LAB 7 TCP/IP UTILITIES 2

1) Why do we need to ping?

Ping is a basic Internet program that allows a user to verify that a particular IP address exists and can accept requests.

Ping is used diagnostically to ensure that a host computer the user is trying to reach is actually operating. Ping works by sending an Internet Control Message Protocol (ICMP) Echo Request to a specified interface on the network and waiting for a reply. Ping can be used for troubleshooting to test connectivity and determine response time.

As a verb, ping means "to get the attention of" or "to check for the presence of" another party online. The computer acronym (for Packet Internet or Inter-Network Groper) was contrived to match the submariners' term for the sound of a returned sonar pulse.

2) Explain the term Sent,Received,Lost and TTL

Sent = 4, Received = 4

One of the things TCP/IP is designed to deal with is packet loss. Ideally, every packet you send should get to where it’s going, but for various reasons, that doesn’t always happen. As long as the packets can get there after a retry or two, in normal usage you’d never notice. Ping sends multiple packets and reports specifically on the success rate, so you can see if a particular connection is prone to packet loss.

0% Loss

As far as this network connection goes, it can communicate with Google's website just fine.

TTL

Time-to-live (TTL) is a value in an Internet Protocol (IP) packet that tells a network router whether or not the packet has been in the network too long and should be discarded. In IPv6 the TTL field in each packet has been renamed the hop limit.

An IP TTL is set initially by the system sending the packet. It can be set to any value between 1 and 255; different operating systems set different defaults. Each router that receives the packet subtracts at least 1 from the count; if the count remains greater than 0, the router forwards the packet, otherwise it discards it and sends an Internet Control Message Protocol (ICMP) message back to the originating host, which may trigger a resend.

The point of the TTL/hop limit is to keep streams of undeliverable packets stuck in routing loops (perhaps due to incorrect routing tables) from circulating forever and clogging up the networks in question. In Multiprotocol Label Switching (MPLS) clouds, the MPLS TTL is copied from the IP TTL when the IP packet enters the cloud. On egress, the MPLS TTL value is copied into the IP TTL field (as long as it is less than the value in the field).

3) Explain what is happening in Figure 1.

After pinging 117.194.0.24,the round trip time approximately less than 1ms and TTL is 64.According to the statistics,the sent is 4,received is 4,lost is 0.The minimum and maximum is 0ms.

4) 127.0.0.1 refers to 

Loopback Internet Protocol (IP) address also referred to as the “localhost.” The address is used to establish an IP connection to the same machine or computer being used by the end-user.

5) Why do we need to ping 127.0.0.1?

This means that TCP/IP is working on the machine that you are typing on. 127.0.0.1 is a special address that "loops back" to the machine you are pinging from. You can also type ping localhost and receive a similar response, since localhost and 127.0.0.1 mean the same thing.

6) Explain what is happening in Figure 2?

The approximate round trip time is less than 1ms.The TTL is 64.From the ping statistics,the sent is 4,received is 4,Lost is 0.The minimum and maximum is 0ms.Average is 0ms.

7) What does it mean by Request timed out?

Request timed out means that the host you’re pinging might be:

1. down or unreachable (e.g. because it’s on a different network/subnet, it’s shut down, etc.)
2. behind a firewall that drops your ICMP echo request packets
3. the ping command has been disabled for that network by the syadmin
4. You have no Internet connection/network connectivity
5. all of the above.

8) Explain what is happening in Figure 3?

It tells the user that it is tracing the route to google.com, and then it tells the user IP address of the domain and what is the maximum number of hops will it be before time out. After that, it tells information about each router that it went through during its journey. Those three columns refers to the response from the router and the duration it takes. When there is no response from the host, it will display “Request Time Out”. User will be notified that the website is unreachable and the connection is fail.

9) What is the different between Figure 3 and Figure 4?

Request time out shows in Figure 3 means that the destination is reachable but there is no response received. For example, timed out for ping can be due bad configuration of routing back, dua a firewall or simply because the destination has ping disabled. This is a unsuccessful ping results.

In Figure 4, there is no request timed out and other errors so the ICMP Echo Request and ICMP Echo Response are success reach their target computer respectively. This is a successful ping results.

10) What is tracert?

Traceroute is a utility that records the route (the specific gateway computers at each hop) through the Internet between your computer and a specified destination computer. It also calculates and displays the amount of time each hop took. Traceroute is a handy tool both for understanding where problems are in the Internet network and for getting a detailed sense of the Internet itself. Another utility, PING, is often used prior to using traceroute to see whether a host is present on the network.

The traceroute utility comes included with a number of operating systems, including Windows and UNIX-based operating systems (such as IBM's AIX/6000) or as part of a TCP/IP package. If your system doesn't include the utility, you can install it. There are freeware versions that you can download.

11) Explain what us happening in Figure 5?

There are several things that can cause this vague error message. The most common reasons are:

• A firewall or router is blocking access on your network on port 443.
• The private key for the certificate does not match or is not associated correctly with the certificate.
• The DNS entries for the web site are configured incorrectly.
•  The web server is not configured to run on port 443 for https request.
• The web site is not the IIS Default Website and has not been bound to an IP address for https request. (IIS default this to “All Unassigned”)

Nslookup will try to resolve the name for the IP address of the DNS server configured as the primary DNS server on the client by performing a reverse lookup of the IP address. If user do not have a DNS zone set up for he/she network/subnet, the user will get the "server unknown" message as nslookup will be unable to resolve the name for the IP address. Your server is not returning a reverse lookup for its name. That is why you are seeing “Unknown” there.

A non authoritative answer is a response from cache. It is likely to be caused by whatever is servicing the query responding too slowly (that is, too slow in responding to your DNS server).

The client times out before the response is received, but the next query gets an answer because the answer is now cached albeit a bit too late for the original query.

12) Explain Physical Address and IP Address.

A physical address is a binary number in the form of logical high and low states on an address bus that corresponds to a particular cell of primary storage(also called main memory), or to a particular register in a memory-mapped I/O(input/output) device.

In a computer with virtual memory that incorporates memory management, the physical address differs from the virtual address so a memory management unit (MMU) translates the virtual address into a physical address, enabling each running process to "think" that it has all the primary storage to itself.

An Internet Protocol address (IP address) is a logical numeric address that is assigned to every single computer, printer, switch, router or any other device that is part of a TCP/IP-based network.

The IP address is the core component on which the networking architecture is built; no network exists without it. An IP address is a logical address that is used to uniquely identify every node in the network. Because IP addresses are logical, they can change. They are similar to addresses in a town or city because the IP address gives the network node an address so that it can communicate with other nodes or networks, just like mail is sent to friends and relatives.

The numerals in an IP address are divided into 2 parts:

• The network part specifies which networks this address belongs to and
• The host part further pinpoints the exact location

13) What are differences between Physical Address and IP Address.

The IP address is an address bound to the network device, i.e., computer, via software. In a Windows-powered computer, the Windows operating system allows the user to configure the IP address the specific workstation will have. This IP address is used to allow all network aware programs, i.e., Internet Explorer, Netscape, Outlook, etc. to use this address when communicating with other hosts. The seventh layer in the OSI model has the IP addresses.

The physical address is a hardware address, which means it is unique to the network card installed on your PC. No two devices on a local network should ever have the same physical address. In the unlikely event this occurs, the two devices will have major communication problems. During the manufacturing process, the vendor "burns" a specific physical address into each network card's ROM. When the serial numbers have all been used, they start from the beginning, as it's very unlikely anyone would buy two network cards from the same vendor, and they will contain the same physical address.