CCNA - Subnetting 101 - LAB 06/12/2003

Author

Subnetting 101 - LAB 06/12/2003

anchor40

2003-06-12, 9:18 am

Good Morning!

Here's today's question:

Your boss has asked you to audit the IP address allocation and report back with the maximum number of subnets available. For example, if 112.52.46.0 /27 were available, he wants to know the /28, /29, and /30 networks possible from that address.

In use (with IP Subnet-zero)are:

112.52.46.4 /30
112.52.46.8 /30
112.52.46.12 /30
112.52.46.32 /28
112.52.46.48 /28
112.52.46.80 /28
112.52.46.96 /27
112.52.46.128 /26
112.52.46.192 /26
112.52.47.0 /27
112.52.47.64 /26
112.52.47.128 /29
112.52.47.144 /29
112.52.47.160 /27
112.52.47.192 /26

Bonus: What's the summarized network address for all these subnets?

Now, here's the 6/11 question, with answer:

Given the following network address and subnet mask, how many
point-to-point subnets can be created? 6-host subnets?

code:
Address          Mask       P2P     6-host     
-------          ----       ---     ------
192.168.72.208   /28	  4        2

P2P = .208 (.209-.210)
      .212 (.213-.214)
      .216 (.217-.218)
      .220 (.221-.222)


6host = .208 (.209-.214)
        .216 (.217-.222)

djmaplethorpe

2003-06-12, 9:30 am

sorry, to be so dense, but could you expound on yesterday's answer so I know where I went wrong?

TIA

dj

anchor40

2003-06-13, 9:43 am

You're only dense if you don't ask!

The easiest way to explain it is to take it to the lowest level - binary:

192.168.72.208 /28 becomes

code:
                |
192.168. 72.1101|0000
255.255.255.1111|0000
                |

For the "6-host" networks, the /29 mask is required:

code:
                  |
192.168. 72.1101 0| 000
255.255.255.1111 1| 000
                  |

Thus, with the 4th bit, the "8's" value, now available for network addressing it can be 1 or 0, allowing .208 and .216 to be valid network IDs for the /29 networks.

To find the P2Ps, move the mask one more place to the right:

code:
                   |
192.168. 72.1101 00|00
255.255.255.1111 11|00
                   |

Now the 3rd and 4th bits (4's and 8's values) are available for network addressing, they can be 00, 01, 10, or 11 for valid networks. So, .208, .212, .216, and .220 are all valid P2P networks under the original .208 /28 network.

B4yaman3

2003-06-13, 10:01 am

Anchor40 just makes it so simple. Yesterday I was telling a friend of mine the best subnetter I know is Anchor40 at Examnotes.

anchor40

2003-06-13, 10:25 am

You're too kind!

See, if I can explain it to you so that you "get it" you'll take my examples and use that format when someone asks you a subnetting question. Then they'll "get it" use your examples to explain to someone else, and it keeps getting passed on and on...

I'm just the pebble at the top of the mountain - I start tumbling slowly, and drag along another pebble, and we knock loose a few more, and pretty soon, we're a giant subnetting avalanche!

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