Chapter 3 Questions of Network+ A Guide to Networks (7th Edition) Exam for Chapters 1, 2, 3, 4

*What happens when a router receives a packet with a TTL of 0*?

*The router drops the packet and sends an ICMP TTL expired message back to the host* *page 116: Time to Live (TTL) is one field in an IPv4 packet which indicates the* [*maximum number of "hops" the packet has remaining*] before it is DISCARDED off of the network. Although this field was originally mean to represent units of time [ and the duration of time], on modern networks, it represents the Maximum number of times[a.k.a the maximum number of "hops"it has remaining] a packet can still be forwarded by a router. The TTL for packets varies and can be configured; it is usually set at 32 or 64. *Each time a packet passes through a router, its TTL is reduced by 1*. *When a router receives a packet with a TTL equal to 0, it discards that packet and sends an ICMP TTL expired message* BACK TO THE SOURCE HOST *page 119* *Whereas IP [protocol] helps direct data to its correct destination, ICMP (Internet Control Message Protocol) is a network layer core protocol that reports on the SUCCESS or FAILURE of DATA DELIVERY.* *page 120* ICMP can indicate when part of a network is congested, when data fails to reach its destination, and when data has been discarded because the allotted Time to Live (TTL) has expired. ICMP announces these transmission failures TO THE SENDER, but does NOT CORRECT ERRORS it detects--those functions are left to higher-layer protocols, s.a. TCP. However, ICMP's announcements provide CRITICAL info for TROUBLESHOOTING NETWORK PROBLEMS. IPv6 relies on ICMPv6 to perform the functions that ICMPv4, IGMP and ARP perform in IPv4. In other words, ICMPv6 on IPv6 networks performs the functions of IGMP and ARP on IPv4 networks to detect and report data transmission errors, discover other nodes on a network and manage multicasting.

*At what layer of the OSI model would a TCP or UDP header be added to a payload*?

*page 107* *Layer 4, the Transport layer protocol*, usually either TCP or UDP, adds a header to the *payload* from the Layers 7, 6 and 5 from above. This header *includes a port number* to identify the *receiving application on the destination host*. The entire message then becomes a *segment* or *datagram*, depending on the protocol used *TCP* for connection-based datagram and *UDP* for the connectionless-based *segment*

*What is NOT one of the three characteristics of TCP in its role as a reliable delivery protocol*?​

*page 108* *TCP (Transmission Control Protocol) operates in the Transport layer of the OSI model and provides reliable data delivery services. Lets compare TCP to making a phone call, as we look at the three characteristics of TCP in its role as a RELIABLE DELIVERY PROTOCOL:* *Connection-oriented protocol*-- before TCP transmits data, it ensures that a connection or session is established, similar to making sure someone is listening on the other end before speaking *Sequencing and Checksum*-- you check if the person on the other line caught the message by using comprehension check questions *Flow Control*--you might need to slow down if the listener is being a little distracted in the listening environment of where the listener is located in the world at the time which he/she accepted your phonemail

*What TCP field below allows the receiving node to determine whether a TCP segment is corrupted during transmission?​*

*page 108* Checksum* *The three characteristics of Transmission Control Protocol are connection-oriented protocol, sequencing and checksums, and flow control* *checksum: TCP sends a character string called a checksum TCP on the destination host then generates a similar string. If the two checksums FAIL to MATCH, the destination hosts asks the source to retransmit the data.*

*In a TCP segment, what field indicates how many bytes the sender can issue to a receiver while acknowledgement for the segment is outstanding*?​

*page 110* *sliding window* *on the Table entitled, "Fields in a TCP segment* Sliding-window size (or window) is 16 bits and it indicates how many bytes the sender can issue to a receiver while acknowledgment for this segment is outstanding. This field performs flow control, preventing the receiver's buffer from being deluged with bytes.

*Which of the following is not a task handled by a router*?

*page 123* *A router forwards broadcasts over the network.* *Although any one router can be specialized for a variety of tasks, all routers can do the following:* -connect dissimilar networks, s.a. LAN & WAN, which use different types of routing protocols -Interpret Layer 3 and ofter Layer 5 addressing and other info s.a. quality of service indicators -Determine the best path for data to follow from point A to point B. The best path is the most efficient rout to the message's destination calculated by the router, based upon info the router has available to it -Reroute traffic if the path of first choice is down but another path is available

*What command can be used on a Cisco router to view the routing table?*

*page 126* *show ip route* *under the subtitle, "The route Utility", which is under the title, "How Routers Work" ...*On a Cisco-brand router or another brand that uses Cisco command conventions, used the command show ip route*

*What routing protocol criteria is defined as the time it takes to recognize a best path change in the event of a network outage*?

*page 128* *convergence time* *under the subtitle "Routing Protocols", which is under the the chapter's main title of "How Routers Work" To determine the best path, routers communicate w/each other through *routing protocols*. Routing protocol messages, similar to scouting parties exploring unknown terrain, go forth to collect data about current network status and contribute to the selection of the best paths. *Routers use this data to create their routing tables*. Keep in mind that routing protocols ARE NOT THE SAME AS *ROUTABLE PROTOCOLS* s.a. IP, although routing protocols may piggyback on IP to reach their destinations. *Routers rate the reliability and priority of a routing protocol's data based on these three criteria: administrative distance (AD), convergence time, and overhead.* AD concerns the assigned default AD which is a number indicating the protocol's reliability, with the lower values being given higher priority. This assignment can be changed by a network admin. when one protocol should take precedence over a previously higher-rated protocol on that network. *convergence time* concerns routing protocols are also rated on the TIME it takes to RECOGNIZE a best path in the event of a change or network outage* overhead concerns a routing protocol is rated on its overhead, or the burden placed on the underlying network to support the protocol *page 129* *The most common routing protocols are RIP, RIPv2, OSPF and IS-IS* which are IGP (interior- or border-type gateway protocols) and *BGP* which is an EG (an exterior- or border-gateway protocol)

*What type of routing protocol enables routers to communicate beyond neighboring routers, allowing each router to create a map of an entire network?​*

*page 129* *link state* *IS-IS* (Intermediate System to Intermediate System) Routing Protocol which is an IGP type of Routing Protocol (Interior- or border-gateway protocol) that uses the *link state type of algorithm* *Link-State routing protocols enable routers to communicate beyond neighboring routers, after which each router can independently map the network and determine the best path between itself and a message's destination node*. Link-State routing protocols tend to adapt more quickly to changes in the network, but can also be more complex to configure and troubleshoot. *OSPF (Open Shortest Path First) and IS-IS are both link-state- type IGP routing protocols*.

*Which network routing protocol is a path vector protocol that sends updates between routers using TCP*?

*page 131* *BGP,* which is the *Border Gateway Protocol* * In the section of the chapter entitled, "Routers & How They Work*, under the subtitle, "Interior and Exterior Gateway Routing Protocols *page 129*: *[As] you can see that a routing protocol is classified as *IGP* or *EGP*. Here's an explanation of the two types , which are diagrammed in figure 3-18* *IGPs* (interior gateway protocols) are routing protocols used by interior routers and border routers within autonomous systems. *IGPs are often grouped according to the algorithms they use to calculate best paths* *EGP* (exterior gateway protocols) are routing protocols used by border routers and exterior routers to distribute data OUTSIDE of autonomous systems. The one EGP protocol we discuss in this chapter, which is the only EGP currently in use, is BGP* (Border Gateway Protocol)

*What netstat command option lists only current connections, including IP addresses and port numbers*?

*page 133* *netstat -n*

What two fields below are used by IPv4 and IPv6 respectively to limit the number of times that a packet can be forwarded on a network?

TTl and Hop Limit *page 116* indicates *IPv4's Time to Live (TTL)* *page 118* indicate's *IPv6's Hop Limit*