Why do I get packets 'input' on Null0

[Andrew Ward]

Hello,

I have noticed that I am getting a large amount of packets input on my 3825 VPN router when I do a 'show int null0'.

I understand the normal reasons for packets going out of null0 (summarization, desired black holing etc) but why would null0 be a source of packets? The number of packets is only slightly less than the packets going through the router - and I have many succesfull site-to-site VPNs. 

I suspect this is some kind of feature, but didn't want to just ignore it.

Thanks,

Andy.

[Diego Armando Cambronero Arias]

I think these are L2 packets related with ARP

Do you have RTBH configured anywhere?

Input means that the packets are received. When something is received in that interface I think that the interface send an icmp unreachable message so those are the output messages.