passleader 400 101 [May 2021]


The article at Testaimer.com going over http://www.testaimer.com/400-101-test is very comprehensive.

Q481. Which type of OSPF packet is an OSPF link state update packet? 

A. type 1 

B. type 2 

C. type 3 

D. type 4 

E. type 5 

Answer:

Explanation: 

Link State Update packets are OSPF packet type 4. These packets implement the flooding of link state advertisements. Each Link State Update packet carries a collection of link state advertisements one hop further from its origin. Several link state advertisements may be included in a single packet. 

Reference: http://www.freesoft.org/CIE/RFC/1583/107.htm 


Q482. DRAG DROP 

Drag and drop the BGP attribute on the left to the correct category on the right. 

Answer: 


Q483. Which two statements about the BGP community attribute are true? (Choose two.) 

A. Routers send the community attribute to all BGP neighbors automatically. 

B. A router can change a received community attribute before advertising it to peers. 

C. It is a well-known, discretionary BGP attribute. 

D. It is an optional transitive BGP attribute. 

E. A prefix can support only one community attribute. 

Answer: B,D 

Explanation: 

A community is a group of prefixes that share some common property and can be configured with the BGP community attribute. The BGP Community attribute is an optional transitive attribute of variable length. The attribute consists of a set of four octet values that specify a community. The community attribute values are encoded with an Autonomous System (AS) number in the first two octets, with the remaining two octets defined by the AS. A prefix can have more than one community attribute. A BGP speaker that sees multiple community attributes in a prefix can act based on one, some or all the attributes. A router has the option to add or modify a community attribute before the router passes the attribute on to other peers. 

Reference: 

http://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/28784-bgp-community.html 


Q484. What is Nagle's algorithm used for? 

A. To increase the latency 

B. To calculate the best path in distance vector routing protocols 

C. To calculate the best path in link state routing protocols 

D. To resolve issues caused by poorly implemented TCP flow control. 

Answer:

Explanation: 

Silly window syndrome is a problem in computer networking caused by poorly implemented TCP flow control. A serious problem can arise in the sliding window operation when the sending application program creates data slowly, the receiving application program consumes data slowly, or both. If a server with this problem is unable to process all incoming data, it requests that its clients reduce the amount of data they send at a time (the window setting on a TCP packet). If the server continues to be unable to process all incoming data, the window becomes smaller and smaller, sometimes to the point that the data transmitted is smaller than the packet header, making data transmission extremely inefficient. The name of this problem is due to the window size shrinking to a "silly" value. When there is no synchronization between the sender and receiver regarding capacity of the flow of data or the size of the packet, the window syndrome problem is created. When the silly window syndrome is created by the sender, Nagle's algorithm is used. Nagle's solution requires that the sender sends the first segment even if it is a small one, then that it waits until an ACK is received or a maximum sized segment (MSS) is accumulated. 

Reference: http://en.wikipedia.org/wiki/Silly_window_syndrome 


Q485. How many bytes comprise the system ID within an IS-IS NET? 

A. 4 bytes 

B. 6 bytes 

C. 8 bytes 

D. 16 bytes 

E. 20 bytes 

Answer:

Explanation: 

Routers are identified with NETs of 8 to 20 bytes. ISO/IEC 10589 distinguishes only three fields in the NSAP address format: a variable-length area address beginning with a single octet, a system ID, and a 1-byte n-selector. Cisco implements a fixed length of 6 bytes for the system ID, which is like the OSPF router ID. 

Reference: http://www.cisco.com/en/US/products/ps6599/products_white_paper09186a00800a3e6f.sh tml 


Q486. Refer to the exhibit. 

Which option explains why the forwarding address is set to 0.0.0.0 instead of 110.100.1.1? 

A. The interface Ethernet0/1 is in down state. 

B. The next-hop ip address 110.100.1.1 is not directly attached to the redistributing router. 

C. The next-hop interface (Ethernet0/1) is specified as part of the static route command; therefore, the forwarding address is always set to 0.0.0.0. 

D. OSPF is not enabled on the interface Ethernet0/1. 

Answer:

Explanation: 

From the output of the “show ip ospf database” command (although this command is not shown) we can conclude this is an ASBR (with Advertising Router is itself) and E0/1 is the ASBR’s next hop interface for other routers to reach network 192.168.10.0. 

The Forwarding Address is determined by these conditions: 

* The forwarding address is set to 0.0.0.0 if the ASBR redistributes routes and OSPF is not enabled on the next hop interface for those routes. 

* These conditions set the forwarding address field to a non-zero address: 

+ OSPF is enabled on the ASBR’s next hop interface AND 

+ ASBR’s next hop interface is non-passive under OSPF AND 

+ ASBR’s next hop interface is not point-to-point AND 

+ ASBR’s next hop interface is not point-to-multipoint AND 

+ ASBR’s next hop interface address falls under the network range specified in the router ospf command. 

* Any other conditions besides these set the forwarding address to 0.0.0.0. 

-> We can see E0/1 interface is not running OSPF because it does not belong to network 110.110.0.0 0.0.255.255 which is declared under OSPF process -> F.A address is set to 0.0.0.0. 

Reference: http://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/13682-10.html 


Q487. Where is multicast traffic sent, when it is originated from a spoke site in a DMVPN phase 2 cloud? 

A. spoke-spoke 

B. nowhere, because multicast does not work over DMVPN 

C. spoke-spoke and spoke-hub 

D. spoke-hub 

Answer:

Explanation: 

Spokes map multicasts to the static NBMA IP address of the hub, but hub maps multicast packets to the “dynamic” mappings – that is, the hub replicates multicast packets to all spokes registered via NHRP, so multicast traffic is sent to the hub from a spoke instead of to the other spokes directly. 


Q488. Which two statements describe characteristics of HDLC on Cisco routers? (Choose two.) 

A. It supports multiple Layer 3 protocols. 

B. It supports multiplexing. 

C. It supports only synchronous interfaces. 

D. It supports authentication. 

Answer: A,C 

Explanation: 

Cisco High-Level Data Link Controller (HDLC) is the Cisco proprietary protocol for sending data over synchronous serial links using HDLC. Cisco HDLC also provides a simple control protocol called Serial Line Address Resolution Protocol (SLARP) to maintain serial link keepalives. Cisco HDLC is the default for data encapsulation at Layer 2 (data link) of the Open System Interconnection (OSI) stack for efficient packet delineation and error control. The absence of a protocol type field in the HDLC header posed a problem for links that carried traffic from more than one Layer 3 protocol. Cisco, therefore, added an extra Type field to the HDLC header, creating a Cisco-specific version of HDLC. Cisco routers can support multiple network layer protocols on the same HDLC link. For example an HDLC link between two Cisco routers can forward both IPv4 and IPv6 packets because the Type field can identify which type of packet is carried inside each HDLC frame. 

Reference: http://www.cisco.com/c/en/us/td/docs/routers/access/800/819/software/configuration/Guide/ 

819_SCG/6ser_conf.html#pgfId-1073734 


Q489. Which three statements about DMVPN are true? (Choose three.) 

A. It facilitates zero-touch configuration for addition of new spokes. 

B. It supports dynamically addressed spokes using DHCP. 

C. It features automatic IPsec triggering for building an IPsec tunnel. 

D. It requires uses of IPsec to build the DMVPN cloud. 

E. Spokes can build tunnels to other spokes and exchange traffic directly. 

F. It supports server load balancing on the spokes. 

Answer: A,C,E 


Q490. Refer to the exhibit. 

Which LISP component do routers in the public IP network use to forward traffic between the two networks? 

A. EID 

B. RLOC 

C. map server 

D. map resolver 

Answer:

Explanation: 

Locator ID Separation Protocol (LISP) is a network architecture and protocol that implements the use of two namespaces instead of a single IP address: 

. Endpoint identifiers (EIDs)—assigned to end hosts. 

. Routing locators (RLOCs)—assigned to devices (primarily routers) that make up the global routing system. The public networks use the RLOC to forward traffic between networks. 

Reference: http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_lisp/configuration/15-mt/irl-15-mt-book/irl-overview.html