Test environment
Connectivity checks
Applications may behave differently based on connectivity checks. Those can be performed using the following per protocol characteristics.
- Existence of any IP address (including
127.0.0.1or::1 - Existence of non-loopback IP address (including IPv6 link-local addresses)
- Existence of a global IP address
- Existence of a default route (or route for the target we want to reach)
Example: To test application behavior on a host connected via IPv6-only network you should make sure you only have the loopback IPv4 address and that you have a global IPv6 address and a default IPv6 gateway as that what you would normally call an IPv6-only setup. Similarly for IPv4-only setup you would make sure that there are only IPv6 loopback and link-local addresses and that there is a global IPv4 address and a default IPv4 gateway. But there are still many corner cases that may trigger unexpected issues.
IPv4 connectivity
| connectivity | details |
|---|---|
| Global | Host is connected to the Internet using a global IPv4 address. |
| Masqueraded | Host can access Internet services using a masqueraded private IPv4 address. |
| Local | Host has a private address with no global connectivity. |
| Zeroconf | Host has a link-local IPv4 address. |
| None | Host doesn't have any IPv4 addresses except loopback. |
IPv6 connectivity
| connectivity | details |
|---|---|
| Global | Host has at least one link-local address and one global address, the latter being used for global connectivity. |
| Local | Host has at least one link-local address and one unique local address used for local communication. |
| Link-local | Client only has a link-local address. |
| None | Client doesn't have any addresses except loopback. |
Target DNS
| configuration | A query | AAAA query | notes |
|---|---|---|---|
| Dual-stack | At least one A record | At least one AAAA record | |
| IPv4 only | At least one A record | NODATA | |
| Lost IPv6 | At least one A record | Timeout | Typically caused by bad recursive DNS servers |
| IPv6 only | NODATA | Answer with at least one AAAA record | |
| Multiple IPv4 and IPv6 addresses | At least two A records | At least two AAAA records |
Other DNS records typically point to names, not addresses and thus are protocol agnostic but it may still be useful to test e.g. SRV records so that the SRV code path is correct as well.
IPv4 and IPv6 authoritative DNS servers
This is a rather special case important for domain operators. A bad configuration can make otherwise working IPv6 hosts inaccessible from IPv6-only networks with their own recursive servers.
Client software test cases
Dual-stack to dual-stack
This test, among other things, shows whether IPv6 is preferred and whether sequential or parallel name resolution is used.
Connectivity:
- IPv4 connectivity: Public or masqueraded address
- IPv6 connectivity: Public address
Target DNS:
- A record: Yes
- AAAA record: Yes
Expected result (sequential, IPv6 preferred):
- Client requests AAAA record and receives reply
- Client connects to IPv6 address
- No delays, no A query
Expected result (parallel, first result wins):
- Client requests A and AAAA records simultaneously and receives the first reply
- Client sometimes connects to IPv4 address, sometimes to IPv6 address
- No delays
Expected result (parallel, IPv6 preferred):
- Client requests A and AAAA records simultaneously
- Client waits for the AAAA record
- Client connects to IPv6 address
Dual-stack to dual-stack with lost AAAA answer
Same as above, except that the AAAA answer is lost by a broken DNS server.
Connectivity:
- IPv4 connectivity: Public or masqueraded address
- IPv6 connectivity: Public address
Target DNS:
- A record: Yes
- AAAA record: Lost by a broken DNS server
Expected result (sequential, IPv6 preferred):
- Client requests AAAA record and gives up after a delay (e.g. 15 seconds)
- Client requests A record and receives reply
- Client connects to IPv4 address
Expected result (parallel, first result wins):
- Client requests A and AAAA records simultaneously and receives the A reply
- Client connects to IPv4 address
Expected result (parallel, IPv6 preferred):
- Client requests A and AAAA records simultaneously and receives the A reply
- Client gives up waiting for AAAA record after a short delay (e.g. 300 milliseconds)
- Client connects to IPv4 address
Dual-stack to dual-stack with lost IPv6 packets
This test, among other things, shows whether an application can recover from a broken IPv6 connectivity where IPv6 packets are dropped. It works just as well when connectivity is broken on the target network.
Connectivity:
- IPv4 connectivity: Public or masqueraded address
- IPv6 connectivity: Public address but packets are dropped
Target DNS:
- A record: Yes
- AAAA record: Yes
Other:
- Recursive DNS server is on IPv4
Expected result (sequential, IPv6 preferred):
- Client requests AAAA record and receives reply
- Client attempts connecting to IPv6 but times out
- Client requests A record and receives reply
- Client connects via IPv4
Expected result (parallel DNS, first result wins):
- Client requests A and AAAA records simultaneously and receives the first reply
- When the first reply is IPv6, client times out attempting IPv6 connection
- Client connects via IPv4
Expected result (parallel DNS, IPv6 preferred):
- Client requests A and AAAA records simultaneously
- Client waits for the AAAA record
- Client times out connecting to IPv6 address
Expected result (parallel DNS, parallel TCP, IPv6 preferred)
- Client requests A and AAAA records simultaneously
- Client attempts IPv4 and IPv6 connections simultaneously
- IPv4 connection is established, client gives up IPv6 after a short delay
- Client uses IPv4 connection