To give a concrete example, how does OSX choose which of these default entries from netstat -nr
to route to?
Destination Gateway Flags Refs Use Netif Expire
0/1 10.10.99.100 UGSc 0 0 ppp0
default 192.168.1.1 UGSc 5 0 en0
default 192.168.1.1 UGScI 1 0 en1
default 192.0.2.1 UGScI 157 2 ppp0
From what I have been able to tell OSX uses metrics on its interfaces rather than on its routing table entries. But by default all of those interface metrics are 0 so how does it choose? Last created interface?
I've seen some folks suggest its the order in the Network preferences, but in my case the ppp0 interface (from SonicWall NetExtender) isn't listed there.
There is some discussion in this thread, but no answer that I see.
Best Answer
Most systems follows these rules when choosing which route to use:
On Linux (and, I think, on Windows) priority is determined by metric, but it is not the case on macOS as you correctly pointed out. Instead of assigning metrics to individual routes, macOS assigns priorities to interfaces. You can use
networksetup -listnetworkserviceorder
to view this order andnetworksetup -ordernetworkservices
to change it.Now, this route from your output makes me think that in your case specificity also plays its role:
This route covers the bottom half of the address space and therefore I would expect to also find:
in your routing table. This is a standard trick VPN software uses to prioritise its routes over
default
: it adds two routes which together cover all IP addresses, but each of them is more specific than default, so they win.