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Zorluk: ZorPrivate IPv4 Addressing and RFC 1918

A network engineer is auditing perimeter firewall logs on an enterprise WAN edge router. The firewall security policy is configured to drop any outbound packet whose source IP address falls within the RFC 1918 private IPv4 address space unless it has undergone Network Address Translation (NAT). During a routine inspection, the log records outbound packets from four host IP addresses: 11.10.5.1, 172.28.140.22, 172.33.10.1, and 192.169.50.4. Which source IP address will be dropped by the firewall policy for utilizing an RFC 1918 private IPv4 address?

  1. 172.28.140.22Cevap
  2. B
    172.33.10.1
  3. C
    192.169.50.4
  4. D
    11.10.5.1

Cevap

172.28.140.22 is the RFC 1918 private IPv4 address and will be dropped by the firewall.
The IP address 172.28.140.22 falls directly within the RFC 1918 Class B private address space of 172.16.0.0 to 172.31.255.255 (a /12 prefix block). Because it is an un-translated private address destined for an outbound WAN connection, the firewall policy correctly drops the traffic.

Adım Adım Çözüm

1
Recall the defined RFC 1918 private IPv4 address ranges.
Class A: 10.0.0.0 to 10.255.255.255 (10.0.0.0/8)
Class B: 172.16.0.0 to 172.31.255.255 (172.16.0.0/12)
Class C: 192.168.0.0 to 192.168.255.255 (192.168.0.0/16)
These three blocks are set aside by IANA and RFC 1918 for internal network use and are non-routable over the public Internet without NAT.
2
Evaluate host 172.28.140.22 against the Class B RFC 1918 range.
The second octet is 28, which falls inclusively between 16 and 31.
Because 16 <= 28 <= 31, 172.28.140.22 is a valid private IPv4 address.
3
Verify the remaining candidate IP addresses to confirm public vs private classification.
11.10.5.1 is outside 10.0.0.0/8; 172.33.10.1 is above 172.31.255.255; 192.169.50.4 is outside 192.168.0.0/16.
All three remaining options are public IPv4 addresses.

Anahtar Kavram

RFC 1918 Private IPv4 Address Space Boundaries
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Konular

Private IPv4 Addressing and RFC 1918

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