One document matched: draft-wu-nvo3-mac-learning-arp-02.xml
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<front>
<title abbrev="TS Info Discovery Gap Analysis">Tenant system information
discovery approaches Gap analysis</title>
<author fullname="Liang Xia" initials="L." surname="Xia">
<organization>Huawei</organization>
<address>
<postal>
<street>101 Software Avenue, Yuhua District</street>
<city>Nanjing</city>
<region>Jiangsu</region>
<code>210012</code>
<country>China</country>
</postal>
<email>xiangliang1@huawei.com</email>
</address>
</author>
<author fullname="Qin Wu" initials="Q." surname="Wu">
<organization>Huawei</organization>
<address>
<postal>
<street>101 Software Avenue, Yuhua District</street>
<city>Nanjing</city>
<region>Jiangsu</region>
<code>210012</code>
<country>China</country>
</postal>
<email>bill.wu@huawei.com</email>
</address>
</author>
<date year="2013" />
<area>Internet Area</area>
<workgroup>Network Virtualization Overlays Working Group</workgroup>
<keyword>RFC</keyword>
<keyword>Request for Comments</keyword>
<keyword>I-D</keyword>
<keyword>Internet-Draft</keyword>
<keyword>Network Virtualization Overlays</keyword>
<abstract>
<t>This document analyzes various protocol solutions for tenant system
information (e.g. MAC, IP, etc) discovery in the virtualization
environment (e.g.,MAC in MAC, MAC in IP, IP in IP) and identifies the
gap against NVO3 control plane and data plane requirements.</t>
</abstract>
</front>
<middle>
<section anchor="intro" title="Introduction">
<t>The tenant system information in this document is referred to as L2
address and L3 address of VM. As described in [I.D-ietf-nvo3-
framework], for an L2 NVE, the NVE needs to be able to determine MAC
addresses of the tenant system. For an L3 NVE, the NVE needs to be able
to determine IP addresses of the tenant system.</t>
<t>This can be achieved mainly in 3 ways: data plane learning; ARP;
control plane distribution (e.g. by BGP or IS-IS). This document
analyzes various protocol solutions for tenant system information (e.g.
MAC, IP, etc) discovery in the virtualization environment (e.g.,MAC in
MAC, MAC in IP, IP in IP) and identifies the gap against NVO3 control
plane and data plane requirements.</t>
</section>
<section title="Conventions used in this document">
<t>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 <xref
target="RFC2119">RFC2119</xref>.</t>
</section>
<section title="Overview of tenant system information discovery in the virtualization domain using NVO3">
<t>Tenant system information discovery can be achieved either using
dynamic data plane learning or ARP or control plane distribution. This
document addresses how tenant system information discovery works in the
overlay network enviroment. Figure 1 shows the NVO3 reference
architecture for tenant system information discovery. The reference
architecture assumes that: <list style="symbols">
<t>Tenant system A in DC site X wants to establish communication
with tenant system B in the DC site Y.</t>
<t>Tenant system A is connecting to VN by attaching to NVE X. Tenant
System A knows IP address of Tenant System B using out of band means
but does not know MAC address of Tenant System B.</t>
<t>Tenant system B is connecting to VN by attaching to NVE Y. Tenant
System B knows IP address of Tenant System A using out of band means
but does not know MAC address of Tenant System A.</t>
<t>NVE X associated with tenant system A doesn't know IP address and
MAC address of tenant system B.</t>
<t>NVE Y associated with tenant system B doesn't know IP address and
MAC address of tenant system A.</t>
</list></t>
<figure anchor="fig1"
title="Example of NVO3 reference architecture for tenant system information discovery">
<artwork>
,---------.
,' Backend `.
( NVA )
`. ,'
`-+------+'
| |
.--..--. .--. ..
( ' '.--.
.-.' L3 '
( Overlay )
( '-'
.'--'._.'.-._.'.-._)
NVE X = // \\ NVE Y =
(MAC_X,IP_X) +------+ +-------+(MAC_Y,IP_Y)
.-|NVE X | | NVE Y |
( +------+--. ( +-------+.--.
.-.' ' .-.' '
( DC Site X ) ( DC Site Y )
( .'-' ( .'-'
'--'._.'. ) '--'._.'. )
'--' / '--'
/ \ / \
__/_ \ /_ _\__
'--------' '--------' '--------' '--------'
: Tenant : : Tenant : : Tenant : : Tenant :
: SystemA: : SystemC: : SystemD: : SystemB:
'--------' '--------' '--------' '--------'
TSID= TSID=
(VNID,MAC_A,IP_A) (VNID,MAC_B,IP_B)
</artwork>
</figure>
<section title="Issues with tenant system information discovery in the virtualization domain using NVO3">
<t>Here we give an example of tenant system information discovery in
large layer 2 domain using NVO3 using traditional approach for MAC
address learning. The packet flow and control plane operation are as
follows:<list style="numbers">
<t>Tenant system A sends a broadcast ARP message to discover the
MAC address of Tenant system B. The message contains IP_B in the
ARP message payload.</t>
<t>The ARP proxy [RFC1027] in NVE X, receiving the ARP message and
knowing source and destination are in the different subnet will
encapsulate it with overlay header and outer header and flood it
on the overlay network for TSID = <VNID,IP_B,*>. VNID is
included in the overlay header.</t>
<t>The ARP message will be processed by NVE Y which maintains
mapping table matching TSID = <VNID,IP_B,*>. NVE Y, will
forward the ARP message to tenant system B. Tenant System B sends
ARP reply to tenant system A containing MAC_B.</t>
<t>NVE X processes ARP reply message and populates the mapping
table with the received entry, then sends it to Tenant System A
that includes MAC_B and IP_B of Tenant System B.</t>
<t>Tenant system A learns MAC_B from the ARP rely message and can
now send a packet to Tenant system B by including MAC_B, and IP_B,
as destination addresses.</t>
</list></t>
<t>The issues with tenant system information discovery are as
follows:<list style="symbols">
<t>The demand on the forwarding table capacity at each NVE is
increased compared to non-virtualized environments since layer 2
network is no longer constrained to small local network and has a
need for millions of hosts.</t>
<t>If Address resolution protocol is used for control plane
learning, it may cause excessive flooding since ARP packets need
to be flooded over the whole overlay network. the ARP/ND
processing load imposes great challenge on L2/L3 boundary
routers.</t>
<t>Dynamic data plane learning implies that flooding of unknown
destinations be supported and hence implies that broadcast and/or
multicast be supported or that ingress replication, which may
cause excessive flooding issue and lead to significant scalability
limitations.</t>
<t>A control plane protocol (e.g., BGP) that carries both MAC and
IP addresses eliminates the need for ARP, however some NVEs or DC
Gateways may not support complex control plane protocol, for
example, BGP protocol.</t>
</list></t>
</section>
</section>
<section title="Related work for Tenant system information discovery">
<t>Currently, 3 main solutions or their combination can be used to
perform the tenant system information discovery. They are dynamic data
plane learning, ARP, control plane distribution (including two options:
centralized or distributed). Additionally, the ARP proxy [RFC1027]
mechanism can be used for preventing the ARP flooding in the core
network and limiting the MAC table size of NVEs and hosts. Here is a
brief analysis of them and the associated protocols are discussed.</t>
<section title="SPB and TRILL">
<t>Shortest Path Bridging (SPB) [SPB] and TRILL [TRILL] are two
different methods of IS-IS based overlay that operates over L2
Ethernets. They all use the MAC in MAC encapsulation and have the same
default MAC address learning method: <list style="symbols">
<t>Using IS-IS extension for outer MAC address distribution over
the SPB area or TRILL campus network;</t>
<t>Using ARP or data plane snooping for inner MAC address learning
of locally attached hosts.</t>
<t>In addition, the TRILL maybe use
[draft-ietf-trill-directory-framework] distributes the inner MAC
address between all the RBriges</t>
</list></t>
<t>In the centralized approach, TRILL may use TRILL ESADI to
distribute the inner MAC address between all the RBridges however SPB
doesn’t support ESADI distribution mechanism. In the distributed
approach, SPB and TRILL may use combination of the above 3
methods.</t>
</section>
<section title="ARMD and SARP">
<t>The ARMD WG examined data center scaling issues with a focus on
address resolution and developed a problem statement document
[RFC6820]. In this document, the scaling issues of MAC address
learning related to the overlay-based approach are listed as
followed:<list>
<t>ARP processing on Routers: This issue mainly concerns about the
significant amount of ARP traffic or BUM packets traffic in large
L2 broadcast domains and its impact to the routers. Finally, some
optimized method are proposed;</t>
<t>IPv6 Neighbor Discovery has the similar issue as ARP processing
on router;</t>
<t>MAC Address Table Size Limitations at Switches: This issue
mainly concerns on the MAC Address Table Size Limitations when the
VM number is very large in the Virtualized data center
environment.</t>
</list></t>
<t>In order to tackle the above problems, SARP [SARP] seamlessly
supports Layer 2 network virtualization services over the overlay
network and significantly reduces their complexity in terms of table
size and performance. The overlay networks are only required to map
MAC addresses of the SARP proxies, instead of MAC address of the
destination end host, to the correct tunnel.</t>
</section>
<section title="BGP/MPLS IP VPNs – Distributed control plane distribution">
<t>BGP/MPLS IP VPNs [RFC4364] provides IP Virtual Private Networks
(VPNs) for its customers and support VPN traffic isolation, address
overlapping and separation between customer networks. The BGP/MPLS
control plane is used to distribute both the VPN labels and the tenant
system IP addresses that are used to identify the customer. However
BGP/MPLS IP VPN doesn’t support interconnection with Data Center (DC)
overlay networks and provide a virtual end to end tenant network
service to tenant systems in the BGP/MPLS IPVPN.It also has the
scalability related problems when IP addresses of a large number of
VMs need to be propagated in control plane in the Virtualized data
center environments.</t>
<t>For an L3 overlay node, the overlay node only needs to determine IP
addresses of the tenant system but doesn't need to know the MAC
address of the destination system since overlay tunnels the L3 traffic
from the tenant system in an encapsulated format to the final
destination and doesn't care about the MAC address of destination end
system for the inner L3 packet. Therefore overlay node can answer any
address resolution query with its own MAC address or one virtual MAC
address. In [I.D-ietf-l3vpn-end-system], NVE uses XMPP to exchange
information with the tenant system and answer the address resolution
query from tenant system with a virtual router MAC address.</t>
<t>In order to propagate tenant system information to the whole
overlay network environment, [I.D-ietf-l3vpn-end-system]use Route
Server to gather VPN membership on each Forwarder and IP addresses
that are currently associated with each virtual interface of tenant
system and advertise them to the BGP speaker. In addition, BGP speaker
also can interact with Route Server to generate tenant system
information update to the upstream end systems.</t>
</section>
<section title="BGP/MPLS Ethernet VPNs and PBB-EVPN">
<t>Ethernet Virtual Private Networks (E-VPNs) [I-D.ietf-l2vpn-evpn]
provide an emulated L2 service in which each tenant has its own
Ethernet network over a common IP or MPLS infrastructure. PBB-EVPN
[I-D.ietf -l2vpn-pbb-evpn] is a combined solution of PBB and E-VPN.
They all use BGP for MAC address distribution over the core MPLS/IP
network, and use ARP or data plane snooping for MAC address learning
of locally attached hosts. In other words, the mapping table
information <VNID,IP_A,NVE_X> should be distributed to all the
remote overlay nodes that belong to the same VN. After that,the tenant
system information<VNID,IP_A, MAC_X> is distributed from remote
overlay nodes to all the remote tenant system. When all the tenant
system information is populated, overlay nodes will process the packet
from each tenant system and perform a lookup operation in its map
table for the destination TSID=<VNID,IP_B> and determine which
tunnel the packet needs to be sent to. <vspace blankLines="1" />The
analysis of their MAC address learning methods is as followed: <vspace
blankLines="1" />Pros:<list style="symbols">
<t>ARP broadcast Suppression: They all construct ARP caches on the
PEs and synchronize them either via BGP or data plane snooping.
The PEs act as ARP proxies for locally attached hosts, thereby
preventing repeated ARP broadcast over the core MPLS/IP
network;</t>
<t>Comparing E-VPN, PBB-EVPN reduces the number of BGP MAC
advertisement routes, provide C-MAC address mobility, confine the
scope of C-MAC address learning to only active flows, offer per
site policies and avoid C-MAC address flushing on topology
changes.</t>
</list><vspace blankLines="1" />Con: An E-VPN PE sends a BGP MAC
Advertisement Route per customer/client MAC (C-MAC) address. This will
raise the scalability related problems in the case of Virtualized data
center environments where the number of virtual machines (VMs) is very
large.</t>
</section>
<section title="VPLS – ARP + data plane learning">
<t>VPLS is an L2 VPN technology. VPLS uses the ARP and data plane
learning for L2 tenant system information discovery, and not
advertised and distributed via a BGP/LDP control plane. The analysis
of this method is as followed: <vspace blankLines="1" />Pros:<list
style="symbols">
<t>Reducing complexity and work burden of the control plane by
decreasing the control packets;</t>
<t>MAC address learning based on active flows can save the space
of MAC mapping table.</t>
</list><vspace blankLines="1" />Cons:<list style="symbols">
<t>PE will learn all active MACs over the associated PW by BUM
flooding of data plane. But, some active MACs is not destined to
the PE;</t>
<t>Unlike the active MAC withdraw mechanism in control plane, PE
cannot flush MAC address real-time in data plane, when host MACs
behind the PE are changed.</t>
</list></t>
</section>
<section title="LISP – Centralized control plane distribution">
<t>LISP[RFC6830] essentially provides an IP over IP overlay where the
internal addresses are end station Identifiers and the outer IP
addresses represent the location of the end station within the core IP
network topology. [draft-maino-nvo3-lisp-cp-02] discusses L2 over L3
LISP Encapsulation and proposes a LISP Mapping System for ARP
resolution to eliminate the flooding of ARP traffic and further reduce
the need for multicast in the underlay network. This system relies on
mapping system for tenant system information distribution and involves
MAP-request/MAP-Response message exchange between overlay node and
mapping system. With introduced LISP Mapping system, the scalability
is improved for tenant system information discovery. the packet flow
and control plane operation are as follows: <list style="symbols">
<t>Tenant System A sends a broadcast ARP message to discover the
MAC address of Tenant system B. The message contains IP_B in the
ARP message payload.</t>
<t>NVE X as an ARP proxy, receiving the ARP message and knowing
source and destination are in the different subnet[RFC1027], but
rather than flooding it on the overlay network, sends a Map-
Request(i.e.,LISP signaling) to the backend LISP mapping system
(i.e.,NVA) that maintains mapping information for entire overlay
network for TSID = <VNID,IP_B,*>.</t>
<t>The Map-Request is reflected by the backend LISP Mapping system
to NVE Y, that will send a Map-Reply back to NVE X containing the
mapping TSID=<VNID,IP_B,MAC_B>. Alternatively, depending on
the Backend LISP Mapping system configuration, the backend LISP
Mapping system may send directly a Map-Reply to NVE X.</t>
<t>NVE X populates the mapping table with the received entry, and
sends an ARP-Agent Reply to Tenant System A that includes MAC_B
and IP_B.</t>
<t>Tenant system A learns MAC_B from the ARP message and can now
send a packet to Tenant system B by including MAC_B, and IP_B, as
destination addresses.</t>
</list></t>
</section>
</section>
<section title="Gap Analysis and Discuss">
<t>The following table compares several tenant system information
discovery methods from different aspects under the same network topology
and scale.</t>
<figure>
<artwork>
+-----------+-------------+--------------+-------------+------------+
| TS | Forwarding | Packets |Control plane| Directory |
| Discovery | table | flooding |Distribution Support |
| method | size | impact | support | |
+-----------+-------------+--------------+-------------+------------+
| | | | | |
| SPB | | | | Trill:Yes |
| &TRILL | Mediaum | Medium | Yes | SPB:No |
| | | | | |
| | | | | |
+-----------+-------------+--------------+-------------+------------+
| | | | | |
| | | | | |
| ARMD&SARP | Small | Medium | No | No |
| | | | | |
| | | | | |
+-----------+-------------+--------------+-------------+------------+
| | | | | |
| LISP | | | |LISP Mapping|
| + | Medium | Medium | Yes | System |
+ ARP proxy | | | | |
| | | | | |
+-----------+-------------+--------------+-------------+------------+
| | | | | |
| BGP/MPLS | | | | |
| IP | Large | Large | Yes | No |
| VPN | | | | |
| | | | | |
+-----------+-------------+--------------+-------------+------------+
| | | | | |
| BGP/MPLS | | | | |
| Ethernet | Large | Large | Yes | No |
| VPN | | | | |
| | | | | |
+-----------+-------------+--------------+-------------+------------+
| | | | | |
| VPLS | | | | |
| + | Medium | Small | Yes | No |
| ARP proxy | | | | |
| | | | | |
+-----------+-------------+--------------+-------------+------------+
Table 1: The comparison between several tenant system
information discovery methods
</artwork>
</figure>
</section>
<section title="Conclusion">
<t>There are three ways for tenant system information discovery, data
plane learning and control plane ARP learning and control plane
distribution. In large layer 2 domain, the MAC address can not be simply
learnt by looking at the outer layer 2 header, instead, Deeper parsing
inner Ethernet header is required. However it also introduces a lot of
processing overhead. In order to address this issue, the control plane
distribution is proposed, and used to carry both MAC address and IP
address and eliminate the above data plane learning issue. However
distribution protocol is needed. How distribution protocol is used to
propagate tenant system information and mapping table information in
large scale and in a more efficient way is still under study.</t>
</section>
<section title="IANA Considerations">
<t>This document has no actions for IANA.</t>
</section>
<section title="Security Considerations">
<t>TBC.</t>
</section>
</middle>
<back>
<references title="Normative References">
<reference anchor="RFC2119">
<front>
<title abbrev="RFC Key Words">Key words for use in RFCs to Indicate
Requirement Levels</title>
<author fullname="Scott Bradner" initials="S." surname="Bradner">
<organization>Harvard University</organization>
<address>
<postal>
<street>1350 Mass. Ave.</street>
<street>Cambridge</street>
<street>MA 02138</street>
</postal>
<phone>- +1 617 495 3864</phone>
<email>sob@harvard.edu</email>
</address>
</author>
<date month="March" year="1997" />
<area>General</area>
<keyword>keyword</keyword>
<abstract>
<t>In many standards track documents several words are used to
signify the requirements in the specification. These words are
often capitalized. This document defines these words as they
should be interpreted in IETF documents. Authors who follow these
guidelines should incorporate this phrase near the beginning of
their document: <list>
<t>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.</t>
</list></t>
<t>Note that the force of these words is modified by the
requirement level of the document in which they are used.</t>
</abstract>
</front>
</reference>
<reference anchor="I.D-ietf-nvo3-framework">
<front>
<title>Framework for DC Network Virtualization</title>
<author fullname="M.Lasserre" initials="M." surname="Lasserre">
<organization></organization>
</author>
<date month="September" year="2012" />
</front>
<seriesInfo name="ID" value="draft-ietf-nvo3-framework-00" />
</reference>
<reference anchor="SPB">
<front>
<title>IEEE standard for local and metropolitan area networks: Media
access control (MAC) bridges and virtual bridged local area networks
-- Amendment 20: Shortest path bridging</title>
<author>
<organization></organization>
</author>
<date month="June" year="2012" />
</front>
<seriesInfo name="IEEE" value="802.1aq" />
</reference>
<reference anchor="I-D.ietf-l2vpn-evpn">
<front>
<title>BGP MPLS Based Ethernet VPN</title>
<author fullname="A.Sajassi" initials="A." surname="Sajassi">
<organization></organization>
</author>
<author fullname="R.Aggarwal" initials="R." surname="Aggarwal">
<organization></organization>
</author>
<date month="February" year="2013" />
</front>
<seriesInfo name="ID" value="draft-ietf-l2vpn-evpn-03" />
</reference>
<reference anchor="I-D.ietf-trill-directory-framework">
<front>
<title>TRILL (Transparent Interconnection of Lots of Links): Edge
Directory Assistance Framework</title>
<author fullname="Linda Dunbar" initials="L." surname="Dunbar">
<organization></organization>
</author>
<author fullname="Donald Eastlake" initials="D." surname="Eastlake">
<organization></organization>
</author>
<date month="April" year="2013" />
</front>
<seriesInfo name="ID" value="draft-ietf-trill-directory-framework-05" />
</reference>
<reference anchor="ESADI">
<front>
<title>TRILL (Transparent Interconnection of Lots of Links): ESADI
(End Station Address Distribution Information) Protocol </title>
<author fullname="Donald Eastlake" initials="D." surname="Eastlake">
<organization></organization>
</author>
<date month="February" year="2013" />
</front>
<seriesInfo name="ID" value="draft-ietf-trill-esadi-02" />
</reference>
<reference anchor="SARP">
<front>
<title>Scaling the Address Resolution Protocol for Large Data
Centers (SARP)</title>
<author fullname="Linda Dunbar" initials="L." surname="Dunbar">
<organization></organization>
</author>
<author fullname="Ilan Yerushalmi" initials="I."
surname="Yerushalmi">
<organization></organization>
</author>
<date month="February" year="2013" />
</front>
<seriesInfo name="ID" value="draft-nachum-sarp-04" />
</reference>
<reference anchor="RFC6325">
<front>
<title>RBridges: Base Protocol Specification</title>
<author fullname="R.Perlman" initials="R." surname="Perlman">
<organization></organization>
</author>
<date month="July" year="2011" />
</front>
</reference>
<reference anchor="draft-maino-nvo3-lisp-cp">
<front>
<title>LISP Control Plane for Network Virtualization
Overlays</title>
<author fullname="F. Maino" initials="F." surname="Maino">
<organization></organization>
</author>
<author fullname="R.Aggarwal" initials="R." surname="Aggarwal">
<organization></organization>
</author>
<date month="April" year="2013" />
</front>
<seriesInfo name="ID" value="draft-maino-nvo3-lisp-cp-02" />
</reference>
<reference anchor="I.D-ietf-l3vpn-end-system">
<front>
<title>BGP-signaled end-system IP/VPNs</title>
<author fullname="P. Marques" initials="P." surname="Marques">
<organization></organization>
</author>
<date month="April" year="2013" />
</front>
<seriesInfo name="ID" value="draft-maino-nvo3-lisp-cp-02" />
</reference>
<reference anchor="I-D.ietf-l2vpn-pbb-evpn">
<front>
<title>PBB-EVPN</title>
<author fullname="Ali Sajassi" initials="A." surname="Sajassi">
<organization></organization>
</author>
<date month="April" year="2013" />
</front>
<seriesInfo name="ID" value="draft-ietf-l2vpn-pbb-evpn-04" />
</reference>
<reference anchor="RFC6830">
<front>
<title>The Locator/ID Separation Protocol (LISP)</title>
<author fullname="D. Farinacci" initials="D." surname="Farinacci">
<organization></organization>
</author>
<date month="January" year="2013" />
</front>
</reference>
<reference anchor="RFC6820">
<front>
<title>The Locator/ID Separation Protocol (LISP)</title>
<author fullname="D. Farinacci" initials="D." surname="Farinacci">
<organization></organization>
</author>
<date month="January" year="2013" />
</front>
</reference>
<reference anchor="RFC4364">
<front>
<title>BGP/MPLS IP Virtual Private Networks (VPNs)</title>
<author fullname="E. Rosen" initials="E." surname="Rosen">
<organization></organization>
</author>
<date month="February" year="2006" />
</front>
</reference>
<reference anchor="RFC1027">
<front>
<title>Using ARP to Implement Transparent Subnet Gateways</title>
<author fullname="S. Carl-Mitchell" initials="S."
surname="Carl-Mitchell">
<organization></organization>
</author>
<date month="October" year="1987" />
</front>
</reference>
</references>
</back>
</rfc>
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