Okay, now you're confusing me John.
If we take "ip prefix-list elvira permit 172.16.0.0/16 le 32" wouldn't that
permit /16 thru /32, whereas "ip prefix-list elvire permit 172.16.0.0/16 ge
8" would permit /8 thru /32?
But, I guess the error message you included was for the /16 ge 8, which kind
of ends this discussion :-)
Thanks,
Ole
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Ole Drews Jensen
Systems Network Manager
CCNA, MCSE, MCP+I
RWR Enterprises, Inc.
[EMAIL PROTECTED]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
http://www.RouterChief.com
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-----Original Message-----
From: John Neiberger [mailto:[EMAIL PROTECTED]]
Sent: Thursday, July 26, 2001 11:17 AM
To: [EMAIL PROTECTED]
Subject: RE: BGP prefix compiling [7:13828]
I don't see why that wouldn't work. As I mentioned previously, it will
match all prefixes that begin with exactly 172.16 but have a mask of /8
or greater. There are other ways to accomplish the same thing that make
more sense, but at the moment this logic seems valid. Although, I
suppose it doesn't really make any sense to write it like that since it
accomplishes the same thing as
ip prefix-list elvira permit 172.16.0.0/16 le 32
This would match the same prefixes and makes much more sense.
Okay, I just tried it and I received an error that says:
% Invalid prefix range for 172.16.0.0/16, make sure: len
John
>>> Ole Drews Jensen 7/26/01 9:44:20 AM >>>
Yes that does make sense - THANKS - and I wonder why none of the books
I
have read about this mention this small but very important fact, that
ge
stands for >= and le for = and it just didn't occur to me. From
previous
programming experience a long time ago I should have noticed this, but
I
had a brain cloud.
Anyway, this makes this much easier to remember how this works. Let's
use your last example:
Example : ip prefix-list elvira permit 172.16.0.0/16 ge 8
This will match any prefix that begins with 172.16 and has a mask
greater than or equal to 255.0.0.0. Let's modify your example a bit:
ip prefix-list elvira permit 172.16.0.0/16 le 24
This will match any prefix that begins with 172.16 and has a mask
between 255.255.0.0 and 255.255.255.0, or anything between a /16 and
/24
inclusive. Let's say you wanted to deny prefixes longer than /24:
ip prefix-list elvira deny 172.16.0.0/16 ge 25
This will match any prefix that begins with 172.16 but has a mask of
/25 or longer.
Does that make sense? I hope I have that right! ;-)
Regards,
John
>>> "Ole Drews Jensen" 7/25/01 8:33:13 PM >>>
This is to (hopefully) confirm that my understanding of the examples
in
the
BSCN book and the IRA 2nd. ed. book are correct.
If the formel looks like this:
ip prefix-list elvis permit a.b.c.d/n
It will be compiled like this:
1) if neither "ge" nor "le" are added, only the excact prefix (n)
is
allowed.
2) if only "ge x" is added, n is ignored and an invinsible le of
32
are
added so
prefix x thru 32 are permitted.
3) if only "le y" is added, prefix n thru y are permitted.
4) if both "ge x" and "le y" are added, n is ignored and prefix x
thru
y are permitted.
This is to all you BGP experts out there - please comment with true or
false
on the 4 statements above, and add any comments or corrections if
necessary.
One last question, can the ge value be lower than the /n value?
Example : ip prefix-list elvira permit 172.16.0.0/16 ge 8
and would that allow only the prefix 172.16.0.0/8 ?
I thank you in advance,
Ole
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Ole Drews Jensen
Systems Network Manager
CCNA, MCSE, MCP+I
RWR Enterprises, Inc.
[EMAIL PROTECTED]
http://www.RouterChief.com
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
NEED A JOB ???
http://www.oledrews.com/job
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=13888&t=13828
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