AWS second elastic IP not working after correct dhclient results

Question

EDIT: Solved, routing table did not update properly. as was answered.

On AWS and Ubuntu 16.04, a 2nd network interface is attached with 2nd elastic IP.

Instance

Answer 1

This is because you have multiple network interfaces on the same subnet, so your OS is not sending it out of the right interface. You will need to use source based routing on your instance to make this work.

Answer 2

echo 2 > /proc/sys/net/ipv4/conf/default/rp_filter
echo 2 > /proc/sys/net/ipv4/conf/all/rp_filter

To make this change persistence

net.ipv4.conf.default.rp_filter = 2
net.ipv4.conf.all.rp_filter = 2

** Tested AWS Environment