* The pod annotation `security.alpha.kubernetes.io/sysctls` now allows customization of namespaced and well isolated kernel parameters (sysctls), starting with `kernel.shm_rmid_forced`, `net.ipv4.ip_local_port_range` and `net.ipv4.tcp_syncookies` for Kubernetes 1.4. ([#27180](https://github.com/kubernetes/kubernetes/pull/27180), [@sttts](https://github.com/sttts))

 *  Fix: Don't leak connections if web sockets have malformed responses or if `onOpen()` throws.
 *  Fix: Don't retry when request bodies fail due to `FileNotFoundException`.
 *  Fix: Don't crash when URLs have IPv4-mapped IPv6 addresses.
 *  Fix: Don't crash when building `HandshakeCertificates` on Android API 28.
 *  Fix: Permit multipart file names to contain non-ASCII characters.
 *  New: API to get MockWebServer's dispatcher.

  slightly stricter about what values will be accepted as IP addresses and network
  address ranges (“CIDR blocks”).
  
  In particular, octets within IPv4 addresses are not allowed to have any leading
  `0`s, and IPv4-mapped IPv6 values (e.g. `::ffff:192.168.0.1`) are forbidden.
  These sorts of values can potentially cause security problems when different

- PodLifecycleSleepAction is graduated to GA ([#128046](https://github.com/kubernetes/kubernetes/pull/128046), [@AxeZhan](https://github.com/AxeZhan)) [SIG Architecture, Node and Testing]
- Pods were allowed to use the `net.ipv4.tcp_rmem` and `net.ipv4.tcp_wmem` sysctl by default
  when the kernel version was 4.15 or higher. With the kernel 4.15 the sysctl became namespaced.

- IPVS proxier now set net/ipv4/vs/conn_reuse_mode to 0 by default, which will highly improve IPVS proxier performance. ([#71114](https://github.com/kubernetes/kubernetes/pull/71114), [@Lion-Wei](https://github.com/Lion-Wei))

- Kube-proxy doesn't set the sysctl `net.ipv4.conf.all.route_localnet=1` if no IPv4 loopback address is selected by the `nodePortAddresses` configuration parameter. ([#107684](https://github.com/kubernetes/kubernetes/pull/107684), [@aojea](https://github.com/aojea))

### **Network**

#### **IPv6**

*   [alpha] IPv6 support has been added. Notable IPv6 support details include:
    *   Support for IPv6-only Kubernetes cluster deployments. **<span style="text-decoration:underline;">Note:</span>** This feature does not provide dual-stack support.
    *   Support for IPv6 Kubernetes control and data planes.
    *   Support for Kubernetes IPv6 cluster deployments using kubeadm.

- Fix a bug that caused to panic the apiserver when trying to allocate a Service with a dynamic ClusterIP and it has been configured with Service CIDRs with a /28 mask for IPv4 and a /124 mask for IPv6 ([#115333](https://github.com/kubernetes/kubernetes/pull/115333), [@aojea](https://github.com/aojea)) [SIG Testing]

- Fixed the EndpointSliceController to correctly create endpoints for IPv6-only pods.
  
  Fixed the EndpointController to allow IPv6 headless services, if the IPv6DualStack
  feature gate is enabled, by specifying `ipFamily: IPv6` on the service. (This already

### OpenStack

* Fixed a bug in the OpenStack cloud provider where dual stack deployments (IPv4 and IPv6) did not work well when using kubenet as the network plugin. ([#59749](https://github.com/kubernetes/kubernetes/pull/59749), [@zioproto](https://github.com/zioproto))