MPLS Flashcards 1.0
The ip vrf command supports both IPv4 and IPv6
False, the vrf definition supports both
In IOS the RD is configured in the BGP hierarchy
False, in IOS-XR, yes
What command is used to change legacy VRF configuration to the new model
(config)# vrf upgrade-cli multi-af-mode common-policies
Is it mandatory to delete all configuration to change from ip vrf syntax to vrf definition
False, it is possible to change the configuration
How to enter BGP session configuration mode within a VRF
IOS: address-family ipv4 vrf CUSTOMER-A
Is it necessary to activate the VPNv4 address family to activate a BGP session using VRF Lite
False, it is necessary, even if there is no session with this AF activated
If the no mpls ip propagate-ttl command is executed, what will be the TTL for the label in the imposition?
255, so there will never be ttl expired in any router, therefore there is no response in the traceroute
Does the no mpls ip propagate-ttl forwarded command allow traceroute to be executed from the PE but not from the CE?
True
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
Router alert Label
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
Router Alert Option
MPLS OAM o MPLS ping uses the ________________
router alert label (not CPU intensive)
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
127, 3503
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
LSPV
The ______________ command explores possible paths testing them all and informing which ones are intact and which ones are broken
traceroute mpls multipath
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
Equal to IGP cost
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
Affinity bits
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
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
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.
True
IGP Extensions for traffic engineering OSPF LSA ___ has link local flooding scope LSA ___ has intra area flooding scope LSA ___ has inter area flooding scope
Opaque LSAs 9, 10 and 11
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
10, Router, Link
How does an OSPF router inform TE capability?
by activating the “O” bit in the hellos
IGP Extensions for traffic engineering ISIS The TLV ____ - _______________ that describes neighbors and their costs, it replaced the old TLV 2 ISIS reachability
22, ISIS extended Reachability
IGP Extensions for traffic engineering ISIS The TLV ____ - _______________ that describes neighbors and their costs, it replaced the old TLV 128 and 130 IP reachability
135 Extended IP reachability. The TLV focuses on allowing long metrics
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.
PUSH, CONTINUE, NEXT
IGP Prefix SID, prefix Segment or prefix sid are the same thing
True. global identifier Loopback + SRGB
SR: o ADJ SID supports ECMP
False, the prefix sid does
What are the two steps to configure SR in IOS XE
- 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
_________ 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.
Binding segment
SR is supported in OSPFv2 and also in OSPFv3
False, only in v2, ISIS supports for ipv4 and ipv6
Does SR TE also use RSVP to establish TE tunnels?
False, RSVP is not necessary
