EC2 Redhat - Multiple Private IP

Question

I have one VPC with two Subnets (SubnetA and SubnetB).
My team wants to have multiple IPs assigned to the Instance, each from one subnet.
The Instance already have one Private IP (from SubnetA, Primary one) when I launched it, then I attached another Private IP from another SubnetB via the Console Attach network Interface option.
I can see both of the IPs in the console under Managed IP Address option.
I rebooted the Instance, and I was expecting to see both of the IPs when I do ifconfig, but I can see only the Primary one.

To cross-check if the Private IP is actually attached to the Instance, I queried Instance Metadata using the following commands :

• curl -s http://169.254.169.254/latest/meta-data/network/interfaces/macs/02:14:46:91:bc:34/local-ipv4s
• curl -s http://169.254.169.254/latest/meta-data/network/interfaces/macs/02:1d:2a:75:ax:04/local-ipv4s

I can see both of the IPs in the output for the above two commands respectively.

I checked the status of NETWORKMANAGER systemctl status NetworkManager It was stopped

I started the Service and enabled NetworkManager automatically at boot time, using following commands:
systemctl start NetworkManager
systemctl enable NetworkManager

Then I checked the output of ifconfig

This time it showed me both of the MAC addresses, with the only difference for the second one I was not able to see the IP address. So basically the interface is up, so the underlying device is found. There is no IP address associated with this interface.

So I tried both of the options to associate IP:

Assign an IP address manually:
sudo ifconfig ens6 w.x.y.z

Or contact the DHCP server, if it exists, and let it provides an IP address for the interface:
sudo dhclient -v ens6

Both of them worked and I can see both of the IPs under inet.

The last problem was I have to do this every time I reboot the Instance. So I was trying to add a permanent route using the following command:

sudo /sbin/route add default gw 1xx.xx.2xx.193
Here the IP is the second IP from the SubnetB, but I am getting the error : SIOCADDRT: Network is unreachable

To solve the above problem what I did is, I was already having a file with
/etc/sysconfig/network-scripts/ifcfg-ens5 with details for Primary IP, I added one more file
/etc/sysconfig/network-scripts/ifcfg-ens6 with the necessary details for secondary IP

This is what I referred.

Rebooted and it is working.

But I am not able to ping the secondary IP. I think I have to add one more Gateway from the second subnet but not sure about this.

What else needs to be done so that I can route traffic, ping, ssh using the Secondary IP.

Please refer to my VPC Subnet CIDRS:

Subnet A: 1.7.2.128/26 Subnet B: 1.7.2.192/26

Output of ip route:

Update:

Today when I started the server I am able to ping the Secondary IP(200), but not the Primary one(136), from one of my test Instances. Also, ssh is done using Primary IP.

Answer 1

ip route add default via 1XX.XX.XXX.X9X dev ens6 table 2000;
ip route add 1XX.7X.2XX.X9X dev ens6 table 2000;
ip rule add from 1XX.7X.2XX.1XX lookup 2000;

The above command helps me to resolve this issue and I am able to ping my secondary IP. To make this configuration persist after reboots, the same commands, I have added into rc.local

In the first line, the IP is the Gateway IP (Second IP in the Subnet Range) The IP mentioned in the second and third lines in the command is the actual Secondary IP of my Server.