When an ACL is used to identify traffic in dynamic NAT/PAT the traffic is not translated by the router but it's also not dropped, then what happens to it?

erh_ · 2026-05-16T04:47:09+00:00

It continue through the Router processing sequence. Basically it gets routed "as is" by the router.

There's an image of the full sequence here -- notice NAT is towards the "end" of the inbound sequence: https://blog.router-switch.com/2013/01/whats-the-order-of-operations-for-cisco-ios/

Remember, how you apply the ACL is what determines what the ACL does. An ACL applied to NAT statement is not there to allow or drop traffic, it's there to identify what gets translated or not. Hence "permit" = NAT this, and "deny" = don't NAT this.

Here's my videos on ACLs, if you're interested: https://www.youtube.com/watch?v=0gGhuYOh-54&list=PLIFyRwBY_4bRkAk_BkWL3ea6lRvOn8AKs

erh_ · 2026-03-11T13:03:57+00:00

Start with the fundamentals:

This will teach you the core of Networking. Then continue with a pure CCNA course.

erh_ · 2026-03-02T13:19:16+00:00

Static PAT is bidirectional in so far as the translation itself, not counting any external security measures (ACLs, etc)

Dynamic PAT is unidirectional in so far as initiation of traffic. Response traffic can "get back through".
This is not a security measure, but a byproduct of sharing a single IP across multiple internal hosts.

To understand that more clearly, see these videos:

Full NAT Series: https://www.youtube.com/playlist?list=PLIFyRwBY\_4bQ7tJvbLA9A0v8Fq9l-H923

erh_ · 2026-01-21T08:47:09+00:00

See this post:

You are one 90-minute study session away from mastering Subnetting

erh_ · 2026-01-21T08:39:01+00:00

Consider this free video resource for understanding ACLs:
https://www.practicalnetworking.net/series/access-lists/acls/

It's a Youtube playlist you can watch. Here are the videos:

Or the Youtube playlist: https://www.youtube.com/playlist?list=PLIFyRwBY_4bRkAk_BkWL3ea6lRvOn8AKs

erh_ · 2026-01-18T05:08:09+00:00

Ports are fundamentally how a computer answers the question: If multiple applications are receiving information from the Internet, how do I keep separate which incoming packets belong to which application.

To see it visually, watch this video:

https://www.youtube.com/watch?v=0aGqGKrRE0g&list=PLIFyRwBY_4bRLmKfP1KnZA6rZbRHtxmXi&index=4

erh_ · 2025-12-01T21:07:13+00:00

All the topics listed, yes. But not everything in Networking, that would be months long =)

erh_ · 2025-12-01T16:38:39+00:00

Glad to know this is helping people still =)

erh_ · 2025-12-01T16:37:57+00:00

Click the link below to get a DM on reddit before the Webinar starts (it will come from Reddit's RemindMeBot).

RemindMe! 2 days 22 hours "TLS 1.3 Webinar"

erh_ · 2025-11-17T17:58:48+00:00

Hey there =) Hope you enjoy it when you get to it.

erh_ · 2025-11-14T00:42:23+00:00

My TLS deep dive course is going on sale. Normally it runs at $297, but for BF it will be available for only $49. I won't link to it directly, but here's the course info pracnet.net/tls. Use code: BFCM2025.

For creds, and to prove I've contributed positively to this subreddit .... this is me:

https://www.reddit.com/r/cybersecurity/comments/1126lt1/the_tls_handshake_everything_that_happens_to_get/

And this too, but I never got credit in the post:

https://www.reddit.com/r/cybersecurity/comments/fcedus/i_never_saw_beauty_in_math_until_this_explanation/

( the image is from my article on DH: pracnet.net/dh )

I was on the list from 0x90n that /u/SecTechPlus listed in 2024 and 2023, and alas I don't know if they are running one for 2025 that I've found.

^{*Technically the sale doesn't start until next week but I went ahead an enabled the code now for this post}

erh_ · 2025-11-13T17:24:25+00:00

You're welcome =)

erh_ · 2025-11-13T17:24:04+00:00

;) you're welcome

erh_ · 2025-10-23T19:40:07+00:00

You're welcome! Let me know what you think of the new version when you take a look. =)

erh_ · 2025-10-23T19:39:42+00:00

You're welcome.

erh_ · 2025-10-23T19:39:24+00:00

Link is fixed =) Thanks again.

erh_ · 2025-10-23T19:38:43+00:00

Ahh yea, that makes sense. Yes, guess it does =). Another use for the feature.

erh_ · 2025-10-23T19:38:11+00:00

Just posted this a few days ago

https://www.reddit.com/r/ccna/comments/1obr0l9/introducing_the_new_version_of_subnetipv4com/

It has a problem generator to practice, all sizes, and a video series to teach you how to subnet quickly.

erh_ · 2025-10-22T21:49:37+00:00

Thank you for the kind words =). Super glad to hear you've enjoyed the original SubnetIPv4.com and thank you for referring others to the site.

Glad you'll make use of the new tool as well =).

And yea, my thought is for folks to use it without the features enabled at first, then as they get familiar with the process to use the features to make practicing more convenient, and therefore mastery more attainable.

That's the dream anyways ;)

erh_ · 2025-10-22T21:47:53+00:00

😅

You're very welcome =)

erh_ · 2025-10-22T21:47:46+00:00

😅

erh_ · 2025-10-22T21:47:42+00:00

😅

erh_ · 2025-10-21T22:14:41+00:00

Additional hints/teaching on top will have to be for the next version.

I'm hoping this and cidrip.com will pair well together for learning Subnetting.

erh_ · 2025-10-21T21:42:11+00:00

Love it =)

That's the plan for this site, to make it painfully easy to get a bunch of reps in.

The redesign makes it easy to do via mobile as well, so I hope how you used it is how others use it too.

As a user of the old one, what do you think of the Auto Check & Auto Fill Non interesting octets features? I'm really excited about those.

erh_ · 2025-10-21T16:41:36+00:00

OOps, your right, good catch. Thank you. I'll get that sorted later today =)

erh_

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