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Access-list smtp

Posted on 2009-05-04
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Last Modified: 2013-11-30
When I apply this acl to the external interface connected to the internet it breaks all traffic.

int ser 0/0/0
ip access-group 101 in

Any ideas?
Extended IP access list 101

    10 permit tcp 0.0.0.0 0.0.3.255 0.0.0.0 0.0.0.3 eq smtp

    20 permit tcp 0.0.0.0 0.0.7.255 0.0.0.0 0.0.0.3 eq smtp

    30 deny tcp any any eq smtp

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Question by:kitbarr
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Expert Comment

by:akalbfell
ID: 24296580
what are you trying to do? use the access list to only permit SMTP traffic or you want http/https traffic to pass through also?
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Expert Comment

by:JFrederick29
ID: 24296739
Add permit ip any any at the bottom since there is any implicit "deny all" at the end.

permit tcp 0.0.0.0 0.0.3.255 0.0.0.0 0.0.0.3 eq smtp
permit tcp 0.0.0.0 0.0.7.255 0.0.0.0 0.0.0.3 eq smtp
deny tcp any any eq smtp
permit ip any any
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Author Comment

by:kitbarr
ID: 24298058
adding permit ip any any allows traffic to flow however the deny tcp any any eq smtp seems to be catching all smtp traffic. the first two lines don't seem to be working.
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Expert Comment

by:akalbfell
ID: 24298125
what are you trying to do?
permit SMTP traffic from one host out to the internet but block any SMTP traffic from coming out from another machine?

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Author Comment

by:kitbarr
ID: 24298159
I want to allow all smtp traffic out however only allow smtp traffic in from mx logic. 208.65.144.0/21 and 208.81.64.0/22 is what I am trying to allow in.
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Author Comment

by:kitbarr
ID: 24298168
Yes and I would also like to allow all other http traffic. I'm only trying to block smtp from the outside in.
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Author Comment

by:kitbarr
ID: 24298187
This is what it looks like right now
GWAQUA(config-ext-nacl)#do sh access-list

Extended IP access list 102

    40 permit ip any any (600928 matches)

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Accepted Solution

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akalbfell earned 500 total points
ID: 24298261
gotcha...

permit tcp 208.81.64.0 0.0.3.255 any eq smtp
permit tcp 208.65.144.0 0.0.7.255 any eq smtp
deny tcp any any eq smtp
permit ip any any

applied to the outside interface coming in

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Author Comment

by:kitbarr
ID: 24298526
That worked perfectly. What is the difference between
access-list 101 permit tcp 0.0.0.0 0.0.3.255 eq smtp any eq smtp and
access-list 101 permit tcp 208.65.144.0 0.0.3.255 any eq smtp
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Author Closing Comment

by:kitbarr
ID: 31577607
This person kept right on at answering my questions as we went. Solved my problem and also helped me understand a little bit more.
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Expert Comment

by:akalbfell
ID: 24298665
permit tcp 0.0.0.0 0.0.3.255 0.0.0.0 0.0.0.3 eq smtp
that is saying permit traffic from any host in the 255.255.252.0 subnet going to any host in the 255.255.255.252 subnet

access-list 101 permit tcp 208.65.144.0 0.0.3.255 any eq smtp
this is more specifically saying permit from the 208.65.144.0/22 network to any host in your network

Glad to help!

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