Integrated IS-IS for IPv6

Integrated IS-IS, also known as dual IS, is a link state routing protocol very similar to OSPF that is defined in International Standards Organization (ISO) document 10589. IS-IS supports both IPv4 and Connectionless Network Protocol (CLNP), the Network layer of the Open Systems Interconnect (OSI) protocol suite. IS-IS allows two levels of hierarchical scaling, whereas OSPF allows only one (areas). Integrated IS-IS for IPv6 is described in the Internet draft titled “Routing IPv6 with IS-IS.”

For a detailed explanation of Integrated IS-IS for IPv6, see ISO 10589 and the Internet draft titled “Routing IPv6 with IS-IS.”

BGP-4

Border Gateway Protocol version 4 (BGP-4) is a path vector routing protocol defined in RFC 4271. Unlike RIPng for IPv6 and OSPF for IPv6, which are used within an autonomous system, BGP-4 is designed to exchange information between autonomous systems. BGP-4 routing information is used to create a logical path tree, which describes all the connections between autonomous systems. The path tree information is then used to create loop-free routes in the routing tables of BGP-4 routers. BGP-4 messages are sent using TCP port 179. BGP-4 is the primary interdomain protocol used to maintain routing tables on the IPv4 Internet.

BGP-4 has been defined to be independent of the address family for which routing information is being propagated. For IPv6, BGP-4 has been extended to support IPv6 address prefixes as described in RFCs 2545 and 4760. For a detailed explanation of BGP-4 for IPv6, see RFCs 4271, 2545, and 4760.

Static Routing with the IPv6 Protocol for Windows Server 2008 and Windows Vista

The IPv6 protocol for Windows Server 2008 and Windows Vista supports static routing. You can configure static IPv6 routing in the following ways:

■For computers running Windows Server 2008 or Windows Vista, with commands in the netsh interface ipv6 context

■For computers running Windows Server 2008, with Routing and Remote Access

Configuring Static Routing with Netsh

To create a static IPv6 router with the Netsh tool, you must enable forwarding and advertising on the required interfaces. To enable forwarding and advertising on an interface, use the following command:

netsh interface ipv6 set interface [interface=]InterfaceNameOrIndex [forwarding=]enabled|disabled] [[advertise=]enabled|disabled]

250 Understanding IPv6, Second Edition

By default, forwarding and advertising on all IPv6 interfaces are disabled.

For example, a computer named ROUTER1 running Windows Server 2008 is being configured as a router. ROUTER1 has three interfaces, named Local Area Connection, Local Area Connection 2, and Local Area Connection 3. The Local Area Connection and Local Area Connection 2 interfaces are connected to peripheral subnets. The Local Area Connection 3 interface is connected to a subnet containing a neighboring IPv6 router named ROUTER2. Figure 10-5 shows this example configuration.

Local Area Connection 2

Local Area Connection 3

ROUTER2

Intranet

ROUTER1

fe80::2aa:ff:fe98:2ab1

Local Area Connection

Figure 10-5 Example configuration

To enable forwarding and advertising over Local Area Connection and Local Area Connection 2 and forwarding over Local Area Connection 3, the commands to run on ROUTER1 are

as follows:

netsh interface ipv6 set interface "Local Area Connection" forwarding=enabled advertise=enabled

netsh interface ipv6 set interface "Local Area Connection 2" forwarding=enabled advertise=enabled

netsh interface ipv6 set interface "Local Area Connection 3" forwarding=enabled

The Local Area Connection 3 interface is attached to a subnet that already contains ROUTER2, an advertising router.

After these commands are run, ROUTER1 sends Router Advertisement messages on the two peripheral subnets using the Local Area Connection and Local Area Connection 2 interfaces. However, the router advertisements do not contain any Prefix Information or Route Information options through which hosts on the attached subnets can automatically configure addresses and routes. To advertise Prefix Information or Route Information options, you must configure ROUTER1 to publish routes.

To add a route and configure it to be published, use the following command:

netsh interface ipv6 add route IPv6Address/PrefixLength [interface=]InterfaceNameOrIndex

[[nexthop=]IPv6Address] [[metric=]Integer] [[publish=]no|yes|immortal]

By default, there is no next-hop address (the prefix is on-link), the route metric is automatically determined, and the route is not published.

For example, to configure ROUTER1 to publish the on-link subnet prefix 2001:db8:0:1::/64 on Local Area Connection and publish the on-link subnet prefix 2001:db8:0:2::/64 on Local Area Connection 2, the commands are as follows:

netsh interface ipv6 add route 2001:db8:0:1::/64 "Local Area Connection" publish=yes netsh interface ipv6 add route 2001:db8:0:2::/64 "Local Area Connection 2" publish=yes

Routes that are configured to be published on an interface are advertised on that interface as Prefix Information options with the On-link flag set. If the on-link advertised route has a prefix length of 64, ROUTER2 sets the Autonomous flag in the Prefix Information option to allow hosts to create stateless addresses.

To provide hosts with reachability for directly attached subnets of the advertising routers, ROUTER1 includes the subnet prefixes that are configured to be published on other interfaces in the Router Information option in the Router Advertisement message. RFC 4191 describes the use of the Router Information option. The prefixes in Router Information options are added as static routes on the receiving hosts to make locations on other subnets that are directly attached to the advertising router reachable. For this example, ROUTER1 includes the 2001:db8:0:2::/64 prefix as a Router Information option in the router advertisement sent on Local Area Connection. Similarly, ROUTER1 includes the 2001:db8:0:1::/64 prefix as a Router Information option in the router advertisement sent on Local Area Connection 2.

For this configuration, ROUTER1 does not advertise itself as a default router. Hosts on the 2001:db8:0:1::/64 and 2001:db8:0:2::/64 subnets automatically configure addresses and add routes to their routing tables, but they do not automatically configure a default route (::/0). A computer running Windows Server 2008 or Windows Vista does not advertise itself as a default router unless there is a default route that is configured to be published.

To configure the router to be a default router for hosts on the 2001:db8:0:1::/64 and 2001:db8:0:2::/64 subnets, you must add a default route to the router and publish it. For example, the subnet of Local Area Connection 3 contains ROUTER2 with the link-local address of fe80::2aa:ff:fe98:2ab1. The following command on ROUTER1 adds a default route and publishes it:

netsh interface ipv6 add route ::/0 "Local Area Connection 3" nexthop=fe80::2aa: ff:fe98:2ab1 publish=yes

After this command is run, ROUTER1 sends Router Advertisement messages on Local Area Connection and Local Area Connection 2 with the Router Lifetime field set to 65535, indicating that it is a default router with a maximum lifetime.

Additional Netsh Command Options to Configure IPv6 Router Behavior

The Netsh tool commands to configure IPv6 router behavior described so far in this chapter use only the minimum commands and options to enable forwarding and advertising behavior and to publish routes. This section describes the netsh interface ipv6 set interface and netsh interface ipv6 add route commands in more detail to configure advanced IPv6 router behavior.

252 Understanding IPv6, Second Edition

The command to configure IPv6 router interfaces for forwarding and advertising router behavior with all of its options is the following:

netsh interface ipv6 set interface [interface=]InterfaceNameOrIndex [[forwarding=]enabled|disabled] [[advertise=]enabled|disabled] [[mtu=]Integer] [[metric=]automatic|Integer] [[siteprefixlength=]Integer] [[basereachabletime=]Integer] [[retransmittime=]Integer] [[managedaddress=]enabled|disabled] [[otherstateful=]enabled|disabled] [[store=]active|persistent]

Table 10-3 lists the command option, its default value, and a description.

Table 10-3 The netsh interface ipv6 set interface Command Options for Routing Behavior

There are no Netsh command options to specify the following:

■The Router Lifetime field in the Router Advertisement message. If the router is advertising itself as a default router, IPv6 sets the Router Lifetime to 65,635.

■The Default Router Preference field in the Router Advertisement message. IPv6 sets the Default Router Preference field to 0 for medium preference.