IPv6 Routing

IPv6 is not enabled by default on Cisco routers. To enable IPv6 routing, the command is Router(config)#ipv6 unicast-routing.

After IPv6 is enabled, addresses are assigned to interfaces much like version 4:

Router(config-if)#ipv6 address prefix/prefix-length

To make this less abstract, a more complete example that shows an IPv6 implementation is shown in Example 8-1.


Static Routing

Static routing with IPv6 works exactly like it does with version 4. Aside from understanding the address format, there are no differences. Static routes are not currently on the BSCI test. The syntax for the IPv6 static route command is shown below, and Example 8-2 is supplied so that the command may be viewed in context as it might be applied.

Router(config)# ipv6 route ipv6-prefix/prefix-length {ipv6-address | interface-type interface-number [ipv6-address]} [administrativedistance] [administrative-multicast-distance | unicast | multicast] [tag tag]


RIPng for IPv6

RIPng is the IPv6 of RIP and is defined in RFC 2080. Like RIPv2 for IPv4, RIPng is a distance vector routing protocol that uses a hop count for its metric and has a maximum hop count of 15. RIPng also uses periodic multicast updates—every 30 seconds—to advertise routes. The multicast address is FF02::9.

RIPng is not on the BSCI exam at present, but it is presented here for completeness and to round out your appreciation for IPv6 routing and to prepare the reader for trial implementations of IPv6.

There are two important differences between the old RIP and the nextgeneration RIP. First, RIPng supports multiple concurrent processes, each identified by a process number (this is similar to OSPFv2). Second, RIPng is initialized in global configuration mode and then
enabled on specific interfaces.

Example 8-3 shows the syntax used to apply RIPng to a configuration. Notice that the syntax is very similar to traditional RIP.


Like RIP for IPv4, troubleshoot RIPng by looking at the routing table (show ipv6 route), by reviewing the routing protocols (show ipv6 protocols), and by watching routing updates propagated between routers (debug ipv6 rip).


EIGRP
EIGRP has been expanded to support IPv6, although you’ll need to verify that a specific version of IOS is capable of doing this. EIGRP for IPv6 is based on the IPv4 version. EIGRP is still an advanced distance vector routing protocol that uses a complex metric. EIGRP still has a reliable update mechanism and uses DUAL to retain fall-back paths. Like EIGRP in IPv4, it sends multicast hellos every five seconds (but the multicast address is now FF02::A). EIGRP is enabled as described in the following:

Router(config)#ipv6 router eigrp as
Router(config-rtr)#router-id ipv4-address|ipv6-address
Router(config-rtr)#interface type number
Router(config-if)#ipv6 eigrp as

Like EIGRP for IPv4, troubleshoot by looking at the routing table (show ipv6 route), by reviewing the routing protocols (show ipv6 protocols), and by monitoring neighbors (show ipv6 eigrp neighbors). Example 8-4 shows the configuration for IPv6 EIGRP. Notice that the
routing protocol must be enabled under each interface.

IPv6 Introduction

IPv6 is an extension of IP with several advanced features:

• Larger address space
• Simpler header
• Autoconfiguration
• Extension headers
• Flow labels
• Mobility
• “Baked in” security

Of these, many capabilities have been backported to IPv4. The primary adoption of IPv6 will be driven by the need for more addresses. Given the growth in Internet use and the emergence of large groups of Internet users in developing countries, this is a significant requirement.

IPv6 Routing Prefix

IPv4 addresses are 32 bits long, whereas IPv6 addresses are 128 bits. IPv6 addresses are composed of the following elements (see Figure 8-1):

• The first three bits (/3) of unicast always 001.
• The next 13 bits (/16) are Top-Level Aggregator (TLA) the upstream ISP.
• The next 24 bits (/40) are the next-level aggregator or regional ISP.
• Enterprises are assigned /48 and have 16 bits of subnetting.

IPv6 Interface ID


The host portion of the address is last 64 bits. It can be assigned manually, using DHCP v6, or using stateless autoconfiguration. An end-system uses stateless autoconfiguration by waiting for a router to advertise the local prefix. If the end system has a 64-bit MAC, it concatenates the prefix and its MAC to form an IPv6 address. If the end system has a 48-bit MAC, it flips the global/local bit and inserts 0xFFEE into the middle of the MAC. The resulting 64-bit number is called the EUI64. The prefix and EUI64 are concatenated to form the address. Figure 8-2 shows how a host uses its MAC address to create its IPv6 address.


Simplified Presentation of IPv6 Address
There are two ways to shorten the representation of an IPv6 address. Take the example address
4001:0000:0001:0002:0000:0000:0000:ABCD.

• Leading zeros may be omitted. This makes the example 4001:0:1:2:0:0:0:ABCD.
• Sequential zeros may be shown as double colons once per address. This makes the example 4001:0:1:2::ABCD.

IPv6 Header


The IPv6 header is similar to the IPv4 header. The largest changes have to do with the larger addresses, aligning fields to 64-bit boundaries and moving fragmentation to an extension header.

The fields are:

• Version—6.
• Priority—Similar to DSCP in version 4, this eight-bit field is used to describe relative priority.
• Flow—20-bit flow label allows tagging in a manner similar to MPLS.
• Length—The length of the data in the packet.
• Next Header—Indicates how the bits after the IP header should be interpreted. Could indicate TCP or UDP, or it could show an extension header.
• Hop Limit—Similar to TTL.
• Source and Destination—IPv6 addresses.

Zero or more extension headers could follow, including:

• Hop-by-hop options—Options for intermediate devices.
• Destination options—Options for the end node.
• Source routing—Specifies “way stations” that the route must include.
• Fragmentation—Used to divide packets.
• Authentication—Used to attest to source. Replaces the AH header from IPSec.
• Encryption—Replaces the IPSec ESP header.