Hi,
On 3/16/19 18:29, Grant Taylor wrote:
On 3/16/19 10:33 AM, Erik Auerswald wrote:
BFD echo mode does not require support from the other side.
Full Stop! What‽
…reading hiatus…
Very interesting.
It works by sending an IP packet destined to the sending interface out
an interface. The upstream side is supposed to send this packet back
through the same interface (this is IP, not Ethernet).
I guess BFD Echo Mode is really just an IP packet that exercises the
remote forwarding engine.
It should work on any type of link where you can send a packet addressed
to yourself (that happens to be from yourself) and sent out a link to a
device that that should forward traffic destined to your local IP address.
I wonder if µRPF would interfere with this at all. I doubt it, because
^
u
This is called uRPF for "unicast RPF" as opposed to the multicast RPF
check this is based on.
the source IP would be coming in an interface that is an outgoing route
to said IP as a destination.
Indeed uRPF should allow that packet, as the source address is found
off the receiving interface (usually via a directly attached network).
I can see how some additional checking above and beyond µRPF might take
objection to traffic coming in an interface and immediately going back
out the same interface. As in why is that traffic coming in said
interface in the first place. But that's not µRPF as I understand it.
That could be done via ACLs, but would be unusual AFAIK. The uRPF
functionality itself should not interfere.
I have not yet tried this on Linux, but BFD echo modes is used for
short failure detection times in larger networks, because often the
line card (or port ASIC) can generate and check the packets without
CPU processing. A BFD control session is still usually used between
adjacent devices, but it is not strictly necessary.
I'm very intrigued by the idea of using (what I'm going to call) BFD-EM
/without/ BFD control sessions. I think this means that BFD-EM will
work against any device that will forward packets back to you.
Very interesting.
Thank you for sharing Erik.
You're welcome. :)
Thanks,
Erik
