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. >>
