The routing table of a router is shown below: Destination Sub net mask…

2004

The routing table of a router is shown below: 

 Destination     Sub net mask 	     Interface
 128.75.43.0 	 255.255.255.0 	        Eth0
 128.75.43.0 	 255.255.255.128 	Eth1
 192.12.17.5 	 255.255.255.255 	Eth3
 default 	  	                Eth2

On which interfaces will the router forward packets addressed to destinations 128.75.43.16 and 192.12.17.10 respectively?

Answer: A. Eth1 and Eth2 — Answer: forward to Eth1 and Eth2. Reason: use longest-prefix (most specific) match. Evaluate each destination: For 128.75.43.16: This address falls within…

  1. A.

    Eth1 and Eth2

  2. B.

    Eth0 and Eth2

  3. C.

    Eth0 and Eth3

  4. D.

    Eth1 and Eth3

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Show answer & explanation

Correct answer: A

Answer: forward to Eth1 and Eth2.

Reason: use longest-prefix (most specific) match. Evaluate each destination:

  • For 128.75.43.16: This address falls within 128.75.43.0/25 (network range .0–.127) and also within 128.75.43.0/24, but the /25 route is more specific, so the packet is forwarded to Eth1.

  • For 192.12.17.10: There is a host route only for 192.12.17.5 (a single-address route), so 192.12.17.10 does not match it. No other specific route matches, so the router uses the default route and forwards the packet to Eth2.

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