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| Justin2112 2002-09-18, 2:55 pm |
| Hi
I need you brain-power !
I have the Cisco CCIE Expert LAB CIM. I am working on module 3 OSPF summarization. I came up with a different answer than Cisco. Would you check my work ?
Problem:
Configure two loopbacks on Router R6 using subnets containing no more than 14 hosts using the 130.10.32.x space. Summarize the loopback interfaces.
What I figured out.
IP address
for loopback one:
130.10.32.17 255.255.255.240
IP address
for loopback two
130.10.32.33 255.255.255.240
The summary address I figured out
summary-address 130.10.32.0 255.255.255.240
Ok, ok here's what Cisco has as the answer:
IP address
for loopback one:
130.10.32.33
IP address
for loopback two:
139.10.32.49
and the kicker:
summary-address 130.10.32.32 255.255.255.224
______________________________
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Conclusion: Okay, I kinda see how They chose the Host ID's for the loopbacks, but I think .17 is also a valid host address for the 240 subnet and would work.
I don't see why they are using the .224 mask to summarize ? 256- 244 =32 There are not 32 networks in the range . . .
Any help or insight would be appreciated.
Thanks,
Justin | |
| ZacDogg 2002-09-18, 5:02 pm |
| 130.10.32.33 255.255.255.240= 16 addresses
139.10.32.49 255.255.255.240= 16 addresses
139 is obviously supposed to be 130, and they are summarized to a 32 address mask, 255.255.255.224
Your addresses will work too. You just summarized them wrong. | |
| Justin2112 2002-09-18, 8:21 pm |
| Thanks.
Yeah . . 139 was supposed to be 130.
I doing as many problems like this as I can get my hands on.
I am on the virge . . . I never liked math before I related it Cisco and IP stuff.
Thanks again for the help.
PEACE!
Justin | |
| Justin2112 2002-09-19, 2:33 pm |
| Okay - I've figured out where the .224 comes from.
130.10.32.33 is
10000010.00001010.00100000.00100000
and
130.10.32.49 is
10000010.00001010.00100000.00110001
The first three bits in the fourth octect match to create /224
...and a ray of light shown down upon his head | |
| ZacDogg 2002-09-19, 3:37 pm |
| Keep working at it and eventually it will be like second nature.
Zac |
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