MPLS Flashcards 1.0

Question 1

The ip vrf command supports both IPv4 and IPv6

Answer 1

False, the vrf definition supports both

Question 2

In IOS the RD is configured in the BGP hierarchy

Answer 2

False, in IOS-XR, yes

Question 3

What command is used to change legacy VRF configuration to the new model

Answer 3

(config)# vrf upgrade-cli multi-af-mode common-policies

Question 4

Is it mandatory to delete all configuration to change from ip vrf syntax to vrf definition

Answer 4

False, it is possible to change the configuration

Question 5

How to enter BGP session configuration mode within a VRF

Answer 5

IOS: address-family ipv4 vrf CUSTOMER-A

Question 6

Is it necessary to activate the VPNv4 address family to activate a BGP session using VRF Lite

Answer 6

False, it is necessary, even if there is no session with this AF activated

Question 7

If the no mpls ip propagate-ttl command is executed, what will be the TTL for the label in the imposition?

Answer 7

255, so there will never be ttl expired in any router, therefore there is no response in the traceroute

Question 8

Does the no mpls ip propagate-ttl forwarded command allow traceroute to be executed from the PE but not from the CE?

Answer 8

True

Question 9

MPLS OAM o __________  Defined by RFC 3032  Value 1  Can be in any position in the label stack except the bottom label  When an LSR receives a label with value 1 it knows it must inspect the IP packet

Answer 9

Router alert Label

Question 10

MPLS OAM o ___________ can be signaled within the IP options field of the IP Header o The field indicates that routers along the path should better inspect the packet even if it is not intended for the said routers o If the packet has a label then the LSR will not check the IP packet, it is possible to force this check but this penalizes the CPU

Answer 10

Router Alert Option

Question 11

MPLS OAM o MPLS ping uses the ________________

Answer 11

router alert label (not CPU intensive)

Question 12

MPLS OAM Ping MPLS  The destination IP belongs to the range ____ , as this network should not exist in the FIB the packet will never be forwarded in case of broken LSP  The packet destined to port____ is forwarded to the UDP process that generates the reply to the request’s source address

Answer 12

127, 3503

Question 13

LSP Verification o The_______ is the subsystem in IOS responsible for everything related to mpls ping and traceroute o Functions  Process listening on port 3503  Encode and decode mpls echo and reply  Maintain exceptional requests database  Provide CLI for commands  Interface with IP, MPLS and AToM on LSR for sending and responding to messages  Handle packets with MPLS TTL expired with Router Alert Label

Answer 13

LSPV

Question 14

The ______________ command explores possible paths testing them all and informing which ones are intact and which ones are broken

Answer 14

traceroute mpls multipath

Question 15

Constraint-Based Path Computation: Path Selection  Selects path based on the Administrative weight (TE Cost) of each individual link o By default ____ to IGP cost o If multiple paths exist and tie:  The path with the highest minimum link • EX: Two paths A and B • A has the lowest uplink of 1G • B has the lowest path of 10G (better)  Path with lowest hop count  If tie the path is chosen randomly

Answer 15

Equal to IGP cost

Question 16

Characteristics of the link resource class attribute: o 32-bit value o The link is associated with a traffic tunnel to include or exclude certain links from the path

Answer 16

Affinity bits

Question 17

Consider a tunnel affinity bits is 0000 and the mask is 0011 The links below are configured with the values: Link A 1100 Link B 1101 Link C 1010 Link D 0100 Which links will be used and which will be avoided

Answer 17

Match only with the last two bits, i.e., the tunnel will only be established on paths that have link affinity bits whose last two bits are 00 link A and Link D

Question 18

In CBTS the packet is inserted into the Tunnel if the exp bits match those configured in the tunnel, i.e., routing occurs based on the markings.

Answer 18

True

Question 19

IGP Extensions for traffic engineering OSPF LSA ___ has link local flooding scope LSA ___ has intra area flooding scope LSA ___ has inter area flooding scope

Answer 19

Opaque LSAs 9, 10 and 11

Question 20

LSA ___ carries the TLVs The ____ TLV carries the TE RID The ____ TLV carries the subset of TLV with information describing a Link for MPLS TE

Answer 20

10, Router, Link

Question 21

How does an OSPF router inform TE capability?

Answer 21

by activating the “O” bit in the hellos

Question 22

IGP Extensions for traffic engineering ISIS The TLV ____ - _______________ that describes neighbors and their costs, it replaced the old TLV 2 ISIS reachability

Answer 22

22, ISIS extended Reachability

Question 23

IGP Extensions for traffic engineering ISIS The TLV ____ - _______________ that describes neighbors and their costs, it replaced the old TLV 128 and 130 IP reachability

Answer 23

135 Extended IP reachability. The TLV focuses on allowing long metrics

Question 24

SR Operations: ______ corresponds to pushing one or more labels on top of an incoming packet then sending it out of a particular physical interface In the MPLS forwarding plane, the_________ operation corresponds to swapping the incoming label with an outgoing label In the MPLS forwarding plane,_____ corresponds to popping the topmost label.

Answer 24

PUSH, CONTINUE, NEXT

Question 25

IGP Prefix SID, prefix Segment or prefix sid are the same thing

Answer 25

True. global identifier Loopback + SRGB

Question 26

SR: o ADJ SID supports ECMP

Answer 26

False, the prefix sid does

Question 27

What are the two steps to configure SR in IOS XE

Answer 27

1. Global mode segment-routing mpls ! connected-prefix-sid-map address-family ipv4 10.0.255.2/32 index 2 In IGP router ospf 10 segment-routing mpls segment-routing prefix-sid-map advertise-local

Question 28

_________ is a local segment that is used to map a single segment into a list of segments. It decreases the number of segments that the source node has to impose by aggregating the list of segments behind the binding SID. When the binding segment originator receives a packet with the binding SID, it pops the label and pushes the associated segment list.

Answer 28

Binding segment

Question 29

SR is supported in OSPFv2 and also in OSPFv3

Answer 29

False, only in v2, ISIS supports for ipv4 and ipv6

Question 30

Does SR TE also use RSVP to establish TE tunnels?

Answer 30

False, RSVP is not necessary