< QA | Networking
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.
DNS server IPv4/IPv6 accessibility notes
It usually doesn't matter how recursive servers are accessed, whether via IPv4 and IPv6, the network is expected to be configured correctly.
Authoritative servers inaccessible via one of the protocols 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
| IPv4 connectivity | Global or masuqeraded |
| IPv6 connectivity | Global |
| Target DNS | Dual-stack |
What is tested:
- Whether IPv6 is preferred over IPv4.
- Whether the component is capable of working over IPv6.
- Whether sequential or parallel DNS resolution is in use.
Expected result (sequential, IPv6 preferred):
- Host requests AAAA record and receives a reply.
- Host connects via IPv6.
- No delays, no A query.
Expected result (parallel, IPv6 preferred):
- Host requests A and AAAA records simultaneously and receives the AAAA reply.
- Host connects via IPv6.
- No delays, A reply is ignored if received.
Alternative result (parallel, first result wins, no protocol preference):
- Host requests A and AAAA records simultaneously and receives the first reply.
- Host connects via IPv4 or IPv6.
- No delays.
Dual-stack to dual-stack with lost AAAA answer
Same as above, except that the AAAA answer is lost by a broken DNS server.
| IPv4 connectivity | Global or masuqeraded |
| IPv6 connectivity | Global |
| Target DNS | Lost IPv6 |
What is tested:
- Wheter the component reverts to IPv4 in reasonable time when AAAA answer gets lost.
Expected result (sequential, IPv6 preferred):
- Host requests AAAA record and gives up after a delay (e.g. 15 seconds).
- Host requests A record and receives reply.
- Host connects via IPv4.
Expected result (parallel, IPv6 preferred):
- Host requests A and AAAA records simultaneously and receives the A reply.
- Host gives up waiting for AAAA record after a short delay (e.g. 300 milliseconds).
- Host connects via IPv4.
Alternative result (parallel, first result wins):
- Host requests A and AAAA records simultaneously and receives the A reply.
- Host connects via IPv4.
- No delay.
Dual-stack to dual-stack with lost communication
| IPv4 connectivity | Global or masqueraded |
| IPv6 connectivity | Global but packets to destination get dropped |
| Target DNS | Dual-stack, DNS server accessed via IPv4 |
What is tested:
- Whether the component reverts to IPv4 in reasonable time when local or remote network drops all IPv6 communication.
Expected result (sequential, IPv6 preferred):
- Host requests AAAA record and receives reply.
- Host attempts connecting to IPv6 and times out.
- Host requests A record and receives reply.
- Host connects via IPv4
Expected result (parallel DNS, IPv6 preferred):
- Host requests A and AAAA records simultaneously and waits for AAAA reply.
- Host attempts connecting to IPv6 and times out, receiving A reply in the meantime.
- Host connects via IPv4.
Expected result (parallel DNS, parallel TCP, IPv6 preferred):
- Host requests A and AAAA records simultaneously
- Host attempts IPv4 and IPv6 connections upon receiving the respective records
- IPv4 connection is established
- IPv6 connection is given up after a short delay (e.g. 300 milliseconds)
- Client communicates via IPv4