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.
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On Tue, 12 Aug 1997, C. Jon Larsen wrote:
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.
Ah...I wasn't reading your rules closely enough. As a trick to reduce access-list length on my internet gatway, I nailed up static routes like: ip route 208.215.0.0 255.255.240.0 null0 250 ip route 205.229.48.0 255.255.240.0 null0 250 ip route 10.0.0.0 255.0.0.0 null0 250 ip route 172.16.0.0 255.240.0.0 null0 250 ip route 192.168.0.0 255.255.0.0 null0 250 The first two are our netblocks. The rest just stop packets for the "private IP" nets from leaving our network. I also have access-list rules that prevent them from entering our network. I'm assuming here that route cache hits are faster than access-list testing. ------------------------------------------------------------------ Jon Lewis <jlewis@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____
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