INTERNET DRAFT Brian Haberman
April 1999 IBM
Routing of Scoped Addresses
in the Internet Protocol Version 6 (IPv6)
<draft-ietf-ipngwg-scoped-routing-01.txt>
Status of This Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC 2026.
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Abstract
This document outlines a mechanism for generating routing tables that
include scoped IPv6 addresses. It defines a set of
rules for routers to implement in order to forward scoped unicast and
multicast addresses regardless of the routing protocol. It should be
noted that these rules will apply to all scoped addresses.
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Contents
1. Introduction 1
2. Assumptions and Definitions 1
3. Single Site Routing 1
4. Site Boundary Unicast Routing 2
4.1. Routing Protocols . . . . . . . . . . . . . . . . . . . . 2
4.2. Packet Forwarding . . . . . . . . . . . . . . . . . . . . 4
5. Scoped Multicast Routing 5
5.1. Routing Protocols . . . . . . . . . . . . . . . . . . . . 5
5.2. Packet Forwarding . . . . . . . . . . . . . . . . . . . . 5
6. Protocol Impact 6
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1. Introduction
This document defines a set of rules for the generation of forwarding
tables that contain scoped addresses. This document describes the
handling of scoped addresses for both single site and
site boundary routers. Ideally, these concepts should be included in
followup drafts of IPv6 routing protocols.
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].
2. Assumptions and Definitions
This document makes several assumptions concerning sites :
- Site boundaries cut through nodes
- Site boundaries are identical for unicast and multicast traffic
- A single interface can only be in one site
- Each interface participating in a site has a site identifier
- In the absence of explicit configuration, all site identifiers on
a node default to the same value
A single site router is defined as a router configured with the same
site identifier on all interfaces. A site boundary router is defined
as a router that has at least 2 distinct site identifiers configured.
This could include a router connected to 2 distinct sites or a router
connected to 1 site and a separate global network (Figure ??).
3. Single Site Routing
In a single site router, a routing protocol
can advertise and route all addresses and prefixes on all interfaces.
This configuration does not require any special handling for site
local addresses. The reception and transmission of site local
addresses is handled in the same manner as globally scoped addresses.
This applies to both unicast and multicast routing protocols.
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* *
* *
* Site ID = X *
* *
* *
+-*---|--------|---*-+
| * i/f 1 i/f 2 * |
| **************** |
| |
| |
| Router |
***************** *******************
| * * |
Site ID = Y - i/f 3 * * i/f 4 - Site ID = Default
| * * |
***************** *******************
+--------------------+
Figure 1: Multi-Sited Router
4. Site Boundary Unicast Routing
With respect to site boundaries,
routers must consider which interfaces a packet can be transmitted on
as well as control the propagation of routing information specific to
the site. This includes controlling which prefixes can be advertised
on an interface.
4.1. Routing Protocols
When a routing protocol determines that it is a site boundary router,
it must perform additional work in order to protect inter site
integrity and still maintain intra site connectivity.
In order to maintain connectivity, the routing protocol must be
able to create forwarding information for the global prefixes as well
as for all of the site prefixes for each of its attached sites. The
most straight forward way of doing this is to create up to (n + 1)
routing tables; one for the global prefixes, if any, and one for each
of the (n) sites.
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To protect inter site integrity, routers must be selective in the
forwarding information that is shared with neighboring routers.
Routing protocols routinely transmit their routing information to
neighboring routers. When a router is transmitting this routing
information, it must not include any information about sites other
than the site defined on the interface used to reach a neighbor.
* *
* *
* Site ID = X *
* *
* *
+-*---|--------|---*-+
| * i/f 1 i/f 2 * |
| **************** |
| |
| |
| Router |
***************** *******************
| * * |
Site ID = Y - i/f 3 * * i/f 4 - Site ID = Default
| * * |
***************** *******************
+--------------------+
i/f 1 : global prefix = 3FFE:20::/64
site prefix = FEC0:0:0:N/64
i/f 2 : no global prefix
site prefix = FEC0:0:0:K/64
i/f 3 : global prefix = 3FFE:40::/64
site prefix = FEC0:0:0:M/64
i/f 4 : global prefix = 3FFE:80::/64
no site prefix
Figure 2: Routing Information Exchange
As an example, the router in Figure ?? must advertise routing
information on four interfaces. The information advertised is as
follows :
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- Interface 1
* All global prefixes (3FFE:20::/64, 3FFE:40::/64, and
3FFE:80::/64)
* Site prefix FEC0:0:0:N/64
* Site prefix FEC0:0:0:K/64
- Interface 2
* All global prefixes (3FFE:20::/64, 3FFE:40::/64, and
3FFE:80::/64)
* Site prefix FEC0:0:0:N/64
* Site prefix FEC0:0:0:K/64
- Interface 3
* All global prefixes (3FFE:20::/64, 3FFE:40::/64, and
3FFE:80::/64)
* Site prefix FEC0:0:0:M/64
- Interface 4
* All global prefixes (3FFE:20::/64, 3FFE:40::/64, and
3FFE:80::/64)
By imposing advertisement rules, site integrity is maintained by
keeping all site routing information contained within the site.
4.2. Packet Forwarding
In addition to the extra cost of generating additional
forwarding information for each site, site boundary routers must also
do some additional checking when forwarding packets that contain site
local addresses.
If a packet being forwarded contains a
site local destination address, regardless of the scope of the source
address, the router must perform the following :
- Lookup incoming interface's site identifier
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- Perform route lookup for destination address in arrival
interfaces site scoped routing table
If a packet being forwarded contains a site local source
address and a globally scoped destination address, the following must
be performed :
- Lookup outgoing interface's site identifier
- Compare inbound and outbound interfaces' site identifiers
If the site identifiers match, the
packet can be forwarded. If they do not match, an ICMPv6 destination
unreachable message must be sent to the sender with a new code value,
code = 5 (Scope Mismatch).
This ICMPv6 message will indicate that the destination address is not
reachable with the specified source address.
5. Scoped Multicast Routing
With IPv6 multicast, there are multiple scopes
supported. Multicast routers must be able to control the propagation
of scoped packets based on administratively configured boundaries.
5.1. Routing Protocols
Multicast routing protocols must follow the same rules as the unicast
protocols. They will be required to maintain information about
global prefixes as well as information about all scope boundaries
that pass through the router. Multicast protocols that rely on
underlying unicast protocols (i.e. PIM) will not suffer as much of a
performance impact since the unicast protocol will handle the
forwarding table generation. They must be able to handle the
additional scope boundaries used in multicast addresses. Multicast
protocols that generate and
maintain their own routing tables will have to perform the additional
route calculations for scope. All multicast protocols will be forced
to handle 14 additional scoping identifiers above the site
identifiers supported in IPv6 unicast addresses.
5.2. Packet Forwarding
The forwarding rules for multicast can be described by the following
combinations :
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- Global multicast destination address / Global unicast source
address
- Global multicast destination address / Site local unicast source
address
- Scoped multicast destination address / Global unicast source
address
- Scoped multicast destination address / Site local unicast source
address
The first combination requires no special
processing over what is currently in place for global IPv6 multicast.
Combinations 2,3, and 4 should result in the router performing the
same identifiers check as outlined for site local unicast addresses.
Since IPv6 supports fifteen unique multicast scopes, it is assumed
that scopes 0x1 through 0x4 are strictly less than
the unicast site scope, scope 0x5 (site) is equal to the unicast site
scope, scopes 0x6 through 0xd are strictly greater than the unicast
site scope and strictly less than the unicast global scope, and scope
0xe is equal to the unicast global scope.
6. Protocol Impact
The performance impact on routing protocols is obvious.
Routers implementing scoped address support will be forced to perform
an additional check in the main forwarding path to
determine if the source address is scoped. This will add overhead to
the processing of every packet flowing through the router. In
addition, there will be some storage overhead for
the scope identifiers. If scoped addresses are going to be realized,
this performance impact may be acceptable.
References
[RFC 2119] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, BCP14, March 1997.
Security Considerations
This document specifies a set of guidelines that allow routers to
prevent site
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specific information from leaking out of each site. If site boundary
routers allow site routing information to be forwarded outside of the
site, the integrity of the site could be compromised.
Acknowledgements
I would like to thank Thomas Narten, Steve Deering, and Erik Nordmark
for their comments and reviews of this document.
Author's Address
Brian Haberman
IBM Corporation
800 Park Office Drive
Research Triangle Park, NC 27709
USA
+1-919-254-2673
haberman@raleigh.ibm.com
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