Document MKE VXLAN port conflict for eBPF dataplane

calico-enterprise/operations/ebpf/enabling-ebpf.mdx

@@ -185,6 +185,32 @@ kubectl patch felixconfiguration default --patch='{"spec": {"bpfKubeProxyIptable
 
 If both `kube-proxy` and `BPFKubeProxyIptablesCleanupEnabled` is enabled then `kube-proxy` will write its iptables rules and Felix will try to clean them up resulting in iptables flapping between the two.
 
+### MKE: Change the VXLAN port before enabling eBPF
+
+:::caution
+
+MKE uses Docker Swarm overlay networking, which creates VXLAN devices on UDP port 4789 inside Docker network namespaces.
+When $[prodname] switches to eBPF mode on kernels where BTF is available (typically v5.8+), Felix creates the `vxlan.calico` device in
+flow mode, which acts as a catch-all on its UDP port. The kernel rejects this when another VXLAN device (Docker Swarm's)
+already holds the same port, causing `vxlan.calico` to stay DOWN with `address already in use` errors.
+
+**You must change the VXLAN port before enabling eBPF on MKE clusters:**
+
+```bash
+kubectl patch felixconfiguration default --type merge -p '{"spec":{"vxlanPort":4790}}'
+```
+
+Wait for all calico-node pods to recreate the VXLAN device on the new port, then verify on each node:
+
+```bash
+kubectl exec -n calico-system <calico-node-pod> -- ip -d link show vxlan.calico
+```
+
+Confirm the device shows `dstport 4790` (or your chosen port) and is UP before proceeding.
+Ensure that the chosen UDP port is allowed by your underlying network between all nodes.
+
+:::
+
 ### Enable eBPF mode
 
 To enable eBPF mode, change the `spec.calicoNetwork.linuxDataplane` parameter in the operator's `Installation`

calico-enterprise/operations/ebpf/install.mdx

@@ -175,6 +175,21 @@ can do that by setting `--kube-proxy-mode=disabled` and `--kube-default-drop-mas
 
 More details can be found in [the MKE documentation](https://docs.mirantis.com/mke/current/install/predeployment/configure-networking/cluster-service-networking-options.html)
 
+:::caution VXLAN port conflict
+
+MKE's Docker Swarm overlay networking uses UDP port 4789 for its own VXLAN devices. In eBPF mode, when BTF is available on the node (typically kernel v5.8+),
+$[prodname] creates the `vxlan.calico` device in flow mode, which conflicts with Docker Swarm's use of the same port.
+You must change the VXLAN port before enabling eBPF:
+
+```bash
+kubectl patch felixconfiguration default --type merge -p '{"spec":{"vxlanPort":4790}}'
+```
+
+Ensure the chosen UDP port is allowed by your underlying network between all nodes.
+See [Troubleshoot eBPF mode](troubleshoot-ebpf.mdx#mke-vxlan-device-down) for more details.
+
+:::
+
 </TabItem>
 
 </Tabs>

calico-enterprise/operations/ebpf/troubleshoot-ebpf.mdx

@@ -396,6 +396,55 @@ e2e` command. The command resets the profiling data after dumping it.
 
 ```
 
+## MKE: VXLAN device DOWN
+
+On MKE clusters, after enabling eBPF mode, the `vxlan.calico` device may stay DOWN with Felix logs showing:
+
+```
+Failed to set tunnel device up error=address already in use
+```
+
+This happens because MKE's Docker Swarm overlay networking creates VXLAN devices on UDP port 4789 inside Docker network namespaces (`/run/docker/netns/`). In eBPF mode, when BTF is available on the node (typically kernel v5.8+), Felix creates `vxlan.calico` in flow mode (`external`), which acts as a catch-all on its UDP port. The kernel rejects this because Docker Swarm's VXLAN device already holds port 4789.
+
+In iptables mode this conflict doesn't occur because Calico's VXLAN device binds with a specific VNI (4096), which can coexist with Docker Swarm's VXLAN on the same port.
+
+**Diagnosis:**
+
+```bash
+# Confirm the VXLAN device is DOWN
+kubectl exec -n calico-system <calico-node-pod> -- ip -d link show vxlan.calico
+
+# Check what holds port 4789 (shows a kernel-owned socket with no process name)
+kubectl exec -n calico-system <calico-node-pod> -- ss -ulnp sport = :4789
+
+# Find Docker Swarm VXLAN devices in Docker network namespaces (run on the node via SSH)
+for ns in /run/docker/netns/*; do
+  echo "=== $(basename "$ns") ==="
+  nsenter --net="$ns" ip -d link show type vxlan 2>/dev/null
+done
+```
+
+**Fix:** Change Calico's VXLAN port to avoid the conflict:
+
+```bash
+kubectl patch felixconfiguration default --type merge -p '{"spec":{"vxlanPort":4790}}'
+```
+
+Felix will recreate `vxlan.calico` on the new port within seconds. Verify on each node:
+
+```bash
+kubectl exec -n calico-system <calico-node-pod> -- ip -d link show vxlan.calico
+# Should show: vxlan external ... dstport 4790 ... state UP
+```
+
+Ensure the chosen UDP port is allowed by your underlying network between all nodes.
+
+:::tip
+
+For MKE clusters, set the VXLAN port **before** enabling eBPF mode to avoid any disruption.
+
+:::
+
 ## Debug high CPU usage
 
 If you notice `$[noderunning]` using high CPU:

calico-enterprise_versioned_docs/version-3.23-1/operations/ebpf/enabling-ebpf.mdx

@@ -185,6 +185,32 @@ kubectl patch felixconfiguration default --patch='{"spec": {"bpfKubeProxyIptable
 
 If both `kube-proxy` and `BPFKubeProxyIptablesCleanupEnabled` is enabled then `kube-proxy` will write its iptables rules and Felix will try to clean them up resulting in iptables flapping between the two.
 
+### MKE: Change the VXLAN port before enabling eBPF
+
+:::caution
+
+MKE uses Docker Swarm overlay networking, which creates VXLAN devices on UDP port 4789 inside Docker network namespaces.
+When $[prodname] switches to eBPF mode on kernels where BTF is available (typically v5.8+), Felix creates the `vxlan.calico` device in
+flow mode, which acts as a catch-all on its UDP port. The kernel rejects this when another VXLAN device (Docker Swarm's)
+already holds the same port, causing `vxlan.calico` to stay DOWN with `address already in use` errors.
+
+**You must change the VXLAN port before enabling eBPF on MKE clusters:**
+
+```bash
+kubectl patch felixconfiguration default --type merge -p '{"spec":{"vxlanPort":4790}}'
+```
+
+Wait for all calico-node pods to recreate the VXLAN device on the new port, then verify on each node:
+
+```bash
+kubectl exec -n calico-system <calico-node-pod> -- ip -d link show vxlan.calico
+```
+
+Confirm the device shows `dstport 4790` (or your chosen port) and is UP before proceeding.
+Ensure that the chosen UDP port is allowed by your underlying network between all nodes.
+
+:::
+
 ### Enable eBPF mode
 
 To enable eBPF mode, change the `spec.calicoNetwork.linuxDataplane` parameter in the operator's `Installation`

calico-enterprise_versioned_docs/version-3.23-1/operations/ebpf/install.mdx

@@ -175,6 +175,21 @@ can do that by setting `--kube-proxy-mode=disabled` and `--kube-default-drop-mas
 
 More details can be found in [the MKE documentation](https://docs.mirantis.com/mke/current/install/predeployment/configure-networking/cluster-service-networking-options.html)
 
+:::caution VXLAN port conflict
+
+MKE's Docker Swarm overlay networking uses UDP port 4789 for its own VXLAN devices. In eBPF mode, when BTF is available on the node (typically kernel v5.8+),
+$[prodname] creates the `vxlan.calico` device in flow mode, which conflicts with Docker Swarm's use of the same port.
+You must change the VXLAN port before enabling eBPF:
+
+```bash
+kubectl patch felixconfiguration default --type merge -p '{"spec":{"vxlanPort":4790}}'
+```
+
+Ensure the chosen UDP port is allowed by your underlying network between all nodes.
+See [Troubleshoot eBPF mode](troubleshoot-ebpf.mdx#mke-vxlan-device-down) for more details.
+
+:::
+
 </TabItem>
 
 </Tabs>

calico-enterprise_versioned_docs/version-3.23-1/operations/ebpf/troubleshoot-ebpf.mdx

@@ -396,6 +396,55 @@ e2e` command. The command resets the profiling data after dumping it.
 
 ```
 
+## MKE: VXLAN device DOWN
+
+On MKE clusters, after enabling eBPF mode, the `vxlan.calico` device may stay DOWN with Felix logs showing:
+
+```
+Failed to set tunnel device up error=address already in use
+```
+
+This happens because MKE's Docker Swarm overlay networking creates VXLAN devices on UDP port 4789 inside Docker network namespaces (`/run/docker/netns/`). In eBPF mode, when BTF is available on the node (typically kernel v5.8+), Felix creates `vxlan.calico` in flow mode (`external`), which acts as a catch-all on its UDP port. The kernel rejects this because Docker Swarm's VXLAN device already holds port 4789.
+
+In iptables mode this conflict doesn't occur because Calico's VXLAN device binds with a specific VNI (4096), which can coexist with Docker Swarm's VXLAN on the same port.
+
+**Diagnosis:**
+
+```bash
+# Confirm the VXLAN device is DOWN
+kubectl exec -n calico-system <calico-node-pod> -- ip -d link show vxlan.calico
+
+# Check what holds port 4789 (shows a kernel-owned socket with no process name)
+kubectl exec -n calico-system <calico-node-pod> -- ss -ulnp sport = :4789
+
+# Find Docker Swarm VXLAN devices in Docker network namespaces (run on the node via SSH)
+for ns in /run/docker/netns/*; do
+  echo "=== $(basename "$ns") ==="
+  nsenter --net="$ns" ip -d link show type vxlan 2>/dev/null
+done
+```
+
+**Fix:** Change Calico's VXLAN port to avoid the conflict:
+
+```bash
+kubectl patch felixconfiguration default --type merge -p '{"spec":{"vxlanPort":4790}}'
+```
+
+Felix will recreate `vxlan.calico` on the new port within seconds. Verify on each node:
+
+```bash
+kubectl exec -n calico-system <calico-node-pod> -- ip -d link show vxlan.calico
+# Should show: vxlan external ... dstport 4790 ... state UP
+```
+
+Ensure the chosen UDP port is allowed by your underlying network between all nodes.
+
+:::tip
+
+For MKE clusters, set the VXLAN port **before** enabling eBPF mode to avoid any disruption.
+
+:::
+
 ## Debug high CPU usage
 
 If you notice `$[noderunning]` using high CPU:

calico/operations/ebpf/enabling-ebpf.mdx

@@ -326,6 +326,32 @@ kubectl patch felixconfiguration default --patch='{"spec": {"bpfKubeProxyIptable
 
 If both `kube-proxy` and `BPFKubeProxyIptablesCleanupEnabled` is enabled then `kube-proxy` will write its iptables rules and Felix will try to clean them up resulting in iptables flapping between the two.
 
+### MKE: Change the VXLAN port before enabling eBPF
+
+:::caution
+
+MKE uses Docker Swarm overlay networking, which creates VXLAN devices on UDP port 4789 inside Docker network namespaces.
+When $[prodname] switches to eBPF mode on kernels where BTF is available (typically v5.8+), Felix creates the `vxlan.calico` device in
+flow mode, which acts as a catch-all on its UDP port. The kernel rejects this when another VXLAN device (Docker Swarm's)
+already holds the same port, causing `vxlan.calico` to stay DOWN with `address already in use` errors.
+
+**You must change the VXLAN port before enabling eBPF on MKE clusters:**
+
+```bash
+kubectl patch felixconfiguration default --type merge -p '{"spec":{"vxlanPort":4790}}'
+```
+
+Wait for all calico-node pods to recreate the VXLAN device on the new port, then verify on each node:
+
+```bash
+kubectl exec -n calico-system <calico-node-pod> -- ip -d link show vxlan.calico
+```
+
+Confirm the device shows `dstport 4790` (or your chosen port) and is UP before proceeding.
+Ensure that the chosen UDP port is allowed by your underlying network between all nodes.
+
+:::
+
 ### Enable eBPF mode
 
 **The next step depends on whether you installed $[prodname] using the operator, or a manifest:**

calico/operations/ebpf/install.mdx

@@ -203,6 +203,21 @@ can do that by setting `--kube-proxy-mode=disabled` and `--kube-default-drop-mas
 
 More details can be found in [the MKE documentation](https://docs.mirantis.com/mke/current/install/predeployment/configure-networking/cluster-service-networking-options.html)
 
+:::caution VXLAN port conflict
+
+MKE's Docker Swarm overlay networking uses UDP port 4789 for its own VXLAN devices. In eBPF mode, when BTF is available on the node (typically kernel v5.8+),
+$[prodname] creates the `vxlan.calico` device in flow mode, which conflicts with Docker Swarm's use of the same port.
+You must change the VXLAN port before enabling eBPF:
+
+```bash
+kubectl patch felixconfiguration default --type merge -p '{"spec":{"vxlanPort":4790}}'
+```
+
+Ensure the chosen UDP port is allowed by your underlying network between all nodes.
+See [Troubleshoot eBPF mode](troubleshoot-ebpf.mdx#mke-vxlan-device-down) for more details.
+
+:::
+
 </TabItem>
 
 </Tabs>

calico/operations/ebpf/troubleshoot-ebpf.mdx

@@ -396,6 +396,55 @@ e2e` command. The command resets the profiling data after dumping it.
 
 ```
 
+## MKE: VXLAN device DOWN
+
+On MKE clusters, after enabling eBPF mode, the `vxlan.calico` device may stay DOWN with Felix logs showing:
+
+```
+Failed to set tunnel device up error=address already in use
+```
+
+This happens because MKE's Docker Swarm overlay networking creates VXLAN devices on UDP port 4789 inside Docker network namespaces (`/run/docker/netns/`). In eBPF mode, when BTF is available on the node (typically kernel v5.8+), Felix creates `vxlan.calico` in flow mode (`external`), which acts as a catch-all on its UDP port. The kernel rejects this because Docker Swarm's VXLAN device already holds port 4789.
+
+In iptables mode this conflict doesn't occur because Calico's VXLAN device binds with a specific VNI (4096), which can coexist with Docker Swarm's VXLAN on the same port.
+
+**Diagnosis:**
+
+```bash
+# Confirm the VXLAN device is DOWN
+kubectl exec -n calico-system <calico-node-pod> -- ip -d link show vxlan.calico
+
+# Check what holds port 4789 (shows a kernel-owned socket with no process name)
+kubectl exec -n calico-system <calico-node-pod> -- ss -ulnp sport = :4789
+
+# Find Docker Swarm VXLAN devices in Docker network namespaces (run on the node via SSH)
+for ns in /run/docker/netns/*; do
+  echo "=== $(basename "$ns") ==="
+  nsenter --net="$ns" ip -d link show type vxlan 2>/dev/null
+done
+```
+
+**Fix:** Change Calico's VXLAN port to avoid the conflict:
+
+```bash
+kubectl patch felixconfiguration default --type merge -p '{"spec":{"vxlanPort":4790}}'
+```
+
+Felix will recreate `vxlan.calico` on the new port within seconds. Verify on each node:
+
+```bash
+kubectl exec -n calico-system <calico-node-pod> -- ip -d link show vxlan.calico
+# Should show: vxlan external ... dstport 4790 ... state UP
+```
+
+Ensure the chosen UDP port is allowed by your underlying network between all nodes.
+
+:::tip
+
+For MKE clusters, set the VXLAN port **before** enabling eBPF mode to avoid any disruption.
+
+:::
+
 ## Debug high CPU usage
 
 If you notice `$[noderunning]` using high CPU:

calico_versioned_docs/version-3.31/operations/ebpf/enabling-ebpf.mdx

@@ -326,6 +326,32 @@ kubectl patch felixconfiguration default --patch='{"spec": {"bpfKubeProxyIptable
 
 If both `kube-proxy` and `BPFKubeProxyIptablesCleanupEnabled` is enabled then `kube-proxy` will write its iptables rules and Felix will try to clean them up resulting in iptables flapping between the two.
 
+### MKE: Change the VXLAN port before enabling eBPF
+
+:::caution
+
+MKE uses Docker Swarm overlay networking, which creates VXLAN devices on UDP port 4789 inside Docker network namespaces.
+When $[prodname] switches to eBPF mode on kernels where BTF is available (typically v5.8+), Felix creates the `vxlan.calico` device in
+flow mode, which acts as a catch-all on its UDP port. The kernel rejects this when another VXLAN device (Docker Swarm's)
+already holds the same port, causing `vxlan.calico` to stay DOWN with `address already in use` errors.
+
+**You must change the VXLAN port before enabling eBPF on MKE clusters:**
+
+```bash
+kubectl patch felixconfiguration default --type merge -p '{"spec":{"vxlanPort":4790}}'
+```
+
+Wait for all calico-node pods to recreate the VXLAN device on the new port, then verify on each node:
+
+```bash
+kubectl exec -n calico-system <calico-node-pod> -- ip -d link show vxlan.calico
+```
+
+Confirm the device shows `dstport 4790` (or your chosen port) and is UP before proceeding.
+Ensure that the chosen UDP port is allowed by your underlying network between all nodes.
+
+:::
+
 ### Enable eBPF mode
 
 **The next step depends on whether you installed $[prodname] using the operator, or a manifest:**

calico_versioned_docs/version-3.31/operations/ebpf/install.mdx

@@ -203,6 +203,21 @@ can do that by setting `--kube-proxy-mode=disabled` and `--kube-default-drop-mas
 
 More details can be found in [the MKE documentation](https://docs.mirantis.com/mke/current/install/predeployment/configure-networking/cluster-service-networking-options.html)
 
+:::caution VXLAN port conflict
+
+MKE's Docker Swarm overlay networking uses UDP port 4789 for its own VXLAN devices. In eBPF mode, when BTF is available on the node (typically kernel v5.8+),
+$[prodname] creates the `vxlan.calico` device in flow mode, which conflicts with Docker Swarm's use of the same port.
+You must change the VXLAN port before enabling eBPF:
+
+```bash
+kubectl patch felixconfiguration default --type merge -p '{"spec":{"vxlanPort":4790}}'
+```
+
+Ensure the chosen UDP port is allowed by your underlying network between all nodes.
+See [Troubleshoot eBPF mode](troubleshoot-ebpf.mdx#mke-vxlan-device-down) for more details.
+
+:::
+
 </TabItem>
 
 </Tabs>