There is something wrong with ARP table!!!

Answered Question
Jul 25th, 2006
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Here is my network diagram...


Server----3750---3560---2950---Host1


When i check arp table on 3750, i saw Host1 MAC address... I think i should see 3560 MAC address, right?





Correct Answer by Richard Burts about 11 years 3 weeks ago

Routers and other layer 3 forwarding devices do rewrite the MAC address in the header. Switches and layer 2 devices forward frames without changing the MAC addresses.


HTH


Rick

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hgru Tue, 07/25/2006 - 05:59
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Wrong, you would see the mac adresses of server and host one if you send a ping between them.

Roberto Salazar Tue, 07/25/2006 - 06:00
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If the 3750 have L3 interface (interface vlan) that is in the same subnet as host1, it is normal that you will see it's mac address in 3750's arp table. The router or L3 device will always have arp entry for the hosts in the subnet that routre is default gateway for or the router have interface for that subnet.


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zerozerotito Tue, 07/25/2006 - 06:05
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Can you guys correct me?


WHen i ping to server, the host put its mac address to ping packet.. When this packet arrives to the first switch which 2950, switch will change the source MAC address as the port mac address which is connected to 3560 and so on... So when this packet arrives to 3750, how does 3750 knows the host MAC address... As i know, every switch and router change MAC address...

zerozerotito Tue, 07/25/2006 - 06:11
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Im really stupid...:) The switches are on the Same VLAN... So it is normal to see them...


Thank you guys again...

Correct Answer
Richard Burts Tue, 07/25/2006 - 06:12
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Routers and other layer 3 forwarding devices do rewrite the MAC address in the header. Switches and layer 2 devices forward frames without changing the MAC addresses.


HTH


Rick

ryan.bachman Tue, 07/25/2006 - 06:16
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Depends if it is layer 3 of layer 2. When speaking strictly layer 2, the mac address of the host 1 distributed across the layer 2 network. Only at layer 3 does a packet require a rewrite. If this design you have here, is one flat Vlan, or that host resides in a Vlan on the 3750, that it would still be considered in the same L2 network, in which you will see the Mac address of the end device.

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