value of
0x8809 (the ''Slow Protocols'' Ethertype) and subtype values 01 (for
LACP) and 02 (for LAMP). Note that LACP is used to represent LACP
and LAMP in the following text.
LACP uses 3 different L2CP MAC DAs to determine the scope of
propagation of LACPDUs within a bridged LAN, as Table 2 follows:
+----------------+------------------+-----------------------------+
|Assignment | L2CP MAC DA |Peered or discarded by |
+----------------+------------------+-----------------------------+
|Nearest Customer| 01-80-C2-00-00-00|End Station, Customer Bridge,|
|Bridge | |Provider Edge Bridge |
+----------------+------------------+-----------------------------+
|IEEE 802 Slow | 01-80-C2-00-00-02|End Station, Customer Bridge,|
|Protocols | |Provider Edge Bridge, |
| | |Provider Bridge |
+----------------+------------------+-----------------------------+
|Nearest non-TPRM| 01-80-C2-00-00-03|Bridges except for Two Port |
|Bridge | |MAC Relay |
+----------------+------------------+-----------------------------+
Table 2 LACP specification of L2CP MAC DAs
Base on the summary of Table 2, LACPDUs with the L2CP MAC DA of 01-
80-C2-00-00-02 are peered or discarded by every node, so this kind
of LACPDUs will not be overlaid across the L2 overlay network. For
01-80-C2-00-00-00, it is possible that LACPDUs need to be overlaid
across Provider Bridge and L2 NVEs of L2 overlay network to reach
the other end Custom Bridge, L2 overlay network maybe need to
support to overlay this kind of LACP frame between L2 NVEs. How the
L2 overlay network support LACP frame of 01-80-C2-00-00-03 is TBD.
3.4. Link OAM
Lin OAM defined is defined in [IEEE 802.3ah], as mechanisms for
monitoring and troubleshooting Ethernet access links. Specifically
it defines tools for discovery, remote failure indication, remote
and local loopbacks and status and performance monitoring.
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The Link OAM frames using L2CP MAC DA of 01-80-C2-00-00-02 are
peered or discarded by every node, so this kind of frame will not be
overlaid across the L2 overlay network.
3.5. Port Authentication
[IEEE 802.1X] is an IEEE Standard for Port-based Network Access
Control (PNAC). It is part of the IEEE 802.1 group of networking
protocols. It provides an authentication mechanism to devices
wishing to attach to a LAN or WLAN.
Whether or not the L2 overlay network needs to overlay this L2CP
frames is TBD.
3.6. E-LMI
Ethernet Local Management Interface (E-LMI) is a protocol between
the customer edge (CE) device and the provider edge (PE) device. It
runs only on the PE-CE UNI link and notifies the CE of connectivity
status and configuration parameters of Ethernet services available
on the CE port. E-LMI interoperates with an OAM protocol, such as
Connectivity Fault Management (CFM), that runs within the provider
network to collect OAM status. CFM runs at the provider maintenance
level (UPE to UPE with inward-facing MEPs at the UNI). E-LMI relies
on the OAM Ethernet Infrastructure (EI) to interwork with CFM for
end-to-end status of Ethernet virtual connections (EVCs) across CFM
domains.
The LLDP frames using L2CP MAC DA of 01-80-C2-00-00-07 are peered or
discarded by every node except for the Two Port MAC Relay (TPMR)
bridge, so this kind of frame will not be overlaid across the L2
overlay network.
3.7. LLDP
The Link Layer Discovery Protocol (LLDP) is a vendor-neutral link
layer protocol in the Internet Protocol Suite used by network
devices for advertising their identity, capabilities, and neighbors
on an IEEE 802 local area network, principally wired Ethernet. The
protocol is formally referred to by the IEEE as Station and Media
Access Control Connectivity Discovery specified in standards
document [IEEE 802.1AB].
The LLDP frames using L2CP MAC DA of 01-80-C2-00-00-0E are peered or
discarded by every node, so this kind of frame will not be overlaid
across the L2 overlay network.
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3.8. PTP Peer Delay
PTP Peer Delay frame is specified in [IEEE 1588-2008] to carry PTP
peer time information. It uses L2CP MAC DA of 01-80-C2-00-00-0E and
peered or discarded by every node, so this kind of frame will not be
overlaid across the L2 overlay network.
3.9. ESMC
Ethernet Synchronization Messaging Channel (ESMC) is specified in
[ITU-T Rec. G.8264] for conveying clock information between
Synchronous Ethernet (SyncE) bridges.
The ESMC frames using L2CP MAC DA of 01-80-C2-00-00-02 are peered or
discarded by every node, so this kind of frame will not be overlaid
across the L2 overlay network.
3.10. GARP/MRP Block
Multiple Registration Protocol (MRP), which replaced Generic
Attribute Registration Protocol (GARP), is a generic registration
framework defined by the [IEEE 802.1ak] amendment to the [IEEE
802.1Q] standard. MRP allows bridges, switches or other similar
devices to be able to register and de-register attribute values,
such as VLAN identifiers and multicast group membership across a
large LAN. MRP operates at the Data Link Layer.
The block of L2CP MAC DA from 01-80-C2-00-00-20 to 01-80-C2-00-00-2F
is used for MRP protocol. Now, only 01-80-C2-00-00-20 is for
Multiple MAC Registration Protocol (MMRP) and 01-80-C2-00-00-21 is
for Multiple VLAN Registration Protocol (MVRP), other L2CP MAC DA of
the block are all reserved for future use. Protocol use one address
of this block is passed by all the intervening bridges that does not
participate in the protocol using this address, and peered or
discarded by the bridge that participate in the protocol at last.
This forwarding rule maybe requires MRP frames to be overlaid across
the L2 overlay network.
4. L2CP Process in L2GW
For all L2CP protocols, several differences exist between L2 overlay
network and L2 bridge network on how to process them. As the
demarcation point between L2 overlay network and L2 bridge network,
L2GW keeps the same action to all L2CP frames as before at the L2
bridge network side on the one hand, but maybe processes some L2CP
frames differently at the L2 overlay network side on the other hand.
The following sub sections will describe the L2CP process in L2GW.
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4.1. L2CP Frames Filtered (Peered or Discarded) in L2GW
Although xSTP protocols using Nearest Customer Bridge address of 01-
80-C2-00-00-00 indicate that it can be overlaid across L2 overlay
network, they still are not necessary for L2 overlay network because
L2 overlay network has its own mechanism to prevent bridge loops. So
xSTP frames will be filtered by the L2GW and not go into the L2
overlay network.
Based on the analysis of section 3.3, LACP/LAMP frames using IEEE
802 Slow Protocols of 01-80-C2-00-00-02 are not necessary for L2
overlay network. So, LACP/LAMP frames will be filtered by the L2GW
and not go into the L2 overlay network. ESMC frames using the same
MAC DA will also be filtered by L2GW.
For Link OAM frames, if OAM functions are necessary for the whole L2
network which interconnects L2 bridge network and L2 overlay network,
L2GW needs to support the interworking of OAM as well. This means
that L2GW should peer the Link OAM frames of L2 bridge network and
perform some actions between NVEs in L2 overlay network. The
detailed operation is TBD.
Other L2CP protocols that are filtered by L2GW and do not go into L2
overlay network include PAUSE, E-LMI, LLDP, PTP Peer Delay. The
basic reason is that they all require to be processed hop by hop in
L2 network strictly, but overlay network breaks this rule.
The action of ''filter'' can be ''peer'', or ''discard''. It depends on
the specific service requirement, i.e., does L2GW need to
participate in the L2CP protocol, etc. How to determine the specific
action is TBD.
4.2. L2CP Frames Passed through L2GW
Excepting for the aforementioned L2CP protocols filtered by L2GW,
the left L2CP protocols need to be passed through L2GW. They include:
LACP/LAMP frames using IEEE 802 Slow Protocols of 01-80-C2-00-00-
00;
GARP/MRP series protocols (i.e., MMRP, MVRP) using the MAC DA
block of 01-80-C2-00-00-20 through 01-80-C2-00-00-2F.
All these kinds of L2CP frames are passed through L2GW and traverse
across the L2 overlay network and L2 bridge network to arrive the
bridges that participate in the L2CP protocols. For MRP protocols,
another necessary operation of L2GW is to use the pre-provisioned
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VLAN to virtual network instance (VNI) mappings in NVE locally or by
getting from NVA to map these MRP frames into corresponding VNIs.
5. Other Interworking Cases
There are other L2 bridge network technologies that use L2 Control
Plane protocols such as Provider Bridge [IEEE802.1AD] or Provider
Backbone Bridge [PBB] [IEEE802.1AH]. The use case of L2 Overlay
Network interworking with these types of bridge networks is for the
further study.
Note that VPLS [RFC4761] [RFC4762], EVPN [EVPN], Shortest Path
Bridging [IEEE SPB] and TRILL [RFC6325] are also technologies for L2
private network implementation. These technologies rely on the
control plane protocol and aim for service provider network. SDN
controller interworking with such control plane protocol will be
addressed in separate draft.
6. Security Considerations
TBD.
7. IANA Considerations
The document does not require any IANA action.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC2119, March 1997.
[RFC4761] Kompella, K. and Rekhter, Y. (Editors), "Virtual Private
LAN Service (VPLS) Using BGP for Auto-Discovery and Signaling", RFC
4761, January 2007
[RFC4762] Lasserre, M. and Kompella, V. (Editors), "Virtual Private
LAN Service (VPLS) Using Label Distribution Protocol (LDP)
Signaling", RFC 4762, January 2007.
[RFC6325] Perlman, R., "RBridges: Base Protocol Specification",
July 2011.
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8.2. Informative References
[NVO3ARCH] Black, D, Narten, T., et al, "An Architecture for Overlay
Networks (NVO3)", draft-narten-nvo3-arch-01, work in progress
[NVO3FRWK] LASSERRE, M., Motin, T., et al, "Framework for DC Network
Virtualization", draft-ietf-nvo3-framework-03, work in progress.
[NVGRE] Sridharan, M., et al, "NVGRE: Network Virtualization using
Generic Routing Encapsulation", draft-sridharan-virtualization-
nvgre-03, work in progress
[VXLAN] Mahalingam, M., Dutt, D., etc, "VXLAN: A Framework for
Overlaying Virtualized Layer 2 Networks over Layer 3 Networks",
draft-mahalingam-dutt-dcops-vxlan-05.txt, work in progress
[EVPN] Sajassi, A. and R. Aggarwal, "BGP MPLS Based Ethernet VPN",
draft-ietf-l2vpn-evpn-04, July 2013
[IEEE 802.1Q] "Virtual Bridged Local Area Networks", 2005
[IEEE 802.3-2005] "Part 3: Carrier sense multiple access with
collision detection (CSMA/CD) access method and physical layer
specifications"
[IEEE 802.1AXbk-2012] "IEEE Standard for Local and metropolitan area
networks--Link Aggregation Amendment 1: Protocol Addressing"
[IEEE 802.3ah] "IEEE Standard for Information technology--Local and
metropolitan area networks--Part 3: CSMA/CD Access Method and
Physical Layer Specifications Amendment: Media Access Control
Parameters, Physical Layers, and Management Parameters for
Subscriber Access Networks"
[IEEE 802.1X] "IEEE Standard for Local and metropolitan Area
Networks. Port-based Network Access Control"
[IEEE 802.1AB] "IEEE Standard for Station and Media Access Control,
Connectivity Discovery"
[IEEE 1588-2008] "IEEE Standard for a Precision Clock
Synchronization Protocol for Networked Measurement and Control
Systems"
[IEEE 802.1ak] "IEEE Standard for Local and metropolitan Area
Networks - Virtual Bridged Local Area Networks, Amendment 7:
Multiple Registration Protocol"
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[IEEE 802.1AD], "Virtual Bridged Local Area Networks - Amendment 4:
Provider Bridges", 2005
[PBB] Clauses 25 and 26 of "IEEE Standard for Local and metropolitan
area networks - Media Access Control (MAC) Bridges and Virtual
Bridged Local Area Networks", IEEE Std 802.1Q, 2013.
[IEEE802.1AH] IEEE Draft P802.1ah/D4.2 "Virtual Bridged Local Area
Networks, Amendment 6: Provider Backbone Bridges", 2008
[IEEE SPB] "IEEE standard for local and metropolitan area networks:
Media access control (MAC) bridges and virtual bridged local area
networks -- Amendment 20: Shortest path bridging", IEEE 802.1aq,
June 2012.
[ITU-T Rec. G.8264] "Distribution of Timing Through Packet Networks"
Authors' Addresses
Liang Xia
Huawei Technologies
Email: frank.xialiang@huawei.com
Lucy Yong
Huawei Technologies, USA
Email: lucy.yong@huawei.com
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