On Mon 2016-Sep-26 10:47:24 -0400, Ken Chase <math@sizone.org> wrote:
This might break some of those badly-behaving "dual ISP" COTS routers out there that use different inbound from outbound paths since each is the fastest of either link.
As it should. If you have links from both ISP A and ISP B and decide to send traffic out ISP A's link sourced from addresses ISP B allocated to you, ISP A *should* drop that traffic on the floor. There is no automated or scalable way for ISP A to distinguish this "legitimate" use from spoofing; unless you consider it scalable for ISP A to maintain thousands if not more "exception" ACLs to uRPF and BCP38 egress filters to cover all of the cases of customers X, Y, and Z sourcing traffic into ISP A's network using IPs allocated to them by other ISPs? If you want to play asymmetry tricks, get some PI space and make arrangements. If that's outside your wheelhouse, get an ISP that will sell this to you as a service either with dissimilar links they provide to you or over-the-top with tunnels etc. Playing NAT games with different classes of traffic to e.g. send traffic type 1 over ISP A and traffic type 2 over ISP B *BUT* using the corresponding source addresses in each case and having the traffic return back over the same links is fine and dandy. If you send traffic into an ISP-provided link using addresses from another provider, though, that ISP *should* be dropping that traffic. If they don't, send them here so we can yell at them.
I did this manually when I was messing around with multiple broadband links on a fbsd router years ago, was glad it worked at the time.
/kc
On Mon, Sep 26, 2016 at 07:11:42AM -0700, Paul Ferguson said:
No -- BCP38 only prescribes filtering outbound to ensure that no packets leave your network with IP source addresses which are not from within your legitimate allocation.
- ferg
On September 26, 2016 7:05:49 AM PDT, Stephen Satchell <list@satchell.net> wrote:
Is this an accurate thumbnail summary of BCP38 (ignoring for the moment
the issues of multi-home), or is there something I missed?
The basic philosophy of BCP38 boils down to two axioms:
Don't let the "bad stuff" into your router Don't let the "bad stuff" leave your router
The original definition of "bad stuff" is limited to source- address grooming both inbound and outbound. I've expanded on the original definition by including rule generation to control broadcast address abuse.
-- Sent from my Android device with K-9 Mail. Please excuse my brevity.
-- Ken Chase - math@sizone.org Toronto Canada
-- Hugo Slabbert | email, xmpp/jabber: hugo@slabnet.com pgp key: B178313E | also on Signal