## Upgrade Information
+This section lists important updates and breaking changes that you should be
+aware of *before* starting the upgrade:
+
+Differences to version 26
+
+- **Attention**:
+ Starting with release 27, ngIRCd validates SSL/TLS certificates on outgoing
+ server-server links by default and drops(!) connections when the remote
+ certificate is invalid (for example self-signed, expired, not matching the
+ host name, ...). Therefore you have to make sure that all relevant
+ *certificates are valid* (or to disable certificate validation on this
+ connection using the new `SSLVerify = false` setting in the affected
+ `[Server]` block, where the remote certificate is not valid and you can not
+ fix this issue).
+
Differences to version 25
- **Attention**:
- `--with-gnutls[=<path>]`
Enable support for SSL/TLS using OpenSSL or GnuTLS libraries.
- See `doc/SSL.txt` for details.
+ See `doc/SSL.md` for details.
- IPv6 (autodetected by default):