From: Brian McGahan (bmcgahan@internetworkexpert.com)
Date: Mon Apr 18 2005 - 17:45:12 GMT-3
Lee,
What does the *physical* topology look like? Draw it out. How
is this different from the *logical* topology?
HTH,
Brian McGahan, CCIE #8593
bmcgahan@internetworkexpert.com
Internetwork Expert, Inc.
http://www.InternetworkExpert.com
Toll Free: 877-224-8987 x 705
Outside US: 775-826-4344 x 705
24/7 Support: http://forum.internetworkexpert.com
Live Chat: http://www.internetworkexpert.com/chat/
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> Lee Donald
> Sent: Monday, April 18, 2005 1:33 PM
> To: Ccielab@Groupstudy. Com
> Subject: Associating routed port with vlan
>
> Hi,
>
> I have router 3 with an eth interface 162.1.38.3/24 and this is in
vlan
> 28.
> Then I have a routed interface on the other cat3550 that is
162.1.38.8/24
> How can I configure this routed interface to be in vlan 28?
> What associates the routed interface with a vlan?
>
> Any help greatly received.
>
> Regards
>
> Lee.
>
>
>
> -----Original Message-----
> From: JP [mailto:jenseike@start.no]
> Sent: Sunday, April 17, 2005 12:54 PM
> To: Ccielab@Groupstudy. Com; Lee Donald
> Subject: RE: Access-list question - Allowing even and odd numbers in
3rd
> octet -
>
>
> Hi there.
>
> Here is what I have learned :
>
> This is the solution by the way.. explenation is below : access-list
1
> deny 0.0.1.0 255.255.254.255
>
> We want to block the even third octets of any route coming in our
> Ethernet.
> The first thing we have to do is realize that this has to be a very
> generic
> statement. Anything with an odd third octet should be blocked, no
> particular
> network is stated, it must cover them all. All we are going to care
about
> in
> this access-list is the third octet. The 1st, 2nd, and 4th octets can
be
> ANYTHING, it won't matter to us. So we can formulate the basic
access-list
> already:
>
> access-list 1 deny 0.0.X.0 255.255.X.255
> access-list 1 permit any
>
> The first line we put a 0 for the 1st,2nd,and 4th octets 'standard'.
Then
> we
> put a wildcard mask of 255 for the 1st,2nd,and 4th octets. The 'X'
just
> means we haven't figured that out yet. The 0's in the 1st,2nd, and 4th
> octects are just the smalles number we can put there, and its easy to
> type.
> We could put any number in for our standard, it wouldn't matter, since
we
> don't care about them at all. Remember, for the wild card mask, 1's
are I
> DON'T CARE, and 0's are I CARE. So if we take a look at the 1st octet
we
> get:
>
> 0 - 0 0 0 0 0 0 0 0
> 255 1 1 1 1 1 1 1 1
>
> Our standard of 0 breaks down to 8 0's, while our wildcard mask of 255
> breaks down to all 1's. This means that we DON'T CARE about any of the
> bits
> in the first octet. This is also true for the 2nd and 4th octets. We
don't
> care what is there, it can be anything. Now on to the 3rd octet. We
have
> the
> following bit values in a octet:
>
> 128 64 32 16 8 4 2 1
>
> Out of all of these, the ONLY one that is odd is '1'.
> So if we have the '1' bit OFF any combination of the other bits MUST
be
> EVEN. If we have the '1' bit ON, any combination of the others + the
'1'
> will be ODD. Here are a couple of quick examples:
>
> ....128643216 8 4 2 1
> 2 --- 0 0 0 0 0 0 1 0
> 4 --- 0 0 0 0 0 1 0 0
> 100- 0 1 1 0 0 1 0 0
> 150- 1 0 0 1 0 1 1 0
>
> 3 --- 0 0 0 0 0 0 1 1
> 5 --- 0 0 0 0 0 1 0 1
> 101- 0 1 1 0 0 1 0 1
> 151- 1 0 0 1 0 1 1 1
>
> All of the even numbers have the '1' bit off.
> All of the odd numbers have the '1' bit on.
> This is the bit that we care about. The '1' bit is going to decide if
the
> octet is odd or even. So how do we check this '1' bit. Remember that
1's
> are
> I DON'T CARE bits and 0's are I CARE bits for the wild card mask. So
for
> odds we would use a standard in the third octet of 1:
>
> 0.0.1.0
>
> We could use any odd number, but this is the smallest odd number that
will
> put the '1' bit on.
>
> ...128643216 8 4 2 1
> 1 - 0 0 0 0 0 0 0 1
>
> Now we need to figure out the wild card mask. We put a 1 under any bit
we
> don't care about. And a 0 under the bits we want to check. In this
case we
> are just going to check the '1' bit.
>
> ....128643216 8 4 2 1
> 1 --- 0 0 0 0 0 0 0 1
> mask 1 1 1 1 1 1 1 0
>
> We then add up the values of the 1's for the wild card mask:
> 128+64+32+16+8+4+2 = 254
> So our wild card mask is going to be 254 for our third octet. This
gives
> us
> a complete access list of:
>
> access-list 1 deny 0.0.1.0 255.255.254.255
>
> Out of all 32 bits in the standard, we are only checking the 8th bit
in
> the
> 3rd octet (the '1' bit). Our wild card mask says that we don't care
about
> any bits in the 1st or 2nd octet, in the third octet we care about the
'1'
> bit which in this case our standard says it MUST be on to match, and
don't
> care about any bits in the 4th octet. Now we can't forget the implicit
> deny
> on the access-list. If we leave it like it is, it will deny all odd
3rd
> octets, then deny everything else, so nothing will get through. So the
> complete access-list will look like this:
>
> access-list 1 deny 0.0.1.0 255.255.254.255
> access-list 1 permit any
>
> That will work, however it takes twice the number of lines that we can
do
> it
> in. Instead of denying the odds like it says, we can permit the evens.
If
> we
> permit the evens, then the odd will be implicitly denied and the
access-
> list
> will be just one line. So to permit the even 3rd octets we are only
going
> to
> change one thing. The 3rd octet standard must have the '1' bit OFF to
be
> even:
>
> ...128643216 8 4 2 1
> 0 -- 0 0 0 0 0 0 0 0
>
> We again figure out our wild card mask, we only care about the '1'
bit.
>
> ...128643216 8 4 2 1
> 0 --- 0 0 0 0 0 0 0 0
> mask 1 1 1 1 1 1 1 0
>
> Again, the wild card mask is going to be 254 (64+32+16+8+4+2) it
doesen't
> change between odds and evens, we are still checking the '1' bit. The
only
> thing that changes between checking odds and evens is the standard. We
put
> a
> 1 in the third octet to check for odds, since 1 is the lowest odd
number.
> We
> put a 0 in the third octet to check for evens, since a 0 is the lowest
> even
> number.
>
> So our 1 line access-list looks like this:
>
> access-list 1 permit 0.0.0.0 255.255.254.255
>
> This doesn't care about the 1st, 2nd, or 4th octets. In the 3rd octet
we
> only care about the '1' bit, which in this case must match a 0, making
it
> even.
>
> Remember, if they say to block odds or evens, permit the opposite,
unless
> they are being specific to a subnet.
>
>
> Jens P
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Lee
> Donald
> Sent: 17. april 2005 12:13
> To: ccielab@groupstudy.com
> Subject: Access-list question - Allowing even and odd numbers in 3rd
octet
> -
>
>
> Can anyone put some more logic to this for me, I'm having a bad brain
day.
>
> I need to allow all odd numbers in the 3rd octet in via an access-list
> which
> I know is
>
> Access-list 5 permit 0.0.0.0 0.0.252.0
>
> Then I tried to let just the evens in but got confused, and couldn't
get
> my
> dough brain round it.
>
> Can anybody remind me of this and the way it works?
>
> Thanks in advance.
>
> Regards
>
> Lee.
>
>
This archive was generated by hypermail 2.1.4 : Tue May 03 2005 - 07:55:00 GMT-3