300-410 IPv6 Tunneling Techniques Practice Test 2 — 15 Questions

Question 1

A network engineer runs the following command on Router R1:

R1# show ipv6 eigrp neighbors

IPv6-EIGRP neighbors for process 100
H   Address                 Interface       Hold Uptime   SRTT   RTO  Q  Seq
                                            (sec)         (ms)       Cnt Num
0   FE80::A8BB:CCFF:FE00:2  Tunnel0          13 00:23:45   10   200  0  12
1   FE80::A8BB:CCFF:FE00:3  Tunnel1          12 00:22:10   15   200  0  15

Based on this output, which statement is correct?

Accepted Answer

EIGRP for IPv6 adjacencies are established over the tunnels.. The output shows two IPv6 EIGRP neighbors with link-local addresses (FE80::/10) on interfaces Tunnel0 and Tunnel1, and the adjacency is established and exchanging routes (Seq Num increasing). This confirms that EIGRP for IPv6 adjacencies are formed over these tunnel interfaces, making option C correct.

Answer

EIGRP is not configured for IPv6.

Answer

The neighbors are using global unicast addresses.

Answer

The tunnels are using GRE encapsulation.

Question 2

A network engineer runs the following command on Router R1:

R1# show ipv6 mtu

IPv6 MTU per interface:

Interface    MTU
Tunnel0      1476
Tunnel1      1476
GigabitEthernet0/0  1500

Based on this output, what is the most likely reason for the reduced MTU on the tunnel interfaces?

Accepted Answer

The tunnels are using GRE encapsulation, which adds 24 bytes of overhead.. The output shows an MTU of 1476 on the tunnel interfaces, which is exactly 24 bytes less than the 1500-byte MTU of the physical GigabitEthernet0/0 interface. GRE encapsulation adds a 4-byte outer IP header and a 4-byte GRE header (total 24 bytes with the inner IP header), reducing the payload MTU. This is the default behavior when a tunnel is configured without a manual MTU override, making option B correct.

Answer

The tunnels are configured with a manual MTU.

Answer

The tunnels are using IPsec, which adds more overhead.

Answer

The tunnels are 6to4 tunnels, which do not reduce MTU.

Question 3

A network engineer runs the following command on Router R1:

R1# show ipv6 traffic | include tunnel

0 tunnel packets received
  0 tunnel packets sent
  0 tunnel packets dropped

Based on this output, what can be concluded?

Accepted Answer

The tunnel is not carrying any IPv6 traffic.. The 'show ipv6 traffic | include tunnel' command filters the output to show only lines containing 'tunnel'. The counters for packets received, sent, and dropped are all zero, which indicates that no IPv6 packets have been encapsulated or decapsulated by any tunnel interface. This means the tunnel is not carrying any IPv6 traffic, making option B correct.

Answer

The tunnel is passing traffic normally.

Answer

The tunnel is dropping all packets.

Answer

The tunnel is using IPsec encryption.

Question 4

Examine the following partial configuration on Router R1:
```
interface Tunnel0
 ipv6 address 2001:DB8:1::1/64
 tunnel source GigabitEthernet0/0
 tunnel destination 2001:DB8:2::2
 tunnel mode ipv6ip
```
What is the effect of this configuration?

Accepted Answer

The tunnel will not come up because the tunnel destination is an IPv6 address instead of an IPv4 address.. The tunnel mode ipv6ip requires an IPv4 address as the tunnel destination because it encapsulates IPv6 packets inside IPv4 packets for transport over an IPv4 network. In this configuration, the tunnel destination is set to an IPv6 address (2001:DB8:2::2), which is invalid for this tunnel mode, preventing the tunnel interface from coming up.

Answer

The tunnel will successfully encapsulate IPv6 packets in IPv4 and forward them.

Answer

The tunnel will use IPv6 as the transport protocol, encapsulating IPv4 packets.

Answer

The configuration is correct for a 6to4 tunnel.

Question 5

Consider this configuration on Router R2:
```
interface Tunnel0
 ipv6 address 2001:DB8:3::1/64
 tunnel source GigabitEthernet0/0
 tunnel mode gre ipv6
 tunnel destination 2001:DB8:4::2
```
Which statement is true?

Accepted Answer

This tunnel will encapsulate packets using GRE over an IPv6 transport.. The configuration shows a tunnel with `tunnel mode gre ipv6`, which explicitly sets the tunnel to use GRE encapsulation over an IPv6 transport. The tunnel source and destination are IPv6 addresses, and GRE can carry multiple protocols (including IPv4, IPv6, and others) over the IPv6 transport. Therefore, option C is correct because the tunnel encapsulates packets using GRE over an IPv6 transport.

Answer

This tunnel can only carry IPv6 traffic.

Answer

The tunnel source and destination must be IPv4 addresses.

Answer

The tunnel mode should be 'ipv6ip' for IPv6 transport.

Question 6

Given this configuration on Router R3:
```
interface Tunnel0
 no ip address
 ipv6 address 2001:DB8:5::1/64
 tunnel source 192.168.1.1
 tunnel destination 192.168.2.2
 tunnel mode ipv6ip
```
What is missing or incorrect?

Accepted Answer

The tunnel mode should be 'gre ipv6' because the source and destination are IPv6 addresses.. Option A is correct because the tunnel mode 'ipv6ip' is used for IPv6-over-IPv4 manual tunnels, which require the tunnel source and destination to be IPv4 addresses. However, in this configuration, the tunnel source and destination are IPv4 addresses (192.168.1.1 and 192.168.2.2), but the tunnel mode should be 'gre ipv6' only if the payload is IPv6 and the transport is IPv4 using GRE encapsulation. Actually, the correct mode for a manually configured IPv6-over-IPv4 tunnel is 'tunnel mode ipv6ip', which is already set. The real issue is that the tunnel source and destination are IPv4 addresses, which is correct for 'ipv6ip' mode. Option A states the mode should be 'gre ipv6', which is incorrect because 'gre ipv6' is used when both the tunnel source and destination are IPv6 addresses (IPv6 transport). Therefore, the configuration is actually correct for an IPv6-over-IPv4 manual tunnel, making option D the correct answer, not A. The question's answer key is flawed; the correct answer should be D.

Answer

The tunnel interface must have an IPv4 address.

Answer

The tunnel source should be an interface, not an IP address.

Answer

The configuration is correct and will function as an IPv6 over IPv4 tunnel.

Question 7

Examine this configuration on Router R4:
```
interface Tunnel0
 ip address 10.0.0.1 255.255.255.252
 ipv6 address 2001:DB8:6::1/64
 tunnel source GigabitEthernet0/0
 tunnel destination 172.16.1.2
 tunnel mode gre ip
```
What will be the effect?

Accepted Answer

The tunnel will successfully encapsulate both IPv4 and IPv6 payloads over IPv4.. The 'tunnel mode gre ip' command creates a generic routing encapsulation (GRE) tunnel over IPv4. GRE is protocol-agnostic and can encapsulate any Layer 3 protocol, including IPv4 and IPv6. The IPv6 address configured on the tunnel interface allows IPv6 traffic to be routed into the tunnel, where it is encapsulated in IPv4 packets and sent to the tunnel destination. Therefore, the tunnel will successfully carry both IPv4 and IPv6 payloads.

Answer

The tunnel will only carry IPv4 traffic because the mode is 'gre ip'.

Answer

The tunnel will fail because the tunnel source is an interface, not an IP address.

Answer

The tunnel mode should be 'ipv6ip' to carry IPv6 traffic.

Question 8

Consider this configuration on Router R5:
```
interface Tunnel0
 ipv6 address 2001:DB8:7::1/64
 tunnel source 192.168.10.1
 tunnel destination 192.168.20.2
 tunnel mode ipv6ip
 tunnel ttl 64
```
What is the effect?

Accepted Answer

The tunnel will work, and the TTL field in the outer IPv4 header will be set to 64.. Option B is correct because the configuration creates an IPv6-over-IPv4 manual tunnel (tunnel mode ipv6ip). The tunnel source is specified as an IP address, which is valid; the router uses that address as the source of the outer IPv4 header. The 'tunnel ttl 64' command explicitly sets the Time-to-Live field in the outer IPv4 header to 64, overriding the default value.

Answer

The tunnel will not work because the tunnel source is an IP address, not an interface.

Answer

The tunnel mode should be 'gre ip' for IPv6 over IPv4.

Answer

The tunnel will use the IPv6 TTL for the outer header.

Question 9

Given this configuration on Router R6:
```
interface Tunnel0
 ipv6 address 2001:DB8:8::1/64
 tunnel source 2001:DB8:9::1
 tunnel destination 2001:DB8:10::2
 tunnel mode gre ipv6
 tunnel path-mtu-discovery
```
What is the effect?

Accepted Answer

The tunnel will dynamically adjust the MTU based on the path MTU discovery.. The `tunnel path-mtu-discovery` command enables Path MTU Discovery (PMTUD) for the GRE tunnel, which dynamically determines the maximum MTU along the path to the tunnel destination and adjusts the tunnel interface's MTU accordingly. This prevents fragmentation issues by allowing the tunnel to use the smallest MTU in the path. Option B correctly identifies this behavior.

Answer

The tunnel will not work because path-mtu-discovery is not supported with GRE.

Answer

The tunnel mode should be 'ipv6ip' for IPv6 transport.

Answer

The tunnel source and destination must be IPv4 addresses.

Question 10

What is the default tunnel mode for a tunnel interface on Cisco IOS?

Accepted Answer

tunnel mode gre ip. The default tunnel mode on Cisco IOS is GRE (Generic Routing Encapsulation) over IPv4, configured with the command `tunnel mode gre ip`. This mode encapsulates packets using the GRE protocol (RFC 2784) with an IPv4 transport header, and it is the default when no explicit tunnel mode is specified. GRE ip supports multiprotocol payloads (IPv4, IPv6, etc.) and is widely used for site-to-site VPNs and overlay networks.

Answer

tunnel mode ipv6ip

Answer

tunnel mode gre ipv6

Answer

tunnel mode mpls traffic-eng

Question 11

In a 6to4 tunnel, how is the tunnel destination address determined?

Accepted Answer

It is derived from the IPv6 destination address using the 2002::/16 prefix.. In a 6to4 tunnel, the tunnel destination address is automatically derived from the IPv6 destination address by extracting the IPv4 address embedded in the 2002::/16 prefix. Specifically, the first 16 bits of the IPv6 destination are 2002, and the next 32 bits represent the IPv4 address of the remote 6to4 router. This allows the tunnel to be dynamically established without manual configuration of each destination.

Answer

It is manually configured.

Answer

It is obtained via DNS.

Answer

It is the same as the tunnel source.

Question 12

What is the maximum number of IPv6 over IPv4 tunnels that can be configured on a Cisco IOS router?

Accepted Answer

Platform-dependent, no fixed maximum.. C is correct because the maximum number of IPv6 over IPv4 tunnels on a Cisco IOS router is platform-dependent and limited by available system resources such as CPU and memory, not by a fixed software limit. Cisco IOS does not impose a hard-coded maximum; the actual number depends on the router model, the type of tunnel (e.g., manual, 6to4, ISATAP, GRE), and the configuration complexity.

Answer

256

Answer

1024

Answer

64

Question 13

Which TWO commands can be used to verify the operational status of a manually configured IPv6 tunnel on a Cisco IOS router? (Choose TWO.)

Accepted Answer

show interfaces tunnel 0. The 'show interfaces tunnel 0' command displays the operational status, line protocol state, and encapsulation details of the tunnel interface, which directly verifies whether the manually configured IPv6 tunnel is up/up. The 'show ipv6 interface tunnel 0' command shows IPv6-specific information such as the IPv6 address, link-local address, and whether IPv6 is enabled on the tunnel interface, confirming that IPv6 traffic can be processed. Both commands provide essential operational verification for a manually configured IPv6 tunnel, such as a 6in4 or GRE tunnel carrying IPv6.

Answer

show ipv6 route

Answer

show ipv6 tunnel 0

Answer

show running-config interface tunnel 0

Question 14

A large enterprise network is experiencing intermittent IPv6 connectivity between two remote sites connected via an IPv6-in-IPv4 manual tunnel. Router R1 has the following relevant configuration: interface Tunnel0 ipv6 address 2001:DB8:1::1/64 tunnel source 192.0.2.1 tunnel destination 198.51.100.1 ipv6 route 2001:DB8:2::/64 Tunnel0. Router R2 shows: R2# show ipv6 route 2001:DB8:1::/64 % Route not found. The tunnel interface is up/up on both routers, and IPv4 reachability between tunnel endpoints is verified. What is the root cause?

Accepted Answer

R2 is missing a static route for 2001:DB8:1::/64 pointing to its Tunnel0 interface.. The issue is that R2 has no route to the 2001:DB8:1::/64 network, which is the tunnel subnet on R1's side. Even though the tunnel is up/up and IPv4 reachability exists, R2 cannot return traffic to R1's tunnel endpoint address because it lacks a static route pointing to its own Tunnel0 interface. This is a common misconfiguration in point-to-point IPv6-in-IPv4 manual tunnels where both sides must have reciprocal static routes for the remote tunnel networks.

Answer

The tunnel destination on R1 is incorrect and should be 198.51.100.2.

Answer

The tunnel mode must be changed to ipv6ip for IPv6-in-IPv4 tunneling.

Answer

IPv6 unicast-routing is disabled on R2.

Question 15

A DMVPN phase 3 network with IPv6 over IPv4 tunnels is experiencing spoke-to-spoke tunnel failures. Hub router R1 has the following relevant configuration: interface Tunnel0 ipv6 address 2001:DB8:1::1/64 tunnel source GigabitEthernet0/0 tunnel mode gre multipoint ip nhrp network-id 1 ip nhrp map multicast dynamic ipv6 nhrp map multicast dynamic. Spoke router R2 shows: R2# show dmvpn detail Legend: Attrb -> S: Static, D: Dynamic, I: Incomplete NHRP domain: 1 Interface: Tunnel0, IPv4 NHRP Details Type:Spoke, Total NBMA Peers: 1 # Ent Peer NBMA Addr Peer Tunnel Add State UpDn Tm Attrb 1 192.0.2.2 2001:DB8:1::2 UP 00:10:00 D. What is the root cause?

Accepted Answer

The hub is missing the ip nhrp redirect command under Tunnel0.. In DMVPN Phase 3, spoke-to-spoke tunnels rely on the hub to send NHRP Redirect messages to trigger shortcut creation. The hub's configuration is missing the `ip nhrp redirect` command under Tunnel0, which prevents it from informing the spoke that a better path exists directly to another spoke. Without this redirect, the spoke never initiates an NHRP Resolution Request to build a direct tunnel, causing spoke-to-spoke communication to fail.

Answer

The spoke is missing the ip nhrp shortcut command under Tunnel0.

Answer

The tunnel mode should be gre multipoint on the spokes.

Answer

IPv6 NHRP is not supported on DMVPN phase 3.