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Sasp

May 26, 2018

Tool that permits to use a gateway whatever IP we have

This is a tool that uses ARP poisoning to have a scenario like this we have a LAN and we want offer connectivity to every- one coming here with his laptop for example. It could happen that our customer has his network parameters already configured to work correctly in his own LAN, but not working here. We can have then this scenario Customer’s host 10.0.0.2/8 and default gateway set to 10.0.0.1 Our LAN 192.168.0.0/24 with real gateway 192.168.0.254. All that we want is that our customer plugs his laptop and joins the internet without changing nothing of his network parameters. Here comes this tool installed in my real gw192.168.0.254 It’s a sort of sniffer, because it sniffs broadcast ARP requests for the gateway and answers that the gateway is itself In our example our customer’s laptop sends this request arp who-has 10.0.0.1 tell 10.0.0.2 Now our gateway does the following 1 Sends back this reply to 10.0.0.2 arp reply 10.0.0.1 is-at his_mac_address 2Create the alias 10.0.0.254 ARP is not routable so we need one alias for each subnet that is not our one 3Sends itself an ARP reply to refresh his ARP cache It is different from proxy arp for two reasons first it runs in user space, then in this case we can plug machines belonging to whatever subnet, while proxy arp is used in the case of only two different ones.