Netplan ipv6 "No route to host"

I've clearly misconfigured my ipv6 listener addresses. Question 1: I need someone to spot the error. And a bonus Question 2: is there any risk to removing the "/sbin/ip address add" command below?

This is on a ubuntu 18.04 virtual machine.

Here's a curl command, showing that ipv6 routing is not set up correctly:

curl -vvv -L "http://[2600:1303:d000:1::17c3:4571]"
*   Trying 2600:1303:d000:1::17c3:4571...
* TCP_NODELAY set
* Immediate connect fail for 2600:1303:d000:1::17c3:4571: No route to host
* Closing connection 0
curl: (7) Couldn't connect to server

Previously, when the program started, it issued a native "/sbin/ip address add". That turned out to be problematic because when the network interface was reset, the route would be lost.

So, I added /etc/netplan because configuring the ipv6 routing survives a network restart. However, I didn't remove the "ip addr add" on startup. Currently, two commands are used to setup routing: netplan and "/sbin/ip address add". Here's the order of commands executed:

1.  Manual one-time command of "/etc/netplan apply" which didn't return any errors.  

2.  "ip addr add" every time the server starts.  So, at least once since the manual netplan command.

Here's the ipv6 addresses it's listening on:

netstat -anp | grep redir | grep LISTEN
tcp6       0      0 2600:1303:d000:1::17:80 :::*                    LISTEN      3187/my-service
tcp6       0      0 2600:1303:d000:1::17:80 :::*                    LISTEN      3187/my-service
tcp6       0      0 2600:1303:d000:1::17:80 :::*                    LISTEN      3187/my-service
tcp6       0      0 2600:1303:d000:1::17:80 :::*                    LISTEN      3187/my-service
tcp6       0      0 2600:1303:d000:1::17:80 :::*                    LISTEN      3187/my-service

Here's what I want it to be listening on: [2600:1303:c000:1::15d4:456f]:80" [2600:1303:d000:1::17c3:4570]:80" [2600:1303:d000:1::17c3:4571]:80" [2600:1303:d000:1::17c3:4572]:80"

Here's the "ip address add" command. Notice that the I'm using "/24" and I wonder if that's the problem. Or perhaps using both "ip addr add" and netplan isn't working as intended. This is a legacy application and because my networking skills in this area aren't strong, I wasn't sure if it would be safe to remove the "ip addr add". I didn't think it would hurt to keep the "ip addr add" command, but perhaps I was wrong.

out, e = exec.Command("/sbin/ip", "-6", "addr", "add", ip + "/24", "dev", "eth0").CombinedOutput()

Here's my netplan config file. Note that this is only part of the file; for security reasons I'm not including the mac address, name servers or gateway. However, they are correct because my ipv4 addresses work. Also, I haven't posted the real ipv6 addresses for security reasons as well.

root@ubuntu:~# cat /etc/netplan/50-cloud-init.yaml
# This file is generated from information provided by
# the datasource.  Changes to it will not persist across an instance.
# To disable cloud-init's network configuration capabilities, write a file
# /etc/cloud/cloud.cfg.d/99-disable-network-config.cfg with the following:
# network: {config: disabled}
network:
    version: 2
    ethernets:
        eth0:
            addresses: [ '2600:1303:d000:1::17c3:456e/24', '2600:1303:d000:1::17c3:4570/24', '2600:1303:d000:1::17c3:4572/24', '2600:1303:d000:1::17c3:4571/24', '2600:1303:d000:1::17c3:456f/24' ]

Thanks in Advance ;)

Solution

There were a couple of problems:

There was no gateway6.
The bit mask should have been "/64" instead of "/24"

Netplan wouldn't delete the old routes. I had to do following steps:

1.  ip -6 addr del 2600:1303:d000:1::17c3:456f/24 dev eth0
2.  netplan apply