draft-kompella-mpls-larp-03.txt   draft-kompella-mpls-larp-04.txt 
MPLS WG K. Kompella MPLS WG K. Kompella
Internet-Draft R. Balaji Internet-Draft Juniper Networks
Intended status: Standards Track Juniper Networks Intended status: Standards Track R. Balaji
Expires: November 1, 2015 G. Swallow Expires: March 11, 2016 Juniper Networks, Inc.
G. Swallow
Cisco Systems Cisco Systems
April 30, 2015 September 8, 2015
Label Distribution Using ARP Label Distribution Using ARP
draft-kompella-mpls-larp-03 draft-kompella-mpls-larp-04
Abstract Abstract
This document describes extensions to the Address Resolution Protocol This document describes extensions to the Address Resolution Protocol
to distribute MPLS labels for IPv4 and IPv6 host addresses. to distribute MPLS labels for IPv4 and IPv6 host addresses.
Distribution of labels via ARP enables simple plug-and-play operation Distribution of labels via ARP enables simple plug-and-play operation
of MPLS, which is a key goal of the MPLS Fabric architecture. of MPLS, which is a key goal of the MPLS Fabric architecture.
Requirements Language Requirements Language
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on November 1, 2015. This Internet-Draft will expire on March 11, 2016.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Approach . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Approach . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Overview of Ethernet ARP . . . . . . . . . . . . . . . . . . 3 2. Overview of Ethernet ARP . . . . . . . . . . . . . . . . . . 3
3. L-ARP Protocol Operation . . . . . . . . . . . . . . . . . . 4 3. L-ARP Protocol Operation . . . . . . . . . . . . . . . . . . 4
3.1. Basic Operation . . . . . . . . . . . . . . . . . . . . . 4 3.1. Setup . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Asynchronous operation . . . . . . . . . . . . . . . . . 5 3.2. Egress Operation . . . . . . . . . . . . . . . . . . . . 5
3.3. Client-Server Synchronization . . . . . . . . . . . . . . 5 3.3. Ingress Operation . . . . . . . . . . . . . . . . . . . . 5
3.4. Applicability . . . . . . . . . . . . . . . . . . . . . . 6 4. Attributes . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.5. Backward Compatibility . . . . . . . . . . . . . . . . . 6 5. Client-Server Synchronization . . . . . . . . . . . . . . . . 6
4. For Future Study . . . . . . . . . . . . . . . . . . . . . . 6 6. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 7
5. L-ARP Message Format . . . . . . . . . . . . . . . . . . . . 7 7. Backward Compatibility . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 8. For Future Study . . . . . . . . . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 9. L-ARP Message Format . . . . . . . . . . . . . . . . . . . . 8
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 10. Security Considerations . . . . . . . . . . . . . . . . . . . 10
9. Normative References . . . . . . . . . . . . . . . . . . . . 11 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
13.1. Normative References . . . . . . . . . . . . . . . . . . 11
13.2. Informative References . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction 1. Introduction
This document describes extensions to the Address Resolution Protocol This document describes extensions to the Address Resolution Protocol
(ARP) [RFC0826] to advertise label bindings for IP host addresses. (ARP) [RFC0826] to advertise label bindings for IP host addresses.
While there are well-established protocols, such as LDP, RSVP and While there are well-established protocols, such as LDP, RSVP and
BGP, that provide robust mechanisms for label distribution, these BGP, that provide robust mechanisms for label distribution, these
protocols tend to be relatively complex, and often require detailed protocols tend to be relatively complex, and often require detailed
configuration for proper operation. There are situations where a configuration for proper operation. There are situations where a
simpler protocol may be more suitable from an operational standpoint. simpler protocol may be more suitable from an operational standpoint.
An example is the case where an MPLS Fabric is the underlay An example is the case where an MPLS Fabric is the underlay
technology in a Data Centre; here, MPLS tunnels originate from host technology in a Data Center; here, MPLS tunnels originate from host
machines. The host thus needs a mechanism to acquire label bindings machines. The host thus needs a mechanism to acquire label bindings
to participate in the MPLS Fabric, but in a simple, plug-and-play to participate in the MPLS Fabric, but in a simple, plug-and-play
manner. Existing signaling/routing protocols do not always meet this manner. Existing signaling/routing protocols do not always meet this
need. Labeled ARP (L-ARP) is a proposal to fill that gap. need. Labeled ARP (L-ARP) is a proposal to fill that gap.
[TODO-MPLS-FABRIC] describes the motivation for using MPLS as the [TODO-MPLS-FABRIC] describes the motivation for using MPLS as the
fabric technology. fabric technology.
1.1. Approach 1.1. Approach
skipping to change at page 3, line 32 skipping to change at page 3, line 35
and L-ARP can coexist; a device, as an ARP client, can choose to send and L-ARP can coexist; a device, as an ARP client, can choose to send
out an E-ARP or an L-ARP request, depending on whether it needs out an E-ARP or an L-ARP request, depending on whether it needs
Ethernet or MPLS connectivity. Another device may choose to function Ethernet or MPLS connectivity. Another device may choose to function
as an E-ARP server and/or an L-ARP server, depending on its ability as an E-ARP server and/or an L-ARP server, depending on its ability
to provide an IP-to-Ethernet and/or IP-to-MPLS mapping. to provide an IP-to-Ethernet and/or IP-to-MPLS mapping.
2. Overview of Ethernet ARP 2. Overview of Ethernet ARP
In the most straightforward mode of operation [RFC0826], ARP queries In the most straightforward mode of operation [RFC0826], ARP queries
are sent to resolve "directly connected" IP addresses. The ARP query are sent to resolve "directly connected" IP addresses. The ARP query
is broadcast, with the Target Protocol Address field (see Section 5 is broadcast, with the Target Protocol Address field (see Section 9
for a description of the fields in an ARP message) carrying the IP for a description of the fields in an ARP message) carrying the IP
address of another node in the same subnet. All the nodes in the LAN address of another node in the same subnet. All the nodes in the LAN
receive this ARP query. All the nodes, except the node that owns the receive this ARP query. All the nodes, except the node that owns the
IP address, ignore the ARP query. The IP address owner learns the IP address, ignore the ARP query. The IP address owner learns the
MAC address of the sender from the Source Hardware Address field in MAC address of the sender from the Source Hardware Address field in
the ARP request, and unicasts an ARP reply to the sender. The ARP the ARP request, and unicasts an ARP reply to the sender. The ARP
reply carries the replying node's MAC address in the Source Hardware reply carries the replying node's MAC address in the Source Hardware
Address field, thus enabling two-way communication between the two Address field, thus enabling two-way communication between the two
nodes. nodes.
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the sender's address. the sender's address.
3. L-ARP Protocol Operation 3. L-ARP Protocol Operation
The L-ARP protocol builds on the proxy ARP model, and also leverages The L-ARP protocol builds on the proxy ARP model, and also leverages
gratuitous ARP model for asynchronous updates. gratuitous ARP model for asynchronous updates.
In this memo, we will refer to L-ARP clients (that make L-ARP In this memo, we will refer to L-ARP clients (that make L-ARP
requests) and L-ARP servers (that send L-ARP responses). In requests) and L-ARP servers (that send L-ARP responses). In
Figure 1, H1, H2 and H3 are L-ARP clients, and T1, T2 and T3 are Figure 1, H1, H2 and H3 are L-ARP clients, and T1, T2 and T3 are
L-ARP servers. T is a member of the MPLS Fabric that may not be an L-ARP servers. T4 is a member of the MPLS Fabric that may not be an
L-ARP server. Within the MPLS Fabric, the usual MPLS protocols (IGP, L-ARP server. Within the MPLS Fabric, the usual MPLS protocols (IGP,
LDP, RSVP-TE) are run. Say H1, H2 and H3 want to establish MPLS LDP, RSVP-TE) are run. Say H1, H2 and H3 want to establish MPLS
tunnels to each other (for example, they are using BGP MPLS VPNs as tunnels to each other (for example, they are using BGP MPLS VPNs as
the overlay virtual network technology). H1 might also want to talk the overlay virtual network technology). H1 might also want to talk
to a member of the MPLS Fabric, say T. to a member of the MPLS Fabric, say T.
. . . . . .
. .
H1 --- T1 T4
\ . MPLS .
\ . .
\ . Fabric .
H2 --- T2 T3 --- H3
. .
. . . . . . . . . . . .
. .
H1 --- T1 T4
\ . MPLS .
\ . .
\ . Fabric .
H2 --- T2 T3 --- H3
. .
. . . . . . .
Figure 1 Figure 1
3.1. Basic Operation 3.1. Setup
A node (say H1) that needs an MPLS tunnel to a destination (say H3) In Figure 1, the nodes T1-T4, and those in between making up the
broadcasts over all its interfaces an L-ARP query with the Target "MPLS Fabric" are assumed to be running some protocol whereby they
Protocol Address set to H3. A node that has reachability to H3 (such can signal MPLS reachability to themselves and to other nodes (like
as T1 or T2) sends an L-ARP reply with the Source Hardware Address H1-H3). T1-T3 are L-ARP servers; T4 need not be. H1-H3 are L-ARP
set to a locally-allocated MPLS label plus its Ethernet MAC address. clients.
After receiving one or more L-ARP replies, H1 can select either T1 or 3.2. Egress Operation
T2 to send MPLS packets that are destined to H3. As described later,
the L-ARP response may contain certain parameters that enable the
client to make an informed choice of the routers.
As with standard ARP, the validity of the MPLS label obtained using A node (say T3) that wants an attached node (say H3) to have MPLS
L-ARP is time-bound. The client should periodically resend its L-ARP reachability, allocates a label L3 to reach H3, and advertises this
requests to obtain the latest information, and time out entries in label into the MPLS Fabric. This can be triggered by configuration
its ARP cache if such an update is not forthcoming. Once an L-ARP on T3, or via some other protocol. On receiving a packet with label
server has advertised a label binding, it MUST NOT change the binding L3, T3 pops the label and send the packet to H3. This is the usual
until expiry of the binding's validity time. operation of an MPLS Fabric, with the addition of advertising labels
for nodes outside the fabric.
The mechanism defined here is simplistic; see Section 4. 3.3. Ingress Operation
3.2. Asynchronous operation A node (say H1, the L-ARP client) that needs an MPLS tunnel to a node
(say H3) identified by a host address (either IPv4 or IPv6)
broadcasts over all its interfaces an L-ARP query with the Target
Protocol Address set to H3. A node (say T1, an L-ARP server) that
has MPLS reachability to H3 sends an L-ARP reply with the Source
Hardware Address set to its Ethernet MAC address M1, with a new TLV
containing a label L1. To send a packet to H3 over an MPLS tunnel,
H1 pushes L1 onto the packet, sets the destination MAC address to M1
and sends it to T1. On receiving this packet, T1 swaps the top label
with the label(s) for its MPLS tunnel to H3.
The preceding sections described a request-response based model. In Note that H1 broadcasts its L-ARP request over its attached
some cases, the L-ARP server may want to asynchronously update its interfaces. H1 may receive several L-ARP replies; in that case, H1
clients. L-ARP uses the gratuitous ARP model [RFC2002] to "push" can select any subset of these to send MPLS packets destined to H3.
such changes. As described later, the L-ARP response may contain certain parameters
that enable the client to make an informed choice. If the target H3
belongs to one of the subnets that H1 participates in, and H3 is
capable of sending L-ARP replies, H1 can use H3's response to send
MPLS packets to H3.
In a pure "push" model, a device may send out updates for all 4. Attributes
prefixes it knows about. This naive approach will not scale well.
This memo specifies a mode of operation that is somewhere between
"push" and "pull" model. An L-ARP server does not advertise any
binding for a prefix until at least one L-ARP client expresses
interest in that prefix (by initiating an L-ARP query). As long as
the server has at least one interested client for a prefix, the
server sends unsolicited (aka gratuitous, though the term is less
appropriate in this context) L-ARP replies when a prefix's
reachability changes. The server will deem the client's interest in
a prefix to have ceased when it does not hear any L-ARP queries for
some configured timeout period.
3.3. Client-Server Synchronization In addition to carrying a label stack to be used in the data plane,
an L-ARP reply carries some attributes that are typically used in the
control plane. One of these is a metric. The metric is the distance
from the L-ARP server to the destination. This allows an L-ARP
client that receives multiple responses to decide which ones to use,
and whether to load-balance across some of them. The metric
typically will be the IGP shortest path distance from server to the
destination; this makes comparing metrics from different servers
meaningful.
Another attribute, carried in the LST TLV, is Entropy Label (EL)
Capability. This attribute says whether the destination is EL
capable (ELC). In Figure 1, if T3 advertises a label to reach H3 and
T3 is ELC, T3 can include in its signaling to T1 that it is ELC. In
that case, if T1's L-ARP reply to H1 consists of a single label, T1
can set the ELC bit in the label field of the LST TLV. This tells H1
that it may include (below the outermost label) an Entropy Label
Indicator followed by an Entropy Label. This will help improve load
balancing across the MPLS Fabric, and possibly on the last hop to H3.
5. Client-Server Synchronization
In an L-ARP reply, the server communicates several pieces of In an L-ARP reply, the server communicates several pieces of
information to the client: its hardware address, the MPLS label, information to the client: its hardware address, the MPLS label,
Entropy Label capability and metric. Since ARP is a stateless Entropy Label capability and metric. Since ARP is a stateless
protocol, it is possible that one of these changes without the client protocol, it is possible that one of these changes without the client
knowing, which leads to a loss of synchronization between the client knowing, which leads to a loss of synchronization between the client
and the server. This loss of synchronization can have several bad and the server. This loss of synchronization can have several
effects undesirable effects.
If the server's hardware address changes or the MPLS label is If the server's hardware address changes or the MPLS label is
repurposed by the server for a different purpose, then packets may be repurposed by the server for a different purpose, then packets may be
sent to the wrong destination. The consequences can range from sent to the wrong destination. The consequences can range from
suboptimally routed packets to dropped packets to packets being suboptimally routed packets to dropped packets to packets being
delivered to the wrong customer, which may be a security breach. delivered to the wrong customer, which may be a security breach.
This last may be the most troublesome consequence of loss of This last may be the most troublesome consequence of loss of
synchronization. synchronization.
If a destination transitions from entropy label capable to entropy If a destination transitions from entropy label capable to entropy
label incapable (an unlikely event) without the client knowing, then label incapable (an unlikely event) without the client knowing, then
packets encapsulated with entropy labels will be dropped. A packets encapsulated with entropy labels will be dropped. A
transition in the other direction is relatively benign. transition in the other direction is benign.
If the metric changes without the client knowing, packets may be If the metric changes without the client knowing, packets may be
suboptimally routed. This may be the most benign consequence of loss suboptimally routed. This may be the most benign consequence of loss
of synchronization. of synchronization.
3.4. Applicability Standard ARP has similar issues. These are dealt with in two ways:
a) ARP bindings are time-bound; and b) an ARP server, recognizing
that a change has occurred, can send unsolicited ARP messages
([RFC2002]). Both these techniques are used in L-ARP: the validity
of the MPLS label obtained using L-ARP is time-bound; an L-ARP client
should periodically resend L-ARP requests to obtain the latest
information, and time out entries in its ARP cache if such an update
is not forthcoming. Furthermore, an L-ARP server may update an
advertised label binding by sending an unsolicited L-ARP message if
any of the parameters mentioned above change.
6. Applicability
L-ARP can be used between a host and its Top-of-Rack switch in a Data L-ARP can be used between a host and its Top-of-Rack switch in a Data
Center. L-ARP can also be used between a DSLAM and its aggregation Center. L-ARP can also be used between a DSLAM and its aggregation
switch going to the B-RAS. More generally, L-ARP can be used between switch going to the B-RAS. More generally, L-ARP can be used between
an "access node" and its first hop MPLS-enabled device in the context an "Access Node" (AN) (e.g., the DSLAM) and its first hop MPLS-
of Seamless MPLS [reference]. In all these cases, L-ARP can handle enabled device in the context of Seamless MPLS
the presence of multiple connections between the access device and [I-D.ietf-mpls-seamless-mpls]. The first-hop device is part of the
its first hop devices. MPLS Fabric, as is the Service Node (SN) (e.g., the B-RAS). L-ARP
helps create an MPLS tunnel from the AN to the SN, without requiring
that the AN be part of the MPLS Fabric. In all these cases, L-ARP
can handle the presence of multiple connections between the access
device and its first hop devices.
ARP is not a routing protocol. The use of L-ARP should be limited to ARP is not a routing protocol. The use of L-ARP should be limited to
cases where the L-ARP client has a small number of one-hop cases where an L-ARP client has Ethernet connectivity to its L-ARP
connections to L-ARP servers. The presence of a complex topology servers.
between the L-ARP client and server suggests the use of a different
protocol.
3.5. Backward Compatibility 7. Backward Compatibility
Since L-ARP uses a new hardware type, it is backward compatible with Since L-ARP uses a new hardware type, it is backward compatible with
"regular" ARP. ARP servers and clients MUST be able to send out, "regular" ARP. ARP servers and clients MUST be able to send out,
receive and process ARP messages based on hardware type. They MAY receive and process ARP messages based on hardware type. They MAY
choose to ignore requests and replies of some hardware types; they choose to ignore requests and replies of some hardware types; they
MAY choose to log errors if they encounter hardware types they do not MAY choose to log errors if they encounter hardware types they do not
recognize; however, they MUST handle all hardware types gracefully. recognize; however, they MUST handle all hardware types gracefully.
For hardware types that they do understand, ARP servers and clients For hardware types that they do understand, ARP servers and clients
MUST handle operation codes gracefully, processing those they MUST handle operation codes gracefully, processing those they
understand, and ignoring (and possibly logging) others. understand, and ignoring (and possibly logging) others.
4. For Future Study 8. For Future Study
The L-ARP specification is quite simple, and the goal is to keep it The L-ARP specification is quite simple, and the goal is to keep it
that way. However, inevitably, there will be questions and features that way. However, inevitably, there will be questions and features
that will be requested. Some of these are: that will be requested. Some of these are:
1. Keeping L-ARP clients and servers in sync. In particular, 1. Keeping L-ARP clients and servers in sync. In particular,
dealing with: dealing with:
A. client and/or server restart A. client and/or server control plane restart
B. lost packets B. lost packets
C. timeouts C. timeouts
2. Withdrawing a response. 2. Withdrawing a response.
3. Dealing with scale. 3. Dealing with scale.
4. If there are many servers, which one to pick? 4. If there are many servers, which one to pick?
5. How can a client make best use of underlying ECMP paths? 5. How can a client make best use of underlying ECMP paths?
6. and probably many more. 6. and probably many more.
In all of these, it is important to realize that, whenever possible, In all of these, it is important to realize that, whenever possible,
a solution that places most of the burden on the server rather than a solution that places most of the burden on the server rather than
on the client is preferable. on the client is preferable.
5. L-ARP Message Format These questions (and others that come up during discussions) will be
dealt with in future versions of this draft.
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 9. L-ARP Message Format
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ar$hrd | ar$pro | 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ar$hln | ar$pln | ar$op | | ar$hrd | ar$pro |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// ar$sha (ar$hln octets) // | ar$hln | ar$pln | ar$op |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// ar$spa (ar$pln octets) // // ar$sha (ar$hln octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// ar$tha (ar$hln octets) // // ar$spa (ar$pln octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// ar$tpa (ar$pln octets) // // ar$tha (ar$hln octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// ar$lst (variable...) // // ar$tpa (ar$pln octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// ar$att (variable...) // // ar$lst (variable...) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// ar$att (variable...) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: L-ARP Packet Format Figure 2: L-ARP Packet Format
ar$hrd Hardware Type: MPLS-over-Ethernet. The value of the field ar$hrd Hardware Type: MPLS-over-Ethernet. The value of the field
used here is [HTYPE-MPLS]. To start with, we will use the used here is [HTYPE-MPLS]. To start with, we will use the
experimental value HW_EXP2 (256) experimental value HW_EXP2 (256)
ar$pro Protocol Type: IPv4/IPv6. The value of the field used here ar$pro Protocol Type: IPv4/IPv6. The value of the field used here
is 0x0800 to resolve an IPv4 address and 0x86DD to resolve an is 0x0800 to resolve an IPv4 address and 0x86DD to resolve an
IPv6 address. IPv6 address.
skipping to change at page 9, line 5 skipping to change at page 9, line 40
ar$att Attributes: In an L-ARP request, this field is empty. In an ar$att Attributes: In an L-ARP request, this field is empty. In an
L-ARP reply, this field carries attributes for the MPLS label L-ARP reply, this field carries attributes for the MPLS label
stack as an ARP TLV in the format below. stack as an ARP TLV in the format below.
This document introduces the notion of ARP TLVs. These take the form This document introduces the notion of ARP TLVs. These take the form
as in Figure 3. Figure 4 describes the format of Label Stack TLV as in Figure 3. Figure 4 describes the format of Label Stack TLV
carried in L-ARP. Figure 5 describes the format of Attributes TLV carried in L-ARP. Figure 5 describes the format of Attributes TLV
carried in L-ARP. carried in L-ARP.
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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Value (Length octets) ... | | Type | Length | Value (Length octets) ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type is the type of the TLV; Length is the length of the value field Type is the type of the TLV; Length is the length of the value field
in octets; Value is the value field. in octets; Value is the value field.
Figure 3: ARP TLVs Figure 3: ARP TLVs
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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | MPLS Label (20 bits) | | Type | Length | MPLS Label (20 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |E|Z|Z|Z| MPLS Label (20 bits) |E|Z|Z|Z| | |E|Z|Z|Z| MPLS Label (20 bits) |E|Z|Z|Z|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... | ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: MPLS Label Stack Format Figure 4: MPLS Label Stack Format
Label Stack: Type = TLV-LST; Length = n*3 octets, where n is the Label Stack: Type = TLV-LST; Length = n*3 octets, where n is the
number of labels. The Value field contains the MPLS label stack number of labels. The Value field contains the MPLS label stack
for the client to use to get to the target. Each label is 3 for the client to use to get to the target. Each label is 3
octets. This field is valid only in an L-ARP reply message. octets. This field is valid only in an L-ARP reply message.
E-bit: Entropy Label Capable: this flag indicates whether the E-bit: Entropy Label Capable: this flag indicates whether the
corresponding label in the label stack can be followd by an corresponding label in the label stack can be followd by an
Entropy Label. If this flag is set, the client has the option of Entropy Label. If this flag is set, the client has the option of
inserting ELI and EL as specified in [RFC6790]. The client can inserting ELI and EL as specified in [RFC6790]. The client can
choose not to insert ELI/EL pair. If this flag is clear, the choose not to insert ELI/EL pair. If this flag is clear, the
client must not insert ELI/EL after the corresponding label. client must not insert ELI/EL after the corresponding label.
Z These bits are not used, and SHOULD be set to zero on sending and Z These bits are not used, and SHOULD be set to zero on sending and
ignored on receipt. ignored on receipt.
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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Metric (4 octets) ... | | Type | Length | Metric (4 octets) ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... Metric | | ... Metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Attribute TLV Figure 5: Attribute TLV
Attributes TLV: Type = TLV-ATT; Length = 4 octets. The Value field Attributes TLV: Type = TLV-ATT; Length = 4 octets. The Value field
contains the metric (typically, IGP distance) from the responder contains the metric (typically, IGP distance) from the responder
to the destination (device with the requested IP address). This to the destination (device with the requested IP address). This
field is valid only in an L-ARP reply message. field is valid only in an L-ARP reply message.
If other parameters are deemed useful in the ATT TLV, they will be If other parameters are deemed useful in the ATT TLV, they will be
added as needed. added as needed.
6. Security Considerations 10. Security Considerations
There are many possible attacks on ARP: ARP spoofing, ARP cache There are many possible attacks on ARP: ARP spoofing, ARP cache
poisoning and ARP poison routing, to name a few. These attacks use poisoning and ARP poison routing, to name a few. These attacks use
gratuitous ARP as the underlying mechanism, a mechanism used by gratuitous ARP as the underlying mechanism, a mechanism used by
L-ARP. Thus, these types of attacks are applicable to L-ARP. L-ARP. Thus, these types of attacks are applicable to L-ARP.
Furthermore, ARP does not have built-in security mechanisms; defenses Furthermore, ARP does not have built-in security mechanisms; defenses
rely on means external to the protocol. rely on means external to the protocol.
It is well outside the scope of this document to present a general It is well outside the scope of this document to present a general
solution to the ARP security problem. One simple answer is to add a solution to the ARP security problem. One simple answer is to add a
TLV that contains a digital signature of the contents of the ARP TLV that contains a digital signature of the contents of the ARP
message. This TLV would be defined for use only in L-ARP messages, message. This TLV would be defined for use only in L-ARP messages,
although in principle, other ARP messages could use it as well. Such although in principle, other ARP messages could use it as well. Such
an approach would, of course, need a review and approval by the an approach would, of course, need a review and approval by the
Security Directorate. If approved, the type of this TLV and its Security Directorate. If approved, the type of this TLV and its
procedures would be defined in this document. If some other procedures would be defined in this document. If some other
technique is suggested, the authors would be happy to include the technique is suggested, the authors would be happy to include the
relevant text in this document, and refer to some other document for relevant text in this document, and refer to some other document for
the full solution. the full solution.
7. IANA Considerations 11. IANA Considerations
IANA is requested to allocate a new ARP hardware type (from the IANA is requested to allocate a new ARP hardware type (from the
registry hrd) for HTYPE-MPLS. registry hrd) for HTYPE-MPLS.
IANA is also requested to create a new registry ARP-TLV ("tlv"). IANA is also requested to create a new registry ARP-TLV ("tlv").
This is a registry of one octet numbers. Allocation policies: 0 is This is a registry of one octet numbers. Allocation policies: 0 is
not to be allocated; the range 1-127 is Standards Action; the values not to be allocated; the range 1-127 is Standards Action; the values
128-251 are FCFS; and the values 252-255 are Experimental. 128-251 are FCFS; and the values 252-255 are Experimental.
Finally, IANA is requested to allocate two values in the ARP-TLV Finally, IANA is requested to allocate two values in the ARP-TLV
registry, one for TLV-LST and another for TLV-ATT. registry, one for TLV-LST and another for TLV-ATT.
8. Acknowledgments 12. Acknowledgments
Many thanks to Shane Amante for his detailed comments and Many thanks to Shane Amante for his detailed comments and
suggestions. Many thanks to the team in Juniper prototyping this suggestions. Many thanks to the team in Juniper prototyping this
work for their suggestions on making this variant workable in the work for their suggestions on making this variant workable in the
context of existing ARP implementations. Thanks too to Luyuan Fang, context of existing ARP implementations. Thanks too to Luyuan Fang,
Alex Semenyaka and Dmitry Afanasiev for their comments and Alex Semenyaka and Dmitry Afanasiev for their comments and
encouragement. encouragement.
9. Normative References 13. References
13.1. Normative References
[RFC0826] Plummer, D., "Ethernet Address Resolution Protocol: Or [RFC0826] Plummer, D., "Ethernet Address Resolution Protocol: Or
converting network protocol addresses to 48.bit Ethernet Converting Network Protocol Addresses to 48.bit Ethernet
address for transmission on Ethernet hardware", STD 37, Address for Transmission on Ethernet Hardware", STD 37,
RFC 826, November 1982. RFC 826, DOI 10.17487/RFC0826, November 1982,
<http://www.rfc-editor.org/info/rfc826>.
[RFC2002] Perkins, C., "IP Mobility Support", RFC 2002, October [RFC2002] Perkins, C., Ed., "IP Mobility Support", RFC 2002,
1996. DOI 10.17487/RFC2002, October 1996,
<http://www.rfc-editor.org/info/rfc2002>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an <http://www.rfc-editor.org/info/rfc2119>.
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and [RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and
L. Yong, "The Use of Entropy Labels in MPLS Forwarding", L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
RFC 6790, November 2012. RFC 6790, DOI 10.17487/RFC6790, November 2012,
<http://www.rfc-editor.org/info/rfc6790>.
13.2. Informative References
[I-D.ietf-mpls-seamless-mpls]
Leymann, N., Decraene, B., Filsfils, C., Konstantynowicz,
M., and D. Steinberg, "Seamless MPLS Architecture", draft-
ietf-mpls-seamless-mpls-07 (work in progress), June 2014.
Authors' Addresses Authors' Addresses
Kireeti Kompella Kireeti Kompella
Juniper Networks Juniper Networks
1194 N. Mathilda Avenue 1194 N. Mathilda Avenue
Sunnyvale, CA 94089 Sunnyvale, CA 94089
USA USA
Email: kireeti.kompella@gmail.com Email: kireeti.kompella@gmail.com
Balaji Rajagopalan Balaji Rajagopalan
Juniper Networks Juniper Networks, Inc.
Prestige Electra, Exora Business Park Prestige Electra, Exora Business Park
Marathahalli - Sarjapur Outer Ring Road Marathahalli - Sarjapur Outer Ring Road
Bangalore 560103 Bangalore 560103
India India
Email: balajir@juniper.net Email: balajir@juniper.net
George Swallow George Swallow
Cisco Systems Cisco Systems
1414 Massachusetts Ave 1414 Massachusetts Ave
Boxborough, MA 01719 Boxborough, MA 01719
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