MPLS WG K. Kompella
Internet-Draft Juniper Networks
Intended status: Standards Track R. Balaji
Expires: September 11, 2016 Juniper Networks, Inc.
G. Swallow
Cisco Systems
March 10, 2016
Label Distribution Using ARP
draft-kompella-mpls-larp-05
Abstract
This document describes extensions to the Address Resolution Protocol
to distribute MPLS labels for IPv4 and IPv6 host addresses.
Distribution of labels via ARP enables simple plug-and-play operation
of MPLS.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
The term "server" will be used in this document to refer to an ARP/
L-ARP server; the term "host" will be used to refer to a compute
server or other device acting as an ARP/L-ARP client.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 11, 2016.
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Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Approach . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Overview of Ethernet ARP . . . . . . . . . . . . . . . . . . 4
3. L-ARP Protocol Operation . . . . . . . . . . . . . . . . . . 4
3.1. Setup . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Egress Operation . . . . . . . . . . . . . . . . . . . . 5
3.3. Ingress Operation . . . . . . . . . . . . . . . . . . . . 5
4. Attributes . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Client-Server Synchronization . . . . . . . . . . . . . . . . 7
5.1. Restart Handling . . . . . . . . . . . . . . . . . . . . 7
5.1.1. Server Restart . . . . . . . . . . . . . . . . . . . 7
5.1.2. Client Restart . . . . . . . . . . . . . . . . . . . 8
5.2. Expedited Reachability Determination . . . . . . . . . . 8
6. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 8
7. Backward Compatibility . . . . . . . . . . . . . . . . . . . 9
8. OAM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. L-ARP IPv4 FEC . . . . . . . . . . . . . . . . . . . . . 9
8.2. L-ARP IPv6 FEC . . . . . . . . . . . . . . . . . . . . . 9
9. For Future Study . . . . . . . . . . . . . . . . . . . . . . 10
10. L-ARP Message Format . . . . . . . . . . . . . . . . . . . . 11
11. Security Considerations . . . . . . . . . . . . . . . . . . . 13
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
14.1. Normative References . . . . . . . . . . . . . . . . . . 14
14.2. Informative References . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
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1. Introduction
This document describes extensions to the Address Resolution Protocol
(ARP) [RFC0826] to advertise label bindings for IP host addresses.
While there are well-established protocols, such as LDP, RSVP and
BGP, that provide robust mechanisms for label distribution, these
protocols tend to be relatively complex, and often require detailed
configuration for proper operation. There are situations where a
simpler protocol may be more suitable from an operational standpoint.
An example is the case where an MPLS Fabric is the underlay
technology in a Data Center; here, MPLS tunnels originate from host
machines. The host thus needs a mechanism to acquire label bindings
to participate in the MPLS Fabric. [TODO-MPLS-FABRIC] describes the
motivation for using MPLS as the fabric technology.
Another use-case is Egress Peer Traffic-Engineering (EPE)
[I-D.gredler-idr-bgplu-epe]. In EPE, if the host makes the decision
to direct packets towards a specific link using MPLS tunneling
techniques, there needs to a suitable protocol for the host to
acquire MPLS labels from the network.
In both the cases, the mechanism that the host uses to partcipate in
label exchange with the network needs to be simple, and plug-and-
play. Existing signaling/routing protocols do not always meet this
need. Labeled ARP (L-ARP) is a proposal to fill that gap.
1.1. Approach
ARP is a nearly ubiquitous protocol; every device with an Ethernet
interface, from hand-helds to hosts, have an implementation of ARP.
ARP is plug-and-play; ARP clients do not need configuration to use
ARP. That suggests that ARP may be a good fit for devices that want
to source and sink MPLS tunnels, but do so in a zero-config, plug-
and-play manner, with minimal impact to their code.
The approach taken here is to create a minor variant of the ARP
protocol, labeled ARP (L-ARP), which is distinguished by a new
hardware type, MPLS-over-Ethernet. Regular (Ethernet) ARP (E-ARP)
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
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
to provide an IP-to-Ethernet and/or IP-to-MPLS mapping.
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2. Overview of Ethernet ARP
In the most straightforward mode of operation [RFC0826], ARP queries
are sent to resolve "directly connected" IP addresses. The ARP query
is broadcast, with the Target Protocol Address field (see Section 10
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
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
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
reply carries the replying node's MAC address in the Source Hardware
Address field, thus enabling two-way communication between the two
nodes.
A variation of this scheme, known as "proxy ARP" [RFC2002], allows a
node to respond to an ARP request with its own MAC address, even when
the responding node does not own the requested IP address.
Generally, the proxy ARP response is generated by routers to attract
traffic for prefixes they can forward packets to. This scheme
requires the host to send ARP queries for the IP address the host is
trying to reach, rather than the IP address of the router. When
there is more than one router connected to a network, proxy ARP
enables a host to automatically select an exit router without running
any routing protocol to determine IP reachability. Unlike regular
ARP, a proxy ARP request can elicit multiple responses, e.g., when
more than one router has connectivity to the address being resolved.
The sender must be prepared to select one of the responding routers.
Yet another variation of the ARP protocol, called 'Gratuitous ARP'
[RFC2002], allows a node to update the ARP cache of other nodes in an
unsolicited fashion. Gratuitous ARP is sent as either an ARP request
or an ARP reply. In either case, the Source Protocol Address and
Target Protocol Address contain the sender's address, and the Source
Hardware Address is set to the sender's hardware address. In case of
a gratuitous ARP reply, the Target Hardware Address is also set to
the sender's address.
3. L-ARP Protocol Operation
The L-ARP protocol builds on the proxy ARP model, and also leverages
gratuitous ARP model for asynchronous updates.
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
Figure 1, H1, H2 and H3 are L-ARP clients, and T1, T2 and T3 are IP
routers playing the role of L-ARP server. T4 is a member of the MPLS
Fabric that may not be an L-ARP server. Within the MPLS Fabric, the
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usual MPLS protocols (IGP, 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 the overlay virtual network technology). H1
might also want to talk to a member of the MPLS Fabric, say T (not
depicted in the diagram).
. . . . . .
. .
H1 --- T1 T4
\ . MPLS .
\ . .
\ . Fabric .
H2 --- T2 T3 --- H3
. .
. . . . . . .
Figure 1
3.1. Setup
In Figure 1, the nodes T1-T4, and those in between making up the
"MPLS Fabric" are assumed to be running some protocol whereby they
can signal MPLS reachability to themselves and to other nodes (like
H1-H3). T1-T3 are L-ARP servers; T4 need not be. H1-H3 are L-ARP
clients.
3.2. Egress Operation
A node (say T3) that wants an attached node (say H3) to have MPLS
reachability, allocates a label L3 to reach H3, and advertises this
label into the MPLS Fabric. This can be triggered by configuration
on T3, or via some other protocol. On receiving a packet with label
L3, T3 pops the label and send the packet to H3. This is the usual
operation of an MPLS Fabric, with the addition of advertising labels
for nodes outside the fabric.
3.3. Ingress 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.
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Note that H1 broadcasts its L-ARP request over its attached
interfaces. H1 may receive several L-ARP replies; in that case, H1
can select any subset of these to send MPLS packets destined to H3.
As described later, the L-ARP response may contain certain parameters
that enable the client to make an informed choice. However, it is
completely a matter of local policy on H1 which of the many responses
are used. Some possibilites include, but not limited to,
o Use the first reply that arrives, and ignore the rest
o Wait for a certain amount of time, and choose the response
carrying the least metric
o If there is more than one response carrying the least metric,
perform load-balancing among them
o Consult local configuration to select a gateway
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.
4. Attributes
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.
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5. Client-Server Synchronization
In an L-ARP reply, the server communicates several pieces of
information to the client: its hardware address, the MPLS label,
Entropy Label capability and metric. Since ARP is a stateless
protocol, it is possible that one of these changes without the client
knowing, which leads to a loss of synchronization between the client
and the server. This loss of synchronization can have several
undesirable effects.
If the server's hardware address changes or the MPLS label is
repurposed by the server for a different purpose, then packets may be
sent to the wrong destination. The consequences can range from
suboptimally routed packets to dropped packets to packets being
delivered to the wrong customer, which may be a security breach.
This last may be the most troublesome consequence of loss of
synchronization.
If a destination transitions from entropy label capable to entropy
label incapable (an unlikely event) without the client knowing, then
packets encapsulated with entropy labels will be dropped. A
transition in the other direction is benign.
If the metric changes without the client knowing, packets may be
suboptimally routed. This may be the most benign consequence of loss
of synchronization.
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. Likewise, an L-ARP server may withdraw its
earlier advertisement by sending an unsolicited LARP-NAK message.
5.1. Restart Handling
5.1.1. Server Restart
In order to support graceful restart, the L-ARP server must remember
the advertised bindings across restarts. The mechanism that the
L-ARP server uses to accomplish this is outside the scope of this
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document. Some possible mechanisms are, usage of shared memory or
non-volatile storage to store bindings. Upon restart, the L-ARP
server waits until the LSPs advertised in the previous incarnation
are restored. Then, it reconciles the L-ARP bindings with the
current state of the LSPs, updating the clients with unsolicted L-ARP
replies & NAK for bindings that have undergone changes.
During the above procedure, the client does not really know that the
server has restarted. If there were no changes to the LSPs during
restart, the client receives no updates. If there were changes, then
the client would receive unsolicited updates to the bindings, as it
would on a normal change. If the server does not successfully
restart, the client's periodic refresh will detect the loss of
connectivity and purge out the bindings.
If the L-ARP server does not support graceful restart, it SHOULD
withdraw the advertised bindings before shutting down. Unplanned
restarts rely on the slower perioidc refresh mechanism for re-
synchronization.
5.1.2. Client Restart
If the client restarts gracefully, it re-acquires the bindings
immediately after restart to learn about any changes.
If the client does not support graceful restart, it leaves the
bindings to age out.
5.2. Expedited Reachability Determination
As with other control protocols, the client and server may use data
plane liveness detection mechanisms, such as Loss of Signal (LOS)
and/or BFD, to expedite detection of loss of connectivity. However,
usage of these mechanisms are outside the scope of this document.
6. Applicability
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
switch going to the B-RAS. In seamless MPLS terms, L-ARP can be used
between an "Access Node" (AN) (e.g., the DSLAM) and its first hop
MPLS-enabled device in the context of Seamless MPLS
[I-D.ietf-mpls-seamless-mpls]. The first-hop device is part of the
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.
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ARP is not a routing protocol. The use of L-ARP should be limited to
cases where an L-ARP client has Ethernet connectivity to its L-ARP
servers.
7. Backward Compatibility
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,
receive and process ARP messages based on hardware type. They MAY
choose to ignore requests and replies of some hardware types; they
MAY choose to log errors if they encounter hardware types they do not
recognize; however, they MUST handle all hardware types gracefully.
For hardware types that they do understand, ARP servers and clients
MUST handle operation codes gracefully, processing those they
understand, and ignoring (and possibly logging) others.
8. OAM
L-ARP uses standard MPLS OAM procedures defined in [RFC4379] &
[RFC6424]. Extending the definitions in section 3.2 of RFC 4379, we
use a sub-type of [TO-BE-ASSIGNED-BY-IANA-1] to represent L-ARP IPv4
FEC, and [TO-BE-ASSIGNED-BY-IANA-2] to represent L-ARP IPv6 FEC. The
following sub-sections define the format of L-ARP FEC's.
8.1. L-ARP IPv4 FEC
The L-ARP IPv4 FEC is defined as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IPv4 address is the tunnel destination address.
Figure 2: ARP IPv4 FEC
The length of the L-ARP IPv4 FEC is 4 bytes.
8.2. L-ARP IPv6 FEC
The L-ARP IPv6 FEC is defined as follows:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv6 address |
| (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
IPv6 address is the tunnel destination address.
Figure 3: ARP IPv6 FEC
The length of the L-ARP IPv6 FEC is 16 bytes.
9. For Future Study
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 will be requested. Some of these are:
1. Keeping L-ARP clients and servers in sync. In particular,
dealing with:
A. client and/or server control plane restart
B. lost packets
C. timeouts
2. Dealing with scale.
3. If there are many servers, which one to pick?
4. How can a client make best use of underlying ECMP paths?
5. and probably many more.
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
on the client is preferable.
These questions (and others that come up during discussions) will be
dealt with in future versions of this draft.
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10. L-ARP Message Format
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$hrd | ar$pro |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ar$hln | ar$pln | ar$op |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// ar$sha (ar$hln octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// ar$spa (ar$pln octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// ar$tha (ar$hln octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// ar$tpa (ar$pln octets) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// ar$lst (variable...) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// ar$att (variable...) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: L-ARP Packet Format
ar$hrd Hardware Type: MPLS-over-Ethernet. The value of the field
used here is [HTYPE-MPLS]. To start with, we will use the
experimental value HW_EXP2 (256)
ar$pro Protocol Type: IPv4/IPv6. The value of the field used here
is 0x0800 to resolve an IPv4 address and 0x86DD to resolve an
IPv6 address.
ar$hln Hardware Length: 6.
ar$pln Protocol Address Length: for an IPv4 address, the value is 4;
for an IPv6 address, it is 16.
ar$op Operation Code: set to 1 for request, 2 for reply, and 10 for
ARP-NAK. Other op codes may be used as needed.
ar$sha Source Hardware Address: In an L-ARP message, Source Hardware
Address is the 6 octet sender's MAC address.
ar$spa Source Protocol Address: In an L-ARP message, this field
carries the sender's IP address.
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ar$tha Target Hardware Address: In an L-ARP query message, Target
Hardware Address is the all-ones Broadcast MAC address; in an
L-ARP reply message, it is the client's MAC address.
ar$tpa Target Protocol Address: In an L-ARP message, this field
carries the IP address for which the client is seeking an MPLS
label.
ar$lst Label Stack: In an L-ARP request, this field is empty. In an
L-ARP reply, this field carries the MPLS label stack as an ARP
TLV in the format below.
ar$att Attributes: In an L-ARP request, this field is empty. In an
L-ARP reply, this field carries attributes for the MPLS label
stack as an ARP TLV in the format below.
This document introduces the notion of ARP TLVs. These take the form
as in Figure 5. Figure 6 describes the format of Label Stack TLV
carried in L-ARP. Figure 7 describes the format of Attributes TLV
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Value (Length octets) ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type is the type of the TLV; Length is the length of the value field
in octets; Value is the value field.
Figure 5: 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | MPLS Label (20 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |E|Z|Z|Z| MPLS Label (20 bits) |E|Z|Z|Z|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: MPLS Label Stack Format
Label Stack: Type = TLV-LST; Length = n*3 octets, where n is the
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
octets. This field is valid only in an L-ARP reply message.
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E-bit: Entropy Label Capable: this flag indicates whether the
corresponding label in the label stack can be followd by an
Entropy Label. If this flag is set, the client has the option of
inserting ELI and EL as specified in [RFC6790]. The client can
choose not to insert ELI/EL pair. If this flag is clear, the
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
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Metric (4 octets) ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... Metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Attribute TLV
Attributes TLV: Type = TLV-ATT; Length = 4 octets. The Value field
contains the metric (typically, IGP distance) from the responder
to the destination (device with the requested IP address). If the
responder is the destination, then the metric value is zero. This
field is valid only in an L-ARP reply message.
If other parameters are deemed useful in the ATT TLV, they will be
added as needed.
11. Security Considerations
There are many possible attacks on ARP: ARP spoofing, ARP cache
poisoning and ARP poison routing, to name a few. These attacks use
gratuitous ARP as the underlying mechanism, a mechanism used by
L-ARP. Thus, these types of attacks are applicable to L-ARP.
Furthermore, ARP does not have built-in security mechanisms; defenses
rely on means external to the protocol.
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
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,
although in principle, other ARP messages could use it as well. Such
an approach would, of course, need a review and approval by the
Security Directorate. If approved, the type of this TLV and its
procedures would be defined in this document. If some other
technique is suggested, the authors would be happy to include the
relevant text in this document, and refer to some other document for
the full solution.
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12. IANA Considerations
IANA is requested to allocate a new ARP hardware type (from the
registry hrd) for HTYPE-MPLS.
IANA is also requested to create a new registry ARP-TLV ("tlv").
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
128-251 are FCFS; and the values 252-255 are Experimental.
Finally, IANA is requested to allocate two values in the ARP-TLV
registry, one for TLV-LST and another for TLV-ATT.
13. Acknowledgments
Many thanks to Shane Amante for his detailed comments and
suggestions. Many thanks to the team in Juniper prototyping this
work for their suggestions on making this variant workable in the
context of existing ARP implementations. Thanks too to Luyuan Fang,
Alex Semenyaka and Dmitry Afanasiev for their comments and
encouragement.
14. References
14.1. Normative References
[RFC0826] Plummer, D., "Ethernet Address Resolution Protocol: Or
Converting Network Protocol Addresses to 48.bit Ethernet
Address for Transmission on Ethernet Hardware", STD 37,
RFC 826, DOI 10.17487/RFC0826, November 1982,
<http://www.rfc-editor.org/info/rfc826>.
[RFC2002] Perkins, C., Ed., "IP Mobility Support", RFC 2002,
DOI 10.17487/RFC2002, October 1996,
<http://www.rfc-editor.org/info/rfc2002>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol
Label Switched (MPLS) Data Plane Failures", RFC 4379,
DOI 10.17487/RFC4379, February 2006,
<http://www.rfc-editor.org/info/rfc4379>.
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[RFC6424] Bahadur, N., Kompella, K., and G. Swallow, "Mechanism for
Performing Label Switched Path Ping (LSP Ping) over MPLS
Tunnels", RFC 6424, DOI 10.17487/RFC6424, November 2011,
<http://www.rfc-editor.org/info/rfc6424>.
[RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and
L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
RFC 6790, DOI 10.17487/RFC6790, November 2012,
<http://www.rfc-editor.org/info/rfc6790>.
14.2. Informative References
[I-D.gredler-idr-bgplu-epe]
Gredler, H., Vairavakkalai, K., R, C., Rajagopalan, B.,
and L. Fang, "Egress Peer Engineering using BGP-LU",
draft-gredler-idr-bgplu-epe-04 (work in progress),
September 2015.
[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
Kireeti Kompella
Juniper Networks
1194 N. Mathilda Avenue
Sunnyvale, CA 94089
USA
Email: kireeti.kompella@gmail.com
Balaji Rajagopalan
Juniper Networks, Inc.
Prestige Electra, Exora Business Park
Marathahalli - Sarjapur Outer Ring Road
Bangalore 560103
India
Email: balajir@juniper.net
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George Swallow
Cisco Systems
1414 Massachusetts Ave
Boxborough, MA 01719
US
Email: swallow@cisco.com
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