6MAN J. Hui
Internet-Draft Arch Rock Corporation
Intended status: Standards Track JP. Vasseur
Expires: April 14, 2012 Cisco Systems, Inc
D. Culler
UC Berkeley
V. Manral
IP Infusion
October 12, 2011
An IPv6 Routing Header for Source Routes with RPL
draft-ietf-6man-rpl-routing-header-04
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 April 14, 2012.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
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document authors. All rights reserved.
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
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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 Source Routing Headers . . . . . . . . . . . . 9
4.2. Processing Source Routing Headers . . . . . . . . . . . . 9
5. RPL Border Router Behavior . . . . . . . . . . . . . . . . . . 12
6. Security Considerations . . . . . . . . . . . . . . . . . . . 13
6.1. Source Routing Attacks . . . . . . . . . . . . . . . . . . 13
6.2. ICMPv6 Attacks . . . . . . . . . . . . . . . . . . . . . . 13
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
9. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
10.1. Normative References . . . . . . . . . . . . . . . . . . . 17
10.2. Informative References . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18
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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 Source Routing Header (SRH) 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].
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2. Overview
The format of SRH draws from that of the Type 0 Routing header (RH0)
[RFC2460]. However, SRH introduces mechanisms to compact the source
route entries when all entries share the same prefix with the IPv6
Destination Address of a packet carrying a SRH, a typical scenario in
LLNs using source routing. The compaction mechanism reduces
consumption of scarce resources such as channel capacity.
SRH also differs from RH0 in the processing rules to alleviate
security concerns that led to the deprecation of RH0 [RFC5095].
First, routers processing SRH MUST implement a strict source route
policy where each and every IPv6 hop is specified within the datagram
itself. Second, a SRH 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 SRH header to enter or exit the RPL domain.
Third, 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 SRH. There are two cases that determine how
to include an SRH with a datagram.
1. If the SRH specifies the complete path from source to
destination, the SRH should be included directly within the
datagram itself.
2. If the SRH only specifies a subset of the path from source to
destination, the router SHOULD use IPv6-in-IPv6 tunneling, as
specified in [RFC2473]. When tunneling, the router MUST prepend
a new IPv6 header and SRH to the original datagram. Use of
tunneling ensures that the datagram is delivered unmodified and
that ICMP errors return to the source of the SRH 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 SRH header is used to specify the
entire path from source to destination, as shown in the following
figure:
+--------------------+
| |
| (S) -------> (D) |
| |
+--------------------+
RPL Domain
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In the above scenario, datagrams traveling from source, S, to
destination, D, have the following packet structure:
+--------+---------+-------------//-+
| IPv6 | Source | IPv6 |
| Header | Routing | Payload |
| | Header | |
+--------+---------+-------------//-+
S's address is carried in the IPv6 Header's Source Address field.
D's address is carried in the last entry of SRH for all but the last
hop, when D's address is carried in the IPv6 Header's Destination
Address field of the packet carrying the SRH.
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 that include the SRH in tunneled
mode have the following packet structure when traveling within the
RPL domain:
+--------+---------+--------+-------------//-+
| Outer | Source | Inner | IPv6 |
| IPv6 | Routing | IPv6 | Payload |
| Header | Header | Header | |
+--------+---------+--------+-------------//-+
<--- Original Packet --->
<--- Tunneled Packet --->
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Note that the outer header (including the SRH) 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. When including the SRH using tunneled mode, the Border
Router would encapsulate the received datagram unmodified using IPv6-
in-IPv6 and include a SRH 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 SRH. BR1 encapsulates received datagrams
unmodified using IPv6-in-IPv6 and the SRH is included in the outer
IPv6 header.
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3. Format of the RPL Routing Header
The Source 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 | Segments Left |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CmprI | CmprE | 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. Note that when Addresses[1..n] are
compressed (i.e. value of CmprI or CmprE is not
0), Hdr Ext Len does not equal twice the number
of Addresses.
Routing Type 8-bit selector. TBD 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.
CmprI 4-bit unsigned integer. Number of prefix octets
from each segment, except than the last segment,
(i.e. segments 1 through n-1) that are elided.
For example, a SRH carrying full IPv6 addresses
in Addresses[1..n-1] sets CmprI to 0.
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CmprE 4-bit unsigned integer. Number of prefix octets
from the last segment (i.e. segment n) that are
elided. For example, a SRH carrying a full IPv6
address in Addresses[n] sets CmprE to 0.
Pad 4-bit unsigned integer. Number of octets that
are used for padding after Address[n] at the end
of the SRH.
Address[1..n] Vector of addresses, numbered 1 to n. Each
vector element in [1..n-1] has size (16 - CmprI)
and element [n] has size (16-CmprE).
The SRH shares the same basic format as the Type 0 Routing header
[RFC2460]. When carrying full IPv6 addresses, the CmprI, CmprE, and
Pad fields are set to 0 and the only difference between the SRH 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. The SRH introduces the CmprI,
CmprE, 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 packet carrying the SRH. The CmprI and CmprE
field indicates the number of prefix octets that are shared with the
IPv6 Destination Address of the packet carrying the SRH. The shared
prefix octets are not carried within the Routing header and each
entry in Address[1..n-1] has size (16 - CmprI) octets and Address[n]
has size (16 - CmprE) octets. When CmprI or CmprE is non-zero, there
may exist 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 CmprI and
CmprE are both 0, Pad MUST carry a value of 0.
The SRH MUST NOT specify a path that visits a node more than once.
When generating a SRH, 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 SRH.
Multicast addresses MUST NOT appear in a SRH, or in the IPv6
Destination Address field of a datagram carrying a SRH.
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4. RPL Router Behavior
4.1. Generating Source Routing Headers
To deliver an IPv6 datagram to its destination, a router may need to
generate a new SRH and specify a strict source route. Routers MUST
use IPv6-in-IPv6 tunneling, as specified in [RFC2473] to include a
new SRH in datagrams that are sourced by other nodes. Using IPv6-in-
IPv6 tunneling ensures that the delivered datagram remains unmodified
and that ICMPv6 errors generated by a SRH are sent back to the router
that generated the routing header.
To avoid fragmentation, it is desirable to employ MTU sizes that
allow for the header expansion (i.e. at least 1280 + 40 (outer IP
header) + SRH_MAX_SIZE), where SRH_MAX_SIZE is the maximum path
length for a given RPL network. To take advantage of this, however,
the communicating endpoints need to be aware of the MTU along the
path (i.e. through Path MTU Discovery). Unfortunately, the larger
MTU size may not be available on all links (e.g. 1280 octets on
6LoWPAN links). However, it is expected that much of the traffic on
these types of networks consists of much smaller messages than the
MTU, so performance degradation through fragmentation would be
limited.
4.2. Processing Source 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 SRH is intended to be very similar to IPv4's Strict
Source and Record Route option [RFC0791]. After the routing header
has been processed and the IPv6 datagram resubmitted to the IPv6
module for processing, the IPv6 Destination Address contains the next
hop's address. When forwarding an IPv6 datagram that contains a SRH
with a non-zero Segments Left value, if the IPv6 Destination Address
is not on-link, a router SHOULD send an ICMP Destination Unreachable
(ICMPv6 Type 1) message with ICMPv6 Code set to (TBD by IANA) to the
packet's Source Address. This ICMPv6 Code indicates that the IPv6
Destination Address is not on-link and the router cannot satisfy the
strict source route requirement. When generating ICMPv6 error
messages, the rules in Section 2.4 of [RFC4443] must be observed.
To detect loops in the SRH, a router MUST determine if the SRH
includes multiple addresses assigned to any interface on that router.
If such addresses appear more than once and are separated by at least
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one address not assigned to that router, the router MUST drop the
packet and SHOULD send an ICMP Parameter Problem, Code 0, to the
Source Address. While this loop check does add significant per-
packet processing overhead, it is required to mitigate traffic
amplification attacks that led to the deprecation of RH0 [RFC5095].
The following describes the algorithm performed when processing a
SRH:
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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 - CmprE)) / (16 - CmprI)) + 1
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 or more entries in Address[1..n] are assigned to
local interface and are separated by at least one
address not assigned to local interface {
send an ICMP Parameter Problem (Code 0) 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
}
}
}
}
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5. RPL Border Router Behavior
RPL Border Routers (referred to as LBRs in
[I-D.ietf-roll-terminology]) are responsible for ensuring that a SRH
is only used within the RPL domain it was created.
For datagrams destined to the RPL Border Router, the router processes
the packet in the usual way. For instance, if the SRH was included
using tunneled mode and the RPL Border Router serves as the tunnel
endpoint, the router removes the outer IPv6 header, at the same time
removing the SRH as well.
Datagrams destined elsewhere within the same RPL domain are forwarded
to the correct interface.
Datagrams destined to nodes outside the RPL domain are dropped if the
outer-most IPv6 header contains a SRH.
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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 SRH is 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 SRH in the IPv6
Extension headers. Furthermore, it is RECOMMENDED that non-RPL
routers and firewalls drop packets with a SRH by default.
6.2. ICMPv6 Attacks
The generation of ICMPv6 error messages may be used to attempt
denial-of-service attacks by sending error-causing SRH in back-to-
back datagrams. An implementation that correctly follows Section 2.4
of [RFC4443] would be protected by the ICMPv6 rate limiting
mechanism.
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7. IANA Considerations
This document defines a new IPv6 Routing Type of TBD by IANA.
This document defines a new ICMPv6 Destination Unreachable Code of
TBD by IANA to indicate that the router cannot satisfy the strict
source-route requirement.
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8. Acknowledgements
The authors thank Jari Arkko, Richard Kelsey, Suresh Krishnan, Erik
Nordmark, Pascal Thubert, and Tim Winter for their comments and
suggestions that helped shape this document.
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9. Changes
(This section to be removed by the RFC editor.)
Draft 04:
- Updated text on recommendations for avoiding fragmentation.
- Clarify definition of CmprE where it is first mentioned.
- Change use of IPv6-in-IPv6 tunneling from SHOULD to MUST.
- Update packet processing pseudocode to match the text on sending
back a parameter problem error.
- Recommend that non-RPL devices drop packets with SRH by default.
- Clarify packet structure figures.
- State that checking for cycles represents significant per-packet
processing.
Draft 03:
- Removed any presumed values that are TBD by IANA.
Draft 02:
- Updated to send ICMP Destination Unreachable error only after
the SRH has been processed.
- Updated pseudocode to reflect encoding changes in draft-01.
- Allow multiple addresses assigned to same node as long as they
are not separated by other addresses.
Draft 01:
- Allow Addresses[1..n-1] and Addresses[n] to have a different
number of bytes elided.
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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
[]
Hui, J., Thubert, P., and J. Vasseur, "Using RPL Headers
Without IP-in-IP", draft-hui-6man-rpl-headers-00 (work in
progress), July 2010.
[I-D.ietf-roll-rpl]
Winter, T., Thubert, P., Brandt, A., Clausen, T., Hui, J.,
Kelsey, R., Levis, P., Pister, K., Struik, R., and J.
Vasseur, "RPL: IPv6 Routing Protocol for Low power and
Lossy Networks", draft-ietf-roll-rpl-19 (work in
progress), March 2011.
[I-D.ietf-roll-terminology]
Vasseur, J., "Terminology in Low power And Lossy
Networks", draft-ietf-roll-terminology-06 (work in
progress), September 2011.
[RFC3232] Reynolds, J., "Assigned Numbers: RFC 1700 is Replaced by
an On-line Database", RFC 3232, January 2002.
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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
Vishwas Manral
IP Infusion
Bamankhola, Bansgali
Almora, Uttarakhand 263601
India
Phone: +91-98456-61911
Email: vishwas@ipinfusion.com
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