For my Kubernetes nodes, I see following entry with a star under the interface column. I do not see this mentioned in "route" command's documentation. The only star mentioned there is for gateway. This entry has been created by Calico for the gateway on current VM.

Destination Gateway Genmask Flags Metric Ref Use Iface --- --- --- U --- 0 --- 0 --- 0 --- *

I have attached the output of route and "ip route" commands.

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  • Where did all those hyphens come from? What command did you run to generate this output? May 23 '19 at 1:25
  • I added the hyphens to the output of "route -n" May 23 '19 at 11:19
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    That's really confusing. It's best to just paste command output without modification, and format it with the code format button {} in the editor. Also, you should run ip route instead of the deprecated and sometimes wrong route. May 23 '19 at 14:36
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    This is a side effect of route output. Some types of routes (unreachable in your case) don't require the interface specification. So, the route tool uses * as flag of empty interface attribute. May 24 '19 at 13:41
  • Thanks for suggesting the "ip route" comand @MichaelHampton. he output of that shows the entry as "blackhole". Further looking at Calico documentation, I see that one purpose of blackhole route is to prevent DDoS attacks, though more relevant to IPV6. I am still trying to find the exact purpose of that routing rule. May 24 '19 at 13:59

An * under the interface column in output of route command denotes a blackhole destination. In this particular case of a route created by Calico, it causes BIRD to export that route to its BGP peers(on other worker VMs), so that those peers think they can reach the CIDR via this node. For local routing it's not supposed to come into play, because we expect that iptables rules programmed by kube-proxy will DNAT to an actual pod IP.

Source : https://github.com/projectcalico/calico/issues/2457#issuecomment-468767265

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