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fix(encapsulation): fall back to tunl0 when cilium_tunl is absent #9

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Merged
kvaps merged 1 commit into from
Feb 17, 2026
+13 −7
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fix(encapsulation): fall back to tunl0 when cilium_tunl is absent #9

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20 changes: 13 additions & 7 deletions pkg/encapsulation/cilium.go
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Original file line number Diff line number Diff line change
Expand Up @@ -27,8 +27,7 @@ import (
const (
ciliumHostIface = "cilium_host"
// ciliumTunlIface is the kernel's default IPIP tunnel (tunl0) renamed
// by Cilium when enable-ipip-termination is active. Unlike cilium_ipip4,
// which is receive-only (for DSR), cilium_tunl supports both TX and RX.
// by Cilium when enable-ipip-termination is enabled.
ciliumTunlIface = "cilium_tunl"
)

Expand Down Expand Up @@ -92,17 +91,24 @@ func (c *cilium) Index() int {
}

// Init initializes the IPIP tunnel interface.
// When Cilium's enable-ipip-termination is active, it renames the kernel's
// tunl0 to cilium_tunl and creates a receive-only cilium_ipip4 device.
// We use cilium_tunl because it supports both sending and receiving IPIP
// traffic, whereas cilium_ipip4 only handles incoming packets (DSR).
// If Cilium is running with enable-ipip-termination, it renames the kernel's
// tunl0 to cilium_tunl. In that case we reuse the existing cilium_tunl.
// Otherwise we create the standard tunl0 ourselves.
func (c *cilium) Init(base int) error {
// If Cilium created cilium_tunl (enable-ipip-termination), reuse it.
if link, err := netlink.LinkByName(ciliumTunlIface); err == nil {
c.iface = link.Attrs().Index
c.ownsTunnel = false
// Ensure the interface is UP — Cilium may leave it DOWN.
if link.Attrs().Flags&net.FlagUp == 0 {
if err := iproute.Set(c.iface, true); err != nil {
return fmt.Errorf("failed to set %s up: %v", ciliumTunlIface, err)
}
}
return nil
}
Comment on lines 99 to 109
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@gemini-code-assist gemini-code-assist bot Feb 17, 2026

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medium

To improve readability and avoid calling link.Attrs() twice, you can store its result in a variable and reuse it.

Suggested change
if link, err := netlink.LinkByName(ciliumTunlIface); err == nil {
c.iface = link.Attrs().Index
c.ownsTunnel = false
// Ensure the interface is UP — Cilium may leave it DOWN.
if link.Attrs().Flags&net.FlagUp == 0 {
if err := iproute.Set(c.iface, true); err != nil {
return fmt.Errorf("failed to set %s up: %v", ciliumTunlIface, err)
}
}
return nil
}
if link, err := netlink.LinkByName(ciliumTunlIface); err == nil {
attrs := link.Attrs()
c.iface = attrs.Index
c.ownsTunnel = false
// Ensure the interface is UP — Cilium may leave it DOWN.
if attrs.Flags&net.FlagUp == 0 {
if err := iproute.Set(c.iface, true); err != nil {
return fmt.Errorf("failed to set %s up: %v", ciliumTunlIface, err)
}
}
return nil
}

iface, err := iproute.NewIPIPWithName(base, ciliumTunlIface)
// No cilium_tunl — create standard tunl0.
iface, err := iproute.NewIPIP(base)
if err != nil {
return fmt.Errorf("failed to create tunnel interface: %v", err)
}
Expand Down