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Networking

A guest that boots at the recovery site is useless if it lands on a bridge that doesn’t exist there, or keeps an IP that belongs to a subnet the recovery site has never heard of. Networking is where you answer that once, per DR Site Pair, so every protected guest inherits the right answer instead of you fixing each one by hand during an outage.

Everything on this page is a pair-level default. Individual guests can override it, and the page shows you which ones do.

These settings are recovery-owned — the recovery site holds the truth, because it’s the side that has to make them work. When you open the page from the source site, Asternodis reads them through the peer, so you see and edit the same values from either end.

Failover networking mode

The pair-wide choice for what happens to a guest’s addressing when it comes up at the recovery site:

  • Keep IPs — the guest boots with the addresses it already had. Right when the two sites share a stretched L2 or you’re failing over a whole subnet.
  • Re-IP — the guest’s addresses are rewritten for the recovery network. Right when the recovery site is a different subnet, which is the common case for a second building or a colo.

Network mapping

The source → recovery bridge and VLAN map. For each bridge a protected guest uses at the source, you say which bridge it should attach to at the recovery site, with an optional VLAN tag.

There’s a separate column for DR test so a non-disruptive test can land on an isolated bridge — the test boots a real copy of the guest, and you rarely want that copy on the production network answering for the same addresses.

Unmapped bridges are the single most common reason a failover boots a guest with no reachable network, so map every bridge your protected guests actually use.

Re-IP default

The subnet rewrite guests inherit when they have no explicit per-guest re-IP — the recovery subnet, gateway, and how source addresses translate into it. Set this and you generally don’t need to touch individual guests at all.

When the mode and the default disagree

If the mode says Keep IPs but a re-IP default is set, the effective behaviour is Re-IP — the default wins, because it’s the more specific instruction. Rather than leave that as a trap, the page computes the effective behaviour live and offers two one-click fixes:

  • clear the default, so Keep IPs genuinely keeps IPs, or
  • promote the mode to Re-IP, so the label matches what already happens.

Either is correct. What matters is that the page never quietly does something other than what it says.

DNS

An Asternodis-managed dnsmasq that the recovery node runs for the pair. When guests are re-IP’d, their names have to resolve to the new addresses or half your estate still points at dead ones. This gives the recovery site a zone that answers for the recovered guests without you touching production DNS.

Per-VM networking

The per-guest view of the same settings: which guests inherit the pair defaults and which carry their own re-IP override, with a link into each guest’s detail page to edit it.

Use the defaults for the bulk of your estate and reserve overrides for the handful of guests that genuinely need a fixed address at the recovery site — domain controllers, load balancers, anything else hard-coded elsewhere.