EVN & VRF -2

Question 1

Cisco EVN related question, a network engineer implemented Cisco EVN. Which feature implements shared services support?

A. Edge interfacing
B. Tunnel feedback
C. Route replication
D. Route redistribution

Answer: C

Route replication allows shared services because routes are replicated between virtual networks and clients who reside in one virtual network can reach prefixes that exist in another virtual network.

Reference: http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/evn/configuration/xe-3s/evn-xe-3s-book/evn-shared-svcs.html

Question 2

What does the “show ip route vrf CISCO” command display?

A. directly connected routes for VRF CISCO.
B. the routing table for VRF CISCO.
C. the global routing table.
D. all routing tables that start with VRF CISCO.
E. the route distinguisher for VRF CISCO.

Answer: B

Question 3

Which two statements about EVN are true? (Choose two)

A. Virtual network tags are assigned per-VRF.
B. It is supported only on access ports.
C. Virtual network tags are assigned globally.
D. Routing metrics can be manipulated only from directly within the routing-context configuration.
E. The VLAN ID in the 802.1q frame carries the virtual network tag.
F. The VLAN ID is the ISL frame carries the virtual network tag.

Answer: A E

Path isolation can be achieved by using a unique tag for each Virtual Network (VN) -> Answer A is correct.

Instead of adding a new field to carry the VNET tag in a packet, the VLAN ID field in 802.1q is repurposed to carry a VNET tag. The VNET tag uses the same position in the packet as a VLAN ID. On a trunk interface, the packet gets re-encapsulated with a VNET tag. Untagged packets carrying the VLAN ID are not EVN packets and could be transported over the same trunk interfaces -> Answer E is correct.

Reference: http://www.cisco.com/c/en/us/products/collateral/ios-nx-os-software/layer-3-vpns-l3vpn/whitepaper_c11-638769.html

Question 4

Refer to Exhibit. R1 is unable to ping interface S0/0 of R2. What is the issue the configuration that is shown here?


A. The route-target configuration command is missing.
B. The interface IP addresses are not in the same subnet.
C. The syntax of the ping command is wrong.
D. The default route configuration is missing.
E. The serial interfaces belong to the global table instead of vrf Yellow.

Answer: E

We are trying to ping the 192.168.1.2 in vrf Yellow but the Serial0/0 interfaces of both routers do not belong to this VRF so the ping fails. We need to configure S0/0 interfaces with the “ip vrf forwarding Yellow” (under interface S0/0) in order to put these interfaces into VRF Yellow.

Question 5

After reviewing the EVN configuration, a network administrator notices that a predefined EVN, which is known as “vnet global” was configured. What is the purpose of this EVN? (OR) What is the purpose of ‘vnet global”?

A. It defines the routing scope for each particular EVN edge interface.
B. It aggregates and carries all dot1q tagged traffic.
C. It refers to the global routing context and corresponds to the default RIB.
D. It safeguards the virtual network that is preconfigured to avoid mismatched routing instances.

Answer: C

Question 6

What is the output of the following command?

show ip vrf

A. show the vrf present in the route and their associated route distinguisher
B. Displays IP routing table information associated with a VRF
C. Show’s routing protocol information associated with a VRF.
D. Displays the ARP table (static and dynamic entries) in the specified VRF.

Answer: A

Question 7

Which two statements about route targets that are configured with VRF-Lite are true? (Choose two)

A. Route targets uniquely identify the customer routing table
B. Route targets control the import and export of routes into a customer routing table
C. Route targets are supported only when BGP is configured
D. When IS-IS is configured, route targets identify the circuit level in which the customer resides
E. When BGP is configured, route targets are transmitted as BGP standard communities
F. Route targets allows customers to be assigned overlapping addresses

Answer: B C

In the link http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst4500/12-2/25ew/configuration/guide/conf/vrf.html there is a notice about route-target command: “Note: This command is effective only if BGP is running.” -> C is correct.

Answer A & F are not correct as only route distinguisher (RD) identifies the customer routing table and “allows customers to be assigned overlapping addresses”.

Answer E is not correct as “When BGP is configured, route targets are transmitted as BGP extended communities”

Question 8

Which two statements about EVNs are true? (Choose two)

A. VRFs using MPLS require a trunk interface that uses EVN
B. VRF-Lite requires a trunk interface that uses EVNs
C. All EVNs within a trunk interface can share the same IP infrastructure
D. Each EVN within a trunk interface must be configured separately
E. Commands that are specified once under a trunk interface can be inherited by all EVNs

Answer: C E

With VRF-Lite, if you want to send traffic for multiple virtual networks (that is, multiple VRFs) between two routers you need to create a subinterface for each VRF on each router -> VRF-Lite requires subinterfaces. However, with Cisco EVN, you instead create a trunk (called a Virtual Network (VNET) trunk) between the routers. Then, traffic for multiple virtual networks can travel over that single trunk interface, which uses tags to identify the virtual networks to which packets belong.

Note: Both Cisco EVN and VRF-Lite allow a single physical router to run multiple virtual router instances, and both technologies allow routes from one VRF to be selectively leaked to other VRFs. However, a major difference is the way that two physical routers interconnect. With VRF-Lite, a router is configured with multiple subinterfaces, one for each VRF. However, with Cisco EVN, routers interconnect using a VNET trunk, which simplifies configuration.

Reference: CCNP Routing and Switching ROUTE 300-101 Official Cert Guide

All EVNs within a trunk interface share the same IP infrastructure as they are on the same physical interface -> Answer C is correct.

With EVNs, a trunk interface is shared among VRFs so each command configured under this trunk is applied by all EVNs -> Answer E is correct.

Question 9

Which values identifies VPNs in an EVN environment?

A. DLCI
B. route target
C. virtual network tag
D. VLAN ID

Answer: C

Question 10

How does an EVN provide end-to-end virtualization and separation of data traffic from multiple networks?

A. It tags traffic with an 802.1q tag at the edge interface.
B. It tags traffic with an 802.1q tag at trunk interface.
C. It tags traffic with a virtual network tag at the trunk interface.
D. It tags traffic with a virtual network tag at the edge interface

Answer: C