Himanshu Shah
Ciena Corp
Eric Rosen
Francois Le Faucheur
Cisco Systems
PPVPN Working Group
Internet Draft
Draft-ietf-l2vpn-ipls-05.txt Giles Heron
Tellabs
October 2005
Expires: April 2006
IP-Only LAN Service (IPLS)
Status of this Memo
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IPR Disclosure Acknowledgement
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Abstract
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A Virtual Private LAN Service (VPLS) [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 which 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 MAC addresses. However, the maintenance
of the MAC forwarding tables is done via signaling, rather than via
the MAC address learning procedures specified in [IEEE 802.1D].
This draft specifies the protocol extensions and procedures for
support of the IPLS service.
Conventions
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
Table of Contents
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Status of this Memo................................................1
Abstract...........................................................1
Table of Contents..................................................2
1.0 Contributing Authors..........................................3
2.0 Overview.......................................................3
2.1 Terminology....................................................6
3.0 Topology.......................................................7
4.0 Configuration..................................................8
5.0 Discovery......................................................9
5.1 CE discovery...................................................9
6.0 Pseudowire Creation............................................9
6.1 Receive Unicast Multipoint-to-point Pseudowire.................9
6.2 Receive Multicast Multipoint-to-point Pseudowire..............10
6.3 Send Multicast Replication tree...............................10
7.0 Signaling.....................................................11
7.1 IPLS PW Signaling.............................................11
7.2 Signaling Advertisement Processing............................13
7.3 IANA Considerations for LDP Status Code.......................13
8.0 Forwarding....................................................13
8.1 Non-IP or non-ARP traffic.....................................14
8.2 Unicast IP Traffic............................................14
8.3 Broadcasts and Multicast IP Traffic...........................14
8.4 ARP Traffic...................................................14
8.5 Encapsulation.................................................15
9.0 Attaching to IPLS via ATM or FR.............................15
10.0 VPLS vs IPLS.................................................16
11.0 IP Protocols.................................................16
12.0 Dual Homing with IPLS........................................17
13.0 Proxy ARP function...........................................17
13.1 ARP Proxy - Responder........................................17
13.2 ARP Proxy - Generator........................................18
14.0 Acknowledgements.............................................18
15.0 Security Considerations......................................18
15.1 Control plane security.......................................18
15.2 Data plane security..........................................19
16.0 References...................................................19
16.1 Normative References.........................................19
16.2 Informative References.......................................20
17.0 Author's Address.............................................20
Intellectual Property Statement...................................21
1.0 Contributing Authors
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 Enterasys Networks
Vach Kompella Alcatel
Vasille Radoaca Consultant
2.0 Overview
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As emphasized in [VPLS], Ethernet has become popular as an access
technology in Metropolitan and Wide Area Networks. [VPLS] 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.
Provider Edge platforms are designed primarily to be IP routers,
rather than to be 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. This may be
fairly complex to add to the forwarding plane architecture of an IP
router. As discussed in [L2VPN-FWK], 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. The requirements for
the IPLS service are described in [L2VPN-REQTS]. 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.
In IPLS, a PE device implements multi-point LAN connectivity for IP
traffic using the following key functions:
1. CE Address Discovery: Each Provider Edge (PE) device discovers
IP/MAC address associations for the locally attached Customer
Edge (CE) devices, for each IPLS instance configured on the PE
device.
2. Pseudowire (PW) for Unicast Traffic: For each locally attached
CE device in a given IPLS instance, a PE device sets up a
pseudo-wire (PW-LSP) 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 pseudowires 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 pseudowires carry traffic only in one
direction. Further, while the pseudowire implicitly identifies
the destination CE of the traffic, it does not identify the
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source CE; packets from different source CEs bound to the same
destination CE are sent on a single pseudowire.
3. Pseudowires for Multicast Traffic: In addition, every PE
supporting a given IPLS instance will set up a special
"broadcast 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 broadcast pseudowire. PEy would then send a
copy of that packet to CEa and a copy to CEb.
The broadcast pseudowire carries Ethernet frames of
multicast/broadcast IP and ARP packets. 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.
4. Signaling: The necessary pseudowires can be set up and
maintained using the LDP-based signaling procedures described
in [PWE3-CONTROL].
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
broadcast 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 IP address and the MAC address of
the corresponding CE device.
5. ARP Packet Forwarding: ARP packets are forwarded from
attachment circuit to broadcast pseudowires in the Ethernet
frame format as described by [PWE3-ETH]. Following rules are
observed when processing ARP packets,
a. Both broadcast (request) and unicast (response) ARP
packets are sent over the broadcast pseudowire.
b. When an ARP packet is received from an attachment circuit,
the packet is copied to control plane for learning IP
and MAC address of the CE.
c. All Ethernet packets, including ARP packets, received from
broadcast pseudowire are forwarded out to all the
attachment circuits associated with the IPLS instance.
These packets are not copied to control plane.
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6. Multicast IP packet Forwarding: An IP Ethernet frame received
from an attachment circuit is replicated to other attachment
circuits and the broadcast pseudowires associated with the IPLS
instance. An IP Ethernet frame received from a broadcast
pseudowire is replicated to all the egress attachment circuits
associated with the IPLS instance.
7. Unicast IP packet Forwarding: An IP packet received from the
attachment circuit is forwarded based on the MAC DA 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 pseudowire, the packet is sent without MAC
header. If the egress interface is a local attachment circuit
the Ethernet frame is forwarded as such. An IP packet received
from the unicast pseudowire is forwarded to egress attachment
circuit with MAC header prepended. The MAC DA is derived from
the forwarding table while the MAC address of PE is used as
MAC SA.
Both VPLS [VPLS] 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 FIB of the ingress PE as
a result of MAC address learning (which occurs in the data
plane) while in IPLS MAC entries are placed in the FIB as a
result of pseudowire signaling operations (control plane).
. In VPLS, the egress PE looks up a frame's destination MAC
address to determine the egress Attachment Circuit; in IPLS,
the egress Attachment Circuit is determined entirely by the
ingress PW-label.
The following sections describe the details of the IPLS scheme.
2.1 Terminology
IPLS IP-only LAN service (a type of Virtual Private
LAN Service that is restricted to IP traffic
only).
mp2p PW Multipoint-to-Point Pseudowire. A pseudowire
that carries traffic from remote PE devices to
a PE device that signals the pseudowire. The
signaling PE device advertises the same PW-
label to all remote PE devices that 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
Attachment Circuit associated with the same
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IPLS instance) and whose root is the signaling
PE. Traffic flows from the leaves towards the
root.
Multicast PW Multicast/broadcast Pseudowire. A special kind
of mp2p PW that carries IP multicast/broadcast
traffic and all ARP frames. In the IPLS
architecture, for each IPLS instance supported
by a PE, that PE device establishes exactly one
multicast/broadcast PW. Multicast PW uses
Ethernet encapsulation.
Unicast PW Unicast Pseudowire carries IP unicast packets.
A PE creates unicast PW for each locally
attached CE. The unicast PW uses IP Layer2
transport encapsulation.
CE Customer Edge device. In this document, a CE is
any IP node (host or router) connected to the
IPLS LAN service.
Replication The collection of all multicast PWs and
Tree attachment circuits that are members of an IPLS
service instance on a given PE. When a PE
receives a multicast/broadcast packet from an
attachment circuit, the PE device sends a copy
of the packet to every broadcast pseudowire and
attachment circuit of the replication tree,
excluding the attachment circuit 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 attachment
circuits of the replication tree and never to
other PWs.
3.0 Topology
The Customer Edge (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 Provider
Edge (PE) routers are MPLS Label Edge Routers (LERs) that serve as
pseudowire endpoints.
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+----+ +----+
+ 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 GRE, L2TPv3, etc.,
could also be used to carry the pseudowires.
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.
4.0 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
Attachment Circuits is identified. Each Attachment Circuit can be
associated with only one IPLS instance. An Attachment Circuit, 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 source MAC address when IP packets are forwarded from
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a pseudowire to an Attachment Circuit. By default, a PE uses the MAC
address of the customer-facing Ethernet interface for this purpose.
5.0 Discovery
The discovery process includes:
. Remote PE discovery
. VPN (i.e., IPLS) membership discovery
. IP CE end station discovery
This draft 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
[BGP-Discovery] or other methods. However, the discovery of the CE
is an important operational step in the IPLS model and is described
below.
5.1 CE discovery
Each PE actively detects the presence of local CEs by snooping IP
and ARP frames received over the Attachment Circuits. During the
discovery phase, the PE examines each multicast/broadcast Ethernet
frame. For link-local IP frames (for example IGP
discovery/multicast/broadcast packets typically 224.0.0.x
addresses), the CE's (source) MAC address is extracted from the
Ethernet header and the (source) IP address is obtained from the IP
header. For ARP frames, the source MAC and IP address are determined
from the ARP PDU.
For each CE, the PE maintains the following tuple: <Attachment
Circuit identification info, VPN-Id, IP address, MAC address>.
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.
6.0 Pseudowire Creation
6.1 Receive Unicast Multipoint-to-point Pseudowire
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 CE's IP address and MAC address 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 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
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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
Attachment Circuit.
The unicast pseudowire uses IP Layer2 Transport encapsulation as
define in [PWE3-Control].
6.2 Receive Multicast Multipoint-to-point Pseudowire
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 pseudowire for IP multicast/broadcast
traffic and ARP packets. There is only one multicast mp2p PW per PE
for each IPLS instance and this pseudowire is used exclusively to
carry IP multicast/broadcast and ARP traffic from the remote PEs to
this PE for this IPLS instance.
Note that no special functionality is expected from this pseudowire.
We call it a "multicast pseudowire" because we use it to carry
multicast and broadcast IP and ARP traffic. The pseudowire itself
need not provide any different service than any of the unicast
pseudowires.
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 needs to replicate a copy of a frame received over
this mp2p PW onto all the attachment circuits that are associated
with the IPLS instance of the mp2p PW.
The multicast mp2p pseudowire is considered the principle pseudowire
in the bundle of mp2p pseudowires that consist of one multicast mp2p
pseudowire and a variable number of unicast mp2p pseudowires for a
given IPLS instance. In a principle 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 reasons,
multicast PW cease to exist, all the associated unicast pseudowires
in the bundle are removed.
The multicast pseudowire uses Ethernet encapsulation as defined in
[PWE3-Ethernet].
The use of pseudowires which are specially optimized for multicast
is for further study.
6.3 Send Multicast Replication tree
The PE creates a send replication tree for each IPLS instance, which
consists of the collection of all attachment circuits and all the
"multicast" pseudowires of the IPLS instance.
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Any ARP or multicast IP Ethernet frame received over an attachment
circuit is replicated to the other attachment circuits and to the
mp2p multicast pseudowire of the send replication tree. The send
replication tree deals mostly with broadcast/multicast Ethernet MAC
frames. One exception to this is unicast ARP frame, the processing
of which is described in the section 8 below.
Any Ethernet frame received over the multicast PW is replicated to
all the attachment circuits of the send replication tree of the IPLS
instance associated with the incoming PW label. One exception is
unicast ARP frame, the processing of which is described in the
section 8 below.
7.0 Signaling
[PWE3-CONTROL] uses the Label Distribution Protocol (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 as the ideal candidate for PW-FEC signaling. The use of
BGP for such purposes is for future study.
7.1 IPLS PW Signaling
An IPLS carries IP packets as payload over its unicast pseudowires
and Ethernet packet as payload over its multicast pseudowire. The
PW-type to be used for unicast pseudowire is the IP PW, defined in
[PWE3-Control] as IP Layer2 Transport. The PW-type to be used for
multicast pseudowire is the Ethernet PW as defined in [PWE3-ETH].
When processing a received PW FEC, the PE matches the PW Id with the
locally configured PW Id. If the PW type is Ethernet, the PW-FEC is
for multicast PW. If the PW type is "IP Layer2 transport", the PW
FEC is for unicast PW. For unicast PW, PE must check the presence of
IP and MAC address TLVs in the optional parameter fields of the
Label Mapping message. If these parameters are absent, a Label
Release message must be issued with a Status Code meaning "IP and/or
MAC Address of the CE is absent" [note: Status Code 0x0000002D is
pending IANA allocation], to reject the establishment of the unicast
PW with the remote PE.
The IPLS uses the Address List TLV as defined in RFC 3036 to signal
the IP and MAC address of the local CE. There are two TLVs defined
below; IP Address TLV and MAC Address TLV. Both TLVs must be
included in the optional parameter field of the Label Mapping
message when establishing the unicast IP PW.
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Encoding of the IP Address TLV is:
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 IP Address ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ CE's IP Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Length
When Address Family is IPV4, Length is equal to 6 bytes;
2 bytes for address family and 4 bytes of IP address.
Address Family
Two octet quantity containing a value from the ADDRESS FAMILY
NUMBERS from ADDRESS FAMILY NUMBERS in [RFC1700] that encodes
the addresses contained in the Addresses field.
CE's 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
Encoding of the MAC Address TLV is:
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 value 8 (2 for address family, 6 for
MAC address)
Address Family
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Two octet quantity containing a value from ADDRESS FAMILY
NUMBERS in [RFC1700] 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
7.2 Signaling Advertisement Processing
A PE should process a received [PWE3-CONTROL] advertisement with PW-
type of IP Layer2 transport for IPLS as follows,
- Verify the IPLS VPN membership by matching the VPN-Id
signaled in the AGI field or the PW-ID field with all the
VPN-Ids configured in the PE. Discard and release the PW
label if VPN-Id is not found.
- Program the Forwarding Information Base (FIB) such that when
a unicast IP packet is received from an attachment circuit
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 [PWE3-CONTROL] 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 PW-ID 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 sending a copy of a
multicast/broadcast IP Ethernet frame or ARP Ethernet frame
from the attachment circuit to this pseudowire.
7.3 IANA Considerations for LDP Status Code
This document uses new LDP status code. IANA already maintains a
registry of name "STATUS CODE NAME SPACE" defined by RFC3036. The
following value is suggested for assignment:
0x0000002D "IP and/or MAC Address of CE is absent"
8.0 Forwarding
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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 Attachment Circuit to the
PW based on the destination MAC address of the layer 2 frame (and
not based on the IP Header).
The PE identifies the FIB associated with an IPLS instance based on
the Attachment Circuit or the PW label. When a frame is received
from an Attachment Circuit, 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.
8.3 Broadcasts and Multicast IP Traffic
When the destination MAC address is either a broadcast or multicast,
a copy of the frame is sent to the control plane for CE discovery
purposes (see section 5.1). It is suggested that frames sent to the
control plane are applied stricter rate limiting criteria to avoid
overwhelming the control plane under adverse conditions such as a
Denial Of Service attack. The service provider should also provide
a configurable limit to prevent 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 Attachment
Circuit, the PE replicates it onto the Send Multicast Replication
Tree (See section 6.3). When a multicast/broadcast IP Ethernet frame
is received from a pseudowire, the PE forwards a copy of the frame
to all attachment circuits associated with the IPLS VPN instance
involved. Note that multicast PW uses Ethernet encapsulation and
hence does not require additional header manipulations.
8.4 ARP Traffic
When a broadcast ARP frame is received over the attachment circuit,
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 6.3), which results in a copy that
will be delivered to all the remote PEs on the broadcast PW and
other local CEs through the egress attachment circuits.
When a broadcast ARP frame is received over the broadcast PW, a copy
of the Ethernet ARP frame is sent to all the attachment circuits
associated with the IPLS instance.
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When a unicast ARP Ethernet frame is received over the attachment
circuit, a copy of the frame is sent to the control plane for CE
discovery purposes. The PE may optionally do a MAC DA lookup in the
forwarding table and send the ARP frame to a specific egress
interface (attachment circuit or broadcast PW to a remote PE) or
replicate the frame onto the Send Multicast Replication Tree (see
section 6.3).
When a unicast ARP Ethernet frame is received over the broadcast PW,
PE may optionally do MAC DA lookup in the forwarding table and
forward it to an attachment circuit where the CE is located. If the
CE is not accessible through any local attachment circuit, the frame
is dropped. Conversely, the PE may simply forward the frame to all
the attachment circuits associated with that IPLS instance without
any lookup in the forwarding table.
8.5 Encapsulation
The Ethernet MAC header of a unicast IP packet received from an
Attachment Circuit is stripped before forwarding the frame to the
unicast pseudowire. However, the MAC header is retained for the
following cases,
. when a frame is unicast or broadcast IP packet that is directed
to one or more local Attachment Circuit(s).
. when a frame is a broadcast IP packet
. when a frame is an ARP packet
An IP frame received over a unicast pseudowire is prepended with a
MAC header before transmitting it on the appropriate Attachment
Circuit(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 which has been specially configured on the PE for
this use.
- The Ethernet Type field is 0x0800
- The frame may be IEEE802.1Q tagged based on the VLAN
information associated with the Attachment Circuit.
An FCS is appended to the frame.
9.0 Attaching to IPLS via ATM or FR
In addition to (i) an Ethernet port and a (ii) combination of
Ethernet port and a VLAN ID, an Attachment Circuit to IPLS may also
be (iii) an ATM or FR 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
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propagated from pseudowire to a ATM or FR VC the PE prepends the
Ethernet frame with the appropriate bridged encapsulation header as
defined in [RFC 2684] and [RFC 2427] respectively. Operation of an
IPLS over ATM/FR VC is exactly as described above, with the
exception that the attachment circuit is then identified via the ATM
VCI/VPI or Frame Relay DLCI (instead of via a local Ethernet port
ID), or a combination of those with a VLAN ID.
10.0 VPLS vs IPLS
The VPLS approach proposed in [VPLS] provides VPN services for IP as
well as other protocols. The IPLS approach described in this draft
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:
- 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.
- Encapsulation is more efficient (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., 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.
11.0 IP Protocols
The solution described in this document offers IPLS service for IPv4
traffic only. For this reason, the MAC Header is not carried over
the unicast pseudowire. It is reconstructed by the PE when receiving
a packet from a unicast pseudowire and the Ethertype 0x0800 is used
in the MAC Header since IPv4 is assumed.
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However, this solution may be extended to carry other types of
important traffic such as ISIS and IPv6 which are not encapsulated
in Ethernet with the use of Ethertype 0x0800. In order to permit the
propagation of such packets correctly, one may create a separate set
of pseudowires, or pass protocol information in the "control word"
of a "multiprotocol" pseudowire, or encapsulate the Ethernet MAC
Header in the pseudowire. The selection of appropriate
multiplexing/demultiplexing scheme is the subject of future study.
The current document focuses on IPLS service for IPv4 traffic.
12.0 Dual Homing with IPLS
As stated in previous sections, IPLS prohibits connection of a
common LAN or VLAN to more than one PE. Alternatively 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.
13.0 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 draft 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 [RFC 2547bis]).
The termination and controlled propagation of ARP frames is still a
desirable option for security, DoS and other purposes. For these
reasons, we re-introduce the ARP Proxy function in this revision as
an optional feature. Following sections describe this option.
13.1 ARP Proxy - Responder
As a local configuration, a PE can enable ARP Proxy responder
function. In this mode, local PE responds to ARP requests received
over the AC via learnt 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 nutshell, when this feature is
enabled, ARP requests are not propagated to remote PE routers that
are members of the same IPLS instance.
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13.2 ARP Proxy - Generator
As a local configuration, a PE can enable ARP Proxy generator
function. In this mode, the PE generates ARP request for each IP and
MAC address associations received from the remote PEs. The IP and
MAC address of the remote CE 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 ARP
Proxy Responder function. An example of a back-to-back IPLS is a
configuration where PE-1 (ASBR) in an IPLS cloud in one Autonomous
System (say, AS-1) is connected via an Attachment Circuit 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 [RFC 2547bis] 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
generate 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
14.0 Acknowledgements
Authors would like to thank Alp Dibirdi from Alcatel and other L2VPN
working group members for their valuable comments.
15.0 Security Considerations
A more comprehensive description of the security issues involved in
L2VPNs are covered in [VPN-SEC]. Most of the security issues can be
avoided through implementation of appropriate guards. The security
aspect of this solution is addressed for two planes; control plane
and data plane.
15.1 Control plane security
The control plane security pertains to establishing the LDP
connection, pseudo-wire establishment and the distribution of IP and
MAC address of the CEs. 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 using MD5 authentication. The pseudo-wire establishments
between two secure LDP peers do not pose security issue but
mis-wiring could occur due to configuration error. Some checks,
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such as, proper pseudo-wire type and other pseudo-wire options may
prevent mis-wiring due to configuration errors.
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 is physically secured. If this is a concern, the PE must be
configured with CE's IP and MAC address statically. During each ARP
frame processing, PE must verify the received information against
the configuration values before accepting any traffic into IPLS
network. 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 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. Although, this may cause
interruption to already connected subscriber, it provides the
operator and the subscriber an opportunity to investigate the
spoofing.
The IPLS learns and distributes CE reachability through the control
plane. This provides greater control over CE topology distribution
through application of local policies.
15.2 Data plane security
The data traffic between CE and PE is not encrypted and it is
possible that in an insecure environment, a malicious user may tap
into the CE to PE connection and generate traffic using the spoofed
destination MAC address on the Ethernet Attachment Circuit. In
order to avoid such hijacking, 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 PW only when
authenticity is verified. When spoofing is detected, PE must severe
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.
16.0 References
16.1 Normative References
[ARP] RFC 826, STD 37, D. Plummer, "An Ethernet Address Resolution
Protocol: Or Converting Network Protocol Addresses to 48.bit
Ethernet Addresses for Transmission on Ethernet Hardware".
[INVARP] RFC 2390, T. Bradley et al., "Inverse Address Resolution
Protocol".
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[PWE3-Control] L. Martini et al., "Pseudowire Setup and Maintenance
using LDP", February 2005, work in progress.
[PWE3-IANA] L. Martini et al,. "IANA Allocations for pseudo Wire
Edge to Edge Emulation (PWE3)", February 2005, work in progress.
[VPLS] Lasserre et al, "Virtual Private LAN Service over MPLS",
draft-ietf-l2vpn-vpls-ldp-06.txt, August 2005 (work in progress).
[RFC3036] "LDP Specification", L. Andersson, et al., RFC 3036,
January 2001.
16.2 Informative References
[L2VPN-FRM] L. Andersson et al., "Framework for L2VPN", December
2004, work in progress.
[PROXY-ARP] RFC 925, J. Postel, "Multi-LAN Address Resolution".
[L2VPN-REQ] Augustyn, W. et.al "Service Requirements for Layer 2
Provider Provisioned Virtual Private Networks", draft-ietf-l2vpn-
requirements-04.txt, Work in Progress, Internet Draft, August 2005.
[BGP-Discovery] "Using BGP as an Auto-Discovery Mechanism for
Provider Provisioned VPNs", Ould-Brahim et al., draft-ietf-l3vpn-
bgpvpn-auto-04.txt, May 2004, (work in progress).
[RFC-1112] Deering, S., "Host Extensions for IP Multicasting", RFC
1112, August, 1989.
[RFC 2547bis] "BGP/MPLS VPNs", draft-ietf-l3vpn-rfc2547bis-03.txt,
Work in Progress, October 2004.
[RFC 2684]
17.0 Author's Address
Himanshu Shah
Ciena Corp
35 Nagog Park,
Acton, MA 01720
Email: hshah@ciena.com
K.Arvind
Enterasys Networks
50 Minuteman Rd, Suite 100
Andover, MA 01810
Email: karvind@enterasys.com
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Eric Rosen
Cisco Systems
300 Apollo Drive,
Chelmsford, MA 01824
Email: erosen@cisco.com
Giles Heron
Tellabs
Abbey Place
24-28 Easton Street
High Wycombe
Bucks
HP11 1NT
UK
Email: giles.heron@tellabs.com
Francois Le Faucheur
Cisco Systems, Inc.
Village d'Entreprise Green Side - Batiment T3
400, Avenue de Roumanille
06410 Biot-Sophia Antipolis, France
Email: flefauch@cisco.com
Vasile Radoaca
Email: vasile@westridgenetworks.com
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