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Finding the right gateway IP address on a /24 network

asked 2021-01-07 03:19:45 +0000

kenchao gravatar image

I'm currently learning how to analyze network packets using wireshark, I was given a pcap file to identify the right gateway address and add a route to my machine and access the internal network.

I take a look on the ARP request "who has x.x.x.x? Tell xx.xx.xx.xx"

However when I add the routing on the table, I got an error: RTNETLINK answers: No such process (Which I think I didn't get the right gateway for the x.x.x.x)

May I know the other ways of identifying the right gateway besides from filtering ARP requests?

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answered 2021-01-07 09:07:33 +0000

Jaap gravatar image

Okay, there's a lot of details missing here, but here's something to think about.

  1. Can you find an IP packet which is addressed to egress this network?
  2. From this packet, can you find the MAC address of the host this packet is sent to?
  3. From this MAC address, can you find out the corresponding IP address?
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This is what I missed, I got it now.

kenchao gravatar imagekenchao ( 2021-01-07 15:11:55 +0000 )edit

answered 2021-01-07 08:35:08 +0000

tomasz gravatar image

updated 2021-01-07 08:35:42 +0000

Select a conversation crossing outside of LAN and check the destination MAC on outgoing packets. That's the gateway.

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Asked: 2021-01-07 03:19:45 +0000

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Last updated: Jan 07 '21