Why virtual machines in Amazon are only available in one direction by ping?

Question

Amazon Web Services

We have two
virtual machines 1 - 172.31.40.107/20
and
2 - 172.31.17.237/20
All in the default config and driven into VPC 172.31.0.0/16
From 1 to 2 connection via ssh is available
C 2 to 1 both via ssh and via ssh is available and also pinged

iptables reset, just in case the 2nd virtualka

is generally default EC2, just created
net.ipv4.ip_forward=1 just in case uncommitted UPD: I decided - the rules in security groups