IPv6 Intro: Global Unicast Address, Link-Local Addresses, and a Brief Intro to Static Routing

In the last lab, we configured a link between R1 and R2, using the IP addresses "2001:co:ffee::4:1" and "2001:co:ffee::4:2," respectively.  Let's try something:
R1#sho ipv6 interface brief
FastEthernet0/0            [up/up]
    FE80::CE00:6BFF:FE8E:0
    2001:C0:FFEE::4:1
Loopback0                  [up/up]
    unassigned
R1#

Well, that's odd! I don't know about you, but I only recall configuring a single IPv6 address on Fa0/0 on R1, but the "sho ipv6 interface brief" command is displaying two addresses.

Actually, it's not odd at all. When you enable IPv6 on an interface, it automatically configures a special class of IPv6 addresses on the interface. Notice how the extra address begins with "FE80?" An IPv6 address that begins with FE80 is a "link-local" address, and they are automatically configured on every interface using IPv6. The IPv6 address that we manually added to the routers is called a "global unicast" address. At this point, you are probably wondering why we bothered to assign an IPv6 address to the interface if the router would automatically assign one, too. There's a hint buried within the names of these address types: "Link-local" and "global-unicast." "Link-local" addresses are locally scoped (where "locally" means local to that one interface), whereas "global-unicast" addresses are, well, globally-scoped. Try to ping the link-local address on R1 from R2:
R2#ping ipv6 fe80:0:0:0:ce00:6bff:fe8e:0
Output Interface: FastEthernet0/0
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to FE80::CE00:6BFF:FE8E:0, timeout is 2 seconds:
Packet sent with a source address of FE80::CE01:6BFF:FE8E:0
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/16/36 ms
R2#

Interesting...notice how the router prompted you to specify an output interface? Since link-local addresses are locally-scoped to one specific interface, you have to specify which interface the ping command should use to reach the destination address. Just for giggles, let's add a new interface, Fa1/0, to R2, and connect a third router to that interface:



We'll add the new IPv6 addresses on both R2 and R3 as we've done in the past, and we'll add a static route so that R3 knows how to reach the 2001:co:ffee::4:0/126 network:
R3(config)#ipv6 route 2001:00c0:ffee:0:0:0:4:0/126 2015:0:0:0:0:0:0:1
R3(config)#exit
R3#ping ipv6 2001:00c0:ffee:0:0:0:4:2

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2001:C0:FFEE::4:2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/12/36 ms
R3#

Good! Let's add a static route for the link-local address on R2, Fa0/0:
R3(config)#ipv6 route fe80:0000:0000:0000:ce01:6bff:fe8e:0/126 2015:0:0:0:0:0:0:1
% Invalid prefix
R3(config)#

"Locally-scoped" means you can't route these addresses. The only place they are valid is on the interface directly connected to the destination address. Therefore, you can't create a static route for a link-local address. Let's try one more thing, just for the fun of it:



We'll configure the subnet 2001::0/125 on each of these interfaces:
R1(config-if)#int fa0/0
R1(config-if)#ipv6 addr 2001:0:0:0:0:0:0:1/125
R1(config-if)#no shut

R2(config-if)#int fa0/0
R2(config-if)#ipv6 addr 2001:0:0:0:0:0:0:2/125
R2(config-if)#no shut

R3(config-if)#int fa0/0
R3(config-if)#ipv6 addr 2001:0:0:0:0:0:0:3/125
R3(config-if)#no shut

Now, let's make sure each router can ping the other two routers:
R1#ping ipv6 2001:0:0:0:0:0:0:2

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2001::2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/12/36 ms
R1#ping ipv6 2001:0:0:0:0:0:0:3

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2001::3, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/19/36 ms
R1#

(I've omitted the output from R2 and R3 for the sake of brevity, but I did test them)

What about the link-local interfaces? Can we ping them? Let's find out:
R1#sho ipv6 int brie
FastEthernet0/0            [up/up]
    FE80::CE00:6BFF:FE8E:0
    2001::1
<...snip...>
R2#sho ipv6 int brie
FastEthernet0/0            [up/up]
    FE80::CE01:6BFF:FE8E:0
    2001::2
<...snip...>
R3#sho ipv6 int brie
FastEthernet0/0            [up/up]
    FE80::CE03:6BFF:FE8E:0
    2001::3
<...snip...>

Now that we have the link-local addresses on each router, we'll try the ping test:
R1#ping ipv6 FE80::CE01:6BFF:FE8E:0
Output Interface: FastEthernet0/0
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to FE80::CE01:6BFF:FE8E:0, timeout is 2 seconds:
Packet sent with a source address of FE80::CE00:6BFF:FE8E:0
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/22/40 ms
R1#ping ipv6 FE80::CE03:6BFF:FE8E:0
Output Interface: FastEthernet0/0
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to FE80::CE03:6BFF:FE8E:0, timeout is 2 seconds:
Packet sent with a source address of FE80::CE00:6BFF:FE8E:0
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/12/36 ms
R1#
<...snip...>

R2#ping ipv6 FE80::CE00:6BFF:FE8E:0
Output Interface: FastEthernet0/0
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to FE80::CE00:6BFF:FE8E:0, timeout is 2 seconds:
Packet sent with a source address of FE80::CE01:6BFF:FE8E:0
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/5/8 ms
R2#ping ipv6 FE80::CE03:6BFF:FE8E:0
Output Interface: FastEthernet0/0
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to FE80::CE03:6BFF:FE8E:0, timeout is 2 seconds:
Packet sent with a source address of FE80::CE01:6BFF:FE8E:0
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/10/20 ms
R2#
<...snip...>

R3#ping ipv6 FE80::CE00:6BFF:FE8E:0
Output Interface: FastEthernet0/0
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to FE80::CE00:6BFF:FE8E:0, timeout is 2 seconds:
Packet sent with a source address of FE80::CE03:6BFF:FE8E:0
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/14/40 ms
R3#ping ipv6 FE80::CE01:6BFF:FE8E:0
Output Interface: FastEthernet0/0
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to FE80::CE01:6BFF:FE8E:0, timeout is 2 seconds:
Packet sent with a source address of FE80::CE03:6BFF:FE8E:0
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/15/36 ms
R3#
<...snip...>


As you can see, the link-local interface is not limited to point-to-point networks; it will also work on multipoint networks.

One other interesting point to raise about IPv6 addresses: there is no broadcast address, as there is in IPv4. Instead, IPv6 uses multicast to replicate the functionality of IPv4 broadcast addresses. In additon to global unicast, link-local and multicast addresses, IPv6 also supports a few other special classes of addresses, but we will save them for another day. With what we have covered in this lab and the previous lab, we now have enough grounding to start playing with routing...but I'll save that for the next lab.