Internet DRAFT - draft-sethom-dynamic-router-selection
draft-sethom-dynamic-router-selection
Internet Draft Kaouthar Sethom
INT-France
Document: draft-sethom-dynamic-router- Sidi-Mohammed
selection-01.txt Senouci
FRANCE TELECOM
Expires: June 2006 Hossam Afifi
INT-France
January 2006
Dynamic router selection
Status of this Memo
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Abstract
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Dynamic router selection January 2006
In a network topology where the host has multiple routers on its
Default Router List, it is important to select the most suitable one
according to node’s application requirements. This document describes
an extension to router advertisement message [RFC 1256, RFC 2461] for
dynamic router selection. This new functionality is implemented in
routers with additional capabilities.
Conventions used in this document
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 RFC-2119 [i].
Table of Contents
1. Introduction...................................................2
2. Terminology....................................................2
3. Protocol Overview..............................................3
3.1 Message Formats............................................4
3.1.1 ICMP Router Advertisement Message 4
3.1.2 IPv6 Router Advertisement Message 6
Security Considerations...........................................8
References........................................................8
Author's Addresses................................................9
1. Introduction
The core of the next generation infrastructure is expected to be the
IP based multi-service network that provides connectivity and
transport via any access technology, including optical fibre,
wireless local area networks (WLAN), 3G systems and future access
technologies. Since each system may be different in terms of QoS
capabilities, availability (coverage), capacity and price; a node
with a list of default routers must be able to choose the most
suitable one in terms of offered QoS.
As current router discovery protocols do not offer such opportunity,
we describe here an optional extension to router discovery process to
support dynamic gateway selection. Each router will be able to
broadcast “fresh” informations about its offered QoS. This improves
the ability of nodes to choose an appropriate router for a
destination.
2. Terminology
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- Router Egress interface: One of the router’s interfaces used to
forward packets upstream to the rest of the Internet.
- Router Ingress interface: one of the router’s interfaces used to
forward packets downstream to the nodes inside a subnet.
3. Protocol Overview
In this section, we describe the dynamic gateway selection process
that is designed to work in the case of IPv4 as well as in the case
of IPv6 addressing system.
Traditionally, nodes on a LAN learn about default routers by
receiving Router Advertisements [1,2]. Each router periodically
multicasts a Router Advertisement from each of its multicast
interfaces, announcing the IP address(es) of that interface.
Delivery of a packet to another subnetwork requires that the packet
be sent to a router on the same subnetwork as the sender for
forwarding to the ultimate destination. Since the only router known
to the end system is the default gateway, this would be the router
used. Routers, on the other hand, learn through their router-to-
router routing protocols of all other routers that they can reach and
that provide the best path to each possible destination. If another
router on the same subnetwork as the sender has a better route to the
desired destination, the router initially receiving the packet would
forward the original packet along the best path available. It would
also send a re-direct packet back to the sending end system,
informing it of the better router available for that destination.
Depending upon the sophistication of the protocol implementation on
the sending end system, that new router information might be
remembered for future use with packets destined to the same
destination, or it might be ignored. Either way, the off-network
packets would be delivered correctly.
A Router Advertisement can includes a "preference field" [1,3] for
each advertised router address. When a node must choose a default
router, it is expected to choose from those router addresses that
have the highest preference level.
These preference values are not automatically derived from routing
table, they are generally pre-configured by the network administrator
to encourage or discourage the use of particular routers as default
routers. Changes in the availability or characteristics of some links
- such as congestion - can result in a situation, where the user
wants to move already established traffic flows from one path to
another. “Fresh” information on the routers’ egress interfaces
characteristics should then always be available to the application
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layers, so that they can dynamically adapt to such changes and choose
the best available router.
To that’s end, we propose to add a new option field “Dynamic router
selection (DRS)” to the router advertisement message that will
contain information about router’s interfaces characteristics such as
throughput, type...
At each node in the network, all received router advertisement
packets (with DRS field) are registered in what we called the gateway
table. This information repository is re-freshed periodically. This
means that entries are deleted as soon as their validity time
expires. Each time a host wants to send IP data datagrams, it uses
the information on its local gateway table to choose among available
router the best one to destination according to its applications
requirements or needs.
Note that, for nodes that do not support dynamic router selection
processing, they simply ignore the DRS field and continue to choose a
default router in the traditional way.
When a new router advertisement message is received, the host updates
its gateway table either by updating an existing entry, or if no
entry exists for the gateway address, creating a new entry.
3.1 Message Formats
3.1.1 ICMP Router Advertisement Message
Changes to ICMP Router Advertisement Message [RFC 1256] section 3 are
as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Num Addrs |Addr Entry Size| Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router Address[1] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DRS option[1] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router Address[2] |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DRS option[2] |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . |
| . |
ICMP Fields:
Type 9
Code 1 to indicate that the IP addresses in the
Router address fields refer to reachable
networks through this router and is not on-link
router interfaces addresses.
Num Addrs the number of router addresses advertised
in this message.
Router Address[i], the address of a network reachable through
i = 1..Num Addrs the engress interface i of this router.
DRS option [i] characteristics of the router’s egress
interface i associated with the Address[i].
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Interface Type | Cost | Throughput |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Interface Type This field indicates the technology used by
the router Egress interface. Example
Bluetooth, 802.11, Ethernet, UMTS...
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Type values can be encoded as follows:
0x00 Ethernet (default)
0x01 Bluetooth
0x10 UMTS
0x11 802.16
…
Cost This field indicates the communication cost
associated with the use of this interface:
high, medium, low. This parameter can be a
combination of different metrics such as
offered QoS, security issues, price and
possibly other preferences.
Throughput This field indicates the throughput
associated with the router egress interface.
3.1.2 IPv6 Router Advertisement Message
Changes to Router Advertisement Message [RFC 2461] section 4.6.2 are
as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Prefix Length |L|A|O|Reserved1|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Valid Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preferred Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DRS option |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix |
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+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fields:
L 1-bit link flag. When set to 1, indicates that this
prefix can be used for on-link determination. When
set to zero, indicates that if the field O is set to
1 this prefix can be used for off-link determination.
A 1-bit autonomous address-configuration flag. When
set indicates that this prefix can be used for
autonomous address configuration as specified in
[ADDRCONF].
O 1-bit off-link flag. When set, indicates that the
router has an egress-interface with this prefix and
can be used for off-link determination.
DRS option characteristics of the router’s egress interface i
associated with the prefix announced in the next
field.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Interface Type | Cost | Throughput |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Interface Type This field indicates the technology used
by the router Egress interface. Example
Bluetooth, 802.11, Ethernet, UMTS ...
Type values can be encoded as follows:
0x00 Ethernet (default)
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0x01 Bluetooth
0x10 UMTS
0x11 802.16
…
Cost This field indicates the communication
cost associated with the use of this
interface: high, medium, low. This
parameter can be a combination of
different metrics such as offered QoS,
security issues, price and possibly
other preferences.
Throughput This field indicates the throughput
associated with the router egress
interface.
Prefix An IP address or a prefix of an IP
address. The Prefix Length field
contains the number of valid leading
bits in the prefix. When the bit L is
set to zero and O to 1, it indicates
the IP address of a network reachable
through this router. The Prefix Length
field contains the number of valid
leading bits in the prefix. The bits
in the prefix after the prefix length
are reserved and MUST be initialized to
zero by the sender and ignored by the
receiver.
Security Considerations
This memo does not specify any security considerations.
References
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[1] Stephen E. Deering. “ICMP router discovery messages”. Internet
RFC 1256, September 1991
[2] Narten, T., E. Nordmark, W. Simpson, "Neighbor Discovery
for IP Version 6 (IPv6)", RFC2461, December 1998.
[3] R. Draves, D. Thaler, "Default Router Preferences and
More-Specific Routes", draft-ietf-ipv6-router-selection-
07.txt, January 2005
Author's Addresses
Kaouthar Sethom
INT-France
9 rue charles fourrier 91011 evry cedex France
Email: kaouthar.sethom@int-evry.fr
Sidi-Mohammed Senouci
France Télécom R&D
2, Avenue Pierre Marzin
22307 Lannion Cedex France
Email : sidimohammed.senouci@francetelecom.com
Hossam Afifi
INT-France
9 rue charles fourrier 91011 evry cedex France
Email: hassam.afifi@int-evry.fr
Copyright (C) The Internet Society (2006)
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
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ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Sethom Expires - June 2006 [Page 10]
