Question

Send Outbound Traffic Over a Reserved IP with a Custom Image

Posted on March 15, 2024
Custom Images Networking
Asked by Kyle Loveless

Hi,

The “Send Outbound Traffic Over a Reserved IP” (https://docs.digitalocean.com/products/networking/reserved-ips/how-to/outbound-traffic/) document mentions for custom images that there is no anchor IP, but yet that is what must be used to send traffic out over the reserved IP.

The explanation of Anchor IP (from https://docs.digitalocean.com/glossary/anchor-ip/), says “Droplets created from custom images do not require an anchor IP to use a reserved IP, instead the reserved IP maps to the Droplet’s public IP address by default.”

I’m trying to confirm if it is tested and expected to work that custom images can send outbound traffic over a reserved IP? And if so, do they need to go through the instructions to enable Anchor IPs (https://docs.digitalocean.com/products/networking/reserved-ips/how-to/enable-old/#enable-anchor-ips-immediately)?

I was able to find an Anchor IP, but was having trouble getting routing to work (but I’m new to custom images and having multiple network ports - I see the the loopback, public IP and private IP before I try to add anchor IP).

I likely have something wrong in my setup, but just wanted to confirm it should be possible.

Thanks!

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Jesse Portnoy • April 18, 2024

Accepted Answer

Found the solution. the IP addr to assign to eth0 is what returns from http://169.254.169.254/metadata/v1/interfaces/public/0/anchor_ipv4/address (10.18.0.12 in this example) and the default GW should be what is returned from http://169.254.169.254/metadata/v1/interfaces/public/0/anchor_ipv4/gateway (10.18.0.1 in this example).

To avoid severing your network connection if something fails, I’d recommend add a non-default route to one specific IP first, for example:

host ifconfig.me

ifconfig.me has address 34.117.118.44

ip route add 34.117.118.44/32 via 10.18.0.1 dev eth0 Then, to test that it worked: curl ifconfig.me Once this works: ip addr add 10.18.0.12/16 dev eth0 route add default gw 10.18.0.1 And: route del default gw $ORIGINAL_GW