OK it took me a bit but I think I worked it out:
access-list 191 deny ip 150.20.66.129 0.0.0.126 150.20.87.0 0.0.0.254
//ACL above says the latter part of this subnet is denied access to
all odd IPs in the 4th octet
not quite:
150.20.66.129 0.0.0.126 if you break down
0.0.0.126 you get 0.0.0.01111110, so this is actually matching the
odds above 128. It then denies them to the even addresses in this
range: 150.20.87.0 0.0.0.254
access-list 191 deny ip 150.20.66.129 0.0.0.126 150.20.80.0 0.0.0.254
//ACL above says the latter part of this subnet is denied access to
all even IPs in the 4th octet
same here, the odd addresses in this range
150.20.87.0 0.0.0.254 are denied from the evens in this range
150.20.80.0 0.0.0.254
?Question: If you inverse 254, you come up with 1, so shouldn't that
be matching odds? (we care about the last bit and if its a 1, it will
match odd numbers) How would this match evens as well? (its the same
as the ACL above it, no?)
So yes both access lists are similar, they deny traffic from odd IP's
bound toward even IP's. I think you may have thought one access list
was blocking evens, and the other odds and that isn't the case.
Hope that helps,
Marc
On Wed, May 18, 2011 at 3:32 PM, Lemish, Christopher
<[email protected]> wrote:
> ?
> Ah, my apologies. I'm sorry. It is Vol2Lab4Task9.1.
>
> ______________________________
> Christopher Lemish, CCNP / MCSE
> Network Engineer
> Blackbox Network Services
> 6000 New Horizons Blvd.
> Amityville, NY 11701
> Mobile: 516-790-1525
> Email: [email protected]
>
> ________________________________
> From: marc abel [mailto:[email protected]]
> Sent: Wed 5/18/2011 3:38 PM
> To: Lemish, Christopher
> Cc: CCIE OSL
> Subject: Re: [OSL | CCIE_RS] Vol2Lab9.1 - Subnetting
>
> Hi Christopher,
>
> Volume 2 lab 9 task 1 appears to deal with initial switch
> configuration (vtp, vlans, etc), I don't see a subnetting question, is
> it possibly a different task?
>
> -Marc
>
> On Wed, May 18, 2011 at 1:47 PM, Lemish, Christopher
> <[email protected]> wrote:
>> ?
>> Guys,
>>
>> Quick question that I'm trying to fully understand the logic.
>>
>> access-list 191 deny ip 150.20.66.0 0.0.0.127 150.21.21.128 0.0.0.127
>> access-list 191 deny ip 150.20.66.0 0.0.0.127 150.20.56.128 0.0.0.127
>> access-list 191 deny ip 150.20.66.129 0.0.0.126 150.20.87.0 0.0.0.254
>> //ACL above says the latter part of this subnet is denied access to all
>> odd IPs in the 4th octet
>> access-list 191 deny ip 150.20.66.129 0.0.0.126 150.20.80.0 0.0.0.254
>> //ACL above says the latter part of this subnet is denied access to all
>> even IPs in the 4th octet
>> ?Question: If you inverse 254, you come up with 1, so shouldn't that be
>> matching odds? (we care about the last bit and if its a 1, it will match odd
>> numbers) �How would this match evens as well? (its the same as the ACL
>> above it, no?)
>>
>> access-list 191 permit ip any any
>> int fa0/1
>> ip access-group 191 in
>> int mu1
>> ip access-group 191 in
>>
>>
>> ______________________________
>> Christopher Lemish, CCNP / MCSE
>> Network Engineer
>> Blackbox Network Services
>> 6000 New Horizons Blvd.
>> Amityville, NY 11701
>> Mobile: 516-790-1525
>> Email: �[email protected]
>>
>>
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