Internet DRAFT - draft-xu-ospf-multi-homing-ipv6
draft-xu-ospf-multi-homing-ipv6
Network Working Group M. Xu
Internet-Draft S. Yang
Expires: April 13, 2016 J. Wu
Tsinghua University
F. Baker
Cisco Systems
October 11, 2015
Extending OSPFv3 to Support Multi-homing
draft-xu-ospf-multi-homing-ipv6-00
Abstract
Traditionally, routing protocols make routing decisions solely based
on destination IP addresses, packets towards the same destination
will be delivered to the same next hop no matter where they come
from. These protocols work well with simple networks that have only
one egress router. However, in the multi-homing scenario, packets
may be dropped if forwarded only based on destination addresses.
This document defines enhancements to the OSPFv3 protocol that allow
simple and flexible operations, with which packets will be routed
towards the corresponding upstream ISPs based on both destination and
source addresses.
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 13, 2016.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
Xu, et al. Expires April 13, 2016 [Page 1]
Internet-Draft Extending OSPFv3 to Support Multi-homing October 2015
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.
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Router Behavior . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Egress Router Behavior . . . . . . . . . . . . . . . . . 5
4.2. Interior Router Behavior . . . . . . . . . . . . . . . . 5
5. TC-LSA Format . . . . . . . . . . . . . . . . . . . . . . . . 6
6. Routing Table Structure . . . . . . . . . . . . . . . . . . . 8
7. Calculation of the Routing Table . . . . . . . . . . . . . . 9
8. Matching Rule . . . . . . . . . . . . . . . . . . . . . . . . 9
9. Compatibility . . . . . . . . . . . . . . . . . . . . . . . . 9
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
12.1. Normative References . . . . . . . . . . . . . . . . . . 10
12.2. Informative References . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
Networks are growing both in device count and in complexity. Today
they are generally connected with multiple upstream providers, and
may require routing to place audio/visual entertainment traffic one
one path, office services on another. Traditionally, we have
Xu, et al. Expires April 13, 2016 [Page 2]
Internet-Draft Extending OSPFv3 to Support Multi-homing October 2015
simplified networks using a single exit router. Increasingly, such
networks are multi-homed.
Traditionally, routing protocols make routing decisions solely based
on destination IP addresses, packets towards the same destination
will be delivered to the same next hop no matter where they come
from. These protocols work well with simple networks that have only
one egress router. However, in the multi-homing scenario, packets
may be dropped if forwarded only based on destination addresses
[RFC3704].
Although many patch-like solutions, like static routing, policy-based
routing (PBR), multi-topology routing (MTR) and layer-3 VPN can solve
the problem, they complex the configurations in networks, and are not
suitable for ISP administrators. We need a simple solution to help
administrators manage their networks in the multi-homing scenario.
In this document, we define enhancements to OSPFv3 that allow
networks route packets towards the corresponding upstream ISPs,
according to both destination and source addresses. The enhancements
defined in this memo are backward-compatible with the OSPFv3
specification defined in [RFC5340], and with the OSPF extensions
defined in [I-D.ietf-ospf-ospfv3-lsa-extend]
2. Terminology
Terminology used in this document:
o Traffic Class (TC): Identified by (destination prefix, source
prefix), all packets falling in the domain belong to the traffic
class.
o TC-Route: Identified by (destination prefix, source prefix,
value), where value is the administrative value applied to the
traffic class (destination prefix, source prefix).
o TC-LSA: Link state advertisement that communicates the
reachability for a traffic classes.
3. Overview
Traditionally, egress routers obtain delegated prefixes from upstream
ISPs using DHCPv6 with prefix options [RFC3633]. The egress routers
will then assign longer sub-prefixes to the other links in the
network. Each router inside the network will act as standard OSPFv3
router, and forward packets based on their destination addresses.
Xu, et al. Expires April 13, 2016 [Page 3]
Internet-Draft Extending OSPFv3 to Support Multi-homing October 2015
With traffic class routing, after obtaining delegated prefixes and
assigning sub-prefixes, egress routers will populate traffic classes
(with extended LSAs), rather than destination address only, into the
network. Each internal router will flood these traffic classes
information. When calculating the path towards a destination
address, routers will take the traffic classes into considerations.
Intrinsically, in traditional routing model, the object being routed
to is a destination prefix; in the new routing model, the object
being routed might be a destination prefix given that the packet
sports a certain source prefix.
Each traffic class is associated with a cost, which is a single
dimensionless metric.
For example, as shown in Figure 1, a site is connected to the
Internet through two ISPs, ISP1 and ISP2. ISP1 delegates prefix P1
to the site, and ISP2 delegates prefix P2 to the site. After being
delegated with P1, the egress router E1 of the site will advertise a
traffic class - {::/0, P1}, into the site. After being delegated
with P2, the egress router E2 of the site will advertise a traffic
class - {::/0, P2}, into the site. Receiving these advertisements,
interior router I1 will compute two paths towards ::/0, one through
router E1 for traffic from P1, the other through E2 for traffic from
P2.
Xu, et al. Expires April 13, 2016 [Page 4]
Internet-Draft Extending OSPFv3 to Support Multi-homing October 2015
+---------------+ +-----------------+
| | | |
| ISP1: P1 | | ISP2: P2 |
| | | |
+--------+------+ +-----+-----------+
| |
+--+---+ +--+---+
|Router| |Router|
| BR1 | | BR2 |
+---+--+ +---+--+
------+---------- -----------+-----
| |
+---+--+ +---+--+
|Router| |Router|
| E1 | | E2 |
+------+ +------+ +------+
-+-------+Router+---------+-
| I1 |
+--+---+
+--+---+ Address A in P1
| Host |
+------+ Address B in P2
Figure 1: Multi-homing Scenario
4. Router Behavior
All routers behave like traditional OSPFv3 routers, however, the
following behaviors are different with traditional OSPFv3 routers.
4.1. Egress Router Behavior
After obtaining delegated prefixes using DHCPv6 with prefix options,
an egress router should originate TC-LSAs, i.e., extended LSAs with
source prefixes appended. Egress routers then will advertise these
TC-LSAs into the network.
Note that an egress router behaves like an interior router if it
receives a TC-LSA from other egress routers.
4.2. Interior Router Behavior
Receiving TC-LSAs from egress routers, an interior router should
store the TC-LSAs into its LSDB, and flood it to other routers.
After calculating a path to an egress router advertising
reachability, i.e., a destination prefix, the interior router should
decide which traffic class can follow this path towards the egress
Xu, et al. Expires April 13, 2016 [Page 5]
Internet-Draft Extending OSPFv3 to Support Multi-homing October 2015
router. If a traffic class can travel through two different paths,
then interior router should compare their costs, and select the path
with the lowest cost.
Interior routers contains a routing table that contains all necessary
information to forward an IP packet following the path of a traffic
class. After computing the path towards a traffic class, interior
routers should update the entry in the routing table if necessary,
e.g., change the next hop towards the traffic class. The routing
table structure will be described in Section 6. Calculation of
routing table will be illustrated in Section 7.
At last, interior routers should update the Forwarding Information
Base (FIB), which will be discussed in the next version of this
document.
5. TC-LSA Format
TC-LSA adds TLV extensions, which contains source prefix information,
based on original OSPFv3 LSA. We follow the TLV format in
[I-D.baker-ipv6-ospf-dst-src-routing] and extended LSA format in
[I-D.ietf-ospf-ospfv3-lsa-extend].
Each extended LSA includes the traditional LSA part in [RFC5340], and
one or more TLVs defined in [I-D.baker-ipv6-ospf-dst-src-routing].
But we do not need all LSAs to be extended, the LSAs need to be
extended are as follows:
o Intra-Area-Prefix-LSA: The extended LSA has type 0x2029.
The extended LSA format for Intra-Area-Prefix-LSA in multi-homing is
shown in Figure 2.
Xu, et al. Expires April 13, 2016 [Page 6]
Internet-Draft Extending OSPFv3 to Support Multi-homing October 2015
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS Age |0|0|1| LSA Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS Checksum | LSA Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| # Prefixes | Referenced LS Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Referenced Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Referenced Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PrefixLength | PrefixOptions | Metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Prefix |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PrefixLength | PrefixOptions | Metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Prefix |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TLV Type | TLV Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SPrefixLength | SPrefixOptions| 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Address Prefix |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Extended Intra-Area-Prefix-LSA format
All LSA header fields are the same as defined in [RFC5340], except
the following:
o LSA type: The LSA type value is 0x2029, according to
[I-D.ietf-ospf-ospfv3-lsa-extend];
Xu, et al. Expires April 13, 2016 [Page 7]
Internet-Draft Extending OSPFv3 to Support Multi-homing October 2015
o LSA length: The length of the whole LSA header, including the
TLVs;
o TLV type: The type of IPv6 source prefix TLV, assigned by IANA;
o TLV length: The value is 20 as defined in
[I-D.baker-ipv6-ospf-dst-src-routing];
o SPrefixLength, SPrefixOptions, Source Address Prefix:
Representation of the IPv6 address prefix, which is delegated from
the upstream ISP providers;
In the extended LSA, suppose there are n destination prefix d1, d2,
..., dn, and 1 source prefix s, then the LSA carries n TC-route
announcement, (d1, s, v1), (d2, s, v2), ..., (dn, s, vn), where vi is
the metric associated with destination prefix di.
6. Routing Table Structure
For traditional routing, the routing table structure contains all
needed information to forward IP packets to the right destination.
For example, destination prefixes are commonly structured into a
prefix trie, where each trie nodes contain the necessary information.
Routers can lookup and update the prefix trie.
With traffic classes, the routing table structure must contain all
needed information to forward IP packets following the right traffic
class, i.e., towards the related destination and from the related
source. For each routing table entry, there are two additional
fields other than the fields mentioned in [RFC5340]:
o Source IP Address: The IP address of the source in traffic class.
o Source Address Mask: If the source is a subnet, then it is
referred to as the subnet mask.
The routing table must provide interface for update and lookup in it.
For example, traffic classes can be structured into a two dimensional
(or two level) trie, where each trie node in the first dimension
points to a sub-trie in the second dimension. The trie nodes in the
second dimension contain the necessary information to forward IP
packets following the right traffic class.
There exist multiple implementation in real routers. For example, 1)
we can add an additional routing table besides the destination-based
routing table; 2) the destination-based routing table can be extended
to support the new structure, in which case all destination-based
rule can be appended with a wildcard IPv6 address prefix as the
Xu, et al. Expires April 13, 2016 [Page 8]
Internet-Draft Extending OSPFv3 to Support Multi-homing October 2015
source prefix. The specific implementation for routing table is out
of scope of this document.
7. Calculation of the Routing Table
The fundamental algorithm in OSPFv3 doesn't change. The algorithm
uses the SPF approach to calculate a path to the router advertising
reachability, and then uses the reachability advertisement to decide
what traffic should follow that route. What we are changing is the
reachability advertisement, in traiditional OSPFv3, the
advertisements, which is one or several kinds of LSAs, represent
destination prefixes; in this document, the advertisements, which is
one or several kinds of TC-LSAs, represent traffic classes.
Note that we do not have to change router-LSA and network-LSA in
[RFC5340]. Thus, the first stage of Section 4.8.1 in [RFC5340]
remains the same in this document. However, the second stage of
Section 4.8.1 in [RFC5340] should change by a little bit. Instead of
examining the list of the intra-area-prefix-LSAs, the list of
extended intra-area-prefix-LSAs is examined. The cost of any
advertised traffic class is the sum of the class' advertised metric
plus the cost of the transit vertex (either router or transit
network) indentified by extended intra-area-prefix-LSAs' referenced
LS type, referenced link state ID, and referenced advertising router
field.
8. Matching Rule
We also adopt the LMF (longest match first) rule when a packet
matches multiple routing entries. However, traffic class has two
dimensions, there might exist ambiguity. For example, if there
exists two routing entries, (d1, s1, nexthop1), (d2, s2, nexthop2),
where d1 is longer than d2 and s2 is longer than s1, then none entry
is longer than the other in both dimensions. In this situation, we
must insert an additional entry into the routing table, e.g., (d1,
s2, nexthop1) in the above example. The entry directs to nexthop1
rather than nexthop2, because we must guarantee consistency among
routers.
9. Compatibility
With the enhancements, incremental deployment is possible. The un-
deployed routers act according to [RFC5340], and will drop the
extended LSA packets when receiving them.
Xu, et al. Expires April 13, 2016 [Page 9]
Internet-Draft Extending OSPFv3 to Support Multi-homing October 2015
10. IANA Considerations
The newly LSA types and TLVs should be assigned by IANA, please refer
to [I-D.baker-ipv6-ospf-dst-src-routing] and
[I-D.ietf-ospf-ospfv3-lsa-extend].
11. Acknowledgments
Zheng Liu and Gautier Bayzelon provided useful input into this
document.
12. References
12.1. Normative References
[RFC3704] Baker, F. and P. Savola, "Ingress Filtering for Multihomed
Networks", BCP 84, RFC 3704, DOI 10.17487/RFC3704, March
2004, <http://www.rfc-editor.org/info/rfc3704>.
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
DOI 10.17487/RFC3633, December 2003,
<http://www.rfc-editor.org/info/rfc3633>.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
<http://www.rfc-editor.org/info/rfc5340>.
12.2. Informative References
[I-D.baker-ipv6-ospf-dst-src-routing]
Baker, F., "IPv6 Source/Destination Routing using OSPFv3",
draft-baker-ipv6-ospf-dst-src-routing-03 (work in
progress), August 2013.
[I-D.ietf-ospf-ospfv3-lsa-extend]
Lindem, A., Mirtorabi, S., Roy, A., and F. Baker, "OSPFv3
LSA Extendibility", draft-ietf-ospf-ospfv3-lsa-extend-07
(work in progress), August 2015.
Authors' Addresses
Xu, et al. Expires April 13, 2016 [Page 10]
Internet-Draft Extending OSPFv3 to Support Multi-homing October 2015
Mingwei Xu
Tsinghua University
Department of Computer Science, Tsinghua University
Beijing 100084
P.R. China
Phone: +86-10-6278-1572
Email: xumw@tsinghua.edu.cn
Shu Yang
Graduate School at Shenzhen, Tsinghua University
Division of Information Science and Technology
Shenzhen 518055
P.R. China
Phone: +86-755-2603-6059
Email: yang.shu@sz.tsinghua.edu.cn
Jianping Wu
Tsinghua University
Department of Computer Science, Tsinghua University
Beijing 100084
P.R. China
Phone: +86-10-6278-5983
Email: jianping@cernet.edu.cn
Fred Baker
Cisco Systems
Santa Barbara, California 93117
USA
Email: fred@cisco.com
Xu, et al. Expires April 13, 2016 [Page 11]
