Filtering Source Addresses on gw-internet
C. Jon Larsen
jlarsen at ajtech.com
Tue Aug 12 19:29:55 UTC 1997
Thats what I thought at first. But if the permit comes first, then packets
with valid source addresses (a.b.c.d) get out because they pass that rule.
So a packet built like:
Source-> a.b.c.d Dest-> 172.17.0.0
will get out and be passed to the ISP, wasting bandwidth. Thats why I deny
them first, and then do the permit later on in the list.
> On Tue, 12 Aug 1997, C. Jon Larsen wrote:
>
> > gw-internet#show access-lists 120
> > Extended IP access list 120
> > deny ip any 10.0.0.0 0.255.255.255 log
> > deny ip any 172.16.0.0 0.0.255.255 log
> > deny ip any 172.17.0.0 0.0.255.255 log
> > deny ip any 192.168.0.0 0.0.255.255 log
> > permit ip a.b.c.0 0.0.0.255 any (27429 matches)
> > deny ip any any log
>
> Aren't the first 4 deny's redundant? Using access-lists, I was under the
> impression, there was an implicit deny at the end, such that all you'd
> need is a single permit line above, and optionally the last deny so you
> get to log violations.
>
> ------------------------------------------------------------------
> Jon Lewis <jlewis at fdt.net> | Unsolicited commercial e-mail will
> Network Administrator | be proof-read for $199/message.
> Florida Digital Turnpike |
> ______http://inorganic5.fdt.net/~jlewis/pgp for PGP public key____
>
>
Linux.
+-------------------+---------------------+
| C. Jon Larsen | jlarsen at ajtech.com |
| Systems Engineer | Tel: 804.353.2800 |
| A&J Technologies | |
|-------------------+---------------------|
| http://www.ajtech.com |
+-----------------------------------------+
More information about the NANOG
mailing list