Network Working Group M. Bagnulo
Internet-Draft A. Garcia-Martinez
Expires: July 23, 2004 UC3M
January 23, 2004
Multi-Homing Tunnel Broker (MHTB)
draft-bagnulo-multi6-mhtb-00
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Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
RFC 3178 [1] describes a solution to provide site multi-homing
support in IPv6. RFC 3178 multi-homing solution uses tunnels between
the different ISPs and the multi-homed site to provide alternative
paths in case that one of the exit links is down, protecting the
multi-homed site from outages in the direct link with its providers.
However, the wide adoption of RFC 3178 multi-homing solution implies
the manual configuration of numerous tunnels on the ISPs, which may
impose an important workload in ISP network administrators. This note
proposes the usage of Multi-Homing Tunnel Brokers to automatically
configure the ISP tunnel endpoint in order to ease the adoption of
the solution.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Overview of the RFC 3178 Multi-Homing Solution . . . . . . . . 4
3. The Tunnel Broker Model . . . . . . . . . . . . . . . . . . . 6
4. The Multi-Homing Tunnel Broker Service . . . . . . . . . . . . 7
4.1 The Tunnel Broker Service . . . . . . . . . . . . . . . . . . 7
4.2 The Tunnel Server . . . . . . . . . . . . . . . . . . . . . . 8
5. Security Considerations. . . . . . . . . . . . . . . . . . . . 10
References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 11
Intellectual Property and Copyright Statements . . . . . . . . 12
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1. Introduction
RFC 3178 [1] describes a solution to provide site multi-homing
support in IPv6. RFC 3178 multi-homing solution uses tunnels between
the different ISPs and the multi-homed site to provide alternative
paths in case that one of the exit links is down, protecting the
multi-homed site from outages in the direct link with its providers.
However, the wide adoption of RFC 3178 multi-homing solution implies
the manual configuration of numerous tunnels on the ISPs, which may
impose an important workload in ISP network administrators. This note
proposes the usage of Multi-Homing Tunnel Brokers to automatically
configure the ISP tunnel endpoint in order to ease the adoption of
the solution.
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2. Overview of the RFC 3178 Multi-Homing Solution
The mechanism for multi-homing support described in RFC3178 is
illustrated in the next figure:
+----------------------------------------+
| |
| Internet |
+----------------------------------------+
| |
+----------+ +----------+
|ISPA-PrefA| |ISPB-PrefB|
+----------+ +----------+
| | | |
| \______________________|___ |
| TunnelIA-ERB | ||
linkA | ______________________/ || linkB
| | TunnelIB-ERA ||
| | ||
+--------|-|--------------------------||--------+
| +----|-+ +-|---+ |
| | ERA | | ERB | |
| +------+ +-----+ |
| |
| Multi-Homed PrefA:Site:: |
| Site +------+ PrefB:Site:: |
| | Host1| |
| +------+ |
+-----------------------------------------------+
The multi-homed site has two providers, ISPA and ISPB that have
delegated PrefA:Site::/n and PrefB:Site::/m respectively. In the
depicted scenario, the multi-homed site has only two providers, but
the solution is valid to more general scenarios that include more
than 2 providers. It is assumed that hosts within the multi-homed
site configure at least one address per provider's prefix obtained.
In order to obtain fault tolerance capabilities, RFC 3178 proposes
the creation of two tunnels:
- TunnelIA-ERB: from the ISPA's router to site exit router ERB
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- TunnelIB-ERA: from the ISPB's router to site exit router ERA
The resulting behaviour is that when one of the two exit links fails,
packets are routed through the correspondent tunnel. That is, if
linkA(linkB) fails, packets arriving to ISPA(ISPB) addressed to
PrefA:Site::/n(PrefB:Site::/m) are routed through TunnelIA-ERB
(TunnelIB-ERA) to the multi-homed end site.
This configuration provides fault tolerance capabilities, including
the preservation of established communications, when one of the site
exit links fails.
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3. The Tunnel Broker Model
RFC 3053 [2] presents a general tunnel broker model and its
particular application to the creation of IPv6 over IPv4 tunnels for
the Internet's transition to IPv6. Since the tunnels used in RFC 3178
are IPv6 in IPv6 tunnels used for redundancy, the particular
implementation details will differ in the two configurations.
However, the general model of the tunnel broker presented in RFC 3053
can still be applied to the multi-homing environment.
The tunnel broker model presented in RFC 3053 is illustrated in the
next figure and it consists in the following components:
- The Tunnel Broker (TB) is the element to which the end-users
connect themselves to create, modify and delete tunnels. Then the TB
communicates with one or several Tunnel Servers to actually create
the tunnels requested by the users.
- The Tunnel Server (TS) is the server's tunnel endpoint that is
created, modified or deleted upon reception of a request from the TB.
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4. The Multi-Homing Tunnel Broker Service
In order to provide a Tunnel Broker Service for the RFC3178
multi-homing solution, both a Tunnel Broker and one or more Tunnel
Servers are needed.
4.1 The Tunnel Broker Service
The TB will receive user requests to create tunnels. Potential users
are all the clients of the ISP. We assume that the ISP clients have a
commercial relationship with the ISP, so that the ISP can identify
its clients and the prefix that the ISP has assigned to them. We also
assume that, because of the existent business relationship between
the ISP and its customer, the ISP has created the appropriate means
to identify its clients through the network, such as a user name and
a password or a public key certificate.
So, the ISP customer will send a tunnel creation request to the TB.
The TB can accept requests through different type of interfaces, for
instance the TB can accept request submitted through http. Clients
submitting requests have to properly identify themselves through
existent means.
The requests have to contain at least the following information:
- Client identification.
- The IPv6 address of the client side endpoint of the tunnel.
- The IPv6 prefix for which a backup route through the tunnel will be
created.
- Request authorization information generated through available
means, such as client's password or client's private/public key plus
certificate.
Upon the reception of a request the TB will:
- Verify client identity.
- Verify authorization information.
- Verify that the prefix included in the request is contained in the
address range that the ISP has delegated to this particular client.
- Send configuration order to the appropriate TS to configure the
requested tunnel.
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- Inform the client of the IP address of the endpoint of ISP side of
the tunnel.
4.2 The Tunnel Server
The Tunnel Server service can be placed in different devices within
the ISP network.
An option is to use the exit router connecting the ISP to the client
as the tunnel server. In this case, packets will always be forwarded
to this exit router, and if the route through the direct link is not
available, the exit router will forward the packets through the
tunnel interface. This option requires the TB to be capable of
communicating with the exit routers through the protocol selected for
the task (rsh, smnp, others).
+----------------------------------------+
| |
| Internet |
+----------------------------------------+
| |
+----------------------+ +-----+
|ISPA-PrefA | |ISPB |
| | |PrefB|
| +---+ | +-----+
| |TB | route to | |
| +---+ PrefA:Site::| |
| | ^ | |
| v | | |
| | +----+ | |
| ->->->->->|IAER| | |
| tunnel conf +----+ | |
+----------------|-|---+ |
| | |
| \_______________ |
| TunnelIA-ERB ||
| ||
| ||
+--------|-----------------||--------+
| +-----+ +-|---+ |
| | ERA | | ERB | |
| +-----+ +-----+ |
| |
| Multi-Homed PrefA:Site:: |
| Site PrefB:Site:: |
| |
+------------------------------------+
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Another option is to place specific TS devices. In this case, the TB
will configure the tunnel in this specific TS device. The TS will
then, upon the reception of this configuration orders, create the
tunnel and will also start announcing the clients prefix through a
route with a preference lower than the one contained in the route
announced by the exit router.
+----------------------------------------+
| |
| Internet |
+----------------------------------------+
| |
+-----------------------+ +-----+
|ISPA-PrefA | |ISPB |
| | |PrefB|
| +---+ +---+ | +-----+
| |TS |-----------|TB | | |
| +---+tunnel conf+---+ | |
| | | |
| v route | |
| route PrefA:Site| |
| PrefA:Site pref high | |
| pref low ^ | |
| | | |
| +----+ | |
| |IAER| | |
| +----+ | |
+----------------|-|----+ |
| | |
| \_______________ |
| TunnelIA-ERB ||
| ||
| ||
+--------|-----------------||--------+
| +-----+ +-|---+ |
| | ERA | | ERB | |
| +-----+ +-----+ |
| |
| Multi-Homed PrefA:Site:: |
| Site PrefB:Site:: |
| |
+------------------------------------+
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5. Security Considerations.
This note proposes a Tunnel Broker service to simplify the management
of tunnels used to provide multi-homing support as specified by RFC
3178. The creation, modification and deletion of tunnels as well as
the injection of the required routes are operations that affect the
ISP critical infrastructure as it is the internal routing fabric. So,
proper security mechanism has to be adopted in order to prevent
potential attacks.
The following communications have to be secured:
- Communication between the client and the Tunnel Broker: it is
assumed that the ISP has a mechanism to properly identify the client.
Possible options are user name and password or private/public key
pair and certificate. The request sent by the client to the Tunnel
Broker have to contain authorization information based on this
identification information.
- Communication between the Tunnel Broker and the Tunnel Server. As
specified in RFC 3053, this is a critical communication that has to
be properly secured. Since it is a communication between two devices
of the ISP, the particular security mechanism used by the ISP is out
of the scope of this document.
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References
[1] Hagino, J. and H. Snyder, "IPv6 Multihoming Support at Site Exit
Routers", RFC 3178, October 2001.
[2] Durand , A., Fasano , P., Guardini , I. and D. Lento , "IPv6
Tunnel Broker", RFC 3053, January 2001.
Authors' Addresses
Marcelo Bagnulo
Universidad Carlos III de Madrid
Av. Universidad 30
Leganes, Madrid 28911
SPAIN
Phone: 34 91 6249500
EMail: marcelo@it.uc3m.es
URI: http://www.it.uc3m.es
Alberto Garcia-Martinez
Universidad Carlos III de Madrid
Av. Universidad 30
Leganes, Madrid 28911
SPAIN
Phone: 34 91 6249500
EMail: alberto@it.uc3m.es
URI: http://www.it.uc3m.es
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