Internet DRAFT - draft-ietf-ospf-transition-to-ospfv3
draft-ietf-ospf-transition-to-ospfv3
Internet Draft I. Chen
<draft-ietf-ospf-transition-to-ospfv3-07.txt> Ericsson
Intended Status: Standards Track A. Lindem
Updates: 5838 Cisco
R. Atkinson
Consultant
Expires in 6 months May 24, 2016
OSPFv3 over IPv4 for IPv6 Transition
<draft-ietf-ospf-transition-to-ospfv3-07.txt>
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Abstract
This document defines a mechanism to use IPv4 to transport OSPFv3
packets. Using OSPFv3 over IPv4 with the existing OSPFv3 Address
Family extension can simplify transition from an OSPFv2 IPv4-only
routing domain to an OSPFv3 dual-stack routing domain. This document
updates RFC 5838 to support virtual links in the IPv4 unicast address
family when using OSPFv3 over IPv4.
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Table of Contents
1. Introduction ....................................................3
2. Terminology .....................................................4
3. Encapsulation in IPv4 ...........................................4
3.1. Source Address .............................................6
3.2. Destination ................................................6
3.3. Operation over Virtual Link ................................6
4. IPv4-only Use Case ..............................................7
5. Security Considerations .........................................8
6. IANA Considerations .............................................8
7. Acknowledgments .................................................8
8. References ......................................................8
1. Introduction
Using OSPFv3 [RFC5340] over IPv4 [RFC791] with the existing OSPFv3
Address Family extension can simplify transition from an IPv4-only
routing domain to an IPv6 [RFC2460], or dual-stack routing domain.
Dual-stack routing protocols, such as Border Gateway Protocol
[RFC4271], have an advantage during the transition, because both IPv4
and IPv6 address families can be advertised using either IPv4 or
IPv6. Some IPv4-specific and IPv6-specific routing protocols share
enough similarities in their protocol packet formats and protocol
signaling that it is trivial to deploy an initial IPv6 routing domain
by transporting the routing protocol over IPv4, thereby allowing IPv6
routing domains to be deployed and tested before decommissioning IPv4
and moving to an IPv6-only network.
In the case of the Open Shortest Path First (OSPF) interior gateway
routing protocol (IGP), OSPFv2 [RFC2328] is the IGP deployed over
IPv4, while OSPFv3 [RFC5340] is the IGP deployed over IPv6. OSPFv3
further supports multiple address families [RFC5838], including both
the IPv6 unicast address family and the IPv4 unicast address family.
Consequently, it is possible to deploy OSPFv3 over IPv4 without any
changes to either OSPFv3 or to IPv4. During the transition to IPv6,
future OSPF extensions can focus on OSPFv3 and OSPFv2 can move to
maintenance mode.
This document specifies how to use IPv4 to transport OSPFv3 packets.
The mechanism takes advantage of the fact that OSPFv2 and OSPFv3
share the same IP protocol number, 89. Additionally, the OSPF packet
header for both OSPFv2 and OSPFv3 includes the OSPF header version
(i.e., the field that distinguishes an OSPFv2 packet from an OSPFv3
packet) in the same location (i.e., the same offset from the start of
the header).
If the IPv4 topology and IPv6 topology are not identical, the most
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likely cause is that some parts of the network deployment have not
yet been upgraded to support both IPv4 and IPv6. In situations where
the IPv4 deployment is a proper superset of the IPv6 deployment, it
is expected that OSPFv3 packets would be transported over IPv4, until
the rest of the network deployment is upgraded to support IPv6 in
addition to IPv4. In situations where the IPv6 deployment is a
proper superset of the IPv4 deployment, it is expected that OSPFv3
would be transported over IPv6.
Throughout this document, OSPF is used when the text applies to both
OSPFv2 and OSPFv3. OSPFv2 or OSPFv3 is used when the text is
specific to one version of the OSPF protocol. Similarly, IP is used
when the text describes either version of the Internet protocol.
IPv4 or IPv6 is used when the text is specific to a single version of
the Internet protocol.
2. Terminology
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].
3. Encapsulation in IPv4
Unlike 6to4 encapsulation [RFC3056] that tunnels IPv6 traffic through
an IPv4 network, an OSPFv3 packet can be directly encapsulated within
an IPv4 packet as the payload, without the IPv6 packet header, as
illustrated in Figure 1. For OSPFv3 transported over IPv4, the IPv4
packet has an IPv4 protocol type of 89, denoting that the payload is
an OSPF packet. The payload of the IPv4 packet consists of an OSPFv3
packet, beginning with the OSPF packet header having its OSPF version
field set to 3.
An OSPFv3 packet followed by an OSPF link-local signaling (LLS)
extension data block [RFC5613] encapsulated in an IPv4 packet is
illustrated in Figure 2.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ^
| 4 | IHL |Type of Service| Total Length | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Identification |Flags| Fragment Offset | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time to Live | Protocol 89 | Header Checksum | IPv4
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Header
| Source Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Destination Address | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Options | Padding | v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ^
| 3 | Type | Packet length | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router ID | OSPFv3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Header
| Area ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Checksum | Instance ID | 0 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ v
| OSPFv3 Body ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: An IPv4 packet encapsulating an OSPFv3 packet.
+---------------+
| IPv4 Header |
+---------------+
| OSPFv3 Header |
|...............|
| |
| OSPFv3 Body |
| |
+---------------+
| |
| LLS Data |
| |
+---------------+
Figure 2: The IPv4 packet encapsulating an OSPFv3 packet with
a trailing OSPF link-local signaling data block.
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3.1. Source Address
For OSPFv3 over IPv4, the source address is the primary IPv4
address for the interface over which the packet is transmitted.
All OSPFv3 routers on the link SHOULD share the same IPv4 subnet
for IPv4 transport to function correctly.
While OSPFv2 operates on a subnet, OSPFv3 operates on a link
[RFC5340]. Accordingly, an OSPFv3 router implementation MAY
support adjacencies with OSPFv3 neighbors on different IPv4
subnets. If this is supported, the IPv4 data plane MUST resolve
the layer-2 address using Address Resolution Protocol (ARP) on
multi-access networks and point-to-point over LAN [RFC5309] for
direct next-hops on different IPv4 subnets.
3.2. Destination Address
As defined in OSPFv2, the IPv4 destination address of an OSPF
protocol packet is either an IPv4 multicast address or the IPv4
unicast address of an OSPFv2 neighbor. Two well-known link-local
multicast addresses are assigned to OSPFv2, the AllSPFRouters
address (224.0.0.5) and the AllDRouters address (224.0.0.6). The
multicast address used depends on the OSPF packet type, the OSPF
interface type, and the OSPF router's role on multi-access
networks.
Thus, for an OSPFv3 over IPv4 packet to be sent to AllSPFRouters,
the destination address field in the IPv4 packet MUST be 224.0.0.5.
For an OSPFv3 over IPv4 packet to be sent to AllDRouters, the
destination address field in the IPv4 packet MUST be 224.0.0.6.
When an OSPF router sends a unicast OSPF packet over a connected
interface, the destination of such an IP packet is the address
assigned to the receiving interface. Thus, a unicast OSPFv3 packet
transported in an IPv4 packet would specify the OSPFv3 neighbor's
IPv4 address as the destination address.
3.3. Operation over Virtual Links
When an OSPF router sends an OSPF packet over a virtual link, the
receiving router is a router that might not be directly connected
to the sending router. Thus, the destination IP address of the IP
packet must be a reachable unicast IP address for the virtual link
endpoint. Because IPv6 is the presumed Internet protocol and an
IPv4 destination is not routable, the OSPFv3 address family
extension [RFC5838] specifies that only IPv6 address family virtual
links are supported.
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As illustrated in Figure 1, this document specifies OSPFv3
transport over IPv4. As a result, OSPFv3 virtual links can be
supported with IPv4 address families by simply setting the IPv4
destination address to a reachable IPv4 unicast address for the
virtual link endpoint. Hence, the restriction in Section 2.8 of
RFC 5838 [RFC5838] is removed. If IPv4 transport, as specified
herein, is used for IPv6 address families, virtual links cannot be
supported. Hence, it is RECOMMENDED to use the IP transport
matching the address family in OSPF routing domains requiring
virtual links.
4. IPv4-only Use Case
OSPFv3 only requires IPv6 link-local addresses to form adjacencies,
and does not require IPv6 global-scope addresses to establish an IPv6
routing domain. However, IPv6 over Ethernet [RFC2464] uses a
different EtherType (0x86dd) from IPv4 (0x0800) and the Address
Resolution Protocol (ARP) (0x0806) [RFC826] used with IPv4.
Some existing deployed link-layer equipment only supports IPv4 and
ARP. Such equipment contains hardware filters keyed on the EtherType
field of the Ethernet frame to filter which frames will be accepted
by that link-layer equipment. Because IPv6 uses a different
EtherType, IPv6 framing for OSPFv3 will not work with that equipment.
In other cases, PPP might be used over a serial interface, but again
only IPv4 over PPP might be supported over such interface. It is
hoped that equipment with such limitations will be eventually
upgraded or replaced.
In some locations, especially locations with less communications
infrastructure, satellite communications (SATCOM) is used to reduce
deployment costs for data networking. SATCOM often has lower cost to
deploy than running new copper or optical cables over long distances
to connect remote areas. Also, in a wide range of locations
including places with good communications infrastructure, Very Small
Aperture Terminals (VSAT) often are used by banks and retailers to
connect their branches and stores to a central location.
Some widely deployed VSAT equipment has either (A) Ethernet
interfaces that only support Ethernet Address Resolution Protocol
(ARP) and IPv4, or (B) serial interfaces that only support IPv4 and
Point-to-Point Protocol (PPP) packets. Such deployments and
equipment still can deploy and use OSPFv3 over IPv4 today, and then
later migrate to OSPFv3 over IPv6 after equipment is upgraded or
replaced. This can have lower operational costs than running OSPFv2
and then trying to make a flag-day switch to OSPFv3. By running
OSPFv3 over IPv4 now, the eventual transition to dual-stack, and then
to IPv6-only can be optimized.
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5. Security Considerations
As described in [RFC4552], OSPFv3 uses IPsec [RFC4301] for
authentication and confidentiality. Consequently, an OSPFv3 packet
transported within an IPv4 packet requires IPsec to provide
authentication and confidentiality. Further work such as [ipsecospf]
would be required to support IPsec protection for OSPFv3 over IPv4
transport.
An optional OSPFv3 Authentication Trailer [RFC7166] also has been
defined as an alternative to using IPsec. The calculation of the
authentication data in the Authentication Trailer includes the source
IPv6 address to protect an OSPFv3 router from Man-in-the-Middle
attacks. For IPv4 encapsulation as described herein, the IPv4 source
address should be placed in the first 4 octets of Apad followed by
the hexadecimal value 0x878FE1F3 repeated (L-4)/4 times, where L is
the length of hash measured in octets.
The processing of the optional Authentication Trailer is contained
entirely within the OSPFv3 protocol. In other words, each OSPFv3
router instance is responsible for the authentication, without
involvement from IPsec or any other IP layer function. Consequently,
except for calculation of the Apad value, transporting OSPFv3 packets
using IPv4 does not change the generation or validation of the
optional OSPFv3 Authentication Trailer.
6. IANA Considerations
No actions are required from IANA as result of the publication of
this document.
7. Acknowledgments
The authors would like to thank Alexander Okonnikov for his thorough
review and valuable feedback.
8. References
8.1. Normative References
[RFC791] Postel, J., "Internet Protocol", STD 5, RFC 791, September
1981.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, July 2008.
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[RFC2328] Moy, J., "OSPF Version 2", STD54, RFC 2328, April 1998.
[RFC5838] Lindem, A., Ed., Mirtorabi, S., Roy, A., Barnes, M., and
R. Aggarwal, "Support of Address Families in OSPFv3", RFC
5838, April 2010.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5309] Shen, N., Ed., and A. Zinin, Ed., "Point-to-Point
Operation over LAN in Link State Routing Protocols", RFC
5309, October 2008.
8.2. Informative References
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271, January
2006.
[RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains
via IPv4 Clouds", RFC 3056, February 2001.
[RFC5613] Zinin, A., Roy, A., Nguyen, L., Friedman, B., and D.
Yeung, "OSPF Link-Local Signaling", RFC 5613, August 2009.
[RFC826] Plummer, D., "Ethernet Address Resolution Protocol: Or
Converting Network Protocol Addresses to 48.bit Ethernet
Address for Transmission on Ethernet Hardware", STD 37,
RFC 826, November 1982.
[RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet
Networks", RFC 2464, December 1998.
[RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality
for OSPFv3", RFC 4552, June 2006.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC7166] Bhatia, M., Manral, V., and A. Lindem, "Supporting
Authentication Trailer for OSPFv3", RFC 7166, March 2014.
[ipsecospf] Gupta, M. and Melam, M, Work in progress, "draft-gupta-
ospf-ospfv2-sec-01.txt", August 2009.
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Authors' Addresses
I. Chen
Ericsson
Email: ichen@kuatrotech.com
A. Lindem
Cisco
Email: acee@cisco.com
R. Atkinson
Consultant
Email: rja.lists@gmail.com
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