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2021 Mar 400-101 free exam questions
Q471. Which two mechanisms provide Cisco IOS XE Software with control plane and data plane separation? (Choose two.)
A. Forwarding and Feature Manager
B. Forwarding Engine Driver
C. Forwarding Performance Management
D. Forwarding Information Base
Answer: A,B
Explanation:
Control Plane and Data Plane Separation
IOS XE introduces an opportunity to enable teams to now build drivers for new Data Plane ASICs outside the IOS instance and have them program to a set of standard APIs which in turn enforces Control Plane and Data Plane processing separation. IOS XE accomplishes Control Plane / Data Plane separation through the introduction of the Forwarding and Feature Manager (FFM) and its standard interface to the Forwarding Engine Driver (FED). FFM provides a set of APIs to Control Plane processes. In turn, the FFM programs the Data Plane via the FED and maintains forwarding state for the system. The FED is the instantiation of the hardware driver for the Data Plane and is provided by the platform.
Reference: http://www.cisco.com/c/en/us/products/collateral/ios-nx-os-software/ios-xe-3sg/QA_C67-622903.html
Q472. Which two statements about NPTv6 are true? (Choose two.)
A. The translation is invisible to applications that hard code IP information within the application logic.
B. It is a one-way stateful translation for the IPv6 address.
C. Translation is 1:1 at the network layer.
D. It is a two-way stateless translation for the network prefix.
Answer: C,D
Explanation:
This document describes a stateless, transport-agnostic IPv6-to-IPv6 Network Prefix Translation (NPTv6) function that provides the address-independence benefit associated with IPv4-to-IPv4 NAT (NAPT44) and provides a 1:1 relationship between addresses in the "inside" and "outside" prefixes, preserving end-to-end reachability at the network layer NPTv6 Translation is stateless, so a "reset" or brief outage of an NPTv6 Translator does not break connections that traverse the translation function, and if multiple NPTv6 Translators exist between the same two networks, the load can shift or be dynamically load shared among them. NPTv6 is defined to include a two-way, checksum-neutral, algorithmic translation function, and nothing else.
Reference: https://tools.ietf.org/html/rfc6296
Q473. Which BGP feature allows a router to maintain its current BGP configuration while it advertises a different AS number to new connections?
A. local-AS
B. next-hop-self
C. allow-AS in
D. soft reset
Answer: A
Explanation:
The local-AS feature allows a router to appear to be a member of a second autonomous system (AS), in addition to its real AS. This feature can only be used for true eBGP peers. The local-AS feature is useful if ISP-A purchases ISP-B, but ISP-B's customers do not want to modify any peering arrangements or configurations. The local-AS feature allows routers in ISP-B to become members of ISP-A's AS. At the same time, these routers appear to their customers to retain their ISP-B AS number.
Reference: http://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13761-39.html
Q474. You are backing up a server with a 1 Gbps link and a latency of 2 ms. Which two statements about the backup are true? (Choose two.)
A. The bandwidth delay product is 2 Mb.
B. The default TCP send window size is the limiting factor.
C. The default TCP receive window size is the limiting factor.
D. The bandwidth delay product is 500 Mb.
E. The bandwidth delay product is 50 Mb.
Answer: A,C
Explanation:
1 Gbps is the same as 1000 Mbps, and 1000Mb x .0002 = 2 Mbps. With TCP based data transfers, the receive window is always the limiting factor, as the sender is generally able to send traffic at line rate, but then must wait for the acknowledgements to send more data.
Q475. What is the destination multicast MAC address for BPDUs on the native VLAN, for a switch that is running 802.1D?
A. 0185. C400. 0000
B. 0100.0CCC.CCCC
C. 0100.0CCC.CCCD
D. 0180.C200.0000
Answer: D
Explanation:
If the native vlan is 1:
A STP BPDU for VLAN 1 will be sent untagged to MAC 0180.c200.0000 (this is the
common spanning tree)
A PVST+ BPDU for VLAN 1 will be sent untagged to MAC 0100.0ccc.cccd
A PVST+ BPDU for all other vlans will be sent with a 802.1Q tag to MAC 0100.0ccc.cccd
(with a PVID = to the VLAN)
If the native vlan is not 1:
A STP BPDU for VLAN 1 will be sent untagged (on the native vlan) to MAC
0180.c200.0000 (this is the common spanning tree)
A PVST+ BPDU for VLAN1 will be sent with a 802.1Q tag to MAC 0100.0ccc.cccd (with a PVID=1)
A PVST+ BPDU for the native vlan will be sent untagged to MAC 0100.0ccc.cccd (with a PVID=native vlan)
A PVST+ BPDU for all other vlans will be sent with a 802.1Q tag to MAC 0100.0ccc.cccd (with a PVID = to the VLAN)
Up to the immediate present 400-101 test engine:
Q476. Which statement about the BGP originator ID is true?
A. The route reflector always sets the originator ID to its own router ID.
B. The route reflector sets the originator ID to the router ID of the route reflector client that injects the route into the AS.
C. The route reflector client that injects the route into the AS sets the originator ID to its own router ID.
D. The originator ID is set to match the cluster ID.
Answer: B
Explanation:
An RR reflecting the route received from a RR-Client adds:
. Originator ID- a 4-byte BGP attribute that is created by the RR. This attribute carries the Router ID of the originator of the route in the local AS. If the update comes back to the originator, it ignores the update.
. Cluster List- A Cluster List is a list of Cluster IDs that an update has traversed. When a route reflector sends a route received from a client to a non-client, it appends the local Cluster ID. If a route reflector receives a route whose Cluster List contains the local Cluster ID, it ignores the update.
Reference: https://sites.google.com/site/amitsciscozone/home/bgp/bgp-route-reflectors
Q477. As a best practice, when a router is configured as an EIGRP Stub, which routes should be received from its distribution neighbor?
A. the default route
B. static routes
C. internal routes only
D. internal and external routes
Answer: A
Explanation:
Stub routing is commonly used in a hub and spoke network topology. In a hub and spoke network, one or more end (stub) networks are connected to a remote router (the spoke) that is connected to one or more distribution routers (the hub). The remote router is adjacent only to one or more distribution routers. The only route for IP traffic to follow into the remote router is through a distribution router. This type of configuration is commonly used in WAN topologies where the distribution router is directly connected to a WAN. The distribution router can be connected to many more remote routers. Often, the distribution router will be connected to 100 or more remote routers. In a hub and spoke topology, the remote router must forward all nonlocal traffic to a distribution router, so it becomes unnecessary for the remote router to hold a complete routing table. Generally, the distribution router need not send anything more than a default route to the remote router.
Reference: http://www.cisco.com/c/en/us/td/docs/ios/12_0s/feature/guide/eigrpstb.html
Q478. DRAG DROP
Drag and drop each IPv6 neighbor discovery message type on the left to the corresponding description on the right.
Answer:
Q479. Which three conditions can cause excessive unicast flooding? (Choose three.)
A. Asymmetric routing
B. Repeated TCNs
C. The use of HSRP
D. Frames sent to FFFF.FFFF.FFFF
E. MAC forwarding table overflow
F. The use of Unicast Reverse Path Forwarding
Answer: A,B,E
Explanation:
Causes of Flooding
The very cause of flooding is that destination MAC address of the packet is not in the L2 forwarding table of the switch. In this case the packet will be flooded out of all forwarding ports in its VLAN (except the port it was received on). Below case studies display most
common reasons for destination MAC address not being known to the switch.
Cause 1: Asymmetric Routing
Large amounts of flooded traffic might saturate low-bandwidth links causing network performance issues or complete connectivity outage to devices connected across such low-bandwidth links.
Cause 2: Spanning-Tree Protocol Topology Changes
Another common issue caused by flooding is Spanning-Tree Protocol (STP) Topology Change Notification (TCN). TCN is designed to correct forwarding tables after the forwarding topology has changed. This is necessary to avoid a connectivity outage, as after a topology change some destinations previously accessible via particular ports might become accessible via different ports. TCN operates by shortening the forwarding table aging time, such that if the address is not relearned, it will age out and flooding will occur. TCNs are triggered by a port that is transitioning to or from the forwarding state. After the TCN, even if the particular destination MAC address has aged out, flooding should not happen for long in most cases since the address will be relearned. The issue might arise when TCNs are occurring repeatedly with short intervals. The switches will constantly be fast-aging their forwarding tables so flooding will be nearly constant. Normally, a TCN is rare in a well-configured network. When the port on a switch goes up or down, there is eventually a TCN once the STP state of the port is changing to or from forwarding. When the port is flapping, repetitive TCNs and flooding occurs.
Cause 3: Forwarding Table Overflow
Another possible cause of flooding can be overflow of the switch forwarding table. In this case, new addresses cannot be learned and packets destined to such addresses are flooded until some space becomes available in the forwarding table. New addresses will then be learned. This is possible but rare, since most modern switches have large enough forwarding tables to accommodate MAC addresses for most designs. Forwarding table exhaustion can also be caused by an attack on the network where one host starts generating frames each sourced with different MAC address. This will tie up all the forwarding table resources. Once the forwarding tables become saturated, other traffic will be flooded because new learning cannot occur. This kind of attack can be detected by examining the switch forwarding table. Most of the MAC addresses will point to the same port or group of ports. Such attacks can be prevented by limiting the number of MAC addresses learned on untrusted ports by using the port security feature.
Reference: http://www.cisco.com/c/en/us/support/docs/switches/catalyst-6000-series-switches/23563-143.html#causes
Q480. Which technology can be affected when switches are used that do not support jumbo frames?
A. 802.1x
B. BFD
C. OSPFv3
D. 802.1q
Answer: D
Explanation:
The 802.1Q tag is 4 bytes. Therefore, the resulting Ethernet frame can be as large as 1522 bytes. If jumbo frames are not supported, then typically the MTU on an Ethernet link needs to be lowered to 1496 to support this extra 802.1Q tag.