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(Related to this question I posted a while ago on apple.stackexchange.)

What is the difference between the following two routing table entries:

default            E.F.G.H     UGSc            0        0     en1
default            E.F.G.H     UGScI          25        0     en1

(Where E.F.G.H is some gateway IP address.) Specifically what effect does the RTF_IFSCOPE flag have on the routing table entry?

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up vote 2 down vote accepted

You can use the route command's -ifscope option to bind a route to a specific interface. This lets you create multiple routes that point to the same destination, differentiated only by which interface is in play. Routes so bound show up in netstat output with the I flag.

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