Posts Tagged ‘acls’


One of the key facts regarding Access Control Lists (ACLs) that we drill into your head during CCNA is the fact that the lists you create end with what is called the “implicit” deny all. You do not see it, but the effect is undeniable. Any packets that do not match any of the permit statements in your list get deny treatment. In the case of our filtering access lists, this means the packets are dropped. As you recall from the course, this is why we desperately require at least one permit entry in all of our filtering access control lists.

But what if we want to track what we actually drop as a result of this powerful implicit deny all effect? Well, a clever trick is to end the list with an explicit deny statement and log the result. In this post, we will examine this technique.

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1. QoS Policy Propagation through Border Gateway Protocol (BGP) (QPPB)
2. Input common classification
3. Input ACLs
4. Input marking (class-based marking or Committed Access Rate (CAR))
5. Input policing (through a class-based policer or CAR)
6. IP Security (IPSec)
7. Cisco Express Forwarding (CEF) or Fast Switching

1. CEF or Fast Switching
2. Output common classification
3. Output ACLs
4. Output marking
5. Output policing (through a class-based policer or CAR)
6. Queueing (Class-Based Weighted Fair Queueing (CBWFQ) and Low Latency Queueing (LLQ)), and Weighted Random Early Detection (WRED)

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