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CCNA question - IP router

The command "ip route 192.168.24.64 255.255.255.192 192.168.8.2 100" was
configured on a router named TK1. No routing protocols or other static routes are
configured on the Corporate router yet.
Based on this information, which statement is true about this command?

E. Packets destined for host 192.168.24.124 will be sent to 192.168.8.2.

The answer is E. I want to know how did they get 192.168.24.124 number. Could someone explain this to me.

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ittechlab
Asked:
ittechlab
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1 Solution
 
Mad_JasperCommented:
That is an interesting question.

The host 192.168.24.124 is on the 192.168.24.64/26 network. So I guess the command routes all traffic to the subnet 192.168.24.64/26 via the interface with the IP address 192.168.8.2 with an hop count of 100.

I admit, I have never seen a route command such as this.
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ECNSSMTCommented:
ip route network gateway is the proper format so I'm not sure what the 100 is doing there.
192.168.8.2 is the gateway
192.168.24.65 - 192.168.24.126 are valid IPs in the 192.168.24.64/26 subnetwork  and since 192.168.24.124 is a member of that subnetwork, this rule applies so this packet go to the gateway 192.168.8.2

Regards,
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ittechlabLinux SupportAuthor Commented:
can some explain me the following.

192.168.24.64/26 what is this really mean and how did 26 shows herer?  

The host 192.168.24.124 is on the 192.168.24.64/26 network. So I guess the command routes all traffic to the subnet 192.168.24.64/26 via the interface with the IP address 192.168.8.2 with an hop count of 100.
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Mad_JasperCommented:
This is not an easy concept to explain is a forum such as this. Take a look at these links.

http://www.networkcomputing.com/unixworld/tutorial/001.html

http://en.wikipedia.org/wiki/Subnetwork
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giltjrCommented:
IP V4 addresses are 32 bits long grouped in bytes, or 4 sets of 8 bits.  The /26 tells you how many bits are used for the subnet mask.  So you have 26 bits which tell you what part of the IP address is the network part which is:

     11111111 . 1111111 . 11111111 . 110000

or

    255.255.255.192

This tells you which part of a IP hosts address is the IP network address which which part is the host address.  In this case the network address is 192.168.24.64 the address 192.168.24.65 - 192.168.24.126 are usable for host addresses and 192.168.24.127 is the broadcast.

The 192.168.24.124 is a randomly choosen host address that was within the subnet that the add route statement was used to add a route for.  This was done to see if you could figure out that ".124" was within or outside the IP subnet that the route add was specifing.

The 100 is the "hop count" or more commonly known as the metric.  This is used by some routers to determine the "best" (meaning shortest) route.   Some routers will allow you to have mulitple routes the to same IP subnet.  The router will choose the route with the lowest metric to route the packet.  If that router does not respond to arp requests, it will then choose the next best (one with the lowest route)  route.  If that router does not repsoned it keeps doing that until it uses the default (or gateway of last resort).
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ECNSSMTCommented:
Hi giltjr, excellent...
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ravisimpiCommented:
--giltjr--

  Really excelllent, I don't think anyone will get the term subnetiing explained better than this.

 "ittechlab"

 If you are preparing for CCNA test, or self studying.. you should not directly read the routing ( which needs basic understanding of Subnetting). 1st make yourself clear about the network Ip addressing schemes, IP subnetting and other basic things needed before going to Routing.

 This is what I did when i studied CCNA. :-)

Peace and HEalth
Ravi Simpi
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ravisimpiCommented:
and for your general reference here is the table for / notations


Class A Host/Subnet Table
Class A
Number of
Bits Borrowed            Subnet         Effective     Number of      Number of Subnet
from Host Portion        Mask           Subnets       Hosts/Subnet   Mask Bits
-------               ---------------        ---------     -------------  -------------
  1                    255.128.0.0            2       8388606           /9
  2                    255.192.0.0            4       4194302           /10
  3                    255.224.0.0            8       2097150           /11
  4                    255.240.0.0           16       1048574           /12
  5                    255.248.0.0           32        524286           /13
  6                    255.252.0.0           64        262142           /14
  7                    255.254.0.0          128        131070           /15
  8                    255.255.0.0          256         65534           /16
  9                    255.255.128.0        512         32766           /17
  10                   255.255.192.0       1024         16382           /18
  11                   255.255.224.0       2048          8190           /19
  12                   255.255.240.0       4096          4094           /20
  13                   255.255.248.0       8192          2046           /21
  14                   255.255.252.0      16384          1022           /22
  15                   255.255.254.0      32768           510           /23
  16                   255.255.255.0      65536           254           /24
  17                   255.255.255.128   131072           126           /25
  18                   255.255.255.192   262144            62           /26
  19                   255.255.255.224   524288            30           /27
  20                   255.255.255.240  1048576            14           /28
  21                   255.255.255.248  2097152             6           /29
  22                   255.255.255.252  4194304             2           /30
  23                   255.255.255.254  8388608             2*          /31
Class B Host/Subnet Table
Class B           Subnet               Effective       Effective    Number of Subnet
 Bits        Mask                 Subnets         Hosts        Mask Bits
-------  ---------------          ---------       ---------    -------------
  1      255.255.128.0                2             32766        /17
  2      255.255.192.0                4             16382        /18
  3      255.255.224.0                8              8190        /19
  4      255.255.240.0               16              4094        /20
  5      255.255.248.0               32              2046        /21
  6      255.255.252.0               64              1022        /22
  7      255.255.254.0              128               510        /23
  8      255.255.255.0              256               254        /24
  9      255.255.255.128            512               126        /25
  10     255.255.255.192           1024                62        /26
  11     255.255.255.224           2048                30        /27
  12     255.255.255.240           4096                14        /28
  13     255.255.255.248          8192                 6        /29
  14     255.255.255.252          16384                 2        /30
  15     255.255.255.254          32768                 2*       /31
Class C Host/Subnet Table
Class C      Subnet       Effective  Effective  Number of Subnet
 Bits        Mask         Subnets     Hosts     Mask Bits
-------  ---------------  ---------  ---------  --------------
  1      255.255.255.128      2        126        /25
  2      255.255.255.192      4         62        /26
  3      255.255.255.224      8         30        /27
  4      255.255.255.240     16         14        /28
  5      255.255.255.248     32          6        /29
  6      255.255.255.252     64          2        /30
  7      255.255.255.254    128          2*       /31

I think i have pasted the table right

Peace and health
Ravi Simpi
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jhanceCommented:
The question is not really about the ROUTE command but rather to see if you understand the concept of subnetting and the subnet mask.  I suggest you spend some more time studying the material on subnets and subnet masks.  Once you have understood that, the answer to your question will be clear to you.
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pjtemplinCommented:
And the "100" on the tail end of the command is NOT related to hop count or metric.  It's manually setting the "administrative distance".  AD comes into play if the router learns a specific prefix from two sources and needs to decide which one to trust more; it will trust the route with the lowest AD.

By default, a static route pointing to an interface will have an AD of 0, and a static route pointing to an address will have an AD of 1.  See http://tinyurl.com/zw5u5 for a full table of administrative distance defaults.  Interestingly, the value chosen will tie with IGRP.
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giltjrCommented:
Thanks for the comments guys.  I think I  the biggest issue with learning subnetting, is that you must understand binary and logical and'ing. Hex helps, but is not really required.

jhance has hit the nail squarly on the head, the question was not about understanding the route command, but to see if subnet'ing was understood.  

ittechlab,  IMHO if you don't understand IP addressing and subnet'ing you are going to get lost in the IP world.

I also just noticed I left a few ones and zeros a /26 out it should be:

     11111111 . 11111111 . 11111111 . 11000000
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jhanceCommented:
The ROUTE command can be confusing enough as it is.  But without a solid understanding of how/why things are routed and the concept of subnetting firmly grasped, using or understaning ROUTE.EXE is virturally impossible.
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mikefalconeCommented:
I'll try to explain the entire question to you, however if you are trying to get your CCNA you are going to need to understand binary math and subnetting very well. That seemed to me to be mostly what the test was about.



the /26 is another way of writing the subnet mask. 255.255.255.192 is a 26 bit subnet mask.

A mask that size gives you 62 host addresses, i net id, and the broadcast id

You count up until you find the subnet that contains 192.168.24.64 , whis is 192.168.24.64 - 192.168.24.127

192.168.24.124 is within that range, so it will follow that route command and go through 192.168.8.2 (the "next hop")

the 100 at the end is what priority that route would take. Static routes that you don't specify a value get the value of 1. Different routing protocols give you different values, for example EIGRP is 90.
 Setting a number like this may be helpful in this example because if they plan on adding a routing protocol in the future with a value lower than 100 it would trump the static route.


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ittechlabLinux SupportAuthor Commented:
can someone tell me what is the real meaning and difference between unicast, multicast and broadcast. Thanks a lot.
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pjtemplinCommented:
Unicast goes to one node.
Broadcast goes to all nodes (usually on one subnet, possibly on one network).
Multicast goes to some nodes (who subscribe to a particular multicast address).
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ittechlabLinux SupportAuthor Commented:
any real world examples please.
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giltjrCommented:
Unicast is what you use to access EE.  Traffic between two specific hosts, your computer and EE computer.

Multicast is used when you want to send the same traffic to multiple hosts as the same time.  An example would be using Symantec's Ghost software to image disks computers.  You setup one image server and then send out the same data to 2, 3, 100 computers that you want to duplicate the disk image to.  This way instead of sending the same data out 2, 3, 100 times, you send to once and they all get it.

Broadcasts are generally limited to discovery type functions.  In NETBIOS if you do not have WINS server, when your computer wants to talk to another one, it will send out a IP subnet broadcast and say "hey are any of you named bill?".  If there is a computer named Bill, it will respond with a packet directed to your computer specificly (unicast).
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pjtemplinCommented:
99% of what you do and 95% of the traffic on your network is unicast.  http://www.domain.com is a unicast conversation between your PC and that website.

0-4% of the traffic on your network is broadcast.  When your PC wants to send the first packet to its default gateway, it needs to know the MAC address for it.  It sends a broadcast ARP request, all nodes on the subnet hear it, and the gateway responds to it.

Four routers on a subnet exchanging routes via OSPF do so using multicast.  The routers send announcements to 224.0.0.6, the all-DR address, and the DRs hear the announcements.  The DR processes the LSAs and issues updates to all of the routers by sending to 224.0.0.5; all of the OSPF routers receive this traffic and now have the updates.  One packet magically goes to four routers; there's no need for four otherwise identical packets to eat up bandwidth.
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ittechlabLinux SupportAuthor Commented:
The command "ip route 192.168.24.64 255.255.255.192 192.168.8.2 100" was
configured on a router named TK1. No routing protocols or other static routes are
configured on the Corporate router yet.
Based on this information, which statement is true about this command?

E. Packets destined for host 192.168.24.124 will be sent to 192.168.8.2.
This tells you which part of a IP hosts address is the IP network address which which part is the host address.  In this case the network address is 192.168.24.64 the address 192.168.24.65 - 192.168.24.126 are usable for host addresses and 192.168.24.127 is the broadcast.

I want to know how this person stated that the address 192.168.24.65 - 192.168.24.126 are usable for host addresses and 192.168.24.127 is the broadcast. where did he find theses values? can some one give me better explanation for this thanks.





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giltjrCommented:
This deals with how IP subnet'ing works.  You need to read up on subneting, which requires an understanding of the binary numbering system and logical "and'ing".
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pjtemplinCommented:
The network address of the routing statement, in binary, is:

11000000 10100100 00011000 01000000

The mask shown, in binary, is:

11111111 1111111 11111111 11000000

The AND of these two values is:

11000000 10100100 00011000 01000000

Because the mask is a /26, the last six bits are available for use.

11000000 10100100 00011000 01xxxxxx

All of the possible values end with 01000000-01111111.

Converting the first 24 bits to decimal, and converting the 64 possibilities of the last eight bits to decimal, results in

192.168.24.[64-127].
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giltjrCommented:
To add to pjtemplin explanation:

Once you have figure out the valid range of numbers, you must realize that the 1st number is called the network address the last number is the broadcast address and neither can be assigned to a host.

So:

     Network address is:     192.168.24.64
     Broadcast address is:    192.168.24.127
     Valid host addresses are:  192.168.24.65-126

In each IP subnet the number of valid hosts addresses is the number of valid numbers in the range minus 2
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