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Most IPv6 implementation plans make use of both static IPv6 address configuration and
dynamic configuration options. As is the case with IPv4, the plan assigns infrastructure
devices with static addresses, with client hosts using one of the two dynamic methods for
address assignment.
IPv6 addressing includes many more options than IPv4, and as a result, many more configuration
options exist. A router interface can be configured with a static global unicast
IPv6 address, either with or without using the EUI-64 option. Although less likely, a
router could be configured to dynamically learn its IPv6 address with either stateful
DHCP or stateless autoconfig. The router interface could be configured to either not use a
global unicast address, instead relying solely on its link local address, or to borrow another
interface’s address using the IPv6 unnumbered feature.
This section summarizes the address configuration commands and shows several examples
of configuration and verification commands for IPv6. To that end, Table 16-10 summarizes
the IPv6 configuration commands and their meanings.
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Chapter 16 : IP Version 6 Addressing 557
R1 R3
R2
2000:0:0:0::/64
::1 ::1
::2
::3
f0/0
f0/1
f0/0
s0/0/0 f0/0 f0/1
s0/0/1
eui-64
eui-64
2000:0:0:1::/64 2000:0:0:2::/64 2000:0:0:3::/64
2000:0:0:4::/64
eui-64
Figure 16-12 Sample IPv6 Address Planning Diagram
ipv6 address autoconfig Router uses stateless autoconfig to find address.
ipv6 address dhcp Router uses stateful DHCP to find address.
ipv6 unnumbered interface-type number
Uses the same IPv6 unicast address as the referenced
interface.
ipv6 enable Enables IPv6 on the interface, but results in only a
link local address.
ipv6 address address link-local Overrides the automatically created link local address.
The configured value must conform to the
FE80::/10 prefix.
ipv6 address address/length anycast Designates that the unicast address is an anycast.
Note: All the interface subcommands in Table 16-10 enable IPv6 on the interface, which
means the router derives an IPv6 link local address for the interface. The description shows
what the command does in addition to enabling IPv6.
Configuring Static IPv6 Addresses on Routers
The configuration examples in this section use the internetwork shown in Figure 16-12.
The figure shows a diagram you might see in an implementation plan, with the five IPv6
subnet numbers shown over the five links. The interface ID of each interface is then abbreviated,
or shown as eui-64, as a reminder of whether to configure the whole 128-bit address
or to rely on the EUI-64 feature.
Example 16-1 shows the configuration process on Router R2, which uses EUI-64 on two
interfaces, and a complete IPv6 address on another. Also, note that the configuration includes
the ipv6 unicast-routing global configuration command, which enables the router
to route IPv6 traffic. (The addresses can be configured without also configuring ipv6 unicast-
routing, but without this command, the router acts more like an IPv6 host, and it will
not forward IPv6 packets until this command has been configured.)
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Example 16-1 R2’s IPv6 Configuration
R2# show running-config
! lines omitted for brevity
interface FastEthernet0/0
ipv6 address 2000:0:0:4::/64 eui-64
!
interface FastEthernet0/1
ipv6 address 2000:0:0:2::2/64
!
interface Serial0/0/1
ipv6 address 2000:0:0:1::/64 eui-64
!
!
R2# show ipv6 interface brief
FastEthernet0/0 [up/up]
FE80::213:19FF:FE7B:5004
2000::4:213:19FF:FE7B:5004
FastEthernet0/1 [up/up]
FE80::213:19FF:FE7B:5005
2000:0:0:2::2
Serial0/0/0 [administratively down/down]
unassigned
Serial0/0/1 [up/up]
FE80::213:19FF:FE7B:5004
2000::1:213:19FF:FE7B:5004
Serial0/1/0 [administratively down/down]
unassigned
Serial0/1/1 [administratively down/down]
unassigned
R2# show interfaces fa0/0
FastEthernet0/0 is up, line protocol is up
Hardware is Gt96k FE, address is 0013.197b.5004 (bia 0013.197b.5004)
MTU 1500 bytes, BW 100000 Kbit/sec, DLY 100 usec,
reliability 255/255, txload 1/255, rxload 1/255
! lines omitted for brevity
The ipv6 address commands both enable IPv6 on the associated interfaces and define either
the prefix (with the eui-64 option) or the entire address. The show commands listed
after the configuration confirm the IPv6 addresses. Of particular note
■ All three interfaces now have link local addresses that begin FE80.
■ F0/1 has the address exactly as configured.
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■ S0/0/1 and F0/0 have the configured prefixes (2000:0:0:1 and 2000:0:0:4, respectively),
but with EUI-64 derived interface-IDs.
■ S0/0/1 uses Fa0/0’s MAC address (as shown in the show interfaces f0/0 command)
when forming its EUI-64.
On this last point, whenever IOS needs a MAC address for an interface, and that interface
does not have a built-in MAC address, the router uses the MAC address of the lowestnumbered
LAN interface on the router–in this case, F0/0. The following list shows the derivation
of the last 64 bits (16 digits) of R2’s IPv6 interface IDs for its global unicast IPv6
addresses on F0/0 and S0/0/1:
Step 1. Use F0/0’s MAC Address: 0013.197B.5004.
Step 2. Split and insert FFFE: 0013:19FF:FE7B:5004.
Step 3. Invert bit 7: Hex 00 = 00000000 binary, flip for 00000010, and convert back to
hex 02, resulting in 0213:19FF:FE7B:5004.
Multicast Groups Joined by IPv6 Router Interfaces
Next, consider the deeper information held in the show ipv6 interface f0/0 command on
Router R2, as shown in Example 16-2. Not only does it list the same link local and global
unicast addresses, but it lists other special addresses as well.
Example 16-2 All IPv6 Addresses on an Interface
R2# show ipv6 interface f0/0
FastEthernet0/0 is up, line protocol is up
IPv6 is enabled, link-local address is FE80::213:19FF:FE7B:5004
No Virtual link-local address(es):
Global unicast address(es):
2000::4:213:19FF:FE7B:5004, subnet is 2000:0:0:4::/64 [EUI]
Joined group address(es):
FF02::1
FF02::2
FF02::1:FF7B:5004
MTU is 1500 bytes
ICMP error messages limited to one every 100 milliseconds
ICMP redirects are enabled
ICMP unreachables are sent
ND DAD is enabled, number of DAD attempts: 1
ND reachable time is 30000 milliseconds (using 22807)
ND advertised reachable time is 0 (unspecified)
ND advertised retransmit interval is 0 (unspecified)
ND router advertisements are sent every 200 seconds
ND router advertisements live for 1800 seconds
ND advertised default router preference is Medium
Hosts use stateless autoconfig for addresses.
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The three joined multicast groups should be somewhat familiar after reading this chapter.
The first multicast, FF02::1, represents all IPv6 devices, so router interfaces must listen for
packets sent to this address. FF02::2 represents all IPv6 routers, so again, R2 must listen
for packets sent to this address. Finally, the FF02::1:FF beginning value is the range for an
address’ solicited node multicast address, used by several functions, including the duplicate
address detection (DAD) and neighbor discovery (ND).
Connected Routes and Neighbors
The third example shows some new concepts with the IP routing table. Example 16-3
shows R2’s current IPv6 routing table that results from the configuration shown in
Example 16-1. Note that no IPv6 routing protocols have been configured, and no static
routes have been configured.
Example 16-3 Connected and Local IPv6 Routes
R2# show ipv6 route
IPv6 Routing Table - Default - 7 entries
Codes: C - Connected, L - Local, S - Static, U - Per-user Static route
B - BGP, M - MIPv6, R - RIP, I1 - ISIS L1
I2 - ISIS L2, IA - ISIS interarea, IS - ISIS summary, D - EIGRP
EX - EIGRP external
O - OSPF Intra, OI - OSPF Inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2
ON1 - OSPF NSSA ext 1, ON2 - OSPF NSSA ext 2
C 2000:0:0:1::/64 [0/0]
via Serial0/0/1, directly connected
L 2000::1:213:19FF:FE7B:5004/128 [0/0]
via Serial0/0/1, receive
C 2000:0:0:2::/64 [0/0]
via FastEthernet0/1, directly connected
L 2000:0:0:2::2/128 [0/0]
via FastEthernet0/1, receive
C 2000:0:0:4::/64 [0/0]
via FastEthernet0/0, directly connected
L 2000::4:213:19FF:FE7B:5004/128 [0/0]
via FastEthernet0/0, receive
L FF00::/8 [0/0]
via Null0, receive
First, the IPv6 routing table lists the expected connected routes, but a new type of
route–a “local” route–designated by an L in the output of the show ipv6 route command.
The connected routes occur for any unicast IPv6 addresses on the interface that happen to
have more than link local scope. So, R2 has routes for subnets 2000:0:0:1::/64,
2000:0:0:2::/64, and 2000:0:0:4::/64, but no connected subnets related to R2’s link local
addresses. The Local routes, all /128 routes, are essentially host routes for the router’s unicast
IPv6 addresses. These local routes allow the router to more efficiently process packets
directed to the router itself, rather than for packets directed toward connected subnets.
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Chapter 16 : IP Version 6 Addressing 561
The IPv6 Neighbor Table
The IPv6 neighbor table replaces the IPv4 ARP table, listing the MAC address of other
devices that share the same link. Example 16-4 shows a debug that lists messages during
the NDP process, a ping to R3’s F0/0 IPv6 address, and the resulting neighbor table entries
on R2.
Example 16-4 Creating Entries and Displaying the Contents of R2’s IPv6Neighbor Table
R2# debug ipv6 nd
ICMP Neighbor Discovery events debugging is on
R2# ping 2000:0:0:2::3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2000:0:0:2::3, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 0/0/4 ms
R2#
*Sep 2 17:07:25.807: ICMPv6-ND: DELETE -> INCMP: 2000:0:0:2::3
*Sep 2 17:07:25.807: ICMPv6-ND: Sending NS for 2000:0:0:2::3 on FastEthernet0/1
*Sep 2 17:07:25.807: ICMPv6-ND: Resolving next hop 2000:0:0:2::3 on interface
FastEthernet0/1
*Sep 2 17:07:25.811: ICMPv6-ND: Received NA for 2000:0:0:2::3 on FastEthernet0/1
from 2000:0:0:2::3
*Sep 2 17:07:25.811: ICMPv6-ND: Neighbour 2000:0:0:2::3 on FastEthernet0/1 : LLA
0013.197b.6588
R2# undebug all
All possible debugging has been turned off
R2# show ipv6 neighbors
IPv6 Address Age Link-layer Addr State Interface
2000:0:0:2::3 0 0013.197b.6588 REACH Fa0/1
FE80::213:19FF:FE7B:6588 0 0013.197b.6588 REACH Fa0/1
The example shows the entire NDP process by which R2 discovers R3’s Fa0/0 MAC address.
The example begins with a debug ipv6 nd command, which tells R2 to issue messages
related to NDP messages. The ping 2000:0:0:2::3 command that follows tells IOS to
use IPv6 ping R3’s F0/0 address–but R2 does not know the corresponding MAC address.
The debug output that follows shows R2 sending an NS, with R3 replying with an NA
message, listing R3’s MAC address.
The example ends with the output of the show ipv6 neighbor command, which lists the
neighbor table entries for both R3’s IPv6 addresses.
Stateless Autoconfiguration
The final example in this section demonstrates stateless autoconfiguration using two
routers, R2 and R3. In Example 16-5, R2’s F0/1 configuration will be changed, using the
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ipv6 address autoconfig subcommand on that interface. This tells R2 to use stateless autoconfig
process, with R2 learning its prefix from Router R3. R2 then builds the rest of its
IPv6 address using EUI-64.
Example 16-5 Using Stateless Autoconfig on Router R2
R2# conf t
Enter configuration commands, one per line. End with CNTL/Z.
R2(config)# interface fa0/1
R2(config-if)# no ipv6 address
R2(config-if)# ipv6 address autoconfig
R2(config-if)#^Z
R2# show ipv6 interface brief
FastEthernet0/0 [up/up]
FE80::213:19FF:FE7B:5004
2000::4:213:19FF:FE7B:5004
FastEthernet0/1 [up/up]
FE80::213:19FF:FE7B:5005
2000::2:213:19FF:FE7B:5005
Serial0/0/0 [administratively down/down]
unassigned
Serial0/0/1 [up/up]
FE80::213:19FF:FE7B:5004
2000::1:213:19FF:FE7B:5004
Serial0/1/0 [administratively down/down]
unassigned
Serial0/1/1 [administratively down/down]
unassigned
R2# show ipv6 router
Router FE80::213:19FF:FE7B:6588 on FastEthernet0/1, last update 0 min
Hops 64, Lifetime 1800 sec, AddrFlag=0, OtherFlag=0, MTU=1500
HomeAgentFlag=0, Preference=Medium
Reachable time 0 (unspecified), Retransmit time 0 (unspecified)
Prefix 2000:0:0:2::/64 onlink autoconfig
Valid lifetime 2592000, preferred lifetime 604800
Starting with the configuration, the no ipv6 address command actually removes all configured
IPv6 addresses from the interface and also disables IPv6 on interface F0/1. Then,
the ipv6 address autoconfig command again enables IPv6 on F0/1 and tells R2 to use
stateless autoconfig.
The show commands confirm that R2 does indeed learn its IPv6 address:
2000:0:0:2:0213:19FF:FE7B:5005. The show ipv6 router command, which lists the cached
contents of any received RA messages, lists the information received from R3’s RA message,
including R3’s link local address (used to identify the routers) and R3’s advertised
prefix (2000:0:0:2::/64).
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