From: Tony Olzak (aolzak@xxxxxxxxxxxxxxxxxxx)
Date: Wed Oct 25 2000 - 21:26:28 GMT-3
Yea, that was a typo. I meant port 21.
Anyway, yes your access-list will allow any established sessions to come
back in, but it will allow ANY TCP sessions back instead of just FTP.
In response to Jack, the source port will be 21 but the destination will be
1024 if that's the port the host used when it initiated the session. Caslow
has a section on this in the access-list portion of his book.
Tony
----- Original Message -----
From: "Jack Heney" <jheneyccie@hotmail.com>
To: <ramyers@cisco.com>; <aolzak@buckeye-express.com>;
<ccielab@groupstudy.com>
Sent: Wednesday, October 25, 2000 6:53 PM
Subject: RE: access-list help
> On a somewhat related note, I know FTP uses port 21 for control and port
20
> for data. Let's say a host establishes an FTP connection from port 1024
to
> port 21 and request a file transfer. Is the resultant transfer sourced
from
> or destined for port 20? And if it is sourced from 20, is the destination
> the same port as the original request (i.e. 1024)?
> Thanks,
> jack
>
>
> >From: "Rasheim Myers" <ramyers@cisco.com>
> >Reply-To: "Rasheim Myers" <ramyers@cisco.com>
> >To: "Tony Olzak" <aolzak@buckeye-express.com>, <ccielab@groupstudy.com>
> >Subject: RE: access-list help
> >Date: Wed, 25 Oct 2000 18:23:33 -0400
> >
> >Hi Tony,
> >
> >The following inbound access-list line should help solve that problem:
> >access-list 100 permit tcp any <host ip range> established
> >note:
> >I don't think you need the "eq ftp" for this line
> >
> >This will allow the "server" that you have established a connection with
to
> >return packets to your hosts. You used the telnet tcp port (23) in your
> >email. That is probably just a typo. Remember that FTP uses 2 ports (21
> >and 20).
> >
> >I hope this information helps out.
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
> >Tony Olzak
> > Sent: Wednesday, October 25, 2000 6:03 PM
> > To: ccielab@groupstudy.com
> > Subject: access-list help
> >
> >
> > This should be simple, and I'm probably making this way too difficult,
> >but
> >how would you go about this access-list?
> >
> > This is an inbound access-list on a serial interface. The one line I'm
> >having trouble with is this:
> >
> > FTP sessions are only allowed if established by a host on the router's
> >ethernet segment.
> >
> > OK, that's great. Any host on the ethernet segment will send packets
to
> >port 23, but returning packets will be to whatever port above 1023 that
the
> >host chose to use. If I just say:
> >
> > access-list 100 permit tcp any <host ip range> establish eq ftp
> >
> > This would only allow packets IN that are destined for port 23 and
have
> >the ACK bit. This does me no good because the source host is not using
port
> >23 when trying to initiate an FTP session. If I say to any port greater
> >than
> >1023, then I'm allowing traffic that was not specified in the lab. Am I
way
> >off here? If so, how do I do this?
> >
> > Maybe the author of this practice lab didn't understand this
procedure?
> >
> > Tony
>
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