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arp

leek

Hello,

I just had 2 test questions that have confused me.

1. hosta arps hostb over switch and router, what IP and mac are in hosta 's ARP table ?
Answer the routers mac and IP

So I'm guessing arps cannot traverse routers ? so if a host arps and cannot find the mac it points to the default gateway ?

2 between hosta and hostb is a switch and router, what is the correct addressing for a frame and packet received by hostb from hosta ?
Answer source IP is hosta's and the source mac was not in the exhibit. destination ip and mac was hostb's.

I'm guessing this is because ip's never change whereas macs do ?

Lee

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Comments

networker050184

These are not exam questions are they? If so you can't post them here.

You have the jist of it in your assumptions.

borumas

leek wrote:

Hello,

I just had 2 test questions that have confused me.

1. hosta arps hostb over switch and router, what IP and mac are in hosta 's ARP table ?
Answer the routers mac and IP

So I'm guessing arps cannot traverse routers ? so if a host arps and cannot find the mac it points to the default gateway ?

2 between hosta and hostb is a switch and router, what is the correct addressing for a frame and packet received by hostb from hosta ?
Answer source IP is hosta's and the source mac was not in the exhibit. destination ip and mac was hostb's.

I'm guessing this is because ip's never change whereas macs do ?

Lee

Hosts and switches only communicate and worry about the mac address (layer 2), when host A found that hostB was not on the local network it found that to get to host B it has to direct the data to the port connecting the switch to the router. This is why the router's mac and IP for that port are listed in the arp table, the packet's destination was still host B but the frames destination was to the router's port.
It's kind of like mail, where the mail man is like the switch and the post office is the router. If your letter is for someone in your neighborhood he can deliver it by using just the address (MAC) without it needing to be sorted at the post office, but if your letter is for somewhere not local to you then you need to use the zip code (IP address) to get it through the post office and delivered to the right town. Hope that helps and doesn't just confuse you more.