Sorry, I overlooked the ? in the expression. That would allow AS1.
MLC
Jaeheon Yoo <[EMAIL PROTECTED]> wrote in message
[EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> Hi,
>
> I quite agree with vtam,
>
> From p.376 of "Internet Routing Architectures" Sec. Edition,
>
> ip as-path access-list 4 permit ^1 ?[0-9]*$
>
> This has some side effects, which allow as-paths such as 109, 110, 120
> like vtam has pointed out, in addition to "all the AS paths that start
> with 1 and that are of length 2-that is, AS1 and its direct customers"
> I think the right answer would be as follows:
>
> ip as-path access-list 4 permit ^1 [0-9]*$
> ip as-path access-list 4 permit ^1$
>
> The first line is for its direct cumstomers, and the second line for
> its local networks. I'm afraid there's no one line version of this.
> Am I right?
>
> On 1 Dec 2000 11:41:56 -0500, [EMAIL PROTECTED] ("michael champion")
> wrote:
>
> >Although I am by no means a regular expression expert, I do not believe
that
> >^1 [0-9]*$ will match an AS-path of 1; the space forces a requirement of
a
> >maximum of two path elements, with the first element a 1. A single
AS-path
> >of 1 would not match. Multiple AS-path elements are separated by a space
.
> >Thus, the expression would match 1 100, 1 200, 1 1, 1 {any AS number},
but
> >would not match just 1. What is confusing about regular expressions is
that
> >every element in the expression is an operator, and sometimes you have
> >operators acting on other operators. Thus .* matches all paths because .
is
> >an operator representing any single character and * is an operator
> >representing . repeated as many times as necessary (not just the
particular
> >character that . matched). This is thus equivalent to .., ..., ...., etc.
as
> >many times as necessary.
> >
> >Powerful, but cryptic, and not well-documented at all by Cisco (who knows
> >which type of regular expression engine they are using?) This all comes
from
> >the Unix world, which is why you see it in Perl, Tcl, egrep, etc.
> >
> >Regards,
> >MLC
> >"vtam" <[EMAIL PROTECTED]> wrote in message
907i83$9l6$[EMAIL PROTECTED]">news:907i83$9l6$[EMAIL PROTECTED]...
> >> The space is the books. Because it said it match all the AS_paths that
> >start
> >> with 1 and of length 2, such as AS_path=1, =1 10, =1 200, etc. As you
> >said,
> >> ? # 0 or 1 of the preceding characters (in this case a space). So if
?=0,
> >it
> >> is ^1[0-9]*$; if ?=1, it is ^1 [0-9]*$.
> >> Do i misread your meaning?
> >>
> >>
> >> "Drew Simonis" <[EMAIL PROTECTED]> wrote in message
> >> [EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> >> >
> >> > ^1 ?[0-9]*$
> >> > ^
> >> > ^
> >> >
> >> > Is that space yours or the books? Broken apart, that regex matches
> >> > (assuming standard egrep'ish metachars)
> >> >
> >> > ^ # beginning of line
> >> > 1 # followed by the digit 1
> >> > (space) # followed by a space
> >> > ? # 0 or 1 of the preceding characters (in this case a space)
> >> > [0-9] # a single digit within the range of 0-9
> >> > * # 0 or more of the preceding characters, up to the end of
> >> > # the pattern
> >> > $ # end of line char
> >> >
> >> > So, is this equivalent to ^1[0-9]*$? I don't think so. Assuming
> >> > that the pattern with a space was a typo, we are allowed an
> >> > optional 1. Assuming it wasn't a typo, we are allowed the space
> >> > character. Neither of these options would be matched by your more
> >> > restrictive pattern. As for the specific pattern to match, you
> >> > can't really say without knowing what you are matching with.
> >> >
> >> > Different regex engines support different metachars.
> >>
> >>
> >>
> >> _________________________________
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