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Zorluk: KolayAccess Control Lists (Standard and Extended IPv4 ACLs)

A network technician is reviewing operational characteristics for standard IPv4 Access Control Lists (ACLs) on a Cisco router. Which of the following statements regarding standard IPv4 ACLs are correct? (Select TWO.)

  1. Standard ACLs filter network traffic based strictly on the source IPv4 address.Cevap
  2. Standard ACLs should generally be placed as close to the destination network as possible.Cevap
  3. C
    Standard ACLs inspect Layer 4 transport protocol header details such as TCP and UDP port numbers.
  4. D
    Unmatched traffic is allowed through by default because standard ACLs terminate with an implicit permit rule.

Cevap

Standard IPv4 ACLs filter traffic based only on the source IPv4 address and should be applied as close to the destination as possible to prevent unintentionally blocking traffic intended for other locations.
Standard IPv4 ACLs evaluate packets strictly by their source address. Because they lack the ability to inspect destination addresses or service ports, Cisco best practice is to place standard ACLs as close to the destination network as possible to avoid dropping legitimate traffic destined for other networks.

Adım Adım Çözüm

1
Identify the packet header fields evaluated by standard IPv4 ACLs.
Standard ACLs inspect only the source IPv4 address of incoming packets.
Standard ACL syntax (numbered 1-99 and 1300-1399) does not permit specifying destination addresses or protocol port numbers.
2
Determine the optimal interface placement for standard IPv4 ACLs.
Place standard ACLs near the destination network.
Filtering strictly by source address near the source router would prevent that host from reaching any other destination network.
3
Verify standard ACL default end behavior.
Recognize the presence of the implicit deny rule.
Cisco IOS automatically appends an invisible deny all statement at the end of every ACL list.

Anahtar Kavram

Standard IPv4 ACL Operational Rules and Recommended Placement
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