draft-ietf-l2vpn-arp-mediation-01.txt   draft-ietf-l2vpn-arp-mediation-02.txt 
L2VPN Working Group H. Shah Ciena L2VPN Working Group H. Shah Ciena Corp
Internet Draft E. Rosen Cisco Systems Internet Draft E. Rosen Cisco Systems
W. Augustyn consultant G. Heron Tellabs
April 2005 G. Heron Tellabs July 2005 V. Kompella Alcatel
Expires: September 2005 T. Smith Laurel Networks Expires: January 2006
A. Moranganti Big Band Networks
S. Khandekar Alcatel
V. Kompella Alcatel
A. Malis Tellabs
S. Wright Bell South
V. Radoaca Westridge Networks
A. Vishwanathan Force10 Networks
ARP Mediation for IP Interworking of Layer 2 VPN ARP Mediation for IP Interworking of Layer 2 VPN
draft-ietf-l2vpn-arp-mediation-01.txt draft-ietf-l2vpn-arp-mediation-02.txt
Status of this memo Status of this memo
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aware will be disclosed, in accordance with RFC 3668. will be disclosed, in accordance with RFC 3668.
This document is an Internet-Draft and is in full conformance with
Sections 5 and 6 of RFC3667 and Section 5 of RFC3668.
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Abstract Abstract
The VPWS service [L2VPN Framework] provides point-to-point The VPWS service [L2VPN Framework] provides point-to-point
connections between pairs of Customer Edge (CE) devices. It does connections between pairs of Customer Edge (CE) devices. It does
so by binding two Attachment Circuits (each connecting a CE device so by binding two Attachment Circuits (each connecting a CE device
with a Provider Edge, PE, device) to a Pseudowire (connecting the with a Provider Edge, PE, device) to a pseudo-wire (connecting the
two PEs). In general, the Attachment Circuits must be of the same two PEs). In general, the Attachment Circuits must be of the same
technology (e.g., both ethernet, both ATM), and the Pseudowire must technology (e.g., both Ethernet, both ATM), and the pseudo-wire
carry the frames of that technology. However, if it is known that must carry the frames of that technology. However, if it is known
the frames' payload consists solely of IP datagrams, it is possible that the frames' payload consists solely of IP datagrams, it is
to provide a point-to-point connection in which the Pseudowire possible to provide a point-to-point connection in which the
draft-ietf-l2vpn-arp-mediation-01.txt pseudo-wire connects Attachment Circuits of different technologies.
This requires the PEs to perform a function known as "ARP
Mediation". ARP Mediation refers to the process of resolving Layer
2 addresses when different resolution protocols are used on either
draft-ietf-l2vpn-arp-mediation-02.txt
connects Attachment Circuits of different technologies. This Attachment Circuit. The methods described in this document are
requires the PEs to perform a function known as "ARP Mediation". applicable even when the CEs run a routing protocol between them,
ARP Mediation refers to the process of resolving Layer 2 addresses as long as the routing protocol runs over IP. In particular, the
when different resolution protocols are used on either Attachment applicability of ARP mediation to ISIS is not addressed as IS-IS
Circuit. The methods described in this document are applicable even PDUs are not sent over IP.
when the CEs run a routing protocol between them, as long as the
routing protocol runs over IP. In particular, the applicability of
ARP mediation to ISIS is not addressed.
Table of Contents Table of Contents
1 .0 Introduction................................................2 1 .0 Contributing Authors........................................2
2 .0 ARP Mediation (AM) function.................................3 2 .0 Introduction................................................3
3 .0 IP Layer 2 Interworking Circuits............................4 3 .0 ARP Mediation (AM) function.................................4
4 .0 Discovery of IP Addresses of Locally Attached CE Device.....4 4 .0 IP Layer 2 Interworking Circuit.............................4
4.1 Monitoring Local Traffic.....................................4 5 .0 Discovery of IP Addresses of Locally Attached CE Device.....4
4.2 CE Devices Using ARP.........................................4 5.1 Monitoring Local Traffic.....................................5
4.3 CE Devices Using Inverse ARP.................................5 5.2 CE Devices Using ARP.........................................5
4.4 CE Devices Using PPP.........................................6 5.3 CE Devices Using Inverse ARP.................................6
4.5 Router Discovery method......................................6 5.4 CE Devices Using PPP.........................................7
5 .0 CE IP Address Signaling between PEs.........................7 5.5 Router Discovery method......................................7
5.1 When to Signal a CEs IP Address.............................7 6 .0 CE IP Address Signaling between PEs.........................8
5.2 LDP Based Distribution.......................................7 6.1 When to Signal a CE's IP Address.............................8
5.3 Out-of-band Distribution Configuration.......................8 6.2 LDP Based Distribution.......................................8
6 .0 How a CE Learns the Remote CE's IP address..................8 6.3 Out-of-band Distribution Configuration.......................9
6.1 CE Devices Using ARP.........................................8 7 .0 How a CE Learns the Remote CE's IP address..................9
6.2 CE Devices Using Inverse ARP.................................9 7.1 CE Devices Using ARP.........................................9
6.3 CE Devices Using PPP.........................................9 7.2 CE Devices Using Inverse ARP................................10
7 .0 Use of IGPs with IP L2 Interworking L2VPNs..................9 7.3 CE Devices Using PPP........................................10
7.1 OSPF.........................................................9 8 .0 Use of IGPs with IP L2 Interworking L2VPNs.................10
7.2 RIP.........................................................10 8.1 OSPF........................................................10
8 .0 Security Considerations....................................10 8.2 RIP.........................................................11
8.1 Control plane security......................................10 9 .0 Security Considerations....................................11
8.2 Data plane security.........................................11 9.1 Control plane security......................................11
9 .0 Acknowledgements...........................................11 9.2 Data plane security.........................................12
10 .0 References................................................11 10 .0 Acknowledgements..........................................12
10.1 Normative References.......................................11 11 .0 References................................................12
10.2 Informative References.....................................11 11.1 Normative References.......................................12
11 .0 Authors' Addresses........................................12 11.2 Informative References.....................................13
12 .0 Authors' Addresses........................................13
1.0 Introduction 1.0 Contributing Authors
This document is the combined effort of the following individuals
and many others who have carefully reviewed the document and
provided the technical clarifications.
W. Augustyn consultant
Shah, et. al. Expires January 2006 2
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T. Smith Laurel Networks
A. Moranganti Big Band Networks
S. Khandekar Alcatel
A. Malis Tellabs
S. Wright Bell South
V. Radoaca Westridge Networks
A. Vishwanathan Force10 Networks
2.0 Introduction
Layer 2 Virtual Private Networks (L2VPN) are constructed over a Layer 2 Virtual Private Networks (L2VPN) are constructed over a
Service Provider IP backbone but are presented to the Customer Edge Service Provider IP backbone but are presented to the Customer Edge
(CE) devices as Layer 2 networks. In theory, L2VPNs can carry any (CE) devices as Layer 2 networks. In theory, L2VPNs can carry any
Layer 3 protocol, but in many cases, the Layer 3 protocol is IP. Layer 3 protocol, but in many cases, the Layer 3 protocol is IP.
Thus it makes sense to consider procedures that are optimized for Thus it makes sense to consider procedures that are optimized for
IP. IP.
In a typical implementation, illustrated in the diagram below, the In a typical implementation, illustrated in the diagram below, the
CE devices are connected to the Provider Edge (PE) devices via CE devices are connected to the Provider Edge (PE) devices via
Attachment Circuits (AC). The ACs are Layer 2 links. In a pure Attachment Circuits (AC). The ACs are Layer 2 links. In a pure
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L2VPN, if traffic sent from CE1 via AC1 reaches CE2 via AC2, both L2VPN, if traffic sent from CE1 via AC1 reaches CE2 via AC2, both
ACs would have to be of the same type (i.e., both Ethernet, both ACs would have to be of the same type (i.e., both Ethernet, both
FR, etc.). However, if it is known that only IP traffic will be FR, etc.). However, if it is known that only IP traffic will be
carried, the ACs can be of different technologies, provided that carried, the ACs can be of different technologies, provided that
the PEs provide the appropriate procedures to allow the proper the PEs provide the appropriate procedures to allow the proper
transfer of IP packets. transfer of IP packets.
+-----+ +-----+
+--------------------| CE3 | +--------------------| CE3 |
| +-----+ | +-----+
skipping to change at line 141 skipping to change at line 160
........................ ........................
A CE, which is connected via a given type of AC, may use an IP A CE, which is connected via a given type of AC, may use an IP
Address Resolution procedure that is specific to that type of AC. Address Resolution procedure that is specific to that type of AC.
For example, an Ethernet-attached CE would use ARP, a FR-attached For example, an Ethernet-attached CE would use ARP, a FR-attached
CE might use Inverse ARP. If we are to allow the two CEs to have a CE might use Inverse ARP. If we are to allow the two CEs to have a
Layer 2 connection between them, even though each AC uses a Layer 2 connection between them, even though each AC uses a
different Layer 2 technology, the PEs must intercept and "mediate" different Layer 2 technology, the PEs must intercept and "mediate"
the Layer 2 specific address resolution procedures. the Layer 2 specific address resolution procedures.
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In this draft, we specify the procedures, which the PEs must In this draft, we specify the procedures, which the PEs must
implement in order to mediate the IP address resolution mechanism. implement in order to mediate the IP address resolution mechanism.
We call these procedures "ARP Mediation". We call these procedures "ARP Mediation".
Consider a Virtual Private Wire Service (VPWS) constructed between Consider a Virtual Private Wire Service (VPWS) constructed between
CE1 and CE2 in the diagram above. If AC1 and AC2 are of different CE1 and CE2 in the diagram above. If AC1 and AC2 are of different
technologies, e.g. AC1 is Ethernet and AC2 is Frame Relay (FR), technologies, e.g. AC1 is Ethernet and AC2 is Frame Relay (FR),
then ARP requests coming from CE1 cannot be passed transparently to then ARP requests coming from CE1 cannot be passed transparently to
CE2. PE1 must interpret the meaning of the ARP requests and CE2. PE1 must interpret the meaning of the ARP requests and
mediate the necessary information with PE2 before responding. mediate the necessary information with PE2 before responding.
2.0 ARP Mediation (AM) function 3.0 ARP Mediation (AM) function
The ARP Mediation (AM) function is an element of a PE node that The ARP Mediation (AM) function is an element of a PE node that
deals with the IP address resolution for CE devices connected via deals with the IP address resolution for CE devices connected via
an L2VPN. By placing this function in the PE node, ARP Mediation is an L2VPN. By placing this function in the PE node, ARP Mediation is
transparent to the CE devices. transparent to the CE devices.
For a given point-to-point connection between a pair of CEs, a PE For a given point-to-point connection between a pair of CEs, a PE
must perform three logical steps as part of the ARP Mediation must perform three logical steps as part of the ARP Mediation
procedure: procedure:
1. Discover the IP addresses of the locally attached CE device 1. Discover the IP addresses of the locally attached CE device
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2. Distribute those IP Addresses to the remote PE 2. Distribute those IP Addresses to the remote PE
3. Notify the locally attached CE of the remote CE's IP address. 3. Notify the locally attached CE of the remote CE's IP address.
This information is gathered using the mechanisms described in the This information is gathered using the mechanisms described in the
following sections. following sections.
3.0 IP Layer 2 Interworking Circuits 4.0 IP Layer 2 Interworking Circuit
The IP Layer 2 Interworking Circuits refer to Pseudowires that The IP Layer 2 interworking Circuit refers to interconnection of
carry IP datagrams as payload. The ingress PE removes the data the Attachment Circuit with the IP Layer 2 Transport pseudo-wire
link header of its local Attachment Circuit and transmits the that carries IP datagrams as the payload. The ingress PE removes
payload (an IP frame) over the Pseudowire with or without the the data link header of its local Attachment Circuit and transmits
optional control word. The egress PE encapsulates the IP packet the payload (an IP frame) over the pseudo-wire with or without the
with the data link header used on its local Attachment Circuit. optional control word. In some cases, multiple data link headers
may exist, such as bridged PDU on ATM AC. In this case, ATM header
as well as the Ethernet header is removed to expose the IP frame.
The egress PE encapsulates the IP packet with the data link header
used on its local Attachment Circuit.
The IP Pseudowire encapsulation is described in [PWE3-IANA]. The encapsulation for the IP Layer 2 Transport pseudo-wire is
described in [PWE3-Control].
4.0 Discovery of IP Addresses of Locally Attached CE Device 5.0 Discovery of IP Addresses of Locally Attached CE Device
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An IP Layer 2 Interworking Circuit enters monitoring state An IP Layer 2 Interworking Circuit enters monitoring state
immediately after the configuration. During this state it performs immediately after the configuration is enabled. During this
two functions. state it performs two functions.
. Discovery of locally attached CE IP device . Discovery of locally attached CE IP device
. Establishment of the PW . Establishment of the PW
The establishment of the PW occurs independently from local CE IP The establishment of the PW occurs independently from local CE IP
address discovery. During the period when the (bi-directional) PW address discovery. During the period when the PW has been
has been established but local CE IP device has not been detected, established but local CE IP device has not been detected, only
only datagrams inside of broadcast/multicast frames are propagated; broadcast/multicast IP frames are propagated between the Attachment
IP datagrams inside unicast frames are dropped. The IP datagrams Circuit and pseudo-wire; unicast IP datagrams are dropped. On
from unicast frames flow only when IP end systems on both Ethernet AC, MAC Destination Address is used to classify
Attachment Circuits have been discovered, notified and proxy unicast/multicast packets. However, on non-Ethernet ACs, IP
functions have completed. destination address is used to classify unicast/multicast packets.
The unicast IP frames are propagated between AC and pseudo-wire
only when CE IP devices on both Attachment Circuits have been
discovered, notified and proxy functions have completed.
4.1 Monitoring Local Traffic 5.1 Monitoring Local Traffic
The PE devices may learn the IP addresses of the locally attached The PE devices may learn the IP addresses of the locally attached
CEs from any IP traffic, such as link local multicast packets CEs from any IP traffic, such as link local multicast packets
(e.g., destined to 224.0.0.x), and are not restricted to the (e.g., destined to 224.0.0.x), and are not restricted to the
operations below. operations below.
4.2 CE Devices Using ARP 5.2 CE Devices Using ARP
If a CE device uses ARP to determine the MAC address to IP address If a CE device uses ARP to determine the MAC address to IP address
binding of its neighbor, the PE processes the ARP requests to learn binding of its neighbor, the PE processes the ARP requests to learn
the IP address of local CE for the stated locally attached circuit. the IP address of local CE for the stated locally attached circuit.
If we observe the strict topology restriction whereby only one IP If we observe the strict topology restriction whereby only one IP
router CE can exist for a given attachment circuit then the PE can router CE can exist for a given AC then the PE can assume that ARP
request received is from the candidate IP CE and can learn the IP
Shah, et. al. Expires September 2005 4 to MAC address binding of the local CE.
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assume that ARP request received is from the candidate IP CE and
can learn the IP to MAC address binding of the local CE.
However, if this topology restriction is relaxed, the PE can learn However, if this topology restriction is relaxed, the PE can learn
the MAC address to IP address binding of the local CE but can not the MAC address to IP address binding of the local CE but can not
assume that this CE (possibly amongst many) is the candidate IP assume that this CE (possibly amongst many) is the candidate IP
device that is to be interworked with the remote attachment device that is to be interworked with the remote attachment
circuit. In this case, the PE may select the local CE device using circuit. In this case, the PE may select the local CE device using
following criteria. following criteria.
. Wait to learn the IP address of the remote CE (through PW . Wait to learn the IP address of the remote CE (through PW
signaling) and then select the local CE that is sending the signaling) and then select the local CE that is sending the
ARP request for the remote CEs IP address. ARP request for the remote CE's IP address.
. Augment cross checking with the local IP address learned . Augment cross checking with the local IP address learned
through listening of link local multicast packets (as per through listening of link local multicast packets (as per
section 4.1 above) section 5.1 above)
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. Augment cross checking with the local IP address learned . Augment cross checking with the local IP address learned
through the Router Discovery protocol (as described below in through the Router Discovery protocol (as described below in
section 4.5). section 5.5).
. There is still a possibility that the local PE may not receive . There is still a possibility that the local PE may not receive
an IP address advertisement from the remote PE and there may an IP address advertisement from the remote PE and there may
exist multiple local IP routers that attempt to 'connect' to exist multiple local IP routers that attempt to 'connect' to
remote CEs. In this situation, the local PE may use some other remote CEs. In this situation, the local PE may use some other
criteria to select one IP device from many (such as the first criteria to select one IP device from many (such as "the first
ARP received), or an operator may configure the IP address of ARP received"), or an operator may configure the IP address of
local CE. Note that the operator does not have to configure local CE. Note that the operator does not have to configure
the IP address of the remote CE (as that would be learned the IP address of the remote CE (as that would be learned
through Pseudowire signaling). through pseudo-wire signaling).
Once the local CE has been discovered for the given Attachment Once the local CE has been discovered for the given Attachment
Circuit, the local PE responds to subsequent ARP requests from that Circuit, the local PE responds to subsequent ARP requests from that
device with its own MAC address. The local PE signals the CEs IP device with its own MAC address when the destination IP address in
address to the remote PE and may initiate an unsolicited ARP the ARP request is found to match with the remote CE's IP address.
response to notify local CE MAC address to IP address binding of The local PE signals the CE's IP address to the remote PE and may
the remote CE. Once this is completed, unicast traffic between two initiate an unsolicited ARP response to notify local CE MAC address
CEs can start flowing. to IP address binding of the remote CE. Once the ARP mediation
function is completed, unicast IP frames are propagated between the
AC and the established PW.
The PE may periodically generate ARP request messages to the CE's The PE may periodically generate ARP request messages to the CE's
IP address as a means of verifying the continued existence of the IP address as a means of verifying the continued existence of the
address and its binding to the MAC address. The absence of a address and its binding to the MAC address. The absence of a
response from the CE device for a given number of retries could be response from the CE device for a given number of retries could be
used as cause for withdrawal of the IP address advertisement to the used as a cause for withdrawal of the IP address advertisement to
remote PE. The local PE would then enter into the address the remote PE. The local PE would then enter into the address
resolution phase to rediscover the attached CE's IP address. Note resolution phase to rediscover the attached CE's IP address. Note
that this "heartbeat" scheme is needed only for broadcast links, as that this "heartbeat" scheme is needed only for broadcast links
the loss of a CE may otherwise be undetectable. (such as Ethernet AC), as the loss of a CE may otherwise be
undetectable.
4.3 CE Devices Using Inverse ARP
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If a CE device uses Inverse ARP to determine the IP address of its If a CE device uses Inverse ARP to determine the IP address of its
neighbor, the attached PE processes the Inverse ARP request for neighbor, the attached PE processes the Inverse ARP request for
stated circuit and responds with an Inverse ARP reply containing stated circuit and responds with an Inverse ARP reply containing
the remote CE's IP address, if the address is known. If the PE does the remote CE's IP address, if the address is known. If the PE does
not yet have the remote CE's IP address, it does not respond, but not yet have the remote CE's IP address, it does not respond, but
notes the IP address of the local CE and the circuit information. notes the IP address of the local CE and the circuit information.
Subsequently, when the IP address of the remote CE becomes Subsequently, when the IP address of the remote CE becomes
available, the PE may initiate the Inverse ARP request as a means available, the PE may initiate the Inverse ARP request as a means
to notify the local CE about the IP address of the remote CE. to notify the local CE about the IP address of the remote CE.
This is a typical operation for Frame Relay and ATM attachment This is a typical operation for Frame Relay and ATM attachment
circuits. When the CE does not use Inverse ARP, PE could still circuits. When the CE does not use Inverse ARP, PE could still
discover the local CEs IP address as described in section 4.1 and
4.5.
4.4 CE Devices Using PPP Shah, et. al. Expires January 2006 6
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discover the local CE's IP address as described in section 5.1 and
5.5.
5.4 CE Devices Using PPP
The IP Control Protocol (IPCP) describes a procedure to establish
and configure IP on a point-to-point connection, including the
negotiation of IP addresses. When using IP (Routed) mode L2VPN
interworking, PPP negotiation is not performed end-to-end between
CE devices. In this case, PPP negotiation takes place between the
CE device and its local PE device (on the PPP attachment circuit).
The PE device performs proxy PPP negotiation, and informs the local
CE device of the IP address of the remote CE device during IPCP
negotiation using the IP-Address option [0x03].
When a PPP link becomes operational after the LCP negotiations, the When a PPP link becomes operational after the LCP negotiations, the
local PE performs following actions local PE MAY perform following actions
. If the local PE does not know the IP address of the local CE,
it generates a configure-request without the configure IP
address TLV. The response from CE is accepted as IP address of
the local CE.
. If PE knows the IP address of the remote CE, it sends an IPCP
configure-request with the IP address of the remote CE in the
configure IP address TLV
. If the local PE receives an IPCP configure-request without the
configure IP address TLV, and if it knows the IP address of
the remote CE, it responds with configure NAK with the
configure IP address TLV set with remote CEs IP address.
However, if PE does not know the remote CEs IP address yet,
it responds with a configure NAK.
. If the local PE does not know the IP address of the remote CE,
it sends an IPCP configure-request with IP address as zero.
The response from CE is recorded and used to validate the
incoming remote CEs IP address via PW signaling.
The local PE must deny configurations such as header compression . The PE learns the IP address of the local CE from the Configure-
and encryptions in the NCP packets with such options. Request received with the IP-Address option (0x03). The PE
verifies that the IP address present in the IP-Address option is
non-zero. If the IP address is zero, PE responds with Configure-
Reject (as this is a request from CE to assign him an IP
address). Also, the Configure-Reject copies the IP-Address option
with null value to instruct the CE to not include that option in
new Configure-Request. If the IP address is non-zero, PE responds
with Configure-Ack.
. If the PE receives Configure-Request without the IP-Address
option, PE responds with Configure-Ack. In this case, PE would
not learn the IP address of the local CE using IPCP and hence
would rely on other means as described above (such as link-local
broadcast from OSPF hello). Note that in order to employ other
learning mechanisms, IPCP connection must be open.
. If the PE does not know the IP address of the remote CE, it
generates a Configure-Request without the IP-Address option.
. If the PE knows the IP address of the remote CE, it sends an IPCP
Configure-Request with the IP-Address option containing the
remote CE's IP address.
4.5 Router Discovery method The IPCP IP-Address option MAY be negotiated between the PE and the
local CE device. Configuration of other IPCP option MAY be
rejected. Other NCPs, with the exception of the Compression Control
Protocol (CCP) and Encryption Control Protocol (ECP), MUST be
rejected. The PE device MAY reject configuration of the CCP and
ECP.
5.5 Router Discovery method
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In order to learn the IP address of the CE device for a given In order to learn the IP address of the CE device for a given
Attachment Circuit, the PE device may execute Router Discovery Attachment Circuit, the PE device may execute Router Discovery
Protocol [RFC 1256] whereby a Router Discovery Request (ICMP Protocol [RFC 1256] whereby a Router Discovery Request (ICMP -
router solicitation) message is sent using a source IP address of router solicitation) message is sent using a source IP address of
zero. The IP address of the CE device is extracted from the Router zero. The IP address of the CE device is extracted from the Router
Discovery Response (ICMP router advertisement) message from the Discovery Response (ICMP - router advertisement) message from the
CE. CE. It is possible that the response contains more than one router
addresses with the same preference level; in which case, some
Shah, et. al. Expires September 2005 6 heuristics (such as first on the list) is necessary.
draft-ietf-l2vpn-arp-mediation-01.txt
The use of the Router Discovery method by the PE is optional. The use of the Router Discovery method by the PE is optional.
5.0 CE IP Address Signaling between PEs 6.0 CE IP Address Signaling between PEs
5.1 When to Signal a CEs IP Address 6.1 When to Signal a CE's IP Address
A PE device advertises the IP address of the attached CE only when A PE device advertises the IP address of the attached CE only when
the encapsulation type of the Pseudowire is IP L2 interworking . It the encapsulation type of the pseudo-wire is IP Layer2 Transport
is quite possible that the IP address of a CE device is not (the value 0x0000B, as defined in [PWE3-IANA]). It is quite
available at the time the PW labels are signaled. For example, in possible that the IP address of a CE device is not available at the
Frame Relay the CE device sends an inverse ARP request only when time the PW labels are signaled. For example, in Frame Relay the CE
the DLCI is active; if the PE signals the DLCI to be active only device sends an inverse ARP request only when the DLCI is active;
when it has received the IP address along with the PW FEC from the if the PE signals the DLCI to be active only when it has received
remote PE, a chicken and egg situation arises. In order to avoid the IP address along with the PW FEC from the remote PE, a chicken
such problems, the PE must be prepared to advertise the PW FEC and egg situation arises. In order to avoid such problems, the PE
before the CE's IP address is known. When the IP address of the CE must be prepared to advertise the PW FEC before the CE's IP address
device does become available, the PE re-advertises the PW FEC along is known. When the IP address of the CE device does become
with the IP. available, the PE re-advertises the PW FEC along with the CE's IP
address.
Similarly, if the PE detects a CE's IP address is no longer Similarly, if the PE detects a CE's IP address is no longer valid
valid(by methods described above), the PE must re-advertise the PW (by methods described above), the PE must re-advertise the PW FEC
FEC with null IP address to denote the withdrawal of the CE's IP with null IP address to denote the withdrawal of the CE's IP
address. The receiving PE then waits for notification of the remote address. The receiving PE then waits for notification of the remote
IP address. During this period, propagation of unicast IP traffic IP address. During this period, propagation of unicast IP traffic
is suspended, but multicast IP traffic can continue to flow. is suspended, but multicast IP traffic can continue to flow between
the AC and the pseudo-wire.
If two CE devices are locally attached to the PE where one CE is If two CE devices are locally attached to the PE where one CE is
connected to an Ethernet port and the other to a Frame Relay port, connected to an Ethernet port and the other to a Frame Relay port,
for example, the IP addresses are learned in the same manner for example, the IP addresses are learned in the same manner
described above. However, since the CE devices are local, the described above. However, since the CE devices are local, the
distribution of IP addresses for these CE devices is a local step. distribution of IP addresses for these CE devices is a local step.
5.2 LDP Based Distribution 6.2 LDP Based Distribution
The [PWE3-CONTROL] uses Label Distribution Protocol (LDP) transport The [PWE3-Control] uses Label Distribution Protocol (LDP) transport
to exchange PW FEC in the Label Mapping message in the Downstream to exchange PW FEC in the Label Mapping message in the Downstream
Unsolicited (DU) mode. The PW FEC comes in two flavors; PWid and Unsolicited (DU) mode. The PW FEC comes in two flavors; PWid and
Generalized ID FEC elements and have some common fields between
them. The discussions below refer to these common fields for IP L2
Interworking Circuits.
The IP L2 Interworking uses an IP datagram as payload over the Shah, et. al. Expires January 2006 8
Pseudowire[PWE3-IANA]. draft-ietf-l2vpn-arp-mediation-02.txt
In addition, this document defines an IP address TLV that must be Generalized ID FEC elements and has some common fields between
included as an optional parameter in the Label Mapping message them. The discussions below refer to these common fields for IP L2
when advertising the PW FEC for the IP L2 Interworking Circuit. The Interworking Circuits.
use of optional parameters in the Label Mapping message to extend
the attributes of the PW FEC is specified in the [PWE3-Control].
Shah, et. al. Expires September 2005 7 In addition to PW-FEC, this document defines an IP address TLV that
draft-ietf-l2vpn-arp-mediation-01.txt must be included in the optional parameter field of the Label
Mapping message when advertising the PW FEC for the IP Layer2
Transport. The use of optional parameters in the Label Mapping
message to extend the attributes of the PW FEC is specified in the
[PWE3-Control].
When processing a received PW FEC, the PE matches the PW Id and PW When processing a received PW FEC, the PE matches the PW Id and PW
type with the locally configured PW Id to determine if the PW FEC type with the locally configured PW Id to determine if the PW FEC
is of type IP L2 Interworking. If there is a match, it further is of type IP Layer2 Transport. If there is a match, it further
checks the presence of IP address optional parameter. If absent, a checks the presence of IP address optional parameter. If absent, a
Label Release message is issued to reject the PW establishment. Label Release message is issued to reject the PW establishment.
The optional parameter of the Label Mapping message is defined as The optional parameter of the Label Mapping message is defined as
follows. follows.
Optional Parameter type length value Optional Parameter type length value
IP address TBD 04 CEs IP address IP address TBD 04 CE's IP address
The IP address field is set to value null to denote that The IP address field is set to value null to denote that
advertising PE has not learned the IP address of his local CE advertising PE has not learned the IP address of his local CE
device. The non-zero value of the IP address field denotes IP device. The non-zero value of the IP address field denotes IP
address of advertising PEs attached CE device. address of advertising PE's attached CE device.
The CEs IP address is also supplied in the optional parameter The CE's IP address is also supplied in the optional parameter
field of the LDPs Notification message along with the PW FEC. The field of the LDP's Notification message along with the PW FEC. The
LDP Notification message is used to signal the change in CEs IP LDP Notification message is used to signal the change in CE's IP
address. address.
5.3 Out-of-band Distribution Configuration 6.3 Out-of-band Distribution Configuration
In some cases, it may not be possible either to deduce the IP In some cases, it may not be possible either to deduce the IP
addresses from the VPN traffic nor induce remote PEs to supply the addresses from the VPN traffic nor induce remote PEs to supply the
necessary information on demand. For those cases, out-of-band necessary information on demand. For those cases, out-of-band
methods, such as manual configuration, MAY be used. methods, such as manual configuration, MAY be used.
6.0 How a CE Learns the Remote CE's IP address
7.0 How a CE Learns the Remote CE's IP address
Once the local PE has received the remote CE's IP address Once the local PE has received the remote CE's IP address
information from the remote PE, it will either initiate an address information from the remote PE, it will either initiate an address
resolution request or respond to an outstanding request from the resolution request or respond to an outstanding request from the
attached CE device. attached CE device.
6.1 CE Devices Using ARP 7.1 CE Devices Using ARP
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When the PE learns the remote CE's IP address as described in When the PE learns the remote CE's IP address as described in
section 5.1 and 5.2, it may or may not know the local CE's IP section 6.1 and 6.2, it may or may not know the local CE's IP
address. If the local CE's IP address is not known, the PE must address. If the local CE's IP address is not known, the PE must
wait until it is acquired through one of the methods described in wait until it is acquired through one of the methods described in
sections 4.1, 4.3 and 4.5. If the IP address of the local CE is sections 5.1, 5.3 and 5.5. If the IP address of the local CE is
known, the PE may choose to generate an unsolicited ARP message to known, the PE may choose to generate an unsolicited ARP message to
notify the local CE about the binding of the remote CE's IP address notify the local CE about the binding of the remote CE's IP address
with the PE's own MAC address. with the PE's own MAC address.
When the local CE generates an ARP request, the PE must proxy the When the local CE generates an ARP request, the PE must proxy the
ARP response using its own MAC address as the source hardware ARP response using its own MAC address as the source hardware
Shah, et. al. Expires September 2005 8
draft-ietf-l2vpn-arp-mediation-01.txt
address and remote CE's IP address as the source protocol address. address and remote CE's IP address as the source protocol address.
The PE must respond only to those ARP requests whose destination The PE must respond only to those ARP requests whose destination
protocol address matches the remote CE's IP address. protocol address matches the remote CE's IP address. An exception
to this rule is when the strict topology of one IP end station per
Attachment Circuit is assumed. In which case, PE can promiscuously
respond to the CE's ARP request with his own MAC address.
6.2 CE Devices Using Inverse ARP 7.2 CE Devices Using Inverse ARP
When the PE learns the remote CE's IP address, it should generate When the PE learns the remote CE's IP address, it should generate
an Inverse ARP request. In case, the local circuit requires an Inverse ARP request. In case, the local circuit requires
activation e.g. Frame Relay, PE should activate it first before activation e.g. Frame Relay, PE should activate it first before
sending Inverse ARP request. It should be noted, that PE might sending Inverse ARP request. It should be noted, that PE might
never receive the response to its own request, nor see any CE's never receive the response to its own request, nor see any CE's
Inverse ARP request in cases where CE is pre-configured with remote Inverse ARP request in cases where CE is pre-configured with remote
CE IP address or the use of Inverse ARP is not enabled. In either CE IP address or the use of Inverse ARP is not enabled. In either
case CE has used other means to learn the IP address of his case CE has used other means to learn the IP address of his
neighbor. neighbor.
6.3 CE Devices Using PPP 7.3 CE Devices Using PPP
When the PE learns the remote CE's IP address, it should initiate When the PE learns the remote CE's IP address, it should initiate
the Configure-Request using the remote CE's IP address or respond the Configure-Request and set the IP-Address option to the remote
to pending Configure-Request from the local CE. As noted earlier, CE's IP address to notify local CE the IP address of the remote CE.
all other configuration options related to compression,
encryptions, etc., should be rejected.
7.0 Use of IGPs with IP L2 Interworking L2VPNs 8.0 Use of IGPs with IP L2 Interworking L2VPNs
In an IP L2 interworking L2VPN, when an IGP on a CE connected to a In an IP L2 interworking L2VPN, when an IGP on a CE connected to a
broadcast link is cross-connected with an IGP on a CE connected to broadcast link is cross-connected with an IGP on a CE connected to
a point-to-point link, there are routing protocol related issues a point-to-point link, there are routing protocol related issues
that must be addressed. The link state routing protocols are that must be addressed. The link state routing protocols are
cognizant of the underlying link characteristics and behave cognizant of the underlying link characteristics and behave
accordingly when establishing neighbor adjacencies, representing accordingly when establishing neighbor adjacencies, representing
the network topology, and passing protocol packets. the network topology, and passing protocol packets.
7.1 OSPF 8.1 OSPF
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The OSPF protocol treats a broadcast link type with a special The OSPF protocol treats a broadcast link type with a special
procedure that engages in neighbor discovery to elect a designated procedure that engages in neighbor discovery to elect a designated
and a backup designated router (DR and BDR respectively) with which and a backup designated router (DR and BDR respectively) with which
it forms adjacencies. However, these procedures are neither it forms adjacencies. However, these procedures are neither
applicable nor understood by OSPF running on a point-to-point link. applicable nor understood by OSPF running on a point-to-point link.
By cross-connecting two neighbors with disparate link types, an IP By cross-connecting two neighbors with disparate link types, an IP
L2 interworking L2VPN may experience connectivity issues. L2 interworking L2VPN may experience connectivity issues.
Additionally, the link type specified in the router LSA will not Additionally, the link type specified in the router LSA will not
match for two routers that are supposedly sharing the same link match for two routers that are supposedly sharing the same link
type. Finally, each OSPF router generates network LSAs when type. Finally, each OSPF router generates network LSAs when
connected to a broadcast link such as Ethernet, receipt of which by connected to a broadcast link such as Ethernet, receipt of which by
Shah, et. al. Expires September 2005 9
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an OSPF router on the point-to-point link further adds to the an OSPF router on the point-to-point link further adds to the
confusion. confusion.
Fortunately, the OSPF protocol provides a configuration option Fortunately, the OSPF protocol provides a configuration option
(ospfIfType), whereby OSPF will treat the underlying physical (ospfIfType), whereby OSPF will treat the underlying physical
broadcast link as a point-to-point link. broadcast link as a point-to-point link.
It is strongly recommended that all OSPF protocols on CE devices It is strongly recommended that all OSPF protocols on CE devices
connected to Ethernet interfaces use this configuration option when connected to Ethernet interfaces use this configuration option when
attached to a PE that is participating in an IP L2 Interworking attached to a PE that is participating in an IP L2 Interworking
VPN. VPN.
7.2 RIP 8.2 RIP
RIP protocol broadcasts RIP advertisements every 30 seconds. If the RIP protocol broadcasts RIP advertisements every 30 seconds. If the
group/broadcast address snooping mechanism is used as described group/broadcast address snooping mechanism is used as described
above, the attached PE can learn the advertising (CE) router's IP above, the attached PE can learn the advertising (CE) router's IP
address from the IP header of the advertisement. No special address from the IP header of the advertisement. No special
configuration is required for RIP in this type of Layer 2 IP configuration is required for RIP in this type of Layer 2 IP
Interworking L2VPN. Interworking L2VPN.
8.0 Security Considerations 9.0 Security Considerations
The security aspect of this solution is addressed for two planes; The security aspect of this solution is addressed for two planes;
control plane and data plane. control plane and data plane.
8.1 Control plane security 9.1 Control plane security
The control plane security pertains to establishing the LDP The control plane security pertains to establishing the LDP
connection, Pseudowire establishment and CEs IP address connection, pseudo-wire establishment and CEs IP address
distribution. The LDP connection between two trusted PEs can be distribution. The LDP connection between two trusted PEs can be
achieved by each PE verifying the incoming connection against the achieved by each PE verifying the incoming connection against the
configured peers address and authenticating the LDP messages using configured peers address and authenticating the LDP messages using
MD5 authentication. The Pseudowire establishments between two MD5 authentication. The pseudo-wire establishments between two
secure LDP peers do not pose security issue but mis-wiring could secure LDP peers do not pose security issue but mis-wiring could
occur due to configuration error. Some checks, such as, proper occur due to configuration error. Some checks, such as, proper
Pseudowire type and other Pseudowire options may prevent mis-wiring
due to configuration errors.
The learning of the appropriate CEs IP address can be a security Shah, et. al. Expires January 2006 11
draft-ietf-l2vpn-arp-mediation-02.txt
pseudo-wire type and other pseudo-wire options may prevent mis-
wiring due to configuration errors.
The learning of the appropriate CE's IP address can be a security
issue. It is expected that the local attachment circuit to CE is issue. It is expected that the local attachment circuit to CE is
physically secured. If this is a concern, the PE must be configured physically secured. If this is a concern, the PE must be configured
with CEs IP and MAC address when connected with Ethernet or CEs with CE's IP and MAC address when connected with Ethernet or CE's
IP and virtual circuit information (e.g. DLCI or VPI/VCI). During IP and virtual circuit information (e.g. DLCI or VPI/VCI). During
each ARP/inARP frame processing, PE must verify the received each ARP/inARP frame processing, PE must verify the received
information against the configuration before accepting to protect information against the configuration before accepting to protect
against hijacking the connection. against hijacking the connection.
Shah, et. al. Expires September 2005 10 9.2 Data plane security
draft-ietf-l2vpn-arp-mediation-01.txt
8.2 Data plane security
The data traffic between CE and PE is not encrypted and it is The data traffic between CE and PE is not encrypted and it is
possible that in an insecure environment, a malicious user may tap possible that in an insecure environment, a malicious user may tap
into the CE to PE connection and generate traffic using the spoofed into the CE to PE connection and generate traffic using the spoofed
destination MAC address on the Ethernet Attachment Circuit. In destination MAC address on the Ethernet Attachment Circuit. In
order to avoid such hijacking, local PE may verify the source MAC order to avoid such hijacking, local PE may verify the source MAC
address of the received frame against the MAC address of the address of the received frame against the MAC address of the
admitted connection. The frame is forwarded to PW only when admitted connection. The frame is forwarded to PW only when
authenticity is verified. When spoofing is detected, PE must severe authenticity is verified. When spoofing is detected, PE must severe
the connection with the local CE, tear down the PW and start over. the connection with the local CE, tear down the PW and start over.
9.0 Acknowledgements 10.0 Acknowledgements
The authors would like to thank Yetik Serbest, Prabhu Kavi, Bruce The authors would like to thank Yetik Serbest, Prabhu Kavi, Bruce
Lasley and other folks who participated in the discussions related Lasley, Mark Lewis, Carlos Pignataro and other folks who
to this draft. participated in the discussions related to this draft.
10.0 References 11.0 References
10.1 Normative References 11.1 Normative References
[ARP] RFC 826, STD 37, D. Plummer, "An Ethernet Address Resolution [ARP] RFC 826, STD 37, D. Plummer, "An Ethernet Address Resolution
Protocol: Or Converting Network Protocol Addresses to 48.bit Protocol: Or Converting Network Protocol Addresses to 48.bit
Ethernet Addresses for Transmission on Ethernet Hardware". Ethernet Addresses for Transmission on Ethernet Hardware".
[INVARP] RFC 2390, T. Bradley et al., "Inverse Address Resolution [INVARP] RFC 2390, T. Bradley et al., "Inverse Address Resolution
Protocol". Protocol".
10.2 Informative References [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.
Shah, et. al. Expires January 2006 12
draft-ietf-l2vpn-arp-mediation-02.txt
11.2 Informative References
[L2VPN-FRM] L. Andersson et al., "Framework for L2VPN", June 2004, [L2VPN-FRM] L. Andersson et al., "Framework for L2VPN", June 2004,
work in progress. work in progress.
[PPP-IPCP] RFC 1332, G. McGregor, "The PPP Internet Protocol [PPP-IPCP] RFC 1332, G. McGregor, "The PPP Internet Protocol
Control Protocol (IPCP)". Control Protocol (IPCP)".
[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.
Shah, et. al. Expires September 2005 11
draft-ietf-l2vpn-arp-mediation-01.txt
[PROXY-ARP] RFC 925, J. Postel, "Multi-LAN Address Resolution". [PROXY-ARP] RFC 925, J. Postel, "Multi-LAN Address Resolution".
11.0 Authors' Addresses 12.0 Authors' Addresses
Himanshu Shah Himanshu Shah
35 Nagog Park, 35 Nagog Park,
Acton, MA 01720 Acton, MA 01720
Email: hshah@ciena.com Email: hshah@ciena.com
Eric Rosen Eric Rosen
Cisco Systems Cisco Systems
1414 Massachusetts Avenue, 1414 Massachusetts Avenue,
Boxborough, MA 01719 Boxborough, MA 01719
Email: erosen@cisco.com Email: erosen@cisco.com
Waldemar Augustyn Waldemar Augustyn
Email: waldemar@nxp.com Email: waldemar@nxp.com
Giles Heron Giles Heron
Email: giles@tellabs.com Email: giles.heron@tellabs.com
Sunil Khandekar and Vach Kompella Sunil Khandekar and Vach Kompella
Email: sunil@timetra.com Email: sunil@timetra.com
Email: vkompella@timetra.com Email: vkompella@timetra.com
Toby Smith Toby Smith
Laurel Networks Laurel Networks
Omega Corporate Center Omega Corporate Center
1300 Omega drive 1300 Omega drive
Pittsburgh, PA 15205 Pittsburgh, PA 15205
Email: jsmith@laurelnetworks.com Email: jsmith@laurelnetworks.com
Arun Vishwanathan Arun Vishwanathan
Force10 Networks Force10 Networks
1440 McCarthy Blvd., 1440 McCarthy Blvd.,
Milpitas, CA 95035 Milpitas, CA 95035
Email: arun@force10networks.com Email: arun@force10networks.com
Andrew G. Malis Andrew G. Malis
Shah, et. al. Expires January 2006 13
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Tellabs Tellabs
2730 Orchard Parkway 2730 Orchard Parkway
San Jose, CA 95134 San Jose, CA 95134
Email: Andy.Malis@vivacenetworks.com Email: Andy.Malis@tellabs.com
Steven Wright Steven Wright
Bell South Corp Bell South Corp
Email: steven.wright@bellsouth.com Email: steven.wright@bellsouth.com
Vasile Radoaca Vasile Radoaca
Email: vasile@westridgenetworks.com Email: vasile@westridgenetworks.com
Shah, et. al. Expires September 2005 12 Intellectual Property Statement
draft-ietf-l2vpn-arp-mediation-01.txt
IPR Notice
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The IETF invites any interested party to bring to its attention any The IETF invites any interested party to bring to its attention any
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By submitting this Internet-Draft, I certify that any applicable
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or will be disclosed, and any of which I become aware will be
disclosed, in accordance with RFC 3668.
Full Copyright Statement Full Copyright Statement
Copyright (C) The Internet Society (2004). This document is
subject Copyright (C) The Internet Society (2005).
to the rights, licenses and restrictions contained in BCP 78 and
except as set forth therein, the authors retain all their rights. This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on This document and the information contained herein are provided on
an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
Shah, et. al. Expires January 2006 14
draft-ietf-l2vpn-arp-mediation-02.txt
REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES,
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THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR
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Shah, et. al. Expires September 2005 13 Shah, et. al. Expires January 2006 15
 End of changes. 

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