Re: Failover route

Hi,

On 3/12/19 16:36, Grant Taylor wrote:
> On 3/12/19 8:32 AM, Leroy Tennison wrote:
>> I have a device with two routes to the Internet configured as
>>
>> default nexthop via <IP address 1> dev <NIC 1> weight 1
>> default nexthop via <IP address 2> dev <NIC 2> weight 1
>>  > If I'm understanding what I saw correctly, if (when) one interface 
>> fails
>> it still tries it every other time.  What I saw was an outbound ping 
>> regularly failing then succeeding (a few successes then a few failures 
>> then the success/failure pattern repeated).  I then noticed that one 
>> interface wasn't fully plugged in and, after rectifying that, received 
>> 100% ping response.
>> [...]
> I have long wanted Bidirectional Forwarding Detection to be a thing 
> between my router and my ISPs.  Unfortunately, (it's my understanding 
> that) BFD requires active support from the other side.

BFD echo mode does not require support from the other side. 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 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.

Thanks,
Erik