Subnetting

ip subnet

Part 6:

Determining Broadcast Addresses And Valid IP Address Ranges For A Given Subnet

No matter the format, you can use your knowledge of binary math to solve this question. You will convert the subnet address into binary, and determine the range of valid addresses as well as the broadcast address at the same time.  Let’s examine how to best answer the “range of valid IP address” question first, and then you’ll see how to quickly determine the broadcast address as well.

address

The question: “What is the range of valid IP addresses for the subnet 210.210.210.0 /25?” As with previous sections, you will use your binary math skills to convert the subnet address and subnet mask into binary. This will allow you to quickly spot the host bits, which are key to answering this question and the broadcast address question. The host bits are those bits set to “0” in the subnet mask.

Octet 1            Octet 2            Octet 3            Octet 4

Subnet Address

210.210.210.0                         11010010        11010010        11010010        00000000

Subnet Mask

255.255.255.128(/25)              11111111        11111111        11111111        10000000

There are three basic rules to remember when determining the subnet address, broadcast address, and range of valid addresses once you’ve identified the host bits as shown above:

1. The address with all 0s for host bits is the subnet address, also referred to as the “all-zeroes” address. This is not a valid host address.

2. The address with all 1s for host bits is the broadcast address, also referred to as the “all-ones” address. This is not a valid host address.

3. All addresses between the all-zeroes and all-ones addresses are valid host addresses, unless the question specifically states otherwise.

You can quickly see that the “all-zeroes” address is 210.210.210.0.  What will the value be if those host bits are set to all 1s? Use your knowledge of binary math to determine this!  The “all-ones” address is 210.210.210.127. If you had trouble making that conversion, review Section Two, “Converting Binary To Decimal”.  This conversion actually answers two different questions. This quick conversion shows you what the range of valid IP addresses is, and also gives you the broadcast, or “all-ones”, address. The second example question, “What is the broadcast address for the subnet 210.210.210.0 /25?”, is answered by using the same method.

Let’s look at another set of examples:

“What is the range of valid IP addresses in the subnet 150.10.64.0 /18?”

“What is the broadcast address of the subnet 150.10.64.0 /18?”

Octet 1            Octet 2            Octet 3            Octet 4

Subnet Address

150.10.64.0                 11010010        00001010        01000000        00000000

Subnet Mask

255.255.192.0 (/18)     11111111        11111111        11000000        00000000

If all the host bits are “zeroes”, the address is 150.10.64.0, the subnet address itself. This is not a valid host address.  If all the host bits are “ones”, the address is 150.10.127.255. That is the broadcast address for this subnet.  All bits between the subnet address and broadcast address are considered valid addresses. This gives you the range 150.10.64.1 – 150.10.127.254. 

Again, the method used to arrive at the range of valid IP addresses is the same as that used to discover the broadcast address of a given subnet.  Let’s take a look at the other question type from the first part of this section:

“Which of the following IP addresses are found on the same subnet as the IP address 210.210.210.130 /25?”

“Which of the following IP addresses are not found on the same subnet as the IP address 210.210.210.130 /25?”

subnet

For some subnetting questions, you’re going to have to determine more than one factor before you can give the correct answer. This question looks simple enough on the surface, but to answer this question type correctly, you must determine two things:

1. On what subnet can this address be found?

2. What is the range of valid IP addresses for this subnet?

In the example, you must first determine the subnet address of the IP address in question, which you learned how to do in Section Six:

Octet 1            Octet 2            Octet 3            Octet 4

IP Address

210.210.210.130                     11010010        11010010        11010010        10000010

Subnet Mask

255.255.255.128 (/25)             11111111        11111111        11111111        10000000

Boolean AND Result              11010010        11010010        11010010        10000000

Converting The Boolean AND Into Dotted Decimal:

128      64        32        16        8          4          2          1          Total

First Octet                   1          1          0          1          0          0          1          0          210

Second Octet              1          1          0          1          0          0          1          0          210

Third Octet                 1          1          0          1          0          0          1          0          210

Fourth Octet               1          0          0          0          0          0          0          0          128

If all the host bits are 0, the all-zeroes address is 210.210.210.128. If all the host bits are 1, the all-ones address is 210.210.210.255. All addresses between these two are valid. You would now look at the different IP addresses presented by the question and then determine which ones fall in the range 210.210.210.129 – 210.210.210.254 (or which ones don’t, if that’s what the question asks for.)

At first, it seems like a lot of work, but as with all other binary math operations, once you practice it, it will become second nature. This question seems longer to solve because it is, since two operations are needed to solve it. Since you’re well-versed in the fundamentals of binary math, this question will present no problems for you.

“Determining Broadcast Addresses” and “Determining Valid IP Address Ranges” Questions What is the valid IP address range for the subnet 222.23.48.64 /26?

Determining The All-Zeroes and All-Ones Subnet Addresses

Octet 1            Octet 2            Octet 3            Octet 4

Subnet Address

222.23.48.64               11011110        00010111        00110000        01000000

Subnet Mask

255.255.255.192         11111111        11111111        11111111        11000000

Identify The Host Bits                                                                            000000

All-Zeroes (Subnet) Address: 222.23.48.64 /26                                                                          

All-Ones (Broadcast) Address: 222.23.48.127 /26                                                                    

Valid IP address range: 222.23.48.65 – 222.23.48.126

EXAMPLE:  What is the valid IP address range for the subnet 140.10.10.0 /23?

Determining The All-Zeroes and All-Ones Subnet Addresses

Octet 1            Octet 2            Octet 3            Octet 4

Subnet Address

140.10.10.0                 10001100        00001010        00001010        00000000

Subnet Mask

255.255.254.0             11111111        11111111        11111110        00000000

All-Zeroes (Subnet) Address: 140.10.10.0 /23                                                                            

All-Ones (Broadcast) Address: 140.10.11.255 /23                                                                    

Valid IP address range: 140.10.10.1 – 140.10.11.254

See also:  Part 1, Part 2, Part 3, Part 4, Part 5, Part 6

Works Cited

Bryant, C. (2007). The Ultimate CCNA Study Package – ICND 1 And 2: Valid Hosts. In C. Bryant, The Bryant Advantage (p. 6).

Lammle, T. (2007). CCNA Cisco Certified Network Associate Study Guide. Indianapolis: Wiley Publishing, Inc.

Odom, W. (2012). Official Cert Guide ICND1 640-822. Indianapolis, IN: Cisco Press.

Odom, W. (2011). Official Cert Guide ICND2 640-816. Indianapolis, IN: Cisco Press.

Subnetting

Subnet-Mask2

Part 5:

Determining the Subnet number of a given IP Address

An example of a “determine the subnet number” question:

“What subnet is the address 200.17.49.200 /23 a member of?” or “On what subnet can the address 200.17.49.200 /23 be found?”

Subnet-Mask

This is one of those types of questions that often trips up CCNA candidates. It is because many don’t understand the Boolean AND operation, which is the only way you can properly answer this question. This segment will review the Boolean AND operation and show you how to use it in order to solve this question. As with anything else within this subject matter, once you are used to using the Boolean AND operation, everything else (of similar subject) tends to be easier.

The Boolean AND is, simply put, a bit-by-bit comparison of the IP address and a subnet mask. In this case, the Boolean AND will reveal the subnet upon which this IP address esists.  Your knowledge of binary math will be, and always is, key in you answering this question type as well, since the address and mask must be broken down into binary in order to perform the Boolean AND. 

You must use the skills of “Converting Dotted Decimal To Binary”, to convert the IP address to binary:

128      64       32       16        8         4          2          1

1st Octet: 200                         1          1          0          0          1          0          0          0

2nd Octet: 17             0          0          0          1          0          0          0         1

3rd Octet: 49               0          0          1          1          0          0          0         1

4th Octet: 200                         1          1          0          0          1          0          0         0

The IP address, in binary, is 11001000 00010001 00110001 11001000.  Your knowledge of prefix notation tells you that a subnet mask of /23 is 11111111 11111111 11111110 00000000. (The first 23 bits are ones).  Now that the IP address and subnet mask have been converted to binary, the subnet on which the IP address resides can be found by performing a Boolean AND. Remember, a Boolean AND is simply a bit by-bit comparison of the address and mask.

Bit 1    Bit 2    Bit 3    Bit 4    Bit 5    Bit 6    Bit 7    Bit 8

IP Address      1          1          0          0          1         0         0          0                                       Octet 1

Subnet Mask   1          1          1          1          1         1         1          1                                       Octet 1      

Note that where a bit in the same position is “1” in both the IP address and subnet mask, the Boolean AND result is also “1”. Any other combination results in the Boolean AND resulting in “0”.  And now that we’ve looked at the Boolean AND being run on a single octet, let’s run it on the entire IP address and subnet mask. This is the chart you should use on exam day to answer this question type:

Octet 1                       Octet 2            Octet 3            Octet 4

IP Address                  11001000        00010001        00110001        11001000                      200.17.49.200

Subnet Mask               11111111        11111111        11111110        00000000                      255.255.254.0 (/23)

Boolean AND            11001000        00010001        00110000        00000000                      Result

Subnet-Mask1

Once the Boolean AND result is achieved, it has to be converted into dotted decimal. Using your knowledge of converting binary to dotted decimal, you see that the IP address you were given is found on the 200.17.48.0 /23 subnet.

128      64        32        16        8          4          2          1

First Octet       1          1          0          0         1          0          0          0          200

Second Octet 0          0          0          1          0          0          0          1          17

Third Octet     0          0          1          1          0          0          0          0          48

Fourth Octet   0          0          0          0          0          0          0          0          0

You can now see where the skills you learned in earlier sections come into play in the more complex subnetting questions. When you master the fundamentals of binary math, as you have, you can answer any question Cisco gives you.

See also:  Part 1, Part 2, Part 3, Part 4, Part 5

 

Works Cited

Bryant, C. (2007). The Ultimate CCNA Study Package – ICND 1 And 2: Valid Hosts. In C. Bryant, The Bryant Advantage (p. 6).

Lammle, T. (2007). CCNA Cisco Certified Network Associate Study Guide. Indianapolis: Wiley Publishing, Inc.

Odom, W. (2012). Official Cert Guide ICND1 640-822. Indianapolis, IN: Cisco Press.

Odom, W. (2011). Official Cert Guide ICND2 640-816. Indianapolis, IN: Cisco Press.

Subnetting

ip-classes-5

Part 4:

DETERMINING THE VALID NUMBER OF HOSTS

These are examples of a “number of valid hosts” question:

“How many valid hosts exist on the 150.10.0.0 /20 subnet?”

“How many valid hosts exist on the 150.10.0.0 255.255.240.0 subnet ?”

A /20 mask indicates that the first 20 bits are set to “1”, which in expressed in dotted decimal as 255.255.240.0.  The way to determine the number of valid hosts is much like the previous section in determining the number of valid subnets, in that you must first determine how many subnet bits are present. The difference is that when determining the number of valid hosts, it is the number of host bits you’re concerned with, rather than the number of subnet bits.

Once the number of host bits is determined, use this formula to arrive at the number of valid hosts:

The number of valid hosts = (2 raised to the power of the number of host bits) – 2

In the example question, there is a Class B network, with a default mask of /16. The subnet mask is /20, indicating there are four subnet bits. Here’s where the difference comes in. There are 16 network bits and 4 subnet bits. That’s 20 out of 32 bits, meaning that there are 12 host bits. 2 to the 12th power is 4096; subtract 2 from that, and there are 4094 valid host addresses.

Illustrating the masks in binary illustrates where the host bits lie:

Default Network Mask           1st Octet          2nd Octet          3rd Octet          4th Octet

255.255.0.0                             11111111        11111111        00000000        00000000

Subnet Mask

255.255.240.0                         11111111        11111111       11110000        00000000

Remember, previously mentioned, that the bits that are set to “0” in the default mask and “1” in the subnet mask are the subnet bits?  The bits that are set to “0” in both masks are the host bits. That’s the value you need to have for the formula to determine the number of valid hosts.  Note that in both the formula for determining the number of valid hosts and valid subnets, 2 is subtracted at the end. What two hosts are being subtracted? The “all-zeroes” and “all-ones” host addresses, which are considered unusable.

How many valid host addresses exist in the 220.11.10.0 /26 subnet?

This is a Class C network, with a default mask of /24. The subnet mask is /26, indicating that there are 2 subnet bits. With 24 network bits and 2 subnet bits, that leaves 6 host bits:

Default Network Mask           1st Octet          2nd Octet          3rd Octet          4th Octet

255.255.0.0                             11111111        11111111        00000000        00000000

Subnet Mask

255.255.240.0                         11111111        11111111       11110000        00000000

(Boldfaced 11 bits are representative of the Host bits.)  2 to the 11th (211 ) power equals 2048; subtract 2 from that and 2046 valid host addresses remain.

 

See also:  Part 1, Part 2, Part 3, Part 4

Works Cited

Bryant, C. (2007). The Ultimate CCNA Study Package – ICND 1 And 2: Valid Hosts. In C. Bryant, The Bryant Advantage (p. 6).

Lammle, T. (2007). CCNA Cisco Certified Network Associate Study Guide. Indianapolis: Wiley Publishing, Inc.

Odom, W. (2012). Official Cert Guide ICND1 640-822. Indianapolis, IN: Cisco Press.

Odom, W. (2011). Official Cert Guide ICND2 640-816. Indianapolis, IN: Cisco Press.

 

 

Subnetting

ipv4-subnetting-sm

Part 3:

DETERMINING THE VALID NUMBER OF SUBNETS

1.  How many valid subnets exist on the 192.168.1.100/27 network?

OR,

2.  How many valid subnets exist on the 192.168.1.100 255.255.255.224 network?

The /27 in question one is called prefix notation and the 255.255.255.224 designation is the dotted decimal mask.  Both questions are the same, just written differently.

The /27 is an indicator as to how many ones (1s) are at the beginning of this network’s mask.  255.255.255.224, or /27, converted to decimal is 11111111 111111111 11111111 11100000.  One nice little tid-bit of information is that the number of network bits never changes.  Subnetting always borrows bits from the host bits, ALWAYS!

1st Octet 2nd Octet 3rd Octet 4th Octet
Default Classs C Network 11111111 11111111 11111111              00000000
This IP’s Subnet Mask 11111111 11111111 11111111 11100000

So, the question remains, how many valid subnets exist on the 192.168.1.100/27 network?

By comparison we can determine that a class C network has 24 network bits and therefore possess only 8 host bits.  On this network, we borrowed (remember) 3 bits from the host bits for our subnet.  [The number of valid subnets = 2x; where x is the number of set subnet bits (1’s)]  Therefore, 23 = 2 x 2 x 2 = 8, which is the number of valid subnets.

See also:  Part 1, Part 2, Part 3, Part 4

Works Cited

Lammle, T. (2007). CCNA Cisco Certified Network Associate Study Guide. Indianapolis: Wiley Publishing, Inc.

Odom, W. (2012). Official Cert Guide ICND1 640-822. Indianapolis, IN: Cisco Press.

Odom, W. (2011). Official Cert Guide ICND2 640-816. Indianapolis, IN: Cisco Press.

Subnetting

subnet-adv

Part 2

As mentioned prior to this, one of the key elements to subnetting is Binary, Octal, Decimal, and Hexadecimal conversion.  While I do like the Sybex Study Guide for CCNA by Todd Lammle, I do believe with respect to the subnetting aspect there are other better resources.  For example the Bryant Advantage system, the ICND 1 & 2 Study Guides for CCENT & CCNA by Wendell Odom (especially the Appendicies), and Test King (http://www.testking.com/).  I am certain that there are others, but I have come to an appreciation and an understanding after these; of course, the CCNA Bootcamp was an extreme help as well!

One trick that has stuck with me is this:  Key on the first several digits to the first segment of the IP Address (i.e., 10.0.0.1, 172.10.120.1, 192.168.1.100, 224.10.10.1, & 240.0.0.100)

10   = 00001010 = A first four digits 0000-0111

172 = 10101100 = B first two digits 1000-1011

192 = 11000000 = C first two digits 1100-1101

224 = 11100000 = D first four digits 1110

240 = 11110000 = E first four digits 1111

subnet3

This is a quick assessment trick which can cut off some time while determining to what subnet class the address is a part of.  Of course, it is just as easy to memorize the entire spectrum.

Here are some IPv4 Subnet Cheat Sheets that you may find helpful: http://packetlife.net/library/cheat-sheets/, http://www.subnetonline.com/pages/references/ipv4-cheat-sheet.php, http://www.quest4.org/ccna/subnet_cheat_sheet.htm, http://www.subnetting-secrets.com/subnetting-cheat-sheet.html, http://search.yahoo.com/search?p=subnet+cheat+sheets&ei=UTF-8&fr=moz35, http://search.yahoo.com/r/_ylt=A0oGdVfl9CxRNUgA3GBXNyoA;_ylu=X3oDMTE1ZWJyN2IxBHNlYwNzcgRwb3MDMTcEY29sbwNzazEEdnRpZANRSTAyNl8xMzQ-/SIG=143bk83dn/EXP=1361929573/**https%3a//learningnetwork.cisco.com/servlet/JiveServlet/download/102742-14596/TCPIP-Subnetting%2520cheatsheet.PDF, http://subnetmask.info/

Look through some of these cheat sheets, you may pick something up from them; on the other hand, you may already know it – to which I say GREAT!

homelab

Some questions you need for determining subnets, hosts, etc.:

  1. How many subnets?  2= number of subnets (x is the subnetted masked bits or 1’s; 11000000 2 ones = 22 = 4 subnets)
  2. How many hosts per subnet?  2y-2 where y is the number of unmasked bits or 0’s; 11000000 = 26-2 = 64-2 = 62 hosts.
  3. What are the valid subnets?  256 – subnet mask = block size or increment; 256 – 192 = block size of 64.
  4. What is the broadcast address for each subnet?  Our broadcast address is the last address prior to the next subnet; i.e., our block size is 64 then our starting addresses are 0, 64, 128, 192…therefore, the broadcast address would be the on prior to the last which is 63, 127, 191, & 255.
  5. What are the valid hosts? The valid hosts are all of the addresses in between the subnet and the broadcast addresses; i.e., with the block size of 64 then our valid hosts are: 1-62, 65-126, 129-190, & 193-254.

See also:  Part 1, Part 2, Part 3, Part 4

Works Cited

Lammle, T. (2007). CCNA Cisco Certified Network Associate Study Guide. Indianapolis: Wiley Publishing, Inc.

Odom, W. (2012). Official Cert Guide ICND1 640-822. Indianapolis, IN: Cisco Press.

Odom, W. (2011). Official Cert Guide ICND2 640-816. Indianapolis, IN: Cisco Press.

Subnetting

What-Is-Subnetting

Part 1

I have been debating how to approach this subject of Subnetting, there is not much to say other than it really sucks to learn.  But once you learn it, it just gets easier and more understandable.  Unfortunately, every new subject you learn, with which you have no familiarity with is going to be absolute hell unless you can pick it up quickly.  When I started learning subnetting and then relearned and re-familiarized myself, I have to admit it was tough and I just was not getting it.  But the information super highway, Youtube, and many other tid-bits of information out there in the world can make all the difference in the world.  You might not understand what one method teaches there is always another method that may take hold in your brain.  So, take heart…it may be a roller coaster, but it is our roller coaster.  Just keep looking for the method that makes sense to you, it is out there.  Below are some references, which are not all inclusive as there are a multitude more references for your viewing pleasure.

Youtube, as you probably already know, is an underutilized resource and valuablesubnet-study tool in your arsenal of learning.

Look through these references, videos (you won’t need to view all, just until you are comfortable), and the other web-sites.  To really prepare yourself for the test (CCENT or CCNA) use the IPv4 subnetting – random question generator v1.6  as it will generate random IPv4 subnetting questions for you to practice on (makes it easy for you!)

headerfistAlso, keep in mind that you will be tested on IPv4 for subnetting, so that is what we will be using.  IPv6 is being deployed and you may see it on the test for CCNA, but more likely than not you will not receive test questions on the subnetting of IPv6.

Until we meet again in Part 2…

See also:  Part 1, Part 2, Part 3, Part 4

References:

http://www.vaughns-1-pagers.com/computer/powers-of-2.htm

http://infocenter.guardiandigital.com/manuals/IDDS/node9.html

http://whatismyipaddress.com/cidr

http://wiki.samat.org/CheatSheet/IPv4CIDRNotation

http://www.subnet-calculator.com/cidr.php

VIDEOS:

https://www.youtube.com/results?search_query=boolean+algebra+tutorial&oq=boolean+algebra+tutorial&gs_l=youtube.12..0.2938.2938.0.4782.1.1.0.0.0.0.82.82.1.1.0…0.0…1ac.2.IyvT0psNQTI

https://www.youtube.com/results?search_query=subnetting+made+easy&oq=subnetting+made+easy&gs_l=youtube.12..0l8.5848.5848.0.8952.1.1.0.0.0.0.56.56.1.1.0…0.0…1ac.2.HQ7nSkrQ9tk

https://www.youtube.com/results?search_query=subnetting+tutorial+ccna&oq=subnetting&gs_l=youtube.1.4.0l10.25943.25943.0.36475.1.1.0.0.0.0.56.56.1.1.0…0.0…1ac.1.j6HYrKoahwE

https://www.youtube.com/results?search_query=subnetting&oq=subnetting&gs_l=youtube.3..0l10.43020.43020.0.44157.1.1.0.0.0.0.53.53.1.1.0…0.0…1ac.1.wbNxlIPMxB4

http://video.search.yahoo.com/search/video;_ylt=A0S00MtSWBlRFUEAyxb7w8QF;_ylu=X3oDMTBrMWQyNXBmBHNlYwNzZWFyY2gEdnRpZANWMTM2?p=ip%20subnetting&ei=utf-8&fr=moz35&fr2=sg-gac&sado=1

Other Web-Sites:

http://mrwhatis.com/subnetting-box-method.html

http://www.subnetting-secrets.com/easy_way_to_subnet.html

http://orbit-computer-solutions.com/VLSM.php

http://www.gtcc-it.net/billings/VLSM.htm

http://www.subnetting-secrets.com/vlsm.html

http://www.subnetting-secrets.com/easy_way_to_subnet.html

IPv4 subnetting – random question generator v1.6  http://subnetting.org/

Welcome to TCP/IP Part 6

To further our use and understanding of our introduction of TCP/IP, we will continue on with some necessary protocols.  More importantly, Address Resolution Protocols.

Address Resolution Protocol (ARP) is the protocol which is used to find the address host from a known IP address.  ARP sends out a broadcast to the network asking for the machine with the specific IP address.  In essence, ARP translates the IP address into a hardware address.

ARP

Reverse Address Resolution Protocol (RARP) is the protocol used to discover the identity of the IP address for diskless machines and essentially requests for the IP address of itself through other equipment by sending out its MAC address.  Recall that DHCP is the protocol used to determine who is assigned what IP address (Welcome to TCP/IP Part 2).  On a side note, most home networks set their routers up to assign the IP addresses to their equipment throughout their home.

RARP

Proxy Address Resolution Protocol (PARP) is the protocol used to help machines on a subnet reach remote subnets without configuring routing or a default gateway.  The detriment to using Proxy ARP is that it will severely increase the traffic on your network.  And you thought a slow network was bad?  Most medium to large businesses can handle the traffic, home networks not so easily.  It is configured on all Cisco routers by default.

PrARP

This is what would be shown in the ARP cache memory of Host A.

IP Address

MAC Address

172.16.20.200 00-00-0c-94-36-ab
172.16.20.100 00-00-0c-94-36-ab
172.16.10.99 00-00-0c-94-36-ab
172.16.10.200 00-00-0c-94-36-bb

Next week, we will discuss IP Addressing, until then…

See also:  Part 1, Part 2, Part 3, Part 4, Part 5

Works Cited

Cisco Systems, Inc. (2008, January 28). Document ID: 13718. Retrieved January 08, 2013, from Cisco: http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a0080094adb.shtml

Lammle, T. (2007). CCNA Cisco Certified Network Associate Study Guide. Indianapolis: Wiley Publishing, Inc.

Odom, W. (2012). Official Cert Guide ICND1 640-822. Indianapolis, IN: Cisco Press.

Odom, W. (2011). Official Cert Guide ICND2 640-816. Indianapolis, IN: Cisco Press.

Welcome to TCP/IP Part 5

Internet Control Message Protocol (ICMP) works at the Network Layer (Layer 3) and is used by Internet Protocol for several different purposes. ICMP is a managing protocol and messaging service provider for Internet Protocol.  The ICMP messages are carried as IP datagrams that afford a host’s capability to discover routes to gateways.  ICMP packets can provide hosts with information about network problems and are encapsulated within IP datagrams.

Destination Unreachable is where a router cannot send an IP datagram any further to its intended destination, it therefore uses ICMP to send a message back to the sender advising it that the destination Host is unreachable.

When Host A sends a packet whose destination is Host B, the Lab_B router is what sends and ICMP destination unreachable message back to the sending device, or Host A.

 

Buffer Full is the message sent out to the sending Host by using ICMP and will continue to do so until the congestion has subsided.

 

Hops is the number of routers and IP datagram is permitted to travel, or pass through, if it reaches its limit before arriving at its destination Host the last router to receive that datagram then deletes or drops it.  That router will then use ICMP to send a message back to the sending Host of the loss of the datagram due to the maximum number of hops.

 

Ping (Packet Internet Groper) uses ICMP echo requests and reply messages to check both the physical and logical connectivity of a Host to a network, or internetwork. 

 

Traceroute uses ICMP time-outs and is used to discover the path a packet as it travels through an internetwork.

 

Perhaps it would be good to see the routing of a packet, please click on the URL below the ICMP packet figure.

 

http://images.search.yahoo.com/images/view;_ylt=A0PDoV4r9o9QtGwAXYyJzbkF;_ylu=X3oDMTBlMTQ4cGxyBHNlYwNzcgRzbGsDaW1n?back=http%3A%2F%2Fimages.search.yahoo.com%2Fsearch%2Fimages%3Fp%3Dicmp%2Berror%2Bmessage%26n%3D30%26ei%3Dutf-8%26y%3DSearch%26fr%3Dmoz35%26tab%3Dorganic%26ri%3D16&w=1280&h=720&imgurl=1.bp.blogspot.com%2F-Iixky_-4r8w%2FTc6L_ZOHO7I%2FAAAAAAAAAKc%2FALnRDFPUTxg%2Fs1600%2FICMP%2BPacket.gif&rurl=http%3A%2F%2Frajeshkannab.hubpages.com%2Fhub%2FWhat-a-router-does&size=899.7+KB&name=…+then+routers+drop+the+packet+and+generates+an+%3Cb%3Eicmp+error+message%3C%2Fb%3E&p=icmp+error+message&oid=e695ad36564f15671e9409c3b9ebcf84&fr2=&fr=moz35&tt=…%2Bthen%2Brouters%2Bdrop%2Bthe%2Bpacket%2Band%2Bgenerates%2Ban%2B%253Cb%253Eicmp%2Berror%2Bmessage%253C%252Fb%253E&b=0&ni=120&no=16&ts=&tab=organic&sigr=11n5mar3l&sigb=13jlmdmmd&sigi=12ojn1qo7&.crumb=EMay3CSV8Mf

ICMP in Action shows how the dropped packet will be handled.  Server 1 (10.1.2.2) Telnets to a Host (10.1.1.5) using the DOS prompt.  The packet will be sent to the default gateway, since the Server (1) has no knowledge as to where 10.1.1.0 is located.  The default gateway will drop the packet because there is no listing of 10.1.1.0 in the routing table of the router.  After dropping the packet, the router will send an ICMP packet to Server 1 stating that the destination is unreachable.

See also: Part 1, Part 2, Part 3, Part 4, Part 5

 

Works Cited

Lammle, T. (2007). CCNA Cisco Certified Network Associate Study Guide. Indianapolis: Wiley Publishing, Inc.

Odom, W. (2012). Official Cert Guide ICND1 640-822. Indianapolis, IN: Cisco Press.

Odom, W. (2011). Official Cert Guide ICND2 640-816. Indianapolis, IN: Cisco Press.

 

 

Welcome to TCP/IP Part 4

Key Concepts of Host-to-Host Protocols have been reviewed in our last part, but like me some of you may be more visually oriented, so here you are:

…and just one more for you…

Now, Port Numbers are of great importance for both understanding and troubleshooting purposes.  You can find lists of Port Numbers for various applications, but for the CCENT/CCNA study purposes what follows should be sufficient.

Below is a rather extensive listing, but not all-inclusive, for the TCP/UDP Port Numbers.  It will be helpful in the big picture, but the above picture views will be more than sufficient for anyone testing out.

port / protocol service name common UNIX daemon(s) additional remarks
20/tcp and 21/tcp ftp (file transfer protocol) data and login control in.ftpd,wu.ftpd,proftpd; launched by inetd obsolete:insecure, because unencrypted and difficult to harden service, please use sshd and scp or sftp instead (see below)
22/tcp ssh (Secure SHell) sshd secure, because fully encrypted remote login (ssh) and copy (scp and sftp) service, please use exclusively this full substitute instead of the obsolete ftp, telnet, rlogin, rsh, rcp and so on!
23/tcp telnet (remote login) in.telnetd, launched by inetd obsolete: unencrypted login, use sshd and ssh instead, see above
25/tcp smtp (simple mail transfer protocol) sendmail, postfix, qmail, etc. standard mail protocol since 30 years, only way to communicate world wide with messages without http measures, for your privacy you need to encrypt mails preferably with the free PGP (pretty good privacy)
53/udp and 53/tcp DNS (domain name system) bind (Berkeley Internet Name Domain) the name service of the Internet, used by http, smtp and all others to resolve symbolic names into the IP layer addresses, name resolution is done via udp, zone transfers between several name servers via tcp
80/tcp http (Hyper Text Transfer Protocol) = www (World Wide Web) httpd (= apache, A PAtCHy [web] sErver) the Internet/web service, unencrypted port (see below, 443, for encrypted counterpart) for standard data transfer from web servers to user agents (browsers, robots, download tools)
88/tcp kerberos krshd high security special purpose protocol with ticket system and so on
110/tcp pop3 (Post Office Protocol version 3) popper, launched by inetd post retrieval service of storing mail servers with encryption possibilities
111/udp (sun)rpc (remote procedure call) rpc.statd, rpc.rusersd,rpc.walld insecure remote calls of special information services
119/tcp nntp (Network News Transfer Protocol) leafnode the internet news server query service
123/udp ntp (Network Time Protocol) (x)ntpd modern world wide time service for synchronisation with nuclear clock driven time standard
137/udp netbios-ns (NETBIOS Name Service) nmbd special name service for a still too widespread proprietary OS and its SMB (Server Message Block) system, needed in union with the following service
139/tcp netbios-ssn (NETBIOS Session Service Network) smbd (Samba daemon) special session service for that proprietary OS and its SMB (Server Message Block) system, works together with immediately above service
143/tcp imap2 (Internet Message Access Protocol version 2) imapd (Interactive Mail Access Protocol Daemon), launched by inetd rather insecure and therefore only locally suitable mail retrieval service, for non-local purposes prefer pop3 (see above)
161/tcp snmp (Simple Network Management Protocol) snmpd base of communication between very different technical units (not only computers), they have to share the network capability and these protocol rules only: CAUTION: very insecure (no limiting of allowed requesting IP addresses possible)
194/tcp irc (Internet Relay Chat) ircd the Internet chat service
220/tcp imap3 (Interactive Mail Access Protocol version 3) imapd modern mail retrieval service, successor of imap2 (see above), but still pop3 may the better alternative (see above too)
389/tcp ldap (Lightweight Directory Access Protocol) ldapd network distributed, domain organized directory service, connection part, see also immediately below
389/udp ldap (Lightweight Directory Access Protocol) slapd (Standalone Lightweight Access Protocol Daemon network distributed, domain organized directory service, listener/contoller part, see also immediately above
443/tcp https (HyperText Transfer Protocol Secure) httpd (= apache) encrypted (via TLS/SSL) counterpart to above http/80 entry, the only acceptable way, to do online credit card transactions
514/udp system log listener syslogd always active to log other hosts informations, because otherwise the daemon won’t start
515/tcp print spooler lpd (Line Printer Daemon) network printer queue
554/tcp rtsp (Real Time Stream Protocol) rsvpd (Resource reSerVations Protocol Daemon) used by Real Media for video and audio streaming
631/tcp ipp (Internet Printing Protocol) cupsd — CUPS (Common Unix Printing System) Daemon unencrypted port for (local) printer access via browser and CUPS client
744/udp flexlm (FLEXible License Manager) lmgrd (License ManaGeR Daemon) network bound license evaluation system
901/tcp swat (Samba Web Administration Tool) swat, launched by inetd browser/web bound Samba administration (see above, 137/nmbd and 139/smbd), use with care: it’s not encrypted without additional measures
993/tcp imaps (Interactive Mail Access Protocol Secure version 4) imapd, launched by inetd TLS/SSL encrypted mail retrieval system (see also imap above)
994/tcp ircs (Internet Relay Chat Secure) ircd the Internet chat system TLS/SSL encrypted, see also irc above
995/tcp pop3s (Post Office Protocol Secure version 3) popper, launched by inetd TLS/SSL encrypted mail retrieval system (see also pop3 above)
2049/tcp NFS (Network File System by Sun) nfsd, rpc.nfsd, needs (sun)rpc and portmap too network sharing of filesystems, only suitable for local networks
2049/udp NFS (Network File System by Sun) rpc.mountd needs (sun)rpc and portmap too network sharing of filesystems, only suitable for local networks
2401/tcp cvspserver (Concurrent Version System Password server) cvs, launched by inetd (alternatively by sshd, see above) RCS (revision control system) based network version control, suitable even for Internet cooperation, but than usage via ssh (see above) is recommended, because this pserver protocol does only a not really secure scrambling of passwords (only suitable for anonymous checkout otherwise)
6000/tcp (–6063/tcp) x11 X (X window system server) standard GUI base server of the X/Open Group, the ports above 6000 up to 6063 are addressed via display (variable: upper case) setting to 1, 2 and so on, instead of 0, for the ports 6001, 6002 and so on instead of 6000 (display number part 1 = port offset)
8080/tcp http-alt (alternative http) httpd (= apache) see http above: usually privately=non-public used http port

Important TCP/UDP Port Numbers

Port 21 –> TCP –> FTP (File Transfer Protocol)
Port 22 –> TCP/UDP –> SSH (ssh,scp copy or sftp)
Port 23 –> TCP/UDP –> Telnet
Port 25 –> TCP/UDP –> SMTP (for sending outgoing emails)
Port 43 –> TCP –> WHOIS function
Port 53 –> TCP/UDP –> DNS Server (DNS lookup uses UDP and Zone transfers use TCP)
Port 70 –> TCP –> Gopher Protocol
Port 79 –> TCP –> Finger protocol
Port 110 –> TCP –> POP3 (for receiving email)
Port 119 –> TCP –> NNTP (Network News Transfer Protocol)
Port 143 –> TCP/UDP –> IMAP4 Protocol (for email service)
Port 194 –> TCP –> IRC
Port 389 –> TCP/UDP –> LDAP (light weight directory access)
Port 443 –> TCP –> Secure HTTP over SSL (https)
Port 465 –> TCP –> Secure SMTP (email) using SSL
Port 990 –> TCP/UDP –> Secure FTP using SSL
Port 993 –> TCP –> Secure IMAP protocol over SSL (for emails)
Port 1433 –> TCP/UDP –> Microsoft SQL server port
Port 2082 –> TCP –> CPanel default port
Port 2083 –> TCP –> CPanel over SSL
Port 2086 –> TCP –> CPanel Webhost Manager (default)
Port 2087 –> TCP –> CPanel Webhost Manager (with https)
Port 2095 –> TCP –> CPanel Webmail
Port 2096 –> TCP –> Cpanel secure webmail over SSL
Port 2222 –> TCP –> DirectAdmin Server Control Panel
Port 3306 –> TCP/UDP –> MySQL Database Server
Port 4643 –> TCP –> Virtuosso Power Panel
Port 5432 –> TCP –> PostgreSQL Database Server
Port 8080 –> TCP –> HTTP port (alternative one for port 80)
Port 8087 –> TCP –> Plesk Control Panel Port (default)
Port 8443 –> TCP –> Plesk Server Control Panel over SSL
Port 9999 –> TCP –> Urchin Web Analytics
Port 10000 –> TCP –> Webmin Server Control Panel
Port 19638 –> TCP –> Ensim Server Control Panel

Each and every listing of Port Numbers is in-fact, an important list to someone in some fashion or form.  The reason being is that each list has some meaning for all of the applications that someone is dealing with in the specific system infrastructure that they have to work with.  So, do not limit yourself by having just one list at your fingertips.  It will be helpful to have many and use your search engine to your benefit!

See also: Part 1, Part 2, Part 3, Part 4

Works Cited

Lammle, T. (2007). CCNA Cisco Certified Network Associate Study Guide. Indianapolis: Wiley Publishing, Inc.

Odom, W. (2012). Official Cert Guide ICND1 640-822. Indianapolis, IN: Cisco Press.

Odom, W. (2011). Official Cert Guide ICND2 640-816. Indianapolis, IN: Cisco Press.

http://www.lb.shuttle.de/apastron/ports.htm

http://corpocrat.com/2009/03/10/important-tcpudp-port-numbers/

Welcome to TCP/IP Part 3

Host-to-Host Layer Protocols essentially shields the upper layer applications from the complex inner workings of the network.  This layer takes the data from the application layer along with any specific instructions and prepares the information to be sent.  There are two protocols at this layer:  Transmission Control Protocol (TCP) and User Datagram Protocol (UDP).

Transmission Control Protocol (TCP) is a connection-oriented protocol that takes large blocks of data from an application and breaks it into segments.  Each segment is numbered and sequenced so that the destination TCP stack can reorder and properly sequence the information as was intended by the application layer.  After the segments are sent, TCP (on the sending side) awaits acknowledgement by the receiving end within the TCP virtual circuit session, and any segments not acknowledged will be retransmitted.

User Datagram Protocol (UDP) is essentially the scaled down version of TCP, also known as the thin protocol.  Unlike TCP, UDP does not include all of the bells and whistles; there is no sequencing, no acknowledgement, etc. The purpose is to send the data out and not worry about it.  With TCP there is the necessity for sequencing and acknowledgement because everything is necessary for the data to be complete; on the other hand, with UDP, such as a phone call, not all of the data is necessary for you to understand the message being transmitted.

The information may sound jittery and chunky but it is understandable in the long run.  UDP is classified as a connectionless protocol.

One important thing you need to keep in mind is the ability to differentiate between the two models.

See also: Part 1, Part 2, Part 3

Works Cited

Lammle, T. (2007). CCNA Cisco Certified Network Associate Study Guide. Indianapolis: Wiley Publishing, Inc.

Odom, W. (2012). Official Cert Guide ICND1 640-822. Indianapolis, IN: Cisco Press.

Odom, W. (2011). Official Cert Guide ICND2 640-816. Indianapolis, IN: Cisco Press.