It is pretty common to use arbitrary string values in Option 66 to provision IP Phones. However, VyOS does not accept this for an unknown reason (which I consider a bug):
```
set service dhcp-server shared-network-name <network-name> subnet <subnet> static-mapping <mapping-name> option tftp-server-name "1.2.3.4:65000/provisioning/abcxyzdefghi/cfg{mac}"
```
will fail with:
```
Error: 1.2.3.4:65000/provisioning/abcxyzdefghi/cfg{mac} is not a valid IPv4 address
Invalid value
Value validation failed
Set failed
```
This should be an easy fix and perfectly backwards compatible.