Refer to the exhibit:
What will Router1 do when it receives the data frame shown? (Choose three.)
A.
Router1 will strip off the source MAC address and replace it with the MAC address 0000.0c36.6965.
B.
Router1 will strip off the source IP address and replace it with the IP address 192.168.40.1.
C.
Router1 will strip off the destination MAC address and replace it with the MAC address 0000.0c07.4320.
D.
Router1 will strip off the destination IP address and replace it with the IP address of 192.168.40.1.
E.
Router1 will forward the data packet out interface FastEthernet0/1.
F.
Router1 will forward the data packet out interface FastEthernet0/2.
Explanation:
Could someone explain it please?
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You can see that the destination address is 192.168.40.5 then refer to the arp table and note that this address is destined to fastethernet 0/2 so F is correct and E is incorrect.
Secondly you have never forget that the ip addresses are not change between the source and destination so be sure B and D are incorrect, so obviously A and C are correct.
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how do you say that destination address is 192.168.40.5
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This appears to be a totally process of elimination question as we dont have gateway information and vlan information. Comments?
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I am agree with you Oldguy, there is no enough information, and the question itself is confusing, but since they do not state that we have just to take in consideration the source and destination ip and source and destination MAC address as shown in the exhibit, the answer A, F and C are correct.
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The “Age” field in the “show ip arp” command is the age in minutes of the cache entry. A hyphen (-) means the address is local so in this case 192.168.20.1, 192.168.40.1 & 192.168.60.1 are local to this router.
From the “Data Frame”, we learn that a packet is sent to Router1 and Router1 needs to forward it to the Destination IP 192.138.40.5. Therefore this router will:
+ Strip off the source MAC address and replace it with the MAC address 0000.0c36.6965 (because the IP address of this interface – 192.168.40.1 is in the same subnet with the Destination IP 192.138.40.5).
+ Strip off the destination MAC address and replace it with the MAC address 0000.0c07.4320, which is the MAC of Destination host.
+ Forward the data packet out interface FastEthemet0/2 because this interface has the IP address of 192.168.40.1.
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Awesome explanation 🙂
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Hi, something here is very wrong:
the client that sent that frame sits in 192.168.20.5
the mac-address of this client is: f892
this client wants to send the frame to a different network: 192.168.40.5
but he can not know the mac-address of the client over that network, so he puts inside the frame the mac-address of the router in his network: ae45
AE45 is the mac-address of the router
when the router wants to send the frame out, he needs to change the mac-source from the client to himself, change the mac-destination from himself to the next hop and check what interface should be used.
the mac-destination is changed according to what is written in the arp table about network 192.168.40.5: it`s really 4320.
the interface to reach this network is really fa0/2
but the source-mac, that was the client and now is the sending router, should be AE45 in 192.168.20.1 and NOT 6965. it can NEVER be 6965 because this address belongs to the network this router tries to go to, and thus can NEVER be the new SOURCE-mac.
our client already told us what the mac-address of that router is – it`s AE45, as shown in the frame, so the new source-mac should read what the old destination mac was, again: AE43 and NOT 6965.
I am sorry, but this is how LAN works. if someone knows any better, I`d be more than happy to understand otherwise.
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Read what Bassam wrote, that´s the right explanation about this question. Answers are A,C,F.
Willow, this is your mistake: “but the source-mac, that was the client and now is the sending router, should be AE45 in 192.168.20.1 and NOT 6965”
The packet sent to 40.5 is coming from F0/2´s interface (40.1), not from 20.1. It means the source MAC-ad will be f0/2 int, 0000.0c36.6965. That´s why option A is correct.
Regards
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i stand corrected. thank you.
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Hey guys, this questions pretty confusing but thanks to Bassam I understand it now. Does anyone know where I can find more questions like this one? Thanks everyone !
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Correct Answers:
Router1 will strip off the source MAC address and replace it with the MAC address 0000.0c36.6965. Router1 will strip off the destination MAC address and replace it with the MAC address 0000.0c07.4320. Router1 will forward the data packet out interface FastEthernet0/2.
Explanation:
Remember, the source and destination MAC changes as each router hop along with the TTL being decremented but the source and destination IP address remain the same from source to destination.
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