6MAN J. Hui
Internet-Draft Arch Rock Corporation
Intended status: Standards Track JP. Vasseur
Expires: January 27, 2011 Cisco Systems, Inc
D. Culler
UC Berkeley
July 26, 2010
An IPv6 Routing Header for Source Routes with RPL
draft-ietf-6man-rpl-routing-header-00
Abstract
In Low power and Lossy Networks (LLNs), memory constraints on routers
may limit them to maintaining at most a few routes. In some
configurations, it is necessary to use these memory constrained
routers to deliver datagrams to nodes within the LLN. The Routing
for Low Power and Lossy Networks (RPL) protocol can be used in some
deployments to store most, if not all, routes on one (e.g. the
Directed Acyclic Graph (DAG) root) or few routers and forward the
IPv6 datagram using a source routing technique to avoid large routing
tables on memory constrained routers. This document specifies a new
IPv6 Routing header type for delivering datagrams within a RPL
domain.
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 January 27, 2011.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
Hui, et al. Expires January 27, 2011 [Page 1]
Internet-Draft RPL Source Route Header July 2010
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Format of the RPL Routing Header . . . . . . . . . . . . . . . 7
4. RPL Router Behavior . . . . . . . . . . . . . . . . . . . . . 9
4.1. Generating Type 4 Routing Headers . . . . . . . . . . . . 9
4.2. Processing Type 4 Routing Headers . . . . . . . . . . . . 9
5. RPL Border Router Behavior . . . . . . . . . . . . . . . . . . 11
6. Security Considerations . . . . . . . . . . . . . . . . . . . 12
6.1. Source Routing Attacks . . . . . . . . . . . . . . . . . . 12
6.2. ICMPv6 Attacks . . . . . . . . . . . . . . . . . . . . . . 12
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
8. Protocol Constants . . . . . . . . . . . . . . . . . . . . . . 14
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
10.1. Normative References . . . . . . . . . . . . . . . . . . . 16
10.2. Informative References . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
Hui, et al. Expires January 27, 2011 [Page 2]
Internet-Draft RPL Source Route Header July 2010
1. Introduction
Routing for Low Power and Lossy Networks (RPL) is a distance vector
IPv6 routing protocol designed for Low Power and Lossy networks (LLN)
[I-D.ietf-roll-rpl]. Such networks are typically constrained in
resources (limited communication data rate, processing power, energy
capacity, memory). In particular, some LLN configurations may
utilize LLN routers where memory constraints limit nodes to
maintaining only a small number of default routes and no other
destinations. However, it may be necessary to utilize such memory-
constrained routers to forward datagrams and maintain reachability to
destinations within the LLN.
To utilize paths that include memory-constrained routers, RPL relies
on source routing. In one deployment model of RPL, necessary
mechanisms are used to collect routing information at more capable
routers and form paths from those routers to arbitrary destinations
within the RPL domain. However, a source routing mechanism supported
by IPv6 is needed to deliver datagrams.
This document specifies the Type 4 Routing header (RH4) (to be
confirmed by IANA) for use strictly within a RPL domain.
1.1. 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].
Hui, et al. Expires January 27, 2011 [Page 3]
Internet-Draft RPL Source Route Header July 2010
2. Overview
The basic format of RH4 draws from that of the Type 0 Routing header
(RH0) [RFC2460]. However, RH4 introduces mechanisms to compact the
source route entries when all entries share the same prefix with the
IPv6 Destination Address of the encapsulating header, a typical
scenario in LLNs using source routing. The compaction mechanism
reduces consumption of scarce resources such as bandwidth.
RH4 also differs from RH0 in the processing rules to alleviate
security concerns that lead to the deprecation of RH0 [RFC5095].
First, routers processing RH4 MUST implement a strict source route
policy where each and every IPv6 hop is specified within the datagram
itself. Second, a RH4 header MUST only be used within a RPL domain.
RPL Border Routers, responsible for connecting RPL domains and IP
domains that use other routing protocols, MUST NOT allow datagrams
already carrying a RH4 header to enter or exit the RPL domain.
Third, to avoid some attacks that lead to the deprecation of RH0,
routers along the way MUST verify that loops do not exist with in the
source route.
To deliver a datagram, a router MAY specify a source route to reach
the destination using a RH4. There are two cases that determine how
to include an RH4 with a datagram.
1. If the RH4 specifies the complete path from source to
destination, the RH4 should be included directly within the
datagram itself.
2. If the RH4 only specifies a subset of the path from source to
destination, IPv6-in-IPv6 tunneling MUST be used as specified in
[RFC2473]. The router MUST prepend a new IPv6 header and RH4 to
the original datagram. Use of tunneling ensures that the
datagram is delivered unmodified and that ICMP errors return to
the source of the RH4 rather than the source of the original
datagram.
In a RPL network, Case 1 occurs when both source and destinations are
within a RPL domain and a single RH4 header is used to specify the
entire path from source to destination, as shown in the following
figure:
+--------------------+
| |
| (S) -------> (D) |
| |
+--------------------+
Hui, et al. Expires January 27, 2011 [Page 4]
Internet-Draft RPL Source Route Header July 2010
RPL Domain
In the above scenario, datagrams traveling from source, S, to
destination, D, have the following packet structure:
+------+------+------+--------//-+
| IPv6 | IPv6 | IPv6 | Packet |
| Src | Dst | RH4 | Payload |
+------+------+------+--------//-+
S's address is carried in the IPv6 Source Address field. D's address
is carried in the last entry of RH4 for all but the last hop, when
D's address is carried in the IPv6 Destination Address field.
In a RPL network, Case 2 occurs for all datagrams that have either
source or destination outside the RPL domain, as shown in the
following diagram:
+-----------------+
| |
| (S) -------> (BR1) -------> (D)
| |
+-----------------+
RPL Domain
+-----------------+
| |
| (D) <------- (BR1) <------- (S)
| |
+-----------------+
RPL Domain
In the above scenario, datagrams traveling within the RPL domain have
the following packet structure:
+------+------+------+------+------+--------//-+
| IPv6 | IPv6 | IPv6 | IPv6 | IPv6 | Packet |
| Src | Dst | RH4 | Src | Dst | Payload |
+------+------+------+------+------+--------//-+
<--- Original Packet --->
<--- Tunneled Packet --->
Hui, et al. Expires January 27, 2011 [Page 5]
Internet-Draft RPL Source Route Header July 2010
Note that the outer header (including the RH4) is added and removed
by the RPL Border Router.
Case 2 also occurs whenever a RPL router needs to insert a source
route when forwarding datagram. One such use case with RPL is to
have all RPL traffic flow through a Border Router and have the Border
Router use source routes to deliver datagrams to their final
destination. The Border Router in this case would encapsulate the
received datagram unmodified using IPv6-in-IPv6 and include a RH4 in
the outer IPv6 header.
+-----------------+
| |
| (S) -------\ |
| \ |
| (BR1)
| / |
| (D) <------/ |
| |
+-----------------+
RPL Domain
In the above scenario, datagrams travel from S to D through BR1.
Between S and BR1, the datagrams are routed using the DAG built by
RPL and do not contain a RH4. BR1 encapsulates received datagrams
unmodified using IPv6-in-IPv6 and the RH4 is included in the outer
IPv6 header.
To help avoid IP-layer fragmentation, the RH4 header has a maximum
size of RH4_MAX_SIZE octets and links within a RPL domain SHOULD have
a MTU of at least 1280 + 40 (outer IP header) + RH4_MAX_SIZE (+
additional extension headers or options needed within RPL domain)
octets.
Hui, et al. Expires January 27, 2011 [Page 6]
Internet-Draft RPL Source Route Header July 2010
3. Format of the RPL Routing Header
The Type 4 Routing header has the following format:
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 | Routing Type=4| Segments Left |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Compr | Pad | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Addresses[1..n] .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Next Header 8-bit selector. Identifies the type of header
immediately following the Routing header. Uses
the same values as the IPv4 Protocol field
[RFC3232].
Hdr Ext Len 8-bit unsigned integer. Length of the Routing
header in 8-octet units, not including the first
8 octets. Hdr Ext Len MUST NOT exceed
RH4_MAX_SIZE / 8. Note that when Addresses[1..n]
are compressed (i.e. value of Compr is not 0),
Hdr Ext Len does not equal twice the number of
Addresses.
Routing Type 8-bit selector. Set to 4 (to be confirmed by
IANA).
Segments Left 8-bit unsigned integer. Number of route segments
remaining, i.e., number of explicitly listed
intermediate nodes still to be visited before
reaching the final destination. Value MUST be
between 0 and Segments, inclusive.
Compr 4-bit unsigned integer. Number of prefix octets
from each segment that is elided. For example, a
Type 4 Routing header carrying full IPv6
addresses sets Compr to 0.
Hui, et al. Expires January 27, 2011 [Page 7]
Internet-Draft RPL Source Route Header July 2010
Pad 4-bit unsigned integer. Number of octets that
are used to for padding after Address[n] and the
end of the Type 4 Routing header.
Address[1..n] Vector of addresses, numbered 1 to n. Each
vector element has size (16 - Compr).
The Type 4 Routing header shares the same basic format as the Type 0
Routing header [RFC2460]. When carrying full IPv6 addresses, the
Compr and Pad fields are set to 0 and the only difference between the
Type 4 and Type 0 encodings is the value of the Routing Type field.
A common network configuration for a RPL domain is that all nodes
within a LLN share a common prefix. Type 4 Routing header introduces
the Compr and Pad fields to allow compaction of the Address[1..n]
vector when all entries share the same prefix as the IPv6 Destination
Address field of the encapsulating datagram. The Compr field
indicates the number of prefix octets that are shared with the IPv6
Destination Address of the encapsulating header. The shared prefix
octets are not carried within the Routing header and each entry in
Address[1..n] has size (16 - Compr) octets. When Compr is non-zero,
there may exists unused octets between the last entry, Address[n],
and the end of the Routing header. The Pad field indicates the
number of unused octets that are used for padding. Note that when
Compr is 0, Pad MUST be null and carry a value of 0.
The Type 4 Routing header MUST NOT specify a path that visits a node
more than once. When generating a Type 4 Routing header, the source
may not know the mapping between IPv6 addresses and nodes.
Minimally, the source MUST ensure that IPv6 Addresses do not appear
more than once and the IPv6 Source and Destination addresses of the
encapsulating datagram do not appear in the Type 4 Routing header.
Multicast addresses MUST NOT appear in a Type 4 Routing header, or in
the IPv6 Destination Address field of a datagram carrying a Type 4
Routing header.
Hui, et al. Expires January 27, 2011 [Page 8]
Internet-Draft RPL Source Route Header July 2010
4. RPL Router Behavior
4.1. Generating Type 4 Routing Headers
To deliver an IPv6 datagram to its destination, a router may need to
generate a new Type 4 Routing header and specify a strict source
route. Routers MUST use IPv6-in-IPv6 tunneling, as specified in
[RFC2473] to include a new Type 4 Routing header in datagrams that
are sourced by other nodes. This ensures that the delivered datagram
remains unmodified and that ICMPv6 errors generated by a Type 4
Routing header are sent back to the router that generated the routing
header.
Performing IP-in-IP encapsulation may grow the datagram to a size
larger than the IPv6 min MTU of 1280 octets. To help avoid IP-layer
fragmentation caused by IP-in-IP encapsulation, links within a RPL
domain SHOULD be configured with a MTU of at least 1280 + 40 (outer
IP header) + RH4_MAX_SIZE (+ additional extension headers or options
needed within RPL domain) octets.
4.2. Processing Type 4 Routing Headers
As specified in [RFC2460], a routing header is not examined or
processed until it reaches the node identified in the Destination
Address field of the IPv6 header. In that node, dispatching on the
Next Header field of the immediately preceding header causes the
Routing header module to be invoked.
The function of Type 4 Routing header is intended to be very similar
to IPv4's Strict Source and Record Route option [RFC0791]. When
processing the Type 4 Routing header, a router MUST drop the packet
if the next entry is not on-link and SHOULD send an ICMP Destination
Unreachable (ICMPv6 Type 1) message with ICMPv6 Code set to 7 (to be
confirmed by IANA) to the packet's Source Address. An ICMPv6 Code of
7 indicates that the next Address entry is not on-link and the router
cannot satisfy the strict source route. When generating ICMPv6 error
messages, the rules in Section 2.4 of [RFC4443] must be observed.
To detect loops in the Type 4 Routing headers, a router MUST
determine if the Type 4 Routing header includes more than one address
assigned any interface on that router. If such addresses appear more
than once, the router MUST drop the packet and SHOULD send an ICMP
Parameter Problem, Code 0, to the Source Address.
The following describes the algorithm performed when processing a
Type 4 Routing header:
Hui, et al. Expires January 27, 2011 [Page 9]
Internet-Draft RPL Source Route Header July 2010
if Segments Left = 0 {
proceed to process the next header in the packet, whose type is
identified by the Next Header field in the Routing header
}
else {
compute n, the number of addresses in the Routing header, by
n = ((Hdr Ext Len * 8) - Pad) / (16 - Comp)
if Segments Left is greater than n {
send an ICMP Parameter Problem, Code 0, message to the Source
Address, pointing to the Segments Left field, and discard the
packet
}
else {
decrement Segments Left by 1;
compute i, the index of the next address to be visited in
the address vector, by subtracting Segments Left from n
if Address[i] or the IPv6 Destination Address is multicast {
discard the packet
}
else if 2 entries in Address[1..n] are assigned to local
interface and are separated by an address not assigned
to local interface {
discard the packet
}
else if i < n and Address[i] is not on-link {
send an ICMP Destination Unreachable, Code 7, message to
the Source Address and discard the packet
}
else {
swap the IPv6 Destination Address and Address[i]
if the IPv6 Hop Limit is less than or equal to 1 {
send an ICMP Time Exceeded -- Hop Limit Exceeded in
Transit message to the Source Address and discard the
packet
}
else {
decrement the Hop Limit by 1
resubmit the packet to the IPv6 module for transmission
to the new destination
}
}
}
}
Hui, et al. Expires January 27, 2011 [Page 10]
Internet-Draft RPL Source Route Header July 2010
5. RPL Border Router Behavior
RPL Border Routers (referred to as LBRs in
[I-D.ietf-roll-terminology]) are responsible for ensuring that a Type
4 Routing header is only used within the RPL domain it was created.
For datagrams entering the RPL domain, RPL Border Routers MUST drop
received datagrams that contain a Type 4 Routing header in the IPv6
Extension headers.
For datagrams exiting the RPL domain, RPL Border Routers MUST check
for a Type 4 Routing header. If Segments Left is 0, the router MUST
remove the RH4 header from the datagram and update the IPv6 Payload
Length field accordingly. If Segments Left is non-zero, the router
MUST drop the datagram.
Hui, et al. Expires January 27, 2011 [Page 11]
Internet-Draft RPL Source Route Header July 2010
6. Security Considerations
6.1. Source Routing Attacks
[RFC5095] deprecates the Type 0 Routing header due to a number of
significant attacks that are referenced in that document. Such
attacks include network discovery, bypassing filtering devices,
denial-of-service, and defeating anycast.
Because this document specifies that Type 4 Routing headers are only
for use within a RPL domain, such attacks cannot be mounted from
outside the RPL domain. As described in Section 5, RPL Border
Routers MUST drop datagrams entering or exiting the RPL domain that
contain a Type 4 Routing header in the IPv6 Extension headers.
6.2. ICMPv6 Attacks
The generation of ICMPv6 error messages may be used to attempt
denial-of-service attacks by sending error-causing Type 4 Routing
headers in back-to-back datagrams. An implementation that correctly
follows Section 2.4 of [RFC4443] would be protected by the ICMPv6
rate limiting mechanism.
Hui, et al. Expires January 27, 2011 [Page 12]
Internet-Draft RPL Source Route Header July 2010
7. IANA Considerations
This document defines a new IPv6 Routing Type of 4 (to be confirmed).
This document defines a new ICMPv6 Destination Unreachable Code of 7
to indicate that the router does not have the next Address element as
a neighbor and could not satisfy the strict source route.
Hui, et al. Expires January 27, 2011 [Page 13]
Internet-Draft RPL Source Route Header July 2010
8. Protocol Constants
RH4_MAX_SIZE 136
With a base header size of 8 octets, 136 octets will allow for up to
8 16-octet address entries in the Type 4 Routing header. More
entries are possible within 136 octets when compression is used.
Hui, et al. Expires January 27, 2011 [Page 14]
Internet-Draft RPL Source Route Header July 2010
9. Acknowledgements
The authors thank Vishwas Manral and Erik Nordmark for their comments
and suggestions that helped shape this document.
Hui, et al. Expires January 27, 2011 [Page 15]
Internet-Draft RPL Source Route Header July 2010
10. References
10.1. Normative References
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
September 1981.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in
IPv6 Specification", RFC 2473, December 1998.
[RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control
Message Protocol (ICMPv6) for the Internet Protocol
Version 6 (IPv6) Specification", RFC 4443, March 2006.
[RFC5095] Abley, J., Savola, P., and G. Neville-Neil, "Deprecation
of Type 0 Routing Headers in IPv6", RFC 5095,
December 2007.
10.2. Informative References
[I-D.ietf-roll-rpl]
Winter, T., Thubert, P., and R. Team, "RPL: IPv6 Routing
Protocol for Low power and Lossy Networks",
draft-ietf-roll-rpl-10 (work in progress), June 2010.
[I-D.ietf-roll-terminology]
Vasseur, J., "Terminology in Low power And Lossy
Networks", draft-ietf-roll-terminology-03 (work in
progress), March 2010.
[RFC3232] Reynolds, J., "Assigned Numbers: RFC 1700 is Replaced by
an On-line Database", RFC 3232, January 2002.
Hui, et al. Expires January 27, 2011 [Page 16]
Internet-Draft RPL Source Route Header July 2010
Authors' Addresses
Jonathan W. Hui
Arch Rock Corporation
501 2nd St. Ste. 410
San Francisco, California 94107
USA
Phone: +415 692 0828
Email: jhui@archrock.com
JP Vasseur
Cisco Systems, Inc
11, Rue Camille Desmoulins
Issy Les Moulineaux, 92782
France
Email: jpv@cisco.com
David E. Culler
UC Berkeley
465 Soda Hall
Berkeley, California 94720
USA
Phone: +510 643 7572
Email: culler@cs.berkeley.edu
Hui, et al. Expires January 27, 2011 [Page 17]
