[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]
Versions: 00 01 02 03 04 05 06 07 08 09 10 11
12 13 RFC 5534
Network Working Group J. Arkko
Internet-Draft Ericsson
Expires: June 24, 2006 I. Beijnum
Muada
December 21, 2005
Failure Detection and Locator Pair Exploration Protocol for IPv6
Multihoming
draft-ietf-shim6-failure-detection-03
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
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."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on June 24, 2006.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document defines a mechanism for the detection of communication
failures between two communicating hosts at IP layer, and an
exploration protocol for switching to another pair of interfaces
and/or addresses between the same hosts if a working pair can be
found. The draft also discusses the roles of a multihoming protocol
versus network attachment functions at IP and link layers.
Arkko & Beijnum Expires June 24, 2006 [Page 1]
Internet-Draft Failure Detection Protocol December 2005
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements language . . . . . . . . . . . . . . . . . . . . 4
3. Related Work . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.1. Available Addresses . . . . . . . . . . . . . . . . . . 7
4.2. Locally Operational Addresses . . . . . . . . . . . . . 7
4.3. Operational Address Pairs . . . . . . . . . . . . . . . 8
4.4. Current Address Pair . . . . . . . . . . . . . . . . . . 9
4.5. Miscellaneous . . . . . . . . . . . . . . . . . . . . . 10
5. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 11
5.1. Failure Detection . . . . . . . . . . . . . . . . . . . 11
5.2. Alternative Address Pair Exploration . . . . . . . . . . 13
5.3. Exploration Order . . . . . . . . . . . . . . . . . . . 14
5.4. Protocol Design . . . . . . . . . . . . . . . . . . . . 14
5.5. Example Protocol Runs . . . . . . . . . . . . . . . . . 15
5.6. Limitations . . . . . . . . . . . . . . . . . . . . . . 21
6. Protocol Definition . . . . . . . . . . . . . . . . . . . . . 22
6.1. Keepalive Message . . . . . . . . . . . . . . . . . . . 22
6.1.1. Keepalive Option . . . . . . . . . . . . . . . . 23
6.2. Probe Message . . . . . . . . . . . . . . . . . . . . . 24
6.2.1. Probe Option . . . . . . . . . . . . . . . . . . 25
6.3. Reachability Option . . . . . . . . . . . . . . . . . . 26
6.3.1. Payload Reception Report . . . . . . . . . . . . 27
6.3.2. Probe Reception Report . . . . . . . . . . . . . 28
6.4. Behaviour . . . . . . . . . . . . . . . . . . . . . . . 29
6.5. Protocol Constants . . . . . . . . . . . . . . . . . . . 33
7. Security Considerations . . . . . . . . . . . . . . . . . . . 34
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 36
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 37
9.1. Normative References . . . . . . . . . . . . . . . . . . 37
9.2. Informative References . . . . . . . . . . . . . . . . . 37
Appendix A. Contributors . . . . . . . . . . . . . . . . . . . . 39
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 40
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 41
Intellectual Property and Copyright Statements . . . . . . . . . . 42
Arkko & Beijnum Expires June 24, 2006 [Page 2]
Internet-Draft Failure Detection Protocol December 2005
1. Introduction
The SHIM6 protocol extends IPv6 to support multihoming. This
protocol is an IP layer mechanism that hides multihoming from
applications [18]. A part of the SHIM6 solution involves detecting
when a currently used pair of addresses (or interfaces) between two
communication hosts has failed, and picking another pair when this
occurs. We call the former failure detection, and the latter locator
pair exploration.
This draft defines the mechanism and protocol to achieve both failure
detection and locator pair exploration. This protocol is called
REAchability Protocol (REAP). It designed to be carried within the
SHIM6 protocol, but may also be used in other contexts.
The draft is structured as follows: Section 3 discusses prior work in
this space, Section 4 defines a set of useful terms, Section 5 gives
an overview of REAP, and Section 6 specifies the message formats and
behaviour in detail. Section 7 discusses the security considerations
of REAP.
For the purposes of this draft, we consider an address to be
synonymous with a locator. We assume that there are other, higher
level identifiers such as CGA public keys or HBA bindings that tie
the different locators used by a node together [17].
Arkko & Beijnum Expires June 24, 2006 [Page 3]
Internet-Draft Failure Detection Protocol December 2005
2. Requirements language
In this document, the key words "MAY", "MUST, "MUST NOT", "OPTIONAL",
"RECOMMENDED", "SHOULD", and "SHOULD NOT", are to be interpreted as
described in [2].
Arkko & Beijnum Expires June 24, 2006 [Page 4]
Internet-Draft Failure Detection Protocol December 2005
3. Related Work
In SCTP [10], the addresses of the endpoints are learned in the
connection setup phase either through listing them explicitly or via
giving a DNS name that points to them. In order to provide a
failover mechanism between multihomed hosts, SCTP selects one of the
peer's addresses as the primary address by the application running on
top of SCTP. All data packets are sent to this address until there
is a reason to choose another address, such as the failure of the
primary address.
SCTP also tests the reachability of the peer endpoint's addresses.
This is done both via observing the data packets sent to the peer or
via a periodic heartbeat when there is no data packets to send. Each
time data packet retransmission is initiated (or when a heartbeat is
not answered within the estimated round-trip time) an error counter
is incremented. When a configured error limit is reached, the
particular destination address is marked as inactive. The reception
of an acknowledgement or heartbeat response clears the counter.
Retransmission: When retransmitting the endpoint attempts pick the
most "divergent" source-destination pair from the original source-
destination pair to which the packet was transmitted. Rules for such
selection are, however, left as implementation decisions in SCTP.
SCTP does not define how local knowledge (such as information learned
from the link layer) should be used. SCTP also has no mechanism to
deal with dynamic changes to the set of available addresses, although
mechanisms for that are being developed [20].
The MOBIKE protocol [15] provides multihoming and mobility for VPN
connections. Its failure detection and locator pair exploration is
designed to work across mixed IPv4/IPv6 environments and NATs, as
long as a path that allows bidirectional communication can be found.
Existing mechanisms at lower layers or in IKEv2 are used to detect
failures, and upon failure MOBIKE attempts to explore all
combinations of addresses to find a working pair. Such exploration
is necessary when a problem affects both nodes. For instance, two
nodes connected by two separate point-to-point links will be unable
to switch to the other link if a failure occurs on the first one.
While both communicating hosts are aware of each others' addresses,
only one end of the communication is in charge of deciding what
address pair to use, however.
The mobility and multihoming specification for the HIP protocol [14]
leaves the determination of when address updates are sent to a local
policy, but suggests the use of local information and ICMP error
messages.
Arkko & Beijnum Expires June 24, 2006 [Page 5]
Internet-Draft Failure Detection Protocol December 2005
Network attachment procedures are also relevant for multihoming. The
IPv6 and MIP6 working groups have standardized mechanisms to learn
about networks that a node has attached to. Basic IPv6 Neighbor
Discovery was, however, designed primarily for static situations.
The fully dynamic detection procedure has turned out to be a
relatively complex procedure for mobile hosts, and it was not fully
anticipated at the time IPv6 Neighbor Discovery or DHCP were being
designed. As a result, enhanced or optimized mechanisms are being
designed in the DHC and DNA working groups [13] [7].
ICE [16], STUN [11], and TURN [24] are also related mechanisms. They
are primarily used for NAT detection and communication through NATs
in IPv4 environment, for application such as as voice over IP. STUN
uses a server in the Internet to discover the presence and type of
NATs and the client's public IP addresses and ports. TURN makes it
possible to receive incoming connections in hosts behind NATs. ICE
makes use of these protocols in peer-to-peer cooperative fashion,
allowing participants to discover, create and verify mutual
connectivity, and then use this connectivity for multimedia streams.
While these mechanisms are not designed for dynamic and failure
situations, they have many of the same requirements for the
exploration of connectivity, as well as the requirement to deal with
middleboxes.
Related work in the IPv6 area includes RFC 3484 [6] which defines
source and destination address selection rules for IPv6 in situations
where multiple candidate address pairs exist. RFC 3484 considers
only a static situation, however, and does not take into account the
effect of failures. Reference [23] considers how applications can
re-initiate connections after failures in the best way. This work
differs from the shim-layer approach selected for further development
in the working group with respect to the timing of the address
selection. In the shim-layer approach failure detection and the
selection of new addresses happens at any time, while [23] considers
only the case when an application re-establishes connections.
An earlier SHIM6 document [19] discussed what kind of mechanisms can
be used to detect whether the peer is still reachable at the
currently used address. Two proposed mechanisms, Correspondent
Unreachability Detection (CUD) and Forced Bidirectional Communication
(FBD) were presented. CUD is based on getting upper layer positive
feedback, and IPv6 NUD-like probing if there is no feedback. FBD is
based on forcing bidirectional communication by adding keepalive
messages when there is no other, payload traffic. FBD is the chosen
mechanism in this document.
Arkko & Beijnum Expires June 24, 2006 [Page 6]
Internet-Draft Failure Detection Protocol December 2005
4. Definitions
This section defines terms useful in discussing the problem space.
4.1. Available Addresses
Multihoming nodes need to be aware of what addresses they themselves
have. If a node loses the address it is currently using for
communications, another address must replace this address. And if a
node loses an address that the node's peer knows about, the peer must
be informed. Similarly, when a node acquires a new address it may
generally wish the peer to know about it.
Definition. Available address. An address is said to be available
if the following conditions are fulfilled:
o The address has been assigned to an interface of the node.
o If the address is an IPv6 address, we additionally require that
(a) the address is valid in the sense of RFC 2461 [3], and that
(b) the address is not tentative in the sense of RFC 2462 [4]. In
other words, the address assignment is complete so that
communications can be started.
Note that this explicitly allows an address to be optimistic in
the sense of [8] even though implementations are probably better
off using other addresses as long as there is an alternative.
o The address is a global unicast, unique local address [9], or an
unambiguous IPv6 link-local address. That is, it is not an IPv6
site-local address. Where IPv6 link-local addresses are used,
their use needs to be unambiguous as follows. At most one link-
local address may be used per node within the same connection
between two peers.
o The address and interface is acceptable for use according to a
local policy.
Available addresses are discovered and monitored through mechanisms
outside the scope of the protocol described here. These mechanisms
include IPv6 Neighbor Discovery and Address Autoconfiguration [3]
[4], DHCP [5], and DNA mechanisms [7].
4.2. Locally Operational Addresses
Two different granularity levels are needed for failure detection.
The coarser granularity is for individual addresses:
Arkko & Beijnum Expires June 24, 2006 [Page 7]
Internet-Draft Failure Detection Protocol December 2005
Definition. Locally Operational Address. An available address is
said to be locally operational when its use is known to be possible
locally: the interface is up, at least one default router (if
applicable) that could be used to send a packet with this address as
a source address is known to be reachable, and no other local
information points to the address being unusable.
Locally operational addresses are discovered and monitored through
mechanisms outside the protocol described here. These mechanisms
include IPv6 Neighbor Discovery [3] and link layer specific
mechanisms.
It is also possible for hosts to learn about routing failures for a
particular selected source prefix, if suitable protocols for this
purpose exist. Some proposals in this space have been made, see, for
instance [21] and [23]. Potential approaches include overloading
information in current IPv6 Router Advertisement or adding some new
information in them. Similarly, hosts could learn information from
servers that query the BGP routing tables.
4.3. Operational Address Pairs
The existence of locally operational addresses are not, however, a
guarantee that communications can be established with the peer. A
failure in the routing infrastructure can prevent the sent packets
from reaching their destination. For this reason we need the
definition of a second level of granularity, for pairs of addresses:
Definition. Bidirectionally operational address pair. A pair of
locally operational addresses are said to be an operational address
pair, iff bidirectional connectivity can be shown between the
addresses. That is, a packet sent with one of the addresses in the
source field and the other in the destination field reaches the
destination, and vice versa.
Unfortunately, there are scenarios where bidirectionally operational
address pairs do not exist. For instance, ingress filtering or
network failures may result in one address pair being operational in
one direction while another one is operational from the other
direction. The following definition captures this general situation:
Definition. Undirectionally operational address pair. A pair of
locally operational addresses are said to be an unidirectionally
operational address pair, iff packets sent with the first address as
the source and the second address as the destination can be shown to
reach the destination.
Both types of operational pairs could be discovered and monitored
Arkko & Beijnum Expires June 24, 2006 [Page 8]
Internet-Draft Failure Detection Protocol December 2005
through the following mechanisms:
o Positive feedback from upper layer protocols. For instance, TCP
can indicate to the IP layer that it is making progress. This is
similar to how IPv6 Neighbor Unreachability Detection can in some
cases be avoided when upper layers provide information about
bidirectional connectivity [3]. In the case of unidirectional
connectivity, the upper layer protocol responses come back using
another address pair, but show that the messages sent using the
first address pair have been received.
o Negative feedback from upper layer protocols. It is conceivable
that upper layer protocols give an indication of a problem to the
multihoming layer. For instance, TCP could indicate that there's
either congestion or lack of connectivity in the path because it
is not getting ACKs.
o Explicit reachability tests, such as keepalives or probes added
when there's only unidirectional payload traffic.
o ICMP error messages. Given the ease of spoofing ICMP messages,
one should be careful to not trust these blindly, however. Our
suggestion is to use ICMP error messages only as a hint to perform
an explicit reachability test, but not as a reason to disrupt
ongoing communications without other indications of problems. The
situation may be different when certain verifications of the ICMP
messages are being performed [22]. These verifications can ensure
that (practically) only on-path attackers can spoof the messages.
Note a multihoming protocol needs to perform a return routability
test of an address before it is taken into use. The purpose of this
test is to ensure that fraudulent peers do not trick others into
redirecting traffic streams onto innocent victims [25]. This test
can at the same time work as a means to ensure that an address pair
is operational, as discussed in Section 5.2.
4.4. Current Address Pair
IP-layer solutions need to avoid sending packets concurrently over
multiple paths; TCP behaves rather poorly in such circumstances. For
this reason it is necessary to choose a particular pair of addresses
as the current address pair which is used until problems occur, at
least for the same session.
A current address pair need not be operational at all times. If
there is no traffic to send, we may not know if the primary address
pair is operational. Nevertheless, it makes sense to assume that the
address pair that worked in some time ago continues to work for new
Arkko & Beijnum Expires June 24, 2006 [Page 9]
Internet-Draft Failure Detection Protocol December 2005
communications as well.
4.5. Miscellaneous
Addresses can become deprecated [3]. When other operational
addresses exist, nodes generally wish to move their communications
away from the deprecated addresses.
Similarly, IPv6 source address selection [6] may guide the selection
of a particular source address - destination address pair.
Arkko & Beijnum Expires June 24, 2006 [Page 10]
Internet-Draft Failure Detection Protocol December 2005
5. Protocol Overview
This section discusses the design of the reachability detection and
address pair exploration mechanisms, and gives on overview of the
REAP protocol.
A naive implementation of an (un)reachability detection mechanism
could just probe all possible paths between two hosts periodically.
A "path" is defined as a combination of a source address for host A
and a destination address for host B. In hop-by-hop forwarding the
source address has no effect on reachability, but in the presence of
filters or source address based routing, it may. And although links
almost always work in two directions, routing protocols and filters
only work in one direction so unidirectional reachability is
possible. Without additional mechanisms, the practice of ingress
filtering by ISPs makes unidirectional connectivity likely. Being
able to use the working leg in a unidirectional path is useful, it's
not an essential requirement. It is essential, however, to avoid
assuming bidirectional connectivity when there is in fact a
unidirectional failure.
Exploring the full set of communication options between two hosts
that both have two or more addresses is an expensive operation as the
number of combinations to be explored increases very quickly with the
number of addresses. For instance, with two addresses on both sides,
there are four possible address pairs. Since we can't assume that
reachability in one direction automatically means reachability for
the complement pair in the other direction, the total number of two-
way combinations is eight. (Combinations = nA * nB * 2.)
An important observation in multihoming is that failures are
relatively infrequent, so that a path that worked a few seconds ago
is very likely to work now as well. So it makes sense to have a
light-weight protocol that confirms existing reachability, and only
invoke heavier exploration when a there is a suspected failure.
5.1. Failure Detection
This process consists of three tasks. First, it is necessary to
track local information from lower and upper layers. For instance,
when link layer informs that we have no connection then we know there
is a failure. Nodes SHOULD employ techniques listed in Section 4.1
and Section 4.2 to be aware of the local situation.
Similarly, it is necessary to track remote address information from
the peer. For instance, the peer may inform that its currently used
address is no longer in use. Techniques outside the scope of this
document are used for this, for further information see [18].
Arkko & Beijnum Expires June 24, 2006 [Page 11]
Internet-Draft Failure Detection Protocol December 2005
The third task is to ensure verify reachability with the peer when
the local and remote information indicates that communication should
be possible. This needs to be performed only if there's upper layer
packets to be sent, however.
This document defines the protocol mechanisms only for the third
task. We employ a technique called Forced Bidirectional Detection
(FBD). Reachability for the currently used address pair in a shim
context is determined by making sure that whenever there is data
traffic in one direction, there is also traffic in the other
direction. This can be data traffic as well, but also transport
layer acknowledgments or a REAP reachability keepalive if there is no
other traffic. This way, it is no longer possible to have traffic in
only one direction, so whenever there is data traffic going out, but
there are no return packets, there must be a failure, so the full
path exploration mechanism is started.
A more detailed description of the current pair reachability
evaluation mechanism:
1. The base timing unit for this mechanism is named Keepalive
Timeout. Until a negotiation mechanism to negotiate different
values for this timer becomes available, the value (3 seconds)
specified in Section 6.5 SHOULD be used.
2. Whenever outgoing data packets are generated that are part of a
shim context, a timer is started to reflect the requirement that
the peer should generate return traffic from data packets.
3. Whenever incoming data packets are received that are part of a
shim context, the timer associated with the return traffic from
the peer is stopped, and another timer is started to reflect the
requirement for this node to generate return traffic.
4. The reception of a REAP keepalive packet leads to stopping the
timer associated with the return traffic from the peer.
5. Keepalive Timeout seconds after the last data packet has been
received for a context, and if no other packet has been sent
within this context since the data packet has been received, a
REAP keepalive packet is generated for the context in question
and transmitted to the correspondent. A host may send the
keepalive sooner than Keepalive Timeout seconds if implementation
considerations warrant this. The average time after which
keepalives are sent MUST be at least Keepalive Timeout / 2
seconds. After sending a single keepalive message, no additional
keepalive messages are sent until a data packet is received
within this shim context. Keepalives are not sent at all when a
Arkko & Beijnum Expires June 24, 2006 [Page 12]
Internet-Draft Failure Detection Protocol December 2005
data packet was sent since the last received data packet.
6. Send Timeout seconds (10 s; see Section 6.5) after the
transmission of a data packet with no return traffic on this
context, a full reachability exploration is started. This
timeout period is larger than the Keepalive Timeout to
accommodate for lost keepalives and regular variations in round
trip times.
5.2. Alternative Address Pair Exploration
As explained in previous section, the currently used address pair may
become invalid either through one of the addresses being becoming
unavailable or inoperational, or the pair itself being declared
inoperational. An exploration process attempts to find another
operational pair so that communications can resume.
What makes this process hard is the requirement to support
unidirectionally operational address pairs. It is insufficient to
probe address pairs by a simple request - response protocol.
Instead, the party that first detects the problem starts a process
where it tries each of the different address pairs in turn by sending
a message to its peer. These messages carry information about the
state of connectivity between the peers, such as whether the sender
has seen any traffic from the peer recently. When the peer receives
a message that indicates a problem, it assists the process by
starting its own parallel exploration to the other direction, again
sending information about the recently received payload traffic or
signaling messages.
Specifically, when A decides that it needs to explore for an
alternative address pair to B, it will initiate a set of Probe
messages, in sequence, until it gets an Probe message from B
indicating that (a) B has received one of A's messages and,
obviously, (b) that B's Probe message gets back to A. B uses the same
algorithm, but starts the process from the reception of the first
Probe message from A.
Upon changing to a new address pair, transport layer protocol needs
to be informed so that it can perform a slow start, or some other
form of adaptation to the possibly changed conditions. However, this
functionality is outside the scope of REAP and is rather seen as a
general multihoming issue.
Similarly, one can also envision that applications would be able to
tell the IP or transport layer that the current connection in
unsatisfactory and an exploration for a better one would be
desirable. This would require an API to be developed, however. In
Arkko & Beijnum Expires June 24, 2006 [Page 13]
Internet-Draft Failure Detection Protocol December 2005
any case, this is another issue that we treat as being outside the
scope of pure address exploration.
5.3. Exploration Order
The exploration process assumes an ability to pick current and
alternative address pairs. This process may result in a
combinatorial explosion when there are many addresses on both sides,
but a back-off procedure is employed to avoid a "signaling storm".
Nodes MUST first consult RFC 3484 [6] Section 4 rules to determine
what combinations of addresses are allowed from a local point of
view, as this reduces the search space. RFC 3484 also provides a
priority ordering among different address pairs, making the search
possibly faster. Nodes MAY also use local information, such as known
quality of service parameters or interface types to determine what
addresses are preferred over others, and try pairs containing such
addresses first. The multihoming protocol also carries preference
information in its messages [18].
Discussion note: The preferences may either be learned dynamically
or be configured. It is believed, however, that dynamic learning
based purely on the multihoming protocol is too hard and not the
task this layer should do. Solutions where multiple protocols
share their information in a common pool of locators could provide
this information from transport protocols, however.
One suggested good implementation strategy is to record the
reachability test result (an on/off value) and multiply this by the
age of the information. This allows recently tested address pairs to
be chosen before old ones.
Out of the set of possible candidate address pairs, nodes SHOULD
attempt a test through all of them until a working pair is found, and
retrying the process as is necessary. However, all nodes MUST
perform this process sequentially and with exponential back-off.
This sequential process is necessary in order to avoid a "signaling
storm" when an outage occurs (particularly for a complete site).
However, it also limits the number of addresses that can in practice
be used for multihoming, considering that transport and application
layer protocols will fail if the switch to a new address pair takes
too long.
5.4. Protocol Design
REAP is designed as a modular part of SHIM6 in the hopes that it may
also be useful in other contexts. This document defines how it is
Arkko & Beijnum Expires June 24, 2006 [Page 14]
Internet-Draft Failure Detection Protocol December 2005
carried within SHIM6, but the actual protocol messages are self-
contained so that it could be carried by other protocols as well.
The REAP design allows performing both failure detection and address
pair exploration in the same sequence of messages, without a need to
designate a specific point when the current address pair is declared
inoperational and the search for a new pair begins. This is useful,
as the loss of a small number of packets is not a proof that a
problem exists. Integrated failure detection and exploration allows
us to test multiple address pairs simultaneously, including the
current pair in case it starts working again. For instance, the
exploration process can refer to keepalive message that succeeded in
getting to the peer during the reachability testing phase.
REAP also integrates a return routability function, making it
unnecessary to perform another roundtrip before a newly discovered
address can be taken into use.
This document defines a minimal set of parameters that are carried by
the messages of the protocol. Specifically, we have limited the
parameters to those that are necessary to find a working path. We
note there may be extensions that are needed in the future for
various reasons, such as the desire to support load balancing or
finding best paths. An option format has been specified to allow
this.
5.5. Example Protocol Runs
This section has examples of REAP protocol runs in typical scenarios.
We start with the simplest scenario of two hosts, A and B, that have
a SHIM6 connection with each other but are not currently sending any
data. As neither side sends anything, they also do not expect
anything back, so there are no messages at all:
Peer A Peer B
| |
| |
| |
| |
| |
| |
| |
| |
Our second example involves an active connection with bidirectional
payload packet flows. Here the reception of data from the peer is
taken as an indication of reachability, so again there are no extra
packes:
Arkko & Beijnum Expires June 24, 2006 [Page 15]
Internet-Draft Failure Detection Protocol December 2005
Peer A Peer B
| |
| payload packet |
|-------------------------------------------->|
| |
| payload packet |
|<--------------------------------------------|
| |
| payload packet |
|-------------------------------------------->|
| |
| |
The third example is the first one that involves an actual REAP
message. Here the hosts communicate in just one direction, so REAP
messages are needed to indicate to the peer that sends payload
packets that its packets are getting through:
Peer A Peer B
| |
| payload packet |
|-------------------------------------------->|
| |
| payload packet |
|-------------------------------------------->|
| |
| payload packet |
|-------------------------------------------->|
| |
| Keepalive id=p |
|<--------------------------------------------|
| |
| payload packet |
|-------------------------------------------->|
| |
| |
Finally, our last example involves a failure scenario. Here A has
addresses A1 and A2 and B has addresses B1 and B2. The currently
used address pairs are (A1, B1) and (B1, A1). The first of these
becomes broken, which leads to an exploration process:
Peer A Peer B
| |
| (A1,B1) payload packet |
|-------------------------------------------->|
| |
| (B1,A1) payload packet |
Arkko & Beijnum Expires June 24, 2006 [Page 16]
Internet-Draft Failure Detection Protocol December 2005
|<--------------------------------------------| Time T1
| | Path A1->B1
| (A1,B1) payload packet | is now
|----------------------------------------/ | broken
| |
| (B1,A1) payload packet |
|<--------------------------------------------|
| |
| (A1,B1) payload packet |
|----------------------------------------/ |
| |
| (B1,A1) payload packet |
|<--------------------------------------------|
| |
| (A1,B1) payload packet |
|----------------------------------------/ |
| |
| | 10 seconds after
| | T1, sends a com-
| (B1,A1) Probe id=p, | plaint that
| iseeyou=no | it is not rec-
|<--------------------------------------------| eiving anything
| |
A realizes |
that it needs |
to start the |
exploration |
| |
| (A1, B1) Probe id=q, |
| iseeyou=yes |
| payload reception rep |
| probe reception rep(p) | But it gets lost
|-------------------------------------/ | due to broken path
| |
Retransmission |
to a different |
address |
| |
| (A1, B2) Probe id=r, |
| iseeyou=yes |
| payload reception rep |
| probe reception rep(p) | This one gets
|-------------------------------------------->| through
| |
| |
| | B now knows
| | that A has no
| (B1,A1) Probe id=p, | problem to receive
Arkko & Beijnum Expires June 24, 2006 [Page 17]
Internet-Draft Failure Detection Protocol December 2005
| iseeyou=yes, | its packets and
| probe reception rep(r) | This one gets
|<--------------------------------------------| that A has found
| | a new path to B
| |
| (A1,B2) payload packet |
|-------------------------------------------->| Payload packets
| | flow again
| (B1,A1) payload packet |
|<--------------------------------------------|
The next example shows when the failure for the current locator pair
is in the other direction:
Arkko & Beijnum Expires June 24, 2006 [Page 18]
Internet-Draft Failure Detection Protocol December 2005
Peer A Peer B
| |
| (A1,B1) payload packet |
|-------------------------------------------->|
| |
| (B1,A1) payload packet |
| /-----------------------------------------| Time T1
| | Path B1->A1
| | is now
| | broken
| (B1,A1) payload packet |
| /-----------------------------------------|
| |
| (B1,A1) payload packet |
| /-----------------------------------------|
| |
| | 10 seconds after
| | T1, sends a com-
| (B1,A1) Probe id=p, | plaint that
| iseeyou=no | it is not rec-
| /-----------------------------------------| eiving anything
| |
| (B2,A2) Probe id=q, |
| iseeyou=no | Next try different
|<--------------------------------------------| locator pair
| |
| (A2, B2) Probe id=r, |
| iseeyou=yes |
| payload reception rep |
| probe reception rep(q) | This one gets
|-------------------------------------------->| through
| |
| |
| | B now knows
| | that A has no
| (B2,A2) Probe id=s, | problem to receive
| iseeyou=yes, | its packets and
| probe reception rep(r) | This one gets
|<--------------------------------------------| that A has found
| | a new path to B
| |
| (A2,B2) payload packet |
|-------------------------------------------->| Payload packets
| | flow again
| (B2,A2) payload packet |
|<--------------------------------------------|
In the next case we have even less luck. The response to the REAP
Arkko & Beijnum Expires June 24, 2006 [Page 19]
Internet-Draft Failure Detection Protocol December 2005
probe doesn't make it in the reverse direction, so both ends end up
exploring indepedently:
Peer A Peer B
| |
| (A1,B1) payload packet |
|-------------------------------------------->|
| |
| (B1,A1) payload packet |
| /-----------------------------------------| Time T1
| | Path B1->A1
| | is now
| | broken
| (B1,A1) payload packet |
| /-----------------------------------------|
| |
| (B1,A1) payload packet |
| /-----------------------------------------|
| |
| | 10 seconds after
| | T1, sends a com-
| (B1,A1) Probe id=p, | plaint that
| iseeyou=no | it is not rec-
| /-----------------------------------------| eiving anything
| |
| (B2,A2) Probe id=q, |
| iseeyou=no | Next try different
|<--------------------------------------------| locator pair
| |
A now knows that it needs |
to start exploring |
| |
| (A2, B2) Probe id=r, |
| iseeyou=yes |
| payload reception rep |
| probe reception rep(q) |
|--------------------------------------/ | Doesn't make it
| |
| (A1, B1) Probe id=s, |
| iseeyou=yes |
| payload reception rep |
| probe reception rep(q) | This one gets
|-------------------------------------------->| through
| |
| |
| | B now knows
| | that A has no
| (B2,A2) Probe id=t, | problem to receive
Arkko & Beijnum Expires June 24, 2006 [Page 20]
Internet-Draft Failure Detection Protocol December 2005
| iseeyou=yes, | its packets and
| probe reception rep(r) | This one gets
|<--------------------------------------------| that A has found
| | a new path to B
| |
| (A1,B1) payload packet |
|-------------------------------------------->| Payload packets
| | flow again
| (B2,A2) payload packet |
|<--------------------------------------------|
5.6. Limitations
REAP is designed to support failure recovery even in the case of
having only unidirectionally operational address pairs. However, due
to security concerns discussed in Section 7, the exploration process
can typically be run only for a session that has already been
established. Specifically, while REAP would in theory be capable of
exploration even during connection establishment, its use within the
SHIM6 protocol does not allow this.
Arkko & Beijnum Expires June 24, 2006 [Page 21]
Internet-Draft Failure Detection Protocol December 2005
6. Protocol Definition
6.1. Keepalive Message
The format of the keepalive message is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len |0| Type = 66 | Reserved |0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Checksum |R| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Receiver Context Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Options +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Next Header
This value MUST be set to NO_NXT_HDR (59).
Type
This field identifies the Probe message and MUST be set to 66
(Keepalive).
Reserved
This is a 7-bit field reserved for future use. It is set to zero
on transmit, and MUST be ignored on receipt.
R
This is a 1-bit field reserved for future use. It is set to zero
on transmit, and MUST be ignored on receipt.
Receiver Context Tag
This is a 47-bit field for the Context Tag the receiver has
allocated for the context.
Options
This MUST contain at least the Keepalive option and MAY contain
one or more Reachability options.The inclusion of the latter
Arkko & Beijnum Expires June 24, 2006 [Page 22]
Internet-Draft Failure Detection Protocol December 2005
options is not necessary, however, as there are currenly no
defined options that are useful in a Keepalive message. These
options are provided only for future extensibility reasons.
A valid message conforms to the format above, has a Receiver Context
Tag that matches to context known by the receiver, is valid shim
control message as defined in Section 12.2 of [18], and its shim
context state is ESTABLISHED. The receiver processes a valid message
by inspecting its options, and executing any actions specified for
such options.
The processing rules for this message are the given in more detail in
Section 6.4.
6.1.1. Keepalive Option
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 10 |0| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Res | Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
This value MUST be set to 10 (Keepalive Option).
0
This value MUST be set to 0, as in other SHIM6 options.
Length
This is the length of the option and MUST be calculated as
specified in Section 5.14 of [18].
Res
This 4-bit reserved field MUST be set to zero when sending, and
ignored on receipt.
Identifier
This 28-bit field identifies this particular instance of an
Keepalive message. This value SHOULD be generated using a random
number generator that is known to have good randomness properties
[1]. Upon reception, Identifier values from both Keepalive and
Arkko & Beijnum Expires June 24, 2006 [Page 23]
Internet-Draft Failure Detection Protocol December 2005
Probe messages may be copied onto Probe Reception Report options.
This allows them to be used for both identifying which packets
were received as well as for performing a return routability test.
The processing rules for this option are the given in more detail in
Section 6.4.
6.2. Probe Message
This message performs REAP exploration. Its format is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len |0| Type = 67 | Reserved |0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Checksum |R| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Receiver Context Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Options +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Next Header
This value MUST be set to NO_NXT_HDR (59).
Type
This field identifies the Probe message and MUST be set to 67
(Probe).
Reserved
This is a 7-bit field reserved for future use. It is set to zero
on transmit, and MUST be ignored on receipt.
R
This is a 1-bit field reserved for future use. It is set to zero
on transmit, and MUST be ignored on receipt.
Receiver Context Tag
This is a 47-bit field for the Context Tag the receiver has
allocated for the context.
Arkko & Beijnum Expires June 24, 2006 [Page 24]
Internet-Draft Failure Detection Protocol December 2005
Options
This MUST contain at least the Probe option and MAY contain one or
more Reachability options.
A valid message conforms to the format above, has a Receiver Context
Tag that matches to a context known by the receiver, is valid shim
control message as defined in Section 12.2 of [18], and its shim
context state is ESTABLISHED. The receiver processes a valid message
by inspecting its options, and executing any actions specified such
options. This includes the SHIM6 Probe option found within the
options.
The processing rules for this message are the given in more detail in
Section 6.4.
6.2.1. Probe Option
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 11 |0| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Y| Res | Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
This value MUST be set to 11 (Probe Option).
0
This value MUST be set to 0, as in other SHIM6 options.
Length
This is the length of the option and MUST be calculated as
specified in Section 5.14 of [18].
Y (The "I See You" flag)
This flag is set to 1 if the sender receives either payload
packets or REAP messages from the peer, and 0 otherwise. The
determination of when the sender receives something is made during
the last Send Timeout seconds (see Section 6.5) when traffic was
expected, i.e., when there was either payload traffic or REAP
messages.
Arkko & Beijnum Expires June 24, 2006 [Page 25]
Internet-Draft Failure Detection Protocol December 2005
Upon reception, a value of 1 indicates that the receiver does not
need to change its behaviour as the sender is already seeing its
packets. A value of 0 indicates that the receiver MUST explore
different outgoing address pairs.
Res
This 3-bit reserved field MUST be set to zero when sending, and
ignored on receipt.
Identifier
This 28-bit field identifies this particular instance of an Probe
message. This value SHOULD be generated using a random number
generator that is known to have good randomness properties [1].
Upon reception, Identifier values are copied onto Probe Reception
Report options. This allows them to be used for both identifying
which Probes were received as well as for performing a return
routability test.
The processing rules for this option are the given in more detail in
Section 6.4.
6.3. Reachability Option
Additional information can be included in Keepalive and Probe
messages by the inclusion of the Reachability Options. Their format
is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 12 |0| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
~ Option Data ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
This value MUST be set to 12 (Reachability option).
0
This value MUST be set to 0, as in other SHIM6 options.
Arkko & Beijnum Expires June 24, 2006 [Page 26]
Internet-Draft Failure Detection Protocol December 2005
Length
This is the length of the option and MUST be calculated as
specified in Section 5.14 of [18].
Option Type
This value identifies the option.
Option Data
Option-specific content.
Unrecognized options MUST be ignored upon receipt. All
implementations MUST support the options defined in this
specification, however.
6.3.1. Payload Reception Report
This option SHOULD be included in all Probe messages when the sender
has recently (within the last Send Timeout seconds) received payload
packets from the peer. Its format is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 11 |0| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type = 1 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Suboptions ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type, 0, and Length
These are as specified above.
Reserved
This is a 16-bit field reserved for future use. It is set to zero
on transmit, and MUST be ignored on receipt.
Suboptions
This field is reserved for possible future Reachability options
that are carried (recursively) within this option. Unrecognized
options MUST be ignored upon receipt. Currently there are no
defined options that can be carried here.
Arkko & Beijnum Expires June 24, 2006 [Page 27]
Internet-Draft Failure Detection Protocol December 2005
6.3.2. Probe Reception Report
This option MUST be included in any Probe message when the sender has
recently (within the last Send Timeout seconds) received Probe or
Keepalieve messages from the peer. Depending on MTU and timing
considerations, the sender MAY, however, include options for only
some of the received Probe messages. All implementations MUST
support sending of at least five such options, however.
The format of this option is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 11 |0| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type = 2 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Res | Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Suboptions ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type, 0, and Length
These are as specified above.
Option Type
This value identifies the option and MUST be set to 2 (Probe
Reception Report).
Reserved
This is a 16-bit field reserved for future use. It is set to zero
on transmit, and MUST be ignored on receipt.
Res
This is a 3-bit field reserved for future use. It is set to zero
on transmit, and MUST be ignored on receipt.
Identifier
This 32 bit field carries the identifier of the Probe message that
was recently received.
Arkko & Beijnum Expires June 24, 2006 [Page 28]
Internet-Draft Failure Detection Protocol December 2005
Suboptions
This field is reserved for possible future Reachability options
that are carried (recursively) within this option. Unrecognized
options MUST be ignored upon receipt. Currently there are no
defined options that can be carried here.
6.4. Behaviour
The required behaviour of REAP nodes is specified below in the form
of a state machine. The externally observable behaviour of an
implementation MUST conform to this state machine, but there is no
requirement that the implementation actually employs a state machine.
On a given context with a given peer, the node can be in one of three
states: Operational, Exploring, or ExploringOK. In the Operational
state the underlying address pairs are assumed to be operational. In
the Exploring state this node has observed a problem and has
currently not seen any traffic from the peer. Finally, in the
ExploringOK state this node sees traffic from the peer, but peer may
not yet see any traffic from this node so that the exploration
process needs to continue.
The node maintains also the Send and Keepalive timers. The Send
timer reflects the requirement that when this node sends a payload
packet there should be some return traffic (either payload packets or
Keepalive messages) within Keepalive Timeout seconds. The Keepalive
timer reflects the requirement that when this node receives a payload
packet there should a similar response towards the peer. The
Keepalive timer is only used within the Operational state, and the
Send timer in the Operational and ExploringOK states. No timer is
running in the Exploring state.
Upon the reception of a payload packet in the Operational state, the
node starts the Keepalive timer if it is not yet running, and stops
the Send timer if it was running. If the node is in the Exploring
state it transitions to the ExploringOK state, sends a Probe message
with the I See You flag set to 1 (Yes), and starts the Send timer.
In the ExploringOK state the node stops the Send timer if it was
running, but does not do anything else. The reception of SHIM6
control messages other than the Keepalive and Probe messages are
treated similarly with payload packets.
Upon sending a payload packet in the Operational state, the node
stops the Keepalive timer if it was running and starts the Send timer
if it was not running. In the Exploring state there is no effect,
and in the ExploringOK state the node simply starts the Send timer if
it was not yet running. (The sending of SHIM6 control messages is
Arkko & Beijnum Expires June 24, 2006 [Page 29]
Internet-Draft Failure Detection Protocol December 2005
again treated similarly here.)
Upon a timeout on the Keepalive timer the node sends a Keepalive
message. This can only happen in the Operational state.
Upon a timeout on the Send timer, the node enters the Exploring state
and sends a Probe with I See You set to 0 (No) and stops the
Keepalive timer if it was running.
While in the Exploring state the node keeps retransmitting its Probe
messages to different (or same) addresses as defined in Section 5.3.
A similar process is employed in the ExploringOk state, except that
upon such retransmission the Send timer is started if it was not
running already.
Upon the reception of a Keepalive message in the Operational state,
the node stops the Send timer, if it was running. If the node is in
the Exploring state it transitions to the ExploringOK state, sends a
Probe message with the I See You flag set to 1 (Yes), and starts the
Send timer. In the ExploringOK state the Send timer is stopped, if
it was running.
Upon receiving a Probe with I See You set to 0 (No) the node enters
the ExploringOK state, sends a Probe with I See You set to 1 (Yes),
stops the Keepalive timer if it was running, and restarts the Send
timer.
The behavior upon the reception of a Probe message with I see You set
to 1 (Yes) depends on whether it contains a Probe Reception Report
that refers to a Probe that this node has sent to the peer such that
the I See You was set to 1 in that message. If not, the node sends a
Probe message with I See You set to 1 (Yes), restarts the Send timer,
stops the Keepalive timer if it was running, and transitions to the
Operational state.
If there was no such Probe Reception Report, the stops the Send timer
if it was running, starts the Keepalive timer if it was not yet
running, and transitions to the Operational state.
Note: This check is necessary in order to terminate the
exploration process when both parties are happy and know that
their peers are happy as well.
The reachability detection and exploration process has no effect on
payload communications until a new working address pairs have
actually been confirmed. Prior to that the payload packets continue
to be sent to the previously used addresses.
Arkko & Beijnum Expires June 24, 2006 [Page 30]
Internet-Draft Failure Detection Protocol December 2005
Garbage collection of SHIM6 contexts terminates contexts that are
either unused or have failed due to the inability of the exploration
process to find a working pair.
In the PDF version of this specification, an informational drawing
illustrates the state machine. Where the text and the drawing
differ, the text takes precedence.
A tabular representation of the state machine is shown below. Like
the drawing, this representation is only informational.
1. EVENT: Incoming payload packet
=================================
Operational Exploring ExploringOk
---------------------------------------------------------------
STOP Send; SEND Probe Y=Yes; STOP Send
START Keepalive START Send;
GOTO ExploringOk
2. EVENT: Outgoing payload packet
=================================
Operational Exploring ExploringOk
---------------------------------------------------------------
START Send; - START Send
STOP Keepalive
3. EVENT: Keepalive timeout
Operational Exploring ExploringOk
---------------------------------------------------------------
SEND Keepalive - -
4. EVENT: Send timeout
======================
Operational Exploring ExploringOk
---------------------------------------------------------------
SEND Probe Y=No; - SEND Probe Y=No
STOP Keepalive; GOTO EXPLORING
GOTO EXPLORING
Arkko & Beijnum Expires June 24, 2006 [Page 31]
Internet-Draft Failure Detection Protocol December 2005
5. EVENT: Reception of the Keepalive message
============================================
Operational Exploring ExploringOk
---------------------------------------------------------------
STOP Send SEND Probe Y=Yes; STOP Send
START Send;
GOTO ExploringOk
6. EVENT: Reception of the Probe message with Y=No
==================================================
Operational Exploring ExploringOk
---------------------------------------------------------------
SEND Probe Y=Yes SEND Probe Y=Yes; SEND Probe Y=Yes;
STOP Keepalive; START Send; RESTART Send
RESTART Send; GOTO EXPLORINGOK
GOTO EXPLORINGOK
7. EVENT: Reception of the Probe message with Y=Yes
(peer reports not seeing yet a Probe with Y=Yes)
==========================================================
Operational Exploring ExploringOk
---------------------------------------------------------------
SEND Probe Y=Yes; SEND Probe Y=Yes; SEND Probe Y=Yes;
RESTART Send; RESTART Send; RESTART Send;
STOP Keepalive GOTO OPERATIONAL GOTO OPERATIONAL
8. EVENT: Reception of the Probe message with Y=Yes
(peer reports seeing a Probe with Y=Yes)
===================================================
Operational Exploring ExploringOk
---------------------------------------------------------------
STOP Send STOP Send; STOP Send;
START Keepalive START Keepalive START Keepalive
GOTO OPERATIONAL GOTO OPERATIONAL
9. EVENT: Retransmission
========================
Operational Exploring ExploringOk
---------------------------------------------------------------
Arkko & Beijnum Expires June 24, 2006 [Page 32]
Internet-Draft Failure Detection Protocol December 2005
- SEND Probe Y=No SEND Probe Y=Yes
START Send
6.5. Protocol Constants
The following protocol constants are defined:
Send Timeout 10 seconds
Keepalive Timeout 3 seconds
Arkko & Beijnum Expires June 24, 2006 [Page 33]
Internet-Draft Failure Detection Protocol December 2005
7. Security Considerations
Attackers may spoof various indications from lower layers and the
network in an effort to confuse the peers about which addresses are
or are not working. For example, attackers may spoof ICMP error
messages in an effort to cause the parties to move their traffic
elsewhere or even to disconnect. Attackers may also spoof
information related to network attachments, router discovery, and
address assignments in an effort to make the parties believe they
have Internet connectivity when in reality they do not.
This may cause use of non-preferred addresses or even denial-of-
service.
This protocol does not provide any protection of its own for
indications from other parts of the protocol stack. However, this
protocol has weak resistance against incorrect information from these
sources in the sense that it performs its own tests prior to picking
a new address pair. Denial-of- service vulnerabilities remain,
however, as do vulnerabilities against on path attackers.
Some aspects of these vulnerabilities can be mitigated through the
use of techniques specific to the other parts of the stack, such as
properly dealing with ICMP errors [22], link layer security, or the
use of [12] to protect IPv6 Router and Neighbor Discovery.
This protocol is designed to be used in situations where other parts
of the stack have ensured that a set of addresses belong together,
such as via SHIM6 HBAs [17]. That is, REAP itself provides no
assurance that a set of addresses belongs to the same host.
Similarly, REAP provides only minimal protection against third party
flooding attacks; when REAP is run its Probe identifiers can be used
as a return routability check that the claimed address is indeed
willing to receive traffic. However, this needs to be complemented
with another mechanism to ensure that the claimed address is also the
correct host. In SHIM6 this is performed by binding all operations
to context tags.
Finally, the exploration itself can cause a number of packets to be
sent. As a result it may be used as a tool for packet amplification
in flooding attacks. In order to prevent this it is required that
the protocol employing REAP has built-in mechanisms to prevent this.
For instance, in SHIM6 contexts are created only after a relatively
large number of packets has been exchanged, a cost which reduces the
attractiveness of using SHIM6 and REAP for amplification attacks.
However, such protections are typically not present at connection
establishment time. When exploration would be needed for connection
establishment to succeed, its usage would result in an amplification
Arkko & Beijnum Expires June 24, 2006 [Page 34]
Internet-Draft Failure Detection Protocol December 2005
vulnerability. As a result, SHIM6 does not support the use of REAP
in connection establishment stage.
Arkko & Beijnum Expires June 24, 2006 [Page 35]
Internet-Draft Failure Detection Protocol December 2005
8. IANA Considerations
This document creates one new name spaces under the new SHIM6
Reachability Protocol repository. The name space is for Reachability
Option Type (Section 6.3) and it has one reserved value (0) and two
defined values, 1 (Payload Reception Report defined in Section 6.3.1)
and 2 (Probe Reception Report defined in Section 6.3.2). Further
allocations within this 16-bit field can be made through
Specification Required. The range from 65000 to 65535 is reserved
for experimental use.
Arkko & Beijnum Expires June 24, 2006 [Page 36]
Internet-Draft Failure Detection Protocol December 2005
9. References
9.1. Normative References
[1] Eastlake, D., Crocker, S., and J. Schiller, "Randomness
Recommendations for Security", RFC 1750, December 1994.
[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[3] Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery
for IP Version 6 (IPv6)", RFC 2461, December 1998.
[4] Thomson, S. and T. Narten, "IPv6 Stateless Address
Autoconfiguration", RFC 2462, December 1998.
[5] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M.
Carney, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)",
RFC 3315, July 2003.
[6] Draves, R., "Default Address Selection for Internet Protocol
version 6 (IPv6)", RFC 3484, February 2003.
[7] Choi, J., "Detecting Network Attachment in IPv6 Goals",
draft-ietf-dna-goals-00 (work in progress), June 2004.
[8] Moore, N., "Optimistic Duplicate Address Detection for IPv6",
draft-ietf-ipv6-optimistic-dad-01 (work in progress), June 2004.
[9] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", draft-ietf-ipv6-unique-local-addr-05 (work in
progress), June 2004.
9.2. Informative References
[10] Stewart, R., Xie, Q., Morneault, K., Sharp, C., Schwarzbauer,
H., Taylor, T., Rytina, I., Kalla, M., Zhang, L., and V.
Paxson, "Stream Control Transmission Protocol", RFC 2960,
October 2000.
[11] Rosenberg, J., Weinberger, J., Huitema, C., and R. Mahy, "STUN
- Simple Traversal of User Datagram Protocol (UDP) Through
Network Address Translators (NATs)", RFC 3489, March 2003.
[12] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
Neighbor Discovery (SEND)", RFC 3971, March 2005.
[13] Aboba, B., "Detection of Network Attachment (DNA) in IPv4",
Arkko & Beijnum Expires June 24, 2006 [Page 37]
Internet-Draft Failure Detection Protocol December 2005
draft-ietf-dhc-dna-ipv4-08 (work in progress), July 2004.
[14] Nikander, P., "End-Host Mobility and Multi-Homing with Host
Identity Protocol", draft-ietf-hip-mm-00 (work in progress),
October 2004.
[15] Eronen, P., "IKEv2 Mobility and Multihoming Protocol (MOBIKE)",
draft-ietf-mobike-protocol-03 (work in progress),
September 2005.
[16] Rosenberg, J., "Interactive Connectivity Establishment (ICE): A
Methodology for Network Address Translator (NAT) Traversal for
Multimedia Session Establishment Protocols",
draft-ietf-mmusic-ice-02 (work in progress), July 2004.
[17] Bagnulo, M., "Hash Based Addresses (HBA)",
draft-ietf-shim6-hba-00 (work in progress), July 2005.
[18] Nordmark, E., "Level 3 multihoming shim protocol",
draft-ietf-shim6-proto-00 (work in progress), October 2005.
[19] Beijnum, I., "Shim6 Reachability Detection",
draft-ietf-shim6-reach-detect-00 (work in progress), July 2005.
[20] Stewart, R., "Stream Control Transmission Protocol (SCTP)
Dynamic Address Reconfiguration",
draft-ietf-tsvwg-addip-sctp-10 (work in progress),
January 2005.
[21] Bagnulo, M., "Address selection in multihomed environments",
draft-bagnulo-shim6-addr-selection-00 (work in progress),
October 2005.
[22] Gont, F., "ICMP attacks against TCP",
draft-gont-tcpm-icmp-attacks-00 (work in progress),
August 2004.
[23] Huitema, C., "Address selection in multihomed environments",
draft-huitema-multi6-addr-selection-00 (work in progress),
October 2004.
[24] Rosenberg, J., "Traversal Using Relay NAT (TURN)",
draft-rosenberg-midcom-turn-05 (work in progress), July 2004.
[25] Aura, T., Roe, M., and J. Arkko, "Security of Internet Location
Management", In Proceedings of the 18th Annual Computer
Security Applications Conference, Las Vegas, Nevada, USA.,
December 2002.
Arkko & Beijnum Expires June 24, 2006 [Page 38]
Internet-Draft Failure Detection Protocol December 2005
Appendix A. Contributors
This draft attempts to summarize the thoughts and unpublished
contributions of many people, including the MULTI6 WG design team
members Marcelo Bagnulo Braun, Iljitsch van Beijnum, Erik Nordmark,
Geoff Huston, Margaret Wasserman, and Jukka Ylitalo, the MOBIKE WG
contributors Pasi Eronen, Tero Kivinen, Francis Dupont, Spencer
Dawkins, and James Kempf, and my colleague Pekka Nikander at
Ericsson. This draft is also in debt to work done in the context of
SCTP [10] and HIP [14].
Arkko & Beijnum Expires June 24, 2006 [Page 39]
Internet-Draft Failure Detection Protocol December 2005
Appendix B. Acknowledgements
The author would also like to thank Christian Huitema, Pekka Savola,
and Hannes Tschofenig for interesting discussions in this problem
space, and for their comments on earlier versions of this draft.
Arkko & Beijnum Expires June 24, 2006 [Page 40]
Internet-Draft Failure Detection Protocol December 2005
Authors' Addresses
Jari Arkko
Ericsson
Jorvas 02420
Finland
Email: jari.arkko@ericsson.com
Iljitsch van Beijnum
Muada
The Netherlands
Email: iljitsch@muada.com
Arkko & Beijnum Expires June 24, 2006 [Page 41]
Internet-Draft Failure Detection Protocol December 2005
Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Disclaimer of Validity
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement
Copyright (C) The Internet Society (2005). 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.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Arkko & Beijnum Expires June 24, 2006 [Page 42]
Html markup produced by rfcmarkup 1.129c, available from
https://tools.ietf.org/tools/rfcmarkup/