Lab: IPv6 addressing and static routes | CCNA IPv6

The situation

A small office is adding IPv6 next to its IPv4 network. PC1's LAN is behind R1, the server LAN is behind R2, and the two routers share a link. The PCs use SLAAC. Your job is to make PC1 reach the server at 2001:db8:acad:2::10 over IPv6.

Router	Interface	Global address	Link-local
R1	Gi0/0 (PC1 LAN)	2001:db8:acad:1::1/64	fe80::1
R1	Gi0/1 (to R2)	2001:db8:acad:12::1/64	fe80::1
R2	Gi0/1 (to R1)	2001:db8:acad:12::2/64	fe80::2
R2	Gi0/0 (server LAN)	2001:db8:acad:2::1/64	fe80::2

The same link-local address on two interfaces of one router is fine: a link-local address only has to be unique on its own link.

Task 1: configure R1 and R2

Three things on each router: IPv6 routing, the addresses, and a route to the network on the far side. Write them before you look.

Show the configuration

ipv6 unicast-routing
!
interface GigabitEthernet0/0
 ipv6 address 2001:db8:acad:1::1/64
 ipv6 address fe80::1 link-local
 no shutdown
interface GigabitEthernet0/1
 ipv6 address 2001:db8:acad:12::1/64
 ipv6 address fe80::1 link-local
 no shutdown
!
ipv6 route 2001:db8:acad:2::/64 2001:db8:acad:12::2

R1: a global next hop needs no exit interface.

ipv6 unicast-routing
!
interface GigabitEthernet0/0
 ipv6 address 2001:db8:acad:2::1/64
 ipv6 address fe80::2 link-local
 no shutdown
interface GigabitEthernet0/1
 ipv6 address 2001:db8:acad:12::2/64
 ipv6 address fe80::2 link-local
 no shutdown
!
ipv6 route 2001:db8:acad:1::/64 GigabitEthernet0/1 fe80::1

R2: the return route uses R1's link-local address, so the exit interface is required.

Task 2: verify the routers

Example output written for this lab, based on Cisco IOS documentation

R1#show ipv6 interface brief
GigabitEthernet0/0     [up/up]
    FE80::1
    2001:DB8:ACAD:1::1
GigabitEthernet0/1     [up/up]
    FE80::1
    2001:DB8:ACAD:12::1

Each interface is up/up with its link-local address first and its global address below.

Example output written for this lab, based on Cisco IOS documentation

R2#show ipv6 route static
IPv6 Routing Table - default - 6 entries
Codes: C - Connected, L - Local, S - Static, U - Per-user Static route
       ...
S   2001:DB8:ACAD:1::/64 [1/0]
     via FE80::1, GigabitEthernet0/1

Task 3: check what PC1 learned

Example output from a Windows PC, written for this lab

C:\> ipconfig
Ethernet adapter Ethernet:

   IPv6 Address. . . . . . . . . . . : 2001:db8:acad:1:5d1c:7e2a:93b4:10f7
   Link-local IPv6 Address . . . . . : fe80::5d1c:7e2a:93b4:10f7%12
   Default Gateway . . . . . . . . . : fe80::1%12

Read it before opening the questions below.

Why is the gateway fe80::1 and not 2001:db8:acad:1::1?

Router Advertisements are sent from the router's link-local address, so hosts use that as their default gateway. It is also why the interface ID isn't built from the MAC address: Windows chooses a random one by default, not EUI-64. %12 is the Windows interface index, needed because a link-local address only means something on one interface.

Task 4: break it on purpose

Pick a fault and follow the packet from PC1 to the server. Decide what PC1 would see before you watch.

Fault:

Frame (this link)02:00:00:00:01:10 → 02:00:00:00:00:01

Packet (end to end)2001:db8:acad:1:5d1c:7e2a:93b4:10f7 → 2001:db8:acad:2::10 · ICMPv6 echo request

1. To the gateway: the server is off-link, so PC1 sends the packet to its default gateway, R1.
2. Routed: R1 uses its static route via 2001:db8:acad:12::2; R2 delivers to its connected server LAN.
3. And back: R2 uses its return route via fe80::1 on Gi0/1. Ping succeeds.

A ping needs a route there and a route back.

Check yourself

Predict · scenario 1

On R2 you type ipv6 route 2001:db8:acad:1::/64 fe80::1. What happens?

Predict · scenario 2

PC1 shows only a link-local address and no IPv6 default gateway. R1's Gi0/0 has 2001:db8:acad:1::1/64 and is up/up. What do you check first?

Predict · scenario 3

On R1, ping 2001:db8:acad:2::10 works, but ping 2001:db8:acad:2::10 source GigabitEthernet0/0 fails. What is missing?