The patch proposed and accepted here is a partial fix for this bug. https://marc.info/?l=linux-netdev&m=163579523718765
It adds an option for the wifi supplicant to choose not to clear the ARP cache when roaming. https://github.com/torvalds/linux/commit/fcdb44d08a95003c3d040aecdee286156ec6f34e https://github.com/torvalds/linux/commit/18ac597af25e9760b76471524096f5b29eb820e6 https://github.com/torvalds/linux/commit/f86ca07eb5310a1bdc7032458c7f76862f5a1552 The iwd supplicant adds a patch here to use this which is the other half of the fix: commit 873924a027ad2166436b8117a6bb84ce980ad7f3 Author: James Prestwood <prest...@gmail.com> Date: Wed Nov 3 15:15:01 2021 -0700 station: set evict_nocarrier sysfs option during roaming If the kernel supports evict_nocarrier set this during the roam to prevent packet delays post roam. -- You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux-signed-hwe-5.11 in Ubuntu. https://bugs.launchpad.net/bugs/1944426 Title: Delay sending data after wireless roaming between APs Status in linux-signed-hwe-5.11 package in Ubuntu: New Bug description: ## Summary Any time I roam from one access point to another (same SSID) I start receiving packets instantly after the roam is successful but experience a delay of roughly 1 second before I can send packets out. I have seen this with multiple configurations listed below. I started seeing this delay after upgrading from Ubuntu 16.04 to 18.04 and using the debians from https://kernel.ubuntu.com/~kernel-ppa/mainline/ I can see the bug was introduced between v4.19 and v4.20-rc1. ## Configurations I have tested multiple laptops and machines with different software to narrow down where the bug might be. All of these configurations showed the bug. - Distro(kernel) version - 20.04 (5.4, 5.8, 5.11, 5.14-rc7), Kali 2021.2 (5.10) - Hardware(driver): intel (iwlwifi), qualcomm (ath10k), realtek. - Supplicant: iwd and wpa_supplicant - Manager: iwd, systemd-networkd, NetworkManager - Data: ping, iperf3 (tcp and udp), custom python udp script - APs: Meraki MR46, tp-link decos ## Reproduction The bug is relatively easy to reproduce if you have multiple APs on the same SSID available. The simplest way is to start up a `ping -i 0.2 <any ip>` and then walk between the APs until it roams. It is also possible to use `wpa_cli roam <BSSID>`. For more accurate testing I was using a simple python script that spams udp packets and then using `tcpdump` to record the packets for viewing in wireshark. ## Example output Here is the output of the simplest test that still shows the issue (ping + tcpdump + iwd + 5.11.0-27-generic): [https://pastebin.com/92TKKktb](https://pastebin.com/92TKKktb) My naive tl;dr of that data is: - 30.322638 - we start to roam which falls between icmp_seq=121 and icmp_seq=122. - 30.415411 - roam is complete - 30.424277 - iwd is sending and receiving neighbor reports over the link - 31.358491 - an ARP request is sent out (why is the ARP cache cleared?) - 31.367930 - ARP response - packets start being sent again ProblemType: Bug DistroRelease: Ubuntu 20.04 Package: linux-image-5.11.0-34-generic 5.11.0-34.36~20.04.1 ProcVersionSignature: Ubuntu 5.11.0-34.36~20.04.1-generic 5.11.22 Uname: Linux 5.11.0-34-generic x86_64 NonfreeKernelModules: nvidia_modeset nvidia ApportVersion: 2.20.11-0ubuntu27.20 Architecture: amd64 CasperMD5CheckResult: skip CurrentDesktop: ubuntu:GNOME Date: Tue Sep 21 10:12:40 2021 InstallationDate: Installed on 2019-08-09 (773 days ago) InstallationMedia: Ubuntu 18.04.2 LTS "Bionic Beaver" - Release amd64 (20190210) SourcePackage: linux-signed-hwe-5.11 UpgradeStatus: No upgrade log present (probably fresh install) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux-signed-hwe-5.11/+bug/1944426/+subscriptions -- Mailing list: https://launchpad.net/~kernel-packages Post to : kernel-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
