Internet Engineering Task Force (IETF) H. Shah
Request for Comments: 7436 Cinea Corp.
Category: Historic E. Rosen
ISSN: 2070-1721 Juniper Networks
F. Le Faucheur
G. Heron
Cisco Systems
January 2015
IP-Only LAN Service (IPLS)
Abstract
A Virtual Private LAN Service (VPLS) is used to interconnect systems
across a wide-area or metropolitan-area network, making it appear
that they are on a private LAN. The systems that are interconnected
may themselves be LAN switches. If, however, they are IP hosts or IP
routers, certain simplifications to the operation of the VPLS are
possible. We call this simplified type of VPLS an "IP-only LAN
Service" (IPLS). In an IPLS, as in a VPLS, LAN interfaces are run in
promiscuous mode, and frames are forwarded based on their destination
Media Access Control (MAC) addresses. However, the maintenance of
the MAC forwarding tables is done via signaling, rather than via the
MAC address learning procedures specified in the IEEE's "Media Access
Control (MAC) Bridges". This document specifies the protocol
extensions and procedures for support of the IPLS service.
The original intent was to provide an alternate solution to VPLS for
those Provider Edge (PE) routers that were not capable of learning
MAC addresses through data plane. This became a non-issue with newer
hardware. The concepts put forth by this document are still valuable
and are adopted in one form or other by newer work such as Ethernet
VPN in L2VPN working group and possible data center applications. At
this point, no further action is planned to update this document and
it is published simply as a historic record of the ideas.
Shah, et al. Historic [Page 1]RFC 7436 IPLS January 2015
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for the historical record.
This document defines a Historic Document for the Internet community.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7436.
Copyright Notice
Copyright (c) 2015 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. Overview ........................................................4
1.1. Terminology ................................................7
2. Topology ........................................................9
3. Configuration ..................................................10
4. Discovery ......................................................10
4.1. CE Discovery ..............................................10
4.1.1. IPv4-Based CE Discovery ............................11
4.1.2. IPv6-Based CE Discovery (RFC 4861) .................11
5. PW Creation ....................................................11
5.1. Receive Unicast Multipoint-to-Point PW ....................11
5.2. Receive Multicast Multipoint-to-Point PW ..................12
5.3. Send Multicast Replication Tree ...........................13
Shah, et al. Historic [Page 2]RFC 7436 IPLS January 2015
6. Signaling ......................................................13
6.1. IPLS PW Signaling .........................................13
6.2. IPv6 Capability Advertisement .............................17
6.3. Signaling Advertisement Processing ........................18
7. IANA Considerations ............................................19
7.1. LDP Status Messages .......................................19
7.2. Interface Parameters ......................................19
8. Forwarding .....................................................20
8.1. Non-IP or Non-ARP Traffic .................................20
8.2. Unicast IP Traffic ........................................20
8.3. Broadcasts and Multicast IP Traffic .......................20
8.4. ARP Traffic ...............................................21
8.5. Discovery of IPv6 CE Devices ..............................21
8.5.1. Processing of Neighbor Solicitations ...............22
8.5.2. Processing of Neighbor Advertisements ..............22
8.5.3. Processing of Inverse Neighbor
Solicitations and Advertisement ....................22
8.5.4. Processing of Router Solicitations and
Advertisements .....................................23
8.6. Encapsulation .............................................23
9. Attaching to IPLS via ATM or Frame Relay (FR) ..................24
10. VPLS vs. IPLS .................................................24
11. IP Protocols ..................................................25
12. Dual-Homing with IPLS .........................................25
13. Proxy ARP Function ............................................26
13.1. ARP Proxy - Responder ....................................26
13.2. ARP Proxy - Generator ....................................26
14. Data Center Applicability .....................................27
15. Security Considerations .......................................27
15.1. Control-Plane Security ...................................27
15.2. Data-Plane Security ......................................28
16. References ....................................................29
16.1. Normative References .....................................29
16.2. Informative References ...................................30
Acknowledgements ..................................................31
Contributors ......................................................31
Authors' Addresses ................................................32
Shah, et al. Historic [Page 3]RFC 7436 IPLS January 2015
1. Overview
As emphasized in [RFC4762], Ethernet has become popular as an access
technology in metropolitan- and wide-area networks. [RFC4762]
describes how geographically dispersed customer LANs can be
interconnected over a service provider's network. The VPLS service
is provided by Provider Edge (PE) devices that connect Customer Edge
(CE) devices. The VPLS architecture provides this service by
incorporating bridging functions such as MAC address learning in the
PE devices.
PE platforms are designed primarily to be IP routers rather than LAN
switches. To add VPLS capability to a PE router, one has to add MAC-
address-learning capabilities, along with aging and other mechanisms
native to Ethernet switches [IEEE802.1D]. This may be fairly complex
to add to the forwarding-plane architecture of an IP router. As
discussed in [RFC4664], in scenarios where the CE devices are NOT LAN
switches, but rather are IP hosts or IP routers, it is possible to
provide the VPLS service without requiring MAC address learning and
aging on the PE. Instead, a PE router has to have the capability to
match the destination MAC address in a packet received from a CE to
an outbound pseudowire (PW). The requirements for the IPLS service
are described in [RFC4665]. The purpose of this document is to
specify a solution optimized for IPLS.
IPLS provides a VPLS-like service using PE routers that are not
designed to perform general LAN bridging functions. One must be
willing to accept the restriction that an IPLS be used for IP traffic
only, and not used to interconnect CE devices that are themselves LAN
switches. This is an acceptable restriction in many environments,
given that IP is the predominant type of traffic in today's networks.
The original intent was to provide an alternate solution to VPLS for
those PE routers that were not capable of learning MAC addresses in
the data plane. This became a non-issue with newer hardware. The
concepts put forth by this document are still valuable and are
adopted in one form or other by newer work such as Ethernet VPN in
the L2VPN working group and possible data center applications. At
this point, no further action is planned to update this document and
is published simply as a historic record of the ideas.
Shah, et al. Historic [Page 4]
RFC 7436 IPLS January 2015
In IPLS, a PE device implements multipoint LAN connectivity for IP
traffic using the following key functions:
1. CE Address Discovery: Each PE device discovers the MAC address
of the locally attached CE IP devices, for each IPLS instance
configured on the PE device. In some configurations, the PE
also learns the IP address of the CE device (when performing
ARP proxy functions, described later in the document).
2. Pseudowire (PW) for Unicast Traffic: For each locally attached
CE device in a given IPLS instance, a PE device sets up a
pseudowire (PW) to each of the other PEs that supports the same
IPLS instance.
For instance, if PEx and PEy both support IPLS I, and PEy is
locally attached to CEa and CEb, PEy will initiate the setup of
two PWs between itself and PEx. One of these will be used to
carry unicast traffic from any of PEx's CE devices to CEa. The
other will be used to carry unicast traffic from any of PEx's
CE devices to CEb.
Note that these PWs carry traffic only in one direction.
Further, while the PW implicitly identifies the destination CE
of the traffic, it does not identify the source CE; packets
from different source CEs bound to the same destination CE are
sent on a single PW.
3. Pseudowires for Multicast Traffic: In addition, every PE
supporting a given IPLS instance will set up a special
'multicast' pseudowire to every other PE in that IPLS instance.
If, in the above example, one of PEx's CE devices sends a
multicast packet, PEx would forward the multicast packet to PEy
on the special 'multicast' pseudowire. PEy would then send a
copy of that packet to CEa and a copy to CEb.
The 'multicast' pseudowire carries Ethernet frames of
multicast/broadcast IP, ARP, and ICMP (Inverse) Neighbor
Discovery (ND/IND) packets for IPv6. Thus, when a PE sends a
multicast packet across the network, it sends one copy to each
remote PE (supporting the given IPLS instance). If a
particular remote PE has more than one CE device in that IPLS
instance, the remote PE must replicate the packet and send one
copy to each of its local CEs.
As with the pseudowires that are used for unicast traffic,
packets travel in only one direction on these pseudowires, and
packets from different sources may be freely intermixed.
Shah, et al. Historic [Page 5]RFC 7436 IPLS January 2015
4. Signaling: The necessary pseudowires can be set up and
maintained using the signaling procedures based on the Label
Distribution Protocol (LDP) described in [RFC4447].
A PE may assign the same label to each of the unicast
pseudowires that lead to a given CE device, in effect creating
a multipoint-to-point pseudowire.
Similarly, a PE may assign the same label to each of the
'multicast' pseudowires for a given IPLS instance, in effect
creating a multipoint-to-point pseudowire. When setting up a
pseudowire to be used for unicast traffic, the PE must also
signal the MAC address of the corresponding CE device. It
should also, optionally, advertise the IP address of the local
CE device, especially when ARP proxy function is configured or
simply for operational management purposes. Similarly, for
IPv6 support, PE may optionally advertise the IPv6 addresses of
the local CE device.
5. ARP Packet Forwarding: ARP packets [RFC826] are forwarded from
the attachment circuit (AC) to 'multicast' pseudowires in the
Ethernet frame format as described by [RFC4448]. The following
rules are observed when processing ARP packets:
a. Both broadcast (request) and unicast (response) ARP packets
are sent over the 'multicast' pseudowire.
b. When an ARP packet is received from an AC, the packet is
copied to the control plane for the purpose of learning the
MAC address of the CE. Optionally, an IP address is also
learned to record the association of the IP and MAC address.
c. All Ethernet packets, including ARP packets, received from
the 'multicast' pseudowire are forwarded out to all the ACs
associated with the IPLS instance. These packets are not
copied to the control plane.
6. ICMP IPv6 ND/IND-related Packet Forwarding: ND/IND IPv6 packets
from an AC are replicated and a copy is sent to other ACs and
to 'multicast' PWs associated with the IPLS instance in the
native Ethernet format, unchanged. A copy is also submitted to
the control plane to learn the MAC address and, optionally,
corresponding IPv6 addresses.
Shah, et al. Historic [Page 6]RFC 7436 IPLS January 2015
7. Multicast IP packet forwarding: An IP Ethernet frame received
from an AC is replicated to other ACs and the 'multicast' PWs
associated with the IPLS instance. An IP Ethernet frame
received from a 'multicast' PW is replicated to all the egress
ACs associated with the IPLS instance.
8. Unicast IP packet forwarding: An IP packet received from the AC
is forwarded based on the destination MAC address lookup in the
forwarding table. If a match is found, the packet is forwarded
to the associated egress interface. If the egress interface is
unicast PW, the packet is sent without a MAC header. If the
egress interface is a local AC, the Ethernet frame is forwarded
as such. An IP packet received from the unicast PW is
forwarded to the egress AC with the MAC header prepended. The
destination MAC address is derived from the forwarding table
while the source MAC address is the MAC address of the PE.
Both VPLS [RFC4762] and IPLS require the ingress PE to forward a
frame based on its destination MAC address. However, two key
differences between VPLS and IPLS can be noted from the above
description:
- In VPLS, MAC entries are placed in the Forwarding Information Base
(FIB) of the ingress PE as a result of MAC address learning (which
occurs in the data plane); whereas, in IPLS, MAC entries are
placed in the FIB as a result of PW signaling operations (control
plane).
- In VPLS, the egress PE looks up a frame's destination MAC address
to determine the egress AC; in IPLS, the egress AC is determined
entirely by the ingress PW label.
The following sections describe the details of the IPLS scheme.
1.1. Terminology
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 [RFC2119].
IPLS IPLS stands for IP-only LAN service (a type of Virtual
Private LAN Service that is restricted to IP traffic
only).
MP2P PW A Multipoint-to-Point Pseudowire is a PW that carries
traffic from remote PE devices to a PE device that
signals the PW. The signaling PE device advertises
the same PW label to all remote PE devices that
Shah, et al. Historic [Page 7]RFC 7436 IPLS January 2015
participate in the IPLS service instance. In IPLS,
for a given IPLS instance, an MP2P PW used for IP
unicast traffic is established by a PE for each CE
device locally attached to that PE. It is a
unidirectional tree whose leaves consist of the remote
PE peers (which connect at least one AC associated
with the same IPLS instance) and whose root is the
signaling PE. Traffic flows from the leaves towards
the root.
Multicast PW A Multicast/broadcast Pseudowire is a special kind of
MP2P PW that carries IP multicast/broadcast traffic,
all ARP frames and ICMP (I)ND frames for IPv6. In the
IPLS architecture, for each IPLS instance supported by
a PE, that PE device establishes exactly one multicast
PW. Multicast PW uses Ethernet encapsulation.
Unicast PW A Unicast pseudowire carries IP unicast packets. A PE
creates unicast PW for each locally attached CE. The
unicast PW uses IP Layer 2 (L2) transport
encapsulation.
CE In this document, a Customer Edge (CE) is any IP node
(host or router) connected to the IPLS LAN service.
Send The collection of all multicast PWs and ACs
Multicast that are members of an IPLS service instance on a
Replication given PE. When a PE receives a multicast/broadcast
Tree packet from an AC, the PE device sends a copy of the
packet to every multicast PW and AC of the Send
Multicast Replication Tree, excluding the AC on which
the packet was received. When a PE receives a packet
from a multicast PW, the PE device sends a copy of the
packet to all the ACs of the Send Multicast
Replication Tree and never to other PWs.
(I)ND (Inverse) Neighbor Discovery in IPv6 uses ICMP
Neighbor Solicitation (NS) and Neighbor Advertisement
(NA) packets.
RS Router Solicitation is when hosts generate all-routers
multicast ICMP packets to discover the IPv6 router on
the local link.
RA Router Advertisement occurs when a router generates
all-nodes multicast ICMP packets to advertise its
presence on the link. A unicast response is also sent
when RS is received.
Shah, et al. Historic [Page 8]RFC 7436 IPLS January 2015
NS Neighbor Solicitation in IPv6 uses (multicast) ICMP
packets to resolve the association of the IPv6
interface address to the MAC address.
NA Neighbor Advertisement in IPv6 uses (unicast) ICMP
packets to respond to NS.
2. Topology
The CE devices are IP nodes (hosts or routers) that are connected to
PE devices either directly or via an Ethernet network. We assume
that the PE/CE connection may be regarded by the PE as an "interface"
to which one or more CEs are attached. This interface may be a
physical LAN interface or a VLAN. The PE routers are MPLS Label Edge
Routers (LERs) that serve as PW endpoints.
+----+ +----+
+ S1 +---+ ........................... +---| S2 |
+----+ | | . . | +----+
IPa | | +----+ +----+ | IPe
+ +---| PE1|---MPLS and/or IP---| PE2|---+
/ \ +----+ |Network +----+ |
+----+ +---+ . | . | +----+
+ S1 + | S1| . +----+ . +---| S2 |
+----+ +---+ ..........| PE3|........... +----+
IPb IPc +----+ IPf
|
|
+----+
| S3 |
+----+
IPd
In the above diagram, an IPLS instance is shown with three sites:
site S1, site S2, and site S3. In site S3, the CE device is directly
connected to its PE. In the other two sites, there are multiple CEs
connected to a single PE. More precisely, the CEs at these sites are
on an Ethernet (switched at site 1 and shared at site 2) network (or
VLAN), and the PE is attached to that same Ethernet network or VLAN).
We impose the following restriction: if one or more CEs attach to a
PE by virtue of being on a common LAN or VLAN, there MUST NOT be more
than one PE on that LAN or VLAN.
PE1, PE2, and PE3 are shown as connected via an MPLS network;
however, other tunneling technologies, such as Generic Routing
Encapsulation (GRE), Layer 2 Tunneling Protocol version 3 (L2TPv3),
etc., could also be used to carry the PWs.
Shah, et al. Historic [Page 9]RFC 7436 IPLS January 2015
An IPLS instance is a single broadcast domain, such that each IP end
station (e.g., IPa) appears to be co-located with other IP end
stations (e.g., IPb through IPf) on the same subnet. The IPLS
service is transparent to the CE devices and requires no changes to
them.
3. Configuration
Each PE router is configured with one or more IPLS service instances,
and each IPLS service instance is associated with a unique VPN-ID.
For a given IPLS service instance, a set of ACs is identified. Each
AC can be associated with only one IPLS instance. An AC, in this
document, is either a customer-facing Ethernet port, or a particular
VLAN (identified by an IEEE 802.1Q VLAN ID) on a customer-facing
Ethernet port.
The PE router can optionally be configured with a local MAC address
to be used as a source MAC address when IP packets are forwarded from
a PW to an AC. By default, a PE uses the MAC address of the
customer-facing Ethernet interface for this purpose.
4. Discovery
The discovery process includes:
- Remote PE discovery
- VPN (i.e., IPLS) membership discovery
- IP CE end station discovery
This document does not discuss the remote PE discovery or VPN
membership discovery. This information can either be user configured
or can be obtained using auto-discovery techniques described in
[RFC6074] or other methods. However, the discovery of the CE is an
important operational step in the IPLS model and is described below.
4.1. CE Discovery
Each PE actively detects the presence of local CEs by snooping IP and
ARP frames received over the ACs. When an AC configured in an IPLS
instance becomes operational, it enters the CE discovery phase. In
this phase, the PE examines each multicast/broadcast Ethernet frame.
For link-local IP broadcast/multicast frames (e.g., IPv4 packets with
destination addresses within 224.0.0/24 [RFC5771]), the CE's (source)
MAC address is extracted from the Ethernet header and the (source) IP
address is obtained from the IP header.
For each CE, the PE maintains the following tuple: <Attachment
Circuit identification info, VPN-ID, MAC address, IP address
(optional)>.
Shah, et al. Historic [Page 10]RFC 7436 IPLS January 2015
4.1.1. IPv4-Based CE Discovery
As indicated earlier, a copy of each ARP frame received over the AC
is submitted to the control plane. The PE learns the MAC address and
optionally the IP address of the CE from the source address fields of
the ARP PDU.
Once a CE is discovered, its status is monitored continuously by
examining the received ARP frames and by periodically generating ARP
requests. The absence of an ARP response from a CE after a
configurable number of ARP requests is interpreted as loss of
connectivity with the CE.
4.1.2. IPv6-Based CE Discovery (RFC 4861)
A copy of Neighbor and Router Discovery frames received over the AC
are submitted to the control plane in the PE.
If the PE receives an NS message, and the source IP address of the
message is not the unspecified address, the PE learns the MAC address
and optionally the IP address of the CE.
If the PE receives an unsolicited NA message, the PE learns the
source MAC address and optionally the IP address of the CE.
If the PE receives an RS, and the source IP address of the message is
not the unspecified address, the PE learns source MAC address and
optionally the IP address of the CE.
If the PE receives an RA, it learns the source MAC address and
optionally the IP address of the CE.
The PE will periodically generate NS messages for the IP address of
the CE as a means of verifying the continued existence of the address
and its MAC address binding. The absence of a response from the CE
device for a given number of retries could be interpreted as a loss
of connectivity with the CE.
5. PW Creation
5.1. Receive Unicast Multipoint-to-Point PW
As the PE discovers each locally attached CE, a unicast multipoint-
to-point pseudowire (MP2P PW) associated exclusively with that CE is
created by distributing the MAC address and optionally the IP address
of the CE along with a PW label to all the remote PE peers that
participate in the same IPLS instance. Note that the same value of a
Shah, et al. Historic [Page 11]
RFC 7436 IPLS January 2015
PW label SHOULD be distributed to all the remote PE peers for a given
CE. The MP2P PW thus created is used by remote PEs to send unicast
IP traffic to a specific CE.
(The same functionality can be provided by a set of point-to-point
PWs, and the PE is not required to send the same PW label to all the
other PEs. For convenience, however, we will use the term MP2P PWs,
which may be implemented using a set of point-to-point PWs.)
The PE forwards a frame received over this MP2P PW to the associated
AC.
The unicast PW uses IP Layer 2 Transport encapsulation as defined in
[RFC4447].
5.2. Receive Multicast Multipoint-to-Point PW
When a PE is configured to participate in an IPLS instance, it
advertises a 'multicast' PW label to every other PE that is a member
of the same IPLS. The advertised PW label value is the same for each
PE, which creates an MP2P PW. There is only one such multicast MP2P
PW per PE for each IPLS instance, and this PW is used exclusively to
carry IP multicast/broadcast, ARP traffic, and (inverse) Neighbor
Discovery packets for IPv6 from the remote PEs to this PE for this
IPLS instance.
Note that no special functionality is expected from this PW. We call
it a 'multicast' PW because we use it to carry multicast and
broadcast IP, ARP, and IPv6 Neighbor Discovery traffic. The PW
itself need not provide any different service than any of the unicast
PWs.
In particular, the Receive multicast MP2P PW does not perform any
replication of frames itself. Rather, it is there to signify to the
PE that the PE may need to replicate a copy of a frame received over
this MP2P PW onto all the ACs that are associated with the IPLS
instance of the MP2P PW.
The multicast MP2P PW is considered the principal PW in the bundle of
MP2P PWs that consists of one multicast MP2P PW and a variable number
of unicast MP2P PWs for a given IPLS instance. In a principal role,
multicast PW represents the IPLS instance. The life of all unicast
PWs in the IPLS instance depends on the existence of the multicast
PW. If, for some reason, multicast PWs cease to exist, all the
associated unicast PWs in the bundle would be removed.
The multicast PW uses Ethernet encapsulation as defined in [RFC4448].
Shah, et al. Historic [Page 12]
RFC 7436 IPLS January 2015
The use of PWs that are specially optimized for multicast is for
further study.
5.3. Send Multicast Replication Tree
The PE creates a Send Multicast Replication Tree for each IPLS
instance, which consists of the collection of all ACs and all the
'multicast' PWs of the IPLS instance.
Any ARP, Neighbor Discovery, or broadcast/multicast IP Ethernet frame
received over an AC is replicated to the other ACs and to the MP2P
multicast PW of the Send Multicast Replication Tree. The Send
Multicast Replication Tree deals mostly with broadcast/multicast
Ethernet MAC frames. One exception to this is unicast ARP and IPv6
Neighbor Discovery frame, the processing of which is described in the
following section.
Any Ethernet frame received over the multicast PW is replicated to
all the ACs of the Send Multicast Replication Tree of the IPLS
instance associated with the incoming PW label: one exception is
unicast ARP and Neighbor Discovery frames used for IPv6, the
processing of which is described in the following section.
6. Signaling
[RFC4447] uses LDP to exchange PW FECs in the Label Mapping message
in a downstream unsolicited mode. The PW FEC comes in two forms;
PWid and Generalized PWid FEC elements. These FEC elements define
some fields that are common between them. The discussions below
refer to these common fields for IPLS-related extensions. Note that
the use of multipoint-to-point and unidirectional characteristics of
the PW makes BGP the ideal candidate for PW FEC signaling. The use
of BGP for such purposes is for future study.
6.1. IPLS PW Signaling
An IPLS carries IP packets as payload over its unicast PWs and
Ethernet frames as payload over its multicast PW. The PW type to be
used for unicast PW is the IP PW, defined in [RFC4447] as IP Layer 2
Transport. The PW type to be used for multicast PW is the Ethernet
PW as defined in [RFC4448]. The PW type values for these
encapsulations are defined in [RFC4446].
Shah, et al. Historic [Page 13]
RFC 7436 IPLS January 2015
When processing a received PW FEC, the PE matches the PW Id with the
locally configured PW Id for the IPLS instance. If the PW type is
Ethernet, the PW FEC is for multicast PWs. If the PW type is 'IP
Layer 2 transport', the PW FEC is for unicast PWs.
For unicast PWs, the PE must check the presence of a MAC Address TLV
in the optional parameter fields of the Label Mapping message. If
this parameter is absent, a Label Release message must be issued with
a status code meaning "MAC Address of the CE is absent" (note: status
code 0x000000XX is pending IANA allocation (see Section 7)), to
reject the establishment of the unicast PW with the remote PE.
The PE may optionally include an IP address TLV based on the user
configuration for the advertising of the IP addresses of the local
CE.
The processing of the Address List TLV is as follows.
o If a PW is configured for ACs with IPv4 CEs only, the PE should
advertise an Address List TLV with an Address Family type of an
IPv4 address. The PE should process the IPv4 address list TLV
as described in this document.
o If a PW is configured for ACs with both IPv4 and IPv6 CEs, the
PE should advertise IPv6 capability using the procedures
described in the section below.
o If a PE does not receive any IP Address List TLV or IPv6
capability advertisement, it MAY assume IPv4 behavior.
The IPLS uses the Address List TLV as defined in [RFC5036] to signal
the MAC (and optionally IP) address of the local CE. There are two
TLVs defined below: the IP Address TLV and MAC Address TLV. The MAC
Address TLV must be included in the optional parameter field of the
Label Mapping message when establishing the unicast IP PW for IPLS.
When configured to support a specific type of IP traffic (IPv4 or
IPv6), the PE verifies the type of IP traffic the PW will carry. If
there is a mismatch between the received Address Family value and the
expectation of an IPLS instance to which the PW belongs, the PE must
issue a Label Release message with a status code meaning "IP Address
type mismatch" (status code 0x0000004A) to reject the PW
establishment.
Shah, et al. Historic [Page 14]RFC 7436 IPLS January 2015
The encoding of the IP Address TLV is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| Address List (0x0101) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Family | CE IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CE IP Address | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Length
When an Address Family is IPv4, the Length is equal to 6 bytes; 2
bytes for the Address Family and 4 bytes of IP address. The
Length is 18 bytes when the Address Family is IPv6; 2 bytes for
the Address Family and 16 bytes of IP address.
Address Family
Two-octet quantity containing a value from the "Address Family
Numbers" registry [ADDR-IANA] that encodes the addresses contained
in the Addresses field.
CE IP Address
IP address of the CE attached to the advertising PE. The encoding
of the individual address depends on the Address Family.
The following address encodings are defined by this version of the
protocol:
Address Family Address Encoding
IPv4 (1) 4-octet full IPv4 address
IPv6 (2) 16-octet full IPv6 address
Note that more than one instance of the IP address TLV may exist,
especially when support for IPv6 is configured.
Shah, et al. Historic [Page 15]RFC 7436 IPLS January 2015
The encoding of the MAC Address TLV is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| Address List (0x0101) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Family | CE's MAC Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Length
The Length field is set to a value of 8 (2 bytes for the Address
Family, 6 bytes for the MAC address)
Address Family
Two-octet quantity containing a value from the "Address Family
Numbers" registry [ADDR-IANA] that encodes the addresses contained
in the Addresses field.
CE's MAC Address
MAC address of the CE attached to the advertising PE. The
encoding of the individual address depends on the Address Family.
The following address encodings are defined by this version of the
protocol:
Address Family Address Encoding
MAC (6) 6-octet full Ethernet MAC address
The IPv4 address of the CE is also supplied in the optional
parameters field of the LDP Notification message along with the PW
FEC. The LDP Notification message is used to signal any change in
the status of the CE's IPv4 address.
Note that Notification message does not apply to the MAC Address TLV
since an update to the MAC address of the CE should result in label
withdrawal followed by establishment of a new PW with a new MAC
address of the CE. However, advertisement of IP address(es) of the
CE is optional, and changes may become known after the establishment
of unicast PW.
Shah, et al. Historic [Page 16]RFC 7436 IPLS January 2015
The encoding of the LDP Notification message is as follows.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Notification (0x0001) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status (TLV) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Address List TLV (as defined above) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PWId FEC or Generalized ID FEC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Status TLV status code is set to 0x0000002C "IP address of CE",
to indicate that an IP address update follows. Since this
notification does not refer to any particular message, the Message ID
and Message Type fields are set to 0.
The PW FEC TLV SHOULD NOT include the interface parameters as they
are ignored in the context of this message.
6.2. IPv6 Capability Advertisement
A 'Stack Capability' Interface Parameter sub-TLV is signaled by the
two PEs so that they can agree which stack(s) they should be using.
It is assumed, by default, that the IP PW will always be capable of
carrying IPv4 packets. Thus, this capability sub-TLV is used to
indicate if other stacks need to be supported concurrently with IPv4.
The 'Stack Capability' sub-TLV is part of the interface parameters of
the PW FEC. The proposed format for the 'Stack Capability' Interface
Parameter sub-TLV is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Parameter ID | Length | Stack Capability |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Parameter ID = 0x16
Length = 4
Stack Capability = 0x000X to indicate IPv6 stack capability
Shah, et al. Historic [Page 17]RFC 7436 IPLS January 2015
The value of Stack Capability is dependent on the PW type context.
For IP PW type, a setting of 0x000X indicates IPv6 stack capability.
A PE that supports IPv6 on an IP PW MUST signal the 'Stack
Capability' sub-TLV in the initial Label Mapping message for the PW.
The PE nodes compare the value advertised by the remote PE with the
local configuration and only use a capability that is advertised by
both. If a PE that supports IPv6 does not receive a 'Stack
Capability' sub-TLV from the far-end PE in the initial Label Mapping
message, or one is received but it is set to a reserved value, the PE
MUST send an unsolicited release for the PW label with the LDP status
code meaning "IP Address type mismatch" (status code 0x0000004A).
The behavior of a PE that does not understand an interface parameter
sub-TLV is specified in RFC 4447 [RFC4447].
6.3. Signaling Advertisement Processing
A PE should process a received [RFC4447] advertisement with a PW type
of IP Layer 2 Transport for IPLS as follows:
- Verify the IPLS VPN membership by matching the VPN-ID signaled
in the Attachment Group Identifier (AGI) field or the PWid
field with all the VPN-IDs configured in the PE. Discard and
release the PW label if VPN-ID is not found.
- Program the FIB such that when a unicast IP packet is received
from an AC with its destination MAC address matching the
advertised MAC address, the packet is forwarded out over the
tunnel to the advertising PE with the advertised PW label as
the inner label.
A PE should process a received [RFC4447] advertisement with the PW
type of Ethernet for IPLS as follows:
- Verify the IPLS VPN membership by matching the VPN-ID signaled
in the AGI field or the PWid field with all the VPN-IDs
configured in the PE. Discard and release the PW label if VPN-
ID is not found.
- Add the PW label to the send broadcast replication tree for the
VPN-ID. This enables the sending of a copy of a
multicast/broadcast IP Ethernet frame, ARP Ethernet frame, or
Neighbor Discovery frame from the AC to this PW.
Shah, et al. Historic [Page 18]RFC 7436 IPLS January 2015
7. IANA Considerations
Since this document is being published as Historic, no registration
of IANA code points is necessary. However, in the future, if
interest to pursue this proposal arises, the following IANA code
registrations would become necessary.
7.1. LDP Status Messages
This document uses a new LDP status code. IANA already maintains the
"Status Code Name Space" registry defined by [RFC5036]. The
following allocation would be needed from the LDP Status Code Name
Space.
0x000000XX "MAC Address of CE is absent"
7.2. Interface Parameters
This document proposes a new Interface Parameters sub-TLV, to be
assigned from the "Pseudowire Interface Parameters Sub-TLV type
Registry". The following allocation would be needed for the
Parameter ID:
0xXX "Stack Capability"
IANA would also be requested to set up an "L2VPN PE Stack
Capabilities" registry. This is a 16-bit field. The Stack
Capability value (0x000X) is specified in Section 6.2 of this
document. The remaining bit field values (0x0002,..,0x8000) would be
assigned by IANA using the "IETF Consensus" policy defined in
[RFC5226].
L2VPN PE Stack Capabilities:
Bit (Value) Description
=============== ==========================================
Bit 0 (0x000X) IPv6 stack capability
Bit 1 (0x000X) Reserved
Bit 2 (0x000X) Reserved
.
.
.
Bit 14 (0xX000) Reserved
Bit 15 (0xX000) Reserved
Shah, et al. Historic [Page 19]RFC 7436 IPLS January 2015
8. Forwarding
8.1. Non-IP or Non-ARP Traffic
In an IPLS VPN, a PE forwards only IP and ARP traffic. All other
frames are dropped silently. If the CEs must pass non-IP traffic to
each other, they must do so through IP tunnels that terminate at the
CEs themselves.
8.2. Unicast IP Traffic
In IPLS, IP traffic is forwarded from the AC to the PW based on the
destination MAC address of the L2 frame (and not based on the IP
header).
The PE identifies the FIB associated with an IPLS instance based on
the AC or the PW label. When a frame is received from an AC, the PE
uses the destination MAC address as the lookup key. When a frame is
received from a PW, the PE uses the PW label as the lookup key. The
frame is dropped if the lookup fails.
For IPv6 support, the unicast IP ICMP frame of Neighbor Discovery
Protocol [RFC4861] is bi-casted; one copy is submitted to the control
plane and other copy to the PW, based on the destination MAC address.
8.3. Broadcasts and Multicast IP Traffic
When the destination MAC address is either broadcast or multicast, a
copy of the frame is sent to the control plane for CE discovery
purposes (see Section 4.1). It is important to note that stricter
rate-limiting criteria is applied to frames sent to the control
plane, in order to avoid overwhelming it under adverse conditions
such as DoS attacks. The service provider should also provide a
configurable limitation to prevent the overflowing of the learned
source addresses in a given IPLS instance. Also, caution must be
used such that only link-local multicasts and broadcast IP packets
are sent to the control plane.
When a multicast/broadcast IP packet is received from an AC, the PE
replicates it onto the Send Multicast Replication Tree (see Section
5.3). When a multicast/broadcast IP Ethernet frame is received from
a PW, the PE forwards a copy of the frame to all the ACs associated
with the respective IPLS VPN instance. Note that 'multicast' PW uses
Ethernet encapsulation; hence, it does not require additional header
manipulations.
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8.4. ARP Traffic
When a broadcast ARP frame is received over the AC, a copy of the
frame is sent to the control plane for CE discovery purposes. The PE
replicates the frame onto the Send Multicast Replication Tree (see
Section 5.3), which results in a copy to be delivered to all the
remote PEs on the 'multicast' PW and other local CEs through the
egress ACs.
When a broadcast Ethernet ARP frame is received over the 'multicast'
PW, a copy of the Ethernet ARP frame is sent to all the ACs
associated with the IPLS instance.
When a unicast Ethernet ARP frame is received over the AC, a copy of
the frame is sent to the control plane for CE discovery purposes.
The PE may optionally do destination MAC address lookup in the
forwarding table and send the ARP frame to a specific egress
interface (AC or 'multicast' PW to a remote PE) or replicate the
frame onto the Send Multicast Replication Tree (see Section 5.3).
When a unicast ARP Ethernet frame is received over the 'multicast'
PW, the PE may optionally do destination MAC address lookup in the
forwarding table and forward it to the AC where the CE is located.
If the CE is not accessible through any local AC, the frame is
dropped. Conversely, the PE may simply forward the frame to all the
ACs associated with that IPLS instance without any lookup in the
forwarding table.
8.5. Discovery of IPv6 CE Devices
A PE device that supports IPv6 MUST be capable of:
- Intercepting ICMPv6 Neighbor Discovery [RFC4861] packets
received over the AC.
- Recording the IPv6 interface addresses and CE link-layer
addresses present in these packets
- Forwarding them towards the original destination. A PE device
may also intercept Router Discovery packets in order to
discover the link-layer address and IPv6 interface address(es)
of the CE. The following sections describe the details.
The PE device MUST learn the link-layer address of the local CE and
be able to use it when forwarding traffic between CEs. The PE MAY
also wish to monitor the source link-layer address of data packets
Shah, et al. Historic [Page 21]RFC 7436 IPLS January 2015
received from the CE and discard packets not matching its learned CE
link-layer address. The PE device may also optionally learn a list
of CE IPv6 interface addresses for its directly attached CE.
8.5.1. Processing of Neighbor Solicitations
When a multicast NS frame is received over the AC, a copy of the
frame is sent to the control plane for CE discovery purposes. The PE
replicates the frame onto the Send Multicast Replication Tree (see
Section 5.3), which results in a copy to be delivered to all the
remote PEs on the 'multicast' PW and other local CEs through the
egress ACs. The PE may optionally learn an IPv6 interface address
(If provided -- this will not be the case for Duplicate Address
Detection) when present.
When a multicast Ethernet NS frame is received over the 'multicast'
PW, a copy is sent to all the ACs associated with the IPLS instance.
8.5.2. Processing of Neighbor Advertisements
When a unicast NA is received over the AC, a copy of the frame is
sent to the control plane for the CE discovery purposes. The PE may
optionally do destination MAC address lookup in the forwarding table
and send the NA frame to a specific egress interface (AC or
'multicast' PW to a remote PE) or replicate the frame onto the Send
Multicast Replication Tree (see Section 5.3).
Optionally, the PE could learn the IPv6 Interface address of the CE.
When a unicast NA frame is received over the 'multicast' PW, the PE
may optionally do destination MAC address lookup in the forwarding
table and forward it to the AC where the CE is located. If the CE is
not accessible through any local AC, the frame is dropped.
Conversely, the PE may simply forward the frame to all the ACs
associated with that IPLS instance without any lookup in the
forwarding table.
8.5.3. Processing of Inverse Neighbor Solicitations and Advertisement
Inverse Neighbor Discovery is typically used on non-broadcast links,
but is allowed on broadcast links as well [RFC3122]. A PE may
optionally intercept Inverse Neighbor Solicitation and Advertisement
and learn the MAC and IPv6 interface address list of the attached CE
from the copy of the frame sent to the control plane. The PE may
optionally do destination MAC address lookup in the forwarding table
and send another copy of the frame to a specific egress interface (AC
or 'multicast' PW to a remote PE) or replicate the frame onto the
Send Multicast Replication Tree (see Section 5.3).
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8.5.4. Processing of Router Solicitations and Advertisements
RSs are multicast while RAs can be unicast or multicast Ethernet
frames. The PE could optionally intercept RS and RA frames and send
a copy to the control plane. The PE may learn the MAC address and a
list of interface addresses for the attached CE.
For unicast RA, the PE may optionally do destination MAC address
lookup in the forwarding table and send the RA frame to a specific
egress interface (AC or 'multicast' PW to a remote PE) or replicate
the frame onto the Send Multicast Replication Tree (see Section 5.3).
The multicast RA and RS Ethernet frames are replicated using the Send
Multicast Replication Tree as described in Section 5.3.
8.6. Encapsulation
The Ethernet MAC header of a unicast IP packet received from an AC is
stripped before forwarding the frame to the unicast PW. However, the
MAC header is retained for the following cases,
- when a frame is a unicast IP packet that is directed to a local
AC.
- when a frame is a broadcast/multicast IP packet
- when a frame is an ARP packet
- when a frame is Neighbor/Router Solicitation/Advertisement
An IP frame received over a unicast PW is prepended with a MAC header
before transmitting it on the appropriate AC(s). The fields in the
MAC header are filled in as follows:
- The destination MAC address is the MAC address associated with
the PW label in the FIB.
- The source MAC address is the PE's own local MAC address or a
MAC address that has been specially configured on the PE for
this use.
- The Ethernet Type field is 0x0800 if IPv4 or 0x86DD if IPv6
[RFC2464].
- The frame may be IEEE 802.1Q tagged based on the VLAN
information associated with the AC.
A Frame Check Sequence (FCS) is appended to the frame.
Shah, et al. Historic [Page 23]RFC 7436 IPLS January 2015
9. Attaching to IPLS via ATM or Frame Relay (FR)
In addition to (i) an Ethernet port and a (ii) combination of
Ethernet port and a VLAN ID, an AC to IPLS may also be (iii) an ATM
or FR Virtual Circuit (VC) carrying encapsulated bridged Ethernet
frames or (iv) the combination of an ATM or FR VC and a VLAN ID.
The ATM/FR VC is just used as a way to transport Ethernet frames
between a customer site and the PE. The PE terminates the ATM/FR VC
and operates on the encapsulated Ethernet frames exactly as if those
were received on a local Ethernet interface. When a frame is
propagated from PW to an ATM or FR VC, the PE prepends the Ethernet
frame with the appropriate bridged encapsulation header as defined in
[RFC2684] and [RFC2427], respectively. Operation of an IPLS over
ATM/FR VC is exactly as described above, with the exception that the
AC is then identified via the ATM VCI/VPI or Frame Relay Data Link
Connection Identifier (DLCI) (instead of via a local Ethernet port
ID), or a combination of those with a VLAN ID.
10. VPLS vs. IPLS
The VPLS approach proposed in [RFC4762] provides VPN services for IP
as well as other protocols. The IPLS approach described in this
document is similar to VPLS in many respects:
- It provides a Provider-Provisioned Virtual LAN service with
multipoint capability where a CE connected via a single
attachment circuit can reach many remote CEs
- It appears as a broadcast domain and a single subnet
- Forwarding is based on destination MAC addresses
However, unlike VPLS, IPLS is restricted to IP traffic only. By
restricting the scope of the service to the predominant type of
traffic in today's environment, IPLS eliminates the need for service
provider edge routers to implement some bridging functions such as
MAC address learning in the data path (by, instead, distributing MAC
information in the control plane). Thus, this solution offers a
number of benefits:
- It facilitates Virtual LAN services in instances where PE
devices cannot or cannot efficiently (or are specifically
configured not to) perform MAC address learning.
- Unknown Unicast frames are never flooded as would be the case
in VPLS.
Shah, et al. Historic [Page 24]RFC 7436 IPLS January 2015
- Encapsulation is more efficient (the MAC header is stripped)
for unicast IP packets while traversing the backbone network.
- PE devices are not burdened with the processing overhead
associated with traditional bridging (e.g., Spanning Tree
Protocol (STP) processing, etc.). Note, however, that some of
these overheads (e.g., STP processing) could optionally be
turned off with a VPLS solution in the case where it is known
that only IP devices are interconnected.
- Loops (perhaps through backdoor links) are minimized since a PE
could easily reject (via label release) a duplicate IP to MAC
address advertisement.
- Greater control over CE topology distribution is available.
11. IP Protocols
The solution described in this document offers IPLS service for IPv4
and IPv6 traffic only. For this reason, the MAC header is not
carried over the unicast PW. It is reconstructed by the PE when
receiving a packet from a unicast PW and the Ethertype 0x0800 or
0x86DD is used in the MAC header since IPv4 or IPv6, respectively, is
assumed.
However, this solution may be extended to carry other types of
important traffic such as IS-IS , which does not use Ethernet-II, an
EtherType-based header. In order to permit the propagation of such
packets correctly, one may create a separate set of PWs, or pass
protocol information in the "control word" of a "multiprotocol" PW,
or encapsulate the Ethernet MAC header in the PW. The selection of
appropriate multiplexing/demultiplexing schemes is the subject of
future study. The current document focuses on IPLS service for IPv4
and IPv6 traffic.
12. Dual-Homing with IPLS
As stated in previous sections, IPLS prohibits the connection of a
common LAN or VLAN to more than one PE. However, the CE device
itself can connect to more than one instance of IPLS through two
separate LAN or VLAN connections to separate PEs. To the CE IP
device, these separate connections appear as connections to two IP
subnets. The failure of reachability through one subnet is then
resolved via the other subnet using IP routing protocols.
Shah, et al. Historic [Page 25]RFC 7436 IPLS January 2015
13. Proxy ARP Function
The earlier version of this proposal used IP-PW to carry both the
broadcast/multicast and unicast IP traffic. It also discussed how PE
proxy functionality responds to the ARP requests of the local CE on
behalf of remote CE. The current version of the document eliminated
these functions and instead uses Ethernet PW to carry broadcast,
multicast and ARP frames to remote PEs. The motivation to use
Ethernet PW and propagate ARP frames in the current version is to
support configuration like back-to-back IPLS (similar to Inter-AS
option-A configurations in [RFC4364]).
The termination and controlled propagation of ARP frames is still a
desirable option for security, DoS, and other purposes. For these
reasons, we reintroduce the ARP Proxy [RFC925] function in this
revision as an optional feature. The following sections describe
this option.
13.1. ARP Proxy - Responder
As a local configuration, a PE can enable the ARP Proxy Responder
function. In this mode, the local PE responds to ARP requests
received over the Attachment Circuit via learned IP and MAC address
associations, which are advertised by the remote PEs. In addition,
the PE may utilize local policies to determine if ARP requests should
be responded based on the source of the ARP request, rate at which
the ARP requests are generated, etc. In a nutshell, when this
feature is enabled, ARP requests are not propagated to remote PE
routers that are members of the same IPLS instance.
13.2. ARP Proxy - Generator
As a local configuration, a PE can enable the ARP Proxy Generator
function. In this mode, the PE generates an ARP request for each IP
and MAC address association received from the remote PEs. The remote
CE's IP and MAC address is used as the source information in the ARP
request while the destination IP address in the request is obtained
from the local configuration (that is, user needs to configure an IP
address when this feature is enabled). The ARP request is sent on
the ACs that have ARP Proxy Generator enabled and is associated with
the given IPLS instance.
In addition, the PE may utilize local policies to determine which
IP/MAC addresses are candidate for ARP request generation.
The ARP Proxy Generator feature is required to support back-to-back
IPLS configuration when any member of the IPLS instance is using the
ARP Proxy Responder function. An example of a back-to-back IPLS is a
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RFC 7436 IPLS January 2015
configuration where PE-1 (ASBR) in an IPLS cloud in one Autonomous
System (say, AS-1) is connected via an AC to another PE-2 (ASBR) in
an IPLS cloud in another Autonomous System (say, AS- 2) where each PE
appears as CE to each other. Such configuration is described in
[RFC4364] as option-A for inter-AS connectivity. The Proxy ARP
Responder feature prevents propagation of ARP requests to PE-1 (ASBR)
in AS-1. This necessitates that PE-1 (ASBR) in AS-1 generates an ARP
request on behalf of each CE connected to the IPLS instance in AS-1
as a mean to 'advertise' the reachability to IPLS cloud in AS-2.
14. Data Center Applicability
The resurgence of interest in providing an IP/MPLS-based solution for
Data Center Networks (DCNs) deserves another look at the IPLS
methodologies described in this document. The key requirement of a
DCN to permit Virtual Machine (VM) mobility within or across a DCN
necessitates extending the reachability of IP subnet over a LAN,
transparently. In addition, VMs tendency to generate frequent
gratuitous ARPs for location discovery necessitates a solution that
curbs broadcasts closest to the source.
The IPLS solution facilitates VM mobility by the PE closest to the
new location signaling the MAC address to all remote peers. In
addition, control-plane-based MAC learning mechanisms prevent
flooding of unknown unicast across a DCN. The optional ARP proxy
mechanisms further reduce ARP broadcast floods by preventing its
reach across a local PE.
15. Security Considerations
A more comprehensive description of the security issues involved in
L2VPNs are covered in [RFC4111]. Most of the security issues can be
avoided through implementation of appropriate guards. The security
aspect of this solution is addressed for two planes: the control
plane and data plane.
15.1. Control-Plane Security
The control-plane security pertains to establishing the LDP
connection, PW establishment and CE's IP and MAC address
distribution. The LDP connection between two trusted PEs can be
achieved by each PE verifying the incoming connection against the
configured peer's address and authenticating the LDP messages by
verifying keyed digests. The PW establishments between two secure
LDP peers do not pose security issue but mis-wiring could occur due
to configuration error. Some checks, such as, proper PW type and
other PW options may prevent mis-wiring due to configuration errors.
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The learning of the appropriate CE's IP and MAC address can be a
security issue. It is expected that the local attachment circuit to
CE be physically secured. If this is a concern, the PE must be
configured with the CE's IP and MAC address. During each ARP frame
processing, the PE must verify the received information against the
configuration before accepting. This prevents theft of service,
denial of service to a subscriber, or DoS attacks to all subscribers
by malicious use of network services.
The IPLS also provides MAC anti-spoofing by preventing the use of
already known MAC address. For instance, if a PE has already learned
a presence of a CE through a local connection or from another PE, and
subsequently an advertisement for the same MAC and/or IP address is
received from a different PE, the receiving PE can terminate service
to that CE (either through label release and/or removing the ARP
entry from the FIB) and raise the alarm.
The IPLS learns and distributes CE reachability through the control
plane. This provides greater control over CE topology distribution
through the application of local policies.
15.2. Data-Plane Security
The data traffic between the CE and PE is not encrypted. In an
insecure environment, it is possible that a malicious user may tap
into the CE-to-PE connection and could conduct an active or passive
attack. An example of an active attack would be generating traffic
using the spoofed destination MAC address on the Ethernet Attachment
Circuit and a passive attack could include targeted or passive
monitoring between the CE and PE. In order to avoid such hijacking,
the local PE may verify the source MAC address of the received frame
against the MAC address of the admitted connection. The frame is
forwarded to the PW only when authenticity is verified. When
spoofing is detected, the PE must sever the connection with the local
CE, tear down the PW, and start over.
Each IPLS instance uses its own FIB. This prevents leaking of one
customer data into another.
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16. References
16.1. Normative References
[IEEE802.1D] ISO/IEC 10038, ANSI/IEEE Std 15802-3:1998, "MAC
Bridges".
[RFC826] 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,
<http://www.rfc-editor.org/info/rfc826>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC2464] Crawford, M., "Transmission of IPv6 Packets over
Ethernet Networks", RFC 2464, December 1998,
<http://www.rfc-editor.org/info/rfc2464>.
[RFC3122] Conta, A., "Extensions to IPv6 Neighbor Discovery for
Inverse Discovery Specification", RFC 3122, June 2001,
<http://www.rfc-editor.org/info/rfc3122>.
[RFC4446] Martini, L., "IANA Allocations for Pseudowire Edge to
Edge Emulation (PWE3)", BCP 116, RFC 4446, April 2006,
<http://www.rfc-editor.org/info/rfc4446>.
[RFC4447] Martini, L., Ed., Rosen, E., El-Aawar, N., Smith, T.,
and G. Heron, "Pseudowire Setup and Maintenance Using
the Label Distribution Protocol (LDP)", RFC 4447,
April 2006, <http://www.rfc-editor.org/info/rfc4447>.
[RFC4448] Martini, L., Ed., Rosen, E., El-Aawar, N., and G.
Heron, "Encapsulation Methods for Transport of
Ethernet over MPLS Networks", RFC 4448, April 2006,
<http://www.rfc-editor.org/info/rfc4448>.
Shah, et al. Historic [Page 29]RFC 7436 IPLS January 2015
[RFC4762] Lasserre, M., Ed., and V. Kompella, Ed., "Virtual
Private LAN Service (VPLS) Using Label Distribution
Protocol (LDP) Signaling", RFC 4762, January 2007,
<http://www.rfc-editor.org/info/rfc4762>.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC
4861, September 2007,
<http://www.rfc-editor.org/info/rfc4861>.
[RFC5036] Andersson, L., Ed., Minei, I., Ed., and B. Thomas,
Ed., "LDP Specification", RFC 5036, October 2007,
<http://www.rfc-editor.org/info/rfc5036>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing
an IANA Considerations Section in RFCs", BCP 26, RFC
5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.
16.2. Informative References
[ADDR-IANA] IANA, "Address Family Numbers",
http://www.iana.org/assignments/address-family-
numbers/.
[RFC925] Postel, J., "Multi-LAN address resolution", RFC 925,
October 1984, <http://www.rfc-editor.org/info/rfc925>.
[RFC2427] Brown, C. and A. Malis, "Multiprotocol Interconnect
over Frame Relay", STD 55, RFC 2427, September 1998,
<http://www.rfc-editor.org/info/rfc2427>.
[RFC2684] Grossman, D. and J. Heinanen, "Multiprotocol
Encapsulation over ATM Adaptation Layer 5", RFC 2684,
September 1999,
<http://www.rfc-editor.org/info/rfc2684>.
[RFC4111] Fang, L., Ed., "Security Framework for Provider-
Provisioned Virtual Private Networks (PPVPNs)", RFC
4111, July 2005,
<http://www.rfc-editor.org/info/rfc4111>.
Shah, et al. Historic [Page 30]RFC 7436 IPLS January 2015
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, February 2006,
<http://www.rfc-editor.org/info/rfc4364>.
[RFC4664] Andersson, L., Ed., and E. Rosen, Ed., "Framework for
Layer 2 Virtual Private Networks (L2VPNs)", RFC 4664,
September 2006,
<http://www.rfc-editor.org/info/rfc4664>.
[RFC4665] Augustyn, W., Ed., and Y. Serbest, Ed., "Service
Requirements for Layer 2 Provider-Provisioned Virtual
Private Networks", RFC 4665, September 2006,
<http://www.rfc-editor.org/info/rfc4665>.
[RFC5771] Cotton, M., Vegoda, L., and D. Meyer, "IANA Guidelines
for IPv4 Multicast Address Assignments", BCP 51, RFC
5771, March 2010,
<http://www.rfc-editor.org/info/rfc5771>.
[RFC6074] Rosen, E., Davie, B., Radoaca, V., and W. Luo,
"Provisioning, Auto-Discovery, and Signaling in Layer
2 Virtual Private Networks (L2VPNs)", RFC 6074,
January 2011,
<http://www.rfc-editor.org/info/rfc6074>.
Acknowledgements
Authors would like to thank Alp Dibirdi from Alcatel, Xiaohu Xu from
Huawei, and other L2VPN working group members for their valuable
comments.
Contributors
This document is the combined effort of the following individuals and
many others who have carefully reviewed this document and provided
the technical clarifications.
K. Arvind Fortress
Vach Kompella Alcatel-Lucent
Matthew Bocci Alcatel-Lucent
Shane Amante Apple
Shah, et al. Historic [Page 31]RFC 7436 IPLS January 2015
Authors' Addresses
Himanshu Shah
Ciena Corp
3939 North 1st Street
San Jose, CA 95110
United States
EMail: hshah@ciena.com
Eric Rosen
Juniper Networks, Inc.
10 Technology Park Drive
Westford, MA, 01886
United States
EMail: erosen@juniper.net
Francois Le Faucheur
Cisco Systems, Inc.
Batiment D, 45 Allee des Ormes
06254 Mougins
France
EMail: flefauch@cisco.com
Giles Heron
Cisco Systems
9-11 New Square
Bedfont Lakes
Feltham
Middlesex
TW14 8HA
United Kingdom
EMail: giheron@cisco.com
Shah, et al. Historic [Page 32]
