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This is for either Linux/BSD.

I was just wondering if it was safe to run a firewall off a single ethernet port. The firewall machine would have a single ethernet port that is connected to a switch. The ADSL modem is also connected to the same switch.

The firewall uses the ETHERNET interface as the GREEN interface and uses PPPOE interface as RED interface. Obviously, the PPPOE is routed over the same GREEN interface onto the ADSL modem.

Logically, the two interfaces are separate. So, filtering rules can be applied. However, as they share the same physical connection, I'm wondering if that logical filtering is sufficient isolation.

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up vote 2 down vote accepted

it's safe to run it on single physical nic, although many people would suggest to have dedicated nic for each network, but in some cases only one nic is available so it can work securely on one nic as well

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