On 2018-04-27 13:08, Daniel Suchy wrote:
There's quite good article discussing that: https://b4ldr.wordpress.com/2014/09/06/dummies-link-local-and-the-loop-back/
Thank you for providing the link. Though I'm not sure if I fully understand the implications of the post: In the conclusion they wrote:
Using the loopback interface caused other issues due to the fact that there is no link-local address. with the loopback interface the next hop for the default route becomes unreachable due to the lack of a link-local address so it is probably best to stick with the dummy interface
root@router1:~# ip -6 route 2001:db8:1::/64 dev zzz0 proto kernel metric 256 unreachable 2001:db8::/47 dev lo proto kernel metric 256 error -101 fe80::/64 dev zzz0 proto kernel metric 256 unreachable fe80::/64 dev lo proto kernel metric 256 error -101 unreachable default dev lo proto zebra metric 1024 error -101
Why does the lack of a link-local address result in the default route being marked unreachable? I'm guessing this is, because the lack of a link-local address implies that the interface is not on a IPv6 link and thus won't be able to reach another host (since the v6 spec requires interfaces to at least have a link-local address).
On 04/27/2018 10:52 AM, Wilhelm Schuster wrote:
Hi,
I’m learning about IP-networking and am in the process of setting up a Linux router using bird. During my research I’ve come across the usage of loopback interfaces. I could gather that this is done, because Ethernet interfaces for example (in contrast to loopbacks) can go down making the addresses configured on them unavailable. In addition, the kernel accepts packets destined to loopbacks addresses on other interfaces making these addresses available on multiple interfaces and not just the loopback.
On Linux I found both the lo(opback), and dummy interfaces recommended to achieve the behavior outlined above. What I’m struggling with is understanding the differences between both interface types (besides the obvious difference in packet processing) and when to use which. Searching this mailing list I’ve seen people use lo, on other sites dummy interfaces are recommended. From a quick test (assigning address to lo/dummy; pinging/receiving pings on the host) I wasn’t able to find a difference.
When should I use which interface?
Cheers, Wilhelm.