In sysctl.conf settings, what is the difference between 'all' & 'default'?

Question

In context of sysctl.conf settings, what is the difference between (all vs. default) like net.ipv4.conf.all.accept_source_route & net.ipv4.conf.default.accept_source_route in sysctl settings ?

If I added all values, is it necessary to add default as well ?

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Using Ubuntu 12.04 LTS

Answer 1

Special thanks to Symantec and google:

When you change variables in the /proc/sys/net/ipv4/conf/all directory, the variable for all interfaces and default will be changed as well.

When you change variables in /proc/sys/net/ipv4/conf/default, all future interfaces will have the value you specify.

This should only affect machines that can add interfaces at run time, such as laptops with PCMCIA cards, or machines that create new interfaces via VPNs or PPP, for example.