Answer: A 

Explanation: 

Your CCNA certification exam is likely going to contain questions about Telnet, an application-level protocol that allows remote communication between two networking devices. With Telnet use being as common as it is, you had better know the details of how to configure it in order to pass your CCNA exam and to work in real-world networks. 

The basic concept is pretty simple - we want to configure R1, but we're at R2. If we telnet successfully to R1, we will be able to configure R1 if we've been given the proper permission levels. In this CCNA case study, R2 has an IP address of 172.12.123.2 and R1 an address of 172.12.123.1. Let's try to telnet from R2 to R1. 

R2#telnet 172.12.123.1 Trying 172.12.123.1 ... Open Password required, but none set [Connection to 172.12.123.1 closed by foreign host] 

This seems like a problem, but it's a problem we're happy to have. A Cisco router will not let any user telnet to it by default. That's a good thing, because we don't want just anyone connecting to our router! The "password required" message means that no password has been set on the VTY lines on R1. Let's do so now. 

R1(config)#line vty 0 4 

R1(config-line)#password baseball 

A password of "baseball" has been set on the VTY lines, so we shouldn't have any trouble using Telnet to get from R2 to R1. Let's try that now. 

R2#telnet 172.12.123.1 

Trying 172.12.123.1 ... Open 

User Access Verification 

Password: 

R1> 

We're in, and placed into user exec mode. 

Reference: 

http://www.mcmcse.com/cisco/guides/telnet_passwords_and_privilege_levels.shtml 

Answer: A 

Explanation: 

OSPF elects one DR per multi-access network. In the exhibit there are two DR so there must have more than one multi-access network. 

Answer: B 

Explanation: NAT operation is typically transparent to both the internal and external hosts. Typically the internal host is aware of the true IP address and TCP or UDP port of the external host. Typically the NAT device may function as the default gateway for the internal host. However the external host is only aware of the public IP address for the NAT device and the particular port being used to communicate on behalf of a specific internal host. 

NAT and TCP/UDP 

"Pure NAT", operating on IP alone, may or may not correctly parse protocols that are totally concerned with IP information, such as ICMP, depending on whether the payload is interpreted by a host on the "inside" or "outside" of translation. As soon as the protocol stack is traversed, even with such basic protocols as TCP and UDP, the protocols will break unless NAT takes action beyond the network layer. IP packets have a checksum in each packet header, which provides error detection only for the header. IP datagrams may become fragmented and it is necessary for a NAT to reassemble these fragments to allow correct recalculation of higher-level checksums and correct tracking of which packets belong to which connection. The major transport layer protocols, TCP and UDP, have a checksum that covers all the data they carry, as well as the TCP/UDP header, plus a "pseudo-header" that contains the source and destination IP addresses of the packet carrying the TCP/UDP header. For an originating NAT to pass TCP or UDP successfully, it must recompute the TCP/UDP header checksum based on the translated IP addresses, not the original ones, and put that checksum into the TCP/UDP header of the first packet of the fragmented set of packets. The receiving NAT must recompute the IP checksum on every packet it passes to the destination host, and also recognize and recompute the TCP/UDP header using the retranslated addresses and pseudo-header. This is not a completely solved problem. One solution is for the receiving NAT to reassemble the entire segment and then recompute a checksum calculated across all packets. The originating host may perform Maximum transmission unit (MTU) path discovery to determine the packet size that can be transmitted without fragmentation, and then set the don't fragment (DF) bit in the appropriate packet header field. Of course, this is only a one-way solution, because the responding host can send packets of any size, which may be fragmented before reaching the NAT. 

Answer: A,C,E 

Explanation: 

Routing overhead is the amount of information needed to describe the changes in a dynamic network topology. All routers in an OSPF area have identical copies of the topology database and the topology database of one area is hidden from the rest of the areas to reduce routing overhead because fewer routing updates are sent and smaller routing trees are computed and maintained (allow extensive control of routing updates and confine network instability to one area of the network). 

Answer: D Explanation: 

Answer D is correct because when you type the incomplete command it will not autocomplete if there is more than one option for completing the command. In this case, there is another command that also starts with “show ru” 

Answer: C 

Answer: C 

Explanation: 

TCP is an example of a connection-oriented protocol. It requires a logical connection to be established between the two processes before data is exchanged. The connection must be maintained during the entire time that communication is taking place, then released afterwards. The process is much like a telephone call, where a virtual circuit is established--the caller must know the person's telephone number and the phone must be answered--before the message can be delivered. TCP/IP is also a connection-oriented transport with orderly release. With orderly release, any data remaining in the buffer is sent before the connection is terminated. The release is accomplished in a three-way handshake between client and server processes. The connection-oriented protocols in the OSI protocol suite, on the other hand, do not support orderly release. Applications perform any handshake necessary for ensuring orderly release. Examples of services that use connection-oriented transport services are telnet, rlogin, and ftp. 

Answer: D 

Explanation: 

The Internet Protocol Suite, TCP/IP, is a suite of protocols used for communication over the internet. The TCP/ IP model was created after the OSI 7 layer model for two major reasons. First, the foundation of the Internet was built using the TCP/IP suite and through the spread of the World Wide Web and Internet, TCP/IP has been preferred. Second, a project researched by the Department of Defense (DOD) consisted of creating the TCP/IP protocols. The DOD's goal was to bring international standards which could not be met by the OSI model. Since the DOD was the largest software consumer and they preferred the TCP/IP suite, most vendors used this model rather than the OSI. Below is a side by side comparison of the TCP/IP and OSI models. 

Answer: B 

Explanation: 

The enable secret password takes precedence over the enable password, so sanfran will be used. 

Answer: E 

Explanation: 

A PC will retain its DHCP assigned IP address until the lease time expires, which often times is 24 hours or more. When changes are made to the DHCP server, the client should issue the ipconfig/release and then ipconfig/renew commands to obtain a new IP address lease.