Network Aspects and Wake-On-Lan

As outlined in performance aspects, the network is an important factor. I tried to make Lindenberg Software Backup as fast and as simple to use as possible, but nevertheless you may want to understand some of the features or even tweak them:
  • Lindenberg Software Backup remembers two URLs, one for the Local Aread Network (LAN), one for the Wide Area Network (WAN). Of course you can be in different LANs over time, but in the following, LAN will refer to the network in which the backup server is located. For most users, the URL to be used within your LAN is different than the URL to be used when accessing the backup server from the outside aka WAN. Often the WAN URL also works internally, but unfortunately at significantly lower speed as the backup data needs to traverse (best case) your router, or even through your usually slow network connection (compared to your LAN). Therefore Backup allows you to enter two URLs, and tries the LAN URL first, and if that fails tries the WAN URL second (but only if it is different).
  • The LAN URL will often be a NetBIOS name, as many LANs at least in SoHo environments do not have a dedicated DNS server, however backup does not care how the name is resolved. Also both URLs can use a Dynamic DNS name. If you are using dynamic DNS, then likely because your WAN IP address changes occassionally, often once a night. Some routers allow you to specify when this should happen. I recommend to schedule backups after this address changes to minimize the risk of backups failing because of the address change, however I have seen backups to successfully continue despite the address change.
  • If you know how to set up your own DNS server you can tweak that the WAN URL resolves differently internally and externally, and you can in fact use the same URL for LAN and WAN. There are two advantages of doing that, a) you elminate the timeouts until backup fails over to the WAN URL, b) the WAN URL is more likely globally unique. If you don´t know how to do that, that is most of the time no real issue, it will take backup 15 seconds to time out the LAN URL. If you really encounter a name clash, i.e. the name of the backup server is reused in multiple networks, you may have to rename one of them.
  • Lindenberg Software Backup does support proxies as described in Understanding Web Proxy Configuration and works around the user dependency by remembering which user configured backup and copying the proxy configuration from there to the local system configuration.
  • Lindenberg Software Backup assumes (and checks during test) that the two URLs point to the same server. Also at test time it configures Wake-On-Lan (WOL) and allows to opt-in for otherwise not trusted server certificates.
  • Lindenberg Software Backup supports both IPv4 and IPv6, and either internal or external URL can resolve to an IPv4 or IPv6 address.
  • When backing up, Lindenberg Software Backup first uses Wake-On-Lan before trying to connect to the LAN and WAN URLs as described above. In fact it sends two Wake-On-LAN messages. Now how exactly the WOL messages are sent and processed depends on whether IPv4 or IPv6 is used in your LAN or WAN, or to what address type the WAN URL resolved.
    IPv4 IPv6
    LAN The WOL message is sent as a subnet directed broadcast. If backup server and client are in the same subnet, then this the same as a LAN broadcast. If your network consists of multiple subnets (often the case with Virtual Private Networks) and server and client are on different subnets, then it depends on your network components or configuration whether that broadcast will be delivered. In IPv6 there is no equivalent to a subnet directed broadcast or broadcast in general. The WOL message is sent as a link-local all nodes multicast to address ff02::1.
    WAN The WOL message is sent as a UDP message to the (external) IP address to which the host name in your WAN URL resolves. At the destination network, the router needs to broadcast the WOL message to the LAN or forward the message to some other network entity that does that - usually that choice depends on what your LAN router supports when configuring the broadcast address as the destination of port forwarding. If your router does not support port forwarding to the broadcast address, you need an extra device, which can be a small computer as the Raspberry Pi - see e.g. Wake-On-LAN Proxy with Raspberry PI. You can do similar with almost any other computer as well. With IPv6 the WOL message will be delivered to the network address to which the WAN URL is resolved using DNS. However with dynamic IP addresses you now face an issue. A router supporting dynamic DNS usually does not update the address of specific hosts, and your backup server can do this only if it is turned on somehow after your network address changed. Actually at present WOL via the intenet with IPv6 is an issue in general, see also https://tools.ietf.org/html/draft-vyncke-v6ops-ipv6-only-thin-clients-00. At present you can resolve this only by using a reverse proxy in front of the backup server that also sends a WOL message to the backup server as needed (this is my configuration, but with IPv4)
    Note that in order to leverage WOL you also need to configure your backup server´s network adapter to respond properly. A good source of information is Lights-Out: Questions about Wake-On-Lan/Wan. If you cannot get WOL to work, you can still rely on a scheduling backups to start at a time the backup server is turned on (e.g. using Lights-Out 2.0).
  • Lindenberg Software Backup checks whether a connection is within the same subnet using a direct Gigabit connection (and not passing through either a proxy or a reverse proxy server, but for the latter only if the reverse proxy modifies the Server http header field), and then leverages LZ4 compression (fast, but typically 30-50% compression only). Otherwise it uses GZIP compression (typically 50-70% compression, but compression takes longer than transmission with Gigabit network).