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Merged
merged 2 commits into from
Sep 30, 2025
Merged

firewall: add option to disable fully-random mode for MASQUERADE #2281

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47e897a
firewall: add option to disable fully-random mode for MASQUERADE
Sep 10, 2025
a446c79
golangci-lint: fix iptables_test
Sep 29, 2025
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5 changes: 4 additions & 1 deletion main.go
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Original file line number Diff line number Diff line change
Expand Up @@ -85,6 +85,7 @@ type CmdLineOpts struct {
iface flagSlice
ifaceRegex flagSlice
ipMasq bool
ipMasqRandomFullyDisable bool
ifaceCanReach string
subnetFile string
publicIP string
Expand Down Expand Up @@ -122,6 +123,7 @@ func init() {
flannelFlags.StringVar(&opts.publicIPv6, "public-ipv6", "", "IPv6 accessible by other nodes for inter-host communication")
flannelFlags.IntVar(&opts.subnetLeaseRenewMargin, "subnet-lease-renew-margin", 60, "subnet lease renewal margin, in minutes, ranging from 1 to 1439")
flannelFlags.BoolVar(&opts.ipMasq, "ip-masq", false, "setup IP masquerade rule for traffic destined outside of overlay network")
flannelFlags.BoolVar(&opts.ipMasqRandomFullyDisable, "ip-masq-fully-random-disable", false, "disable fully-random mode for MASQUERADE")
flannelFlags.BoolVar(&opts.kubeSubnetMgr, "kube-subnet-mgr", false, "contact the Kubernetes API for subnet assignment instead of etcd.")
flannelFlags.StringVar(&opts.kubeApiUrl, "kube-api-url", "", "Kubernetes API server URL. Does not need to be specified if flannel is running in a pod.")
flannelFlags.StringVar(&opts.kubeAnnotationPrefix, "kube-annotation-prefix", "flannel.alpha.coreos.com", `Kubernetes annotation prefix. Can contain single slash "/", otherwise it will be appended at the end.`)
Expand Down Expand Up @@ -405,7 +407,8 @@ func main() {
config.IPv6Network, prevIPv6Subnet,
prevIPv6Network,
bn.Lease(),
opts.iptablesResyncSeconds)
opts.iptablesResyncSeconds,
opts.ipMasqRandomFullyDisable)
if err != nil {
log.Errorf("Failed to setup masq rules, %v", err)
cancel()
Expand Down
23 changes: 12 additions & 11 deletions pkg/trafficmngr/iptables/iptables.go
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Original file line number Diff line number Diff line change
Expand Up @@ -92,7 +92,8 @@ func (iptm *IPTablesManager) CleanUp(ctx context.Context) error {
func (iptm *IPTablesManager) SetupAndEnsureMasqRules(ctx context.Context, flannelIPv4Net, prevSubnet, prevNetwork ip.IP4Net,
flannelIPv6Net, prevIPv6Subnet, prevIPv6Network ip.IP6Net,
currentlease *lease.Lease,
resyncPeriod int) error {
resyncPeriod int,
ipMasqRandomFullyDisable bool) error {

if !flannelIPv4Net.Empty() {
// recycle iptables rules only when network configured or subnet leased is not equal to current one.
Expand All @@ -102,14 +103,14 @@ func (iptm *IPTablesManager) SetupAndEnsureMasqRules(ctx context.Context, flanne
newLease := &lease.Lease{
Subnet: prevSubnet,
}
if err := iptm.deleteIP4Tables(iptm.masqRules(prevNetwork, newLease)); err != nil {
if err := iptm.deleteIP4Tables(iptm.masqRules(prevNetwork, newLease, ipMasqRandomFullyDisable)); err != nil {
return err
}
}

log.Infof("Setting up masking rules")
iptm.CreateIP4Chain("nat", "FLANNEL-POSTRTG")
go iptm.setupAndEnsureIP4Tables(ctx, iptm.masqRules(flannelIPv4Net, currentlease), resyncPeriod)
go iptm.setupAndEnsureIP4Tables(ctx, iptm.masqRules(flannelIPv4Net, currentlease, ipMasqRandomFullyDisable), resyncPeriod)
}
if !flannelIPv6Net.Empty() {
// recycle iptables rules only when network configured or subnet leased is not equal to current one.
Expand All @@ -119,19 +120,19 @@ func (iptm *IPTablesManager) SetupAndEnsureMasqRules(ctx context.Context, flanne
newLease := &lease.Lease{
IPv6Subnet: prevIPv6Subnet,
}
if err := iptm.deleteIP6Tables(iptm.masqIP6Rules(prevIPv6Network, newLease)); err != nil {
if err := iptm.deleteIP6Tables(iptm.masqIP6Rules(prevIPv6Network, newLease, ipMasqRandomFullyDisable)); err != nil {
return err
}
}

log.Infof("Setting up masking rules for IPv6")
iptm.CreateIP6Chain("nat", "FLANNEL-POSTRTG")
go iptm.setupAndEnsureIP6Tables(ctx, iptm.masqIP6Rules(flannelIPv6Net, currentlease), resyncPeriod)
go iptm.setupAndEnsureIP6Tables(ctx, iptm.masqIP6Rules(flannelIPv6Net, currentlease, ipMasqRandomFullyDisable), resyncPeriod)
}
return nil
}

func (iptm *IPTablesManager) masqRules(ccidr ip.IP4Net, lease *lease.Lease) []trafficmngr.IPTablesRule {
func (iptm *IPTablesManager) masqRules(ccidr ip.IP4Net, lease *lease.Lease, ipMasqRandomFullyDisable bool) []trafficmngr.IPTablesRule {
cluster_cidr := ccidr.String()

pod_cidr := lease.Subnet.String()
Expand All @@ -153,21 +154,21 @@ func (iptm *IPTablesManager) masqRules(ccidr ip.IP4Net, lease *lease.Lease) []tr
// Prevent performing Masquerade on external traffic which arrives from a Node that owns the container/pod IP address
rules = append(rules, trafficmngr.IPTablesRule{Table: "nat", Action: "-A", Chain: "FLANNEL-POSTRTG", Rulespec: []string{"!", "-s", cluster_cidr, "-d", pod_cidr, "-m", "comment", "--comment", "flanneld masq", "-j", "RETURN"}})
// NAT if it's not multicast traffic
if supports_random_fully {
if supports_random_fully && !ipMasqRandomFullyDisable {
rules = append(rules, trafficmngr.IPTablesRule{Table: "nat", Action: "-A", Chain: "FLANNEL-POSTRTG", Rulespec: []string{"-s", cluster_cidr, "!", "-d", "224.0.0.0/4", "-m", "comment", "--comment", "flanneld masq", "-j", "MASQUERADE", "--random-fully"}})
} else {
rules = append(rules, trafficmngr.IPTablesRule{Table: "nat", Action: "-A", Chain: "FLANNEL-POSTRTG", Rulespec: []string{"-s", cluster_cidr, "!", "-d", "224.0.0.0/4", "-m", "comment", "--comment", "flanneld masq", "-j", "MASQUERADE"}})
}
// Masquerade anything headed towards flannel from the host
if supports_random_fully {
if supports_random_fully && !ipMasqRandomFullyDisable {
rules = append(rules, trafficmngr.IPTablesRule{Table: "nat", Action: "-A", Chain: "FLANNEL-POSTRTG", Rulespec: []string{"!", "-s", cluster_cidr, "-d", cluster_cidr, "-m", "comment", "--comment", "flanneld masq", "-j", "MASQUERADE", "--random-fully"}})
} else {
rules = append(rules, trafficmngr.IPTablesRule{Table: "nat", Action: "-A", Chain: "FLANNEL-POSTRTG", Rulespec: []string{"!", "-s", cluster_cidr, "-d", cluster_cidr, "-m", "comment", "--comment", "flanneld masq", "-j", "MASQUERADE"}})
}
return rules
}

func (iptm *IPTablesManager) masqIP6Rules(ccidr ip.IP6Net, lease *lease.Lease) []trafficmngr.IPTablesRule {
func (iptm *IPTablesManager) masqIP6Rules(ccidr ip.IP6Net, lease *lease.Lease, ipMasqRandomFullyDisable bool) []trafficmngr.IPTablesRule {
cluster_cidr := ccidr.String()
pod_cidr := lease.IPv6Subnet.String()
ipt, err := iptables.NewWithProtocol(iptables.ProtocolIPv6)
Expand All @@ -190,14 +191,14 @@ func (iptm *IPTablesManager) masqIP6Rules(ccidr ip.IP6Net, lease *lease.Lease) [
// Prevent performing Masquerade on external traffic which arrives from a Node that owns the container/pod IP address
rules = append(rules, trafficmngr.IPTablesRule{Table: "nat", Action: "-A", Chain: "FLANNEL-POSTRTG", Rulespec: []string{"!", "-s", cluster_cidr, "-d", pod_cidr, "-m", "comment", "--comment", "flanneld masq", "-j", "RETURN"}})
// NAT if it's not multicast traffic
if supports_random_fully {
if supports_random_fully && !ipMasqRandomFullyDisable {
rules = append(rules, trafficmngr.IPTablesRule{Table: "nat", Action: "-A", Chain: "FLANNEL-POSTRTG", Rulespec: []string{"-s", cluster_cidr, "!", "-d", "ff00::/8", "-m", "comment", "--comment", "flanneld masq", "-j", "MASQUERADE", "--random-fully"}})
} else {
rules = append(rules, trafficmngr.IPTablesRule{Table: "nat", Action: "-A", Chain: "FLANNEL-POSTRTG", Rulespec: []string{"-s", cluster_cidr, "!", "-d", "ff00::/8", "-m", "comment", "--comment", "flanneld masq", "-j", "MASQUERADE"}})
}

// Masquerade anything headed towards flannel from the host
if supports_random_fully {
if supports_random_fully && !ipMasqRandomFullyDisable {
rules = append(rules, trafficmngr.IPTablesRule{Table: "nat", Action: "-A", Chain: "FLANNEL-POSTRTG", Rulespec: []string{"!", "-s", cluster_cidr, "-d", cluster_cidr, "-m", "comment", "--comment", "flanneld masq", "-j", "MASQUERADE", "--random-fully"}})
} else {
rules = append(rules, trafficmngr.IPTablesRule{Table: "nat", Action: "-A", Chain: "FLANNEL-POSTRTG", Rulespec: []string{"!", "-s", cluster_cidr, "-d", cluster_cidr, "-m", "comment", "--comment", "flanneld masq", "-j", "MASQUERADE"}})
Expand Down
3 changes: 2 additions & 1 deletion pkg/trafficmngr/iptables/iptables_windows.go
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Original file line number Diff line number Diff line change
Expand Up @@ -49,7 +49,8 @@ func (iptm *IPTablesManager) SetupAndEnsureForwardRules(ctx context.Context, fla
func (iptm *IPTablesManager) SetupAndEnsureMasqRules(ctx context.Context, flannelIPv4Net, prevSubnet, prevNetwork ip.IP4Net,
flannelIPv6Net, prevIPv6Subnet, prevIPv6Network ip.IP6Net,
currentlease *lease.Lease,
resyncPeriod int) error {
resyncPeriod int,
ipMasqRandomFullyDisable bool) error {
log.Warning(trafficmngr.ErrUnimplemented)
return nil
}
12 changes: 7 additions & 5 deletions pkg/trafficmngr/nftables/nftables.go
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Original file line number Diff line number Diff line change
Expand Up @@ -149,7 +149,8 @@ func (nftm *NFTablesManager) SetupAndEnsureForwardRules(ctx context.Context,
func (nftm *NFTablesManager) SetupAndEnsureMasqRules(ctx context.Context, flannelIPv4Net, prevSubnet, prevNetwork ip.IP4Net,
flannelIPv6Net, prevIPv6Subnet, prevIPv6Network ip.IP6Net,
currentlease *lease.Lease,
resyncPeriod int) error {
resyncPeriod int,
ipMasqRandomFullyDisable bool) error {
if !flannelIPv4Net.Empty() {
log.Infof("nftables: setting up masking rules (ipv4)")
tx := nftm.nftv4.NewTransaction()
Expand All @@ -166,7 +167,7 @@ func (nftm *NFTablesManager) SetupAndEnsureMasqRules(ctx context.Context, flanne
tx.Flush(&knftables.Chain{
Name: postrtgChain,
})
err := nftm.addMasqRules(ctx, tx, flannelIPv4Net.String(), currentlease.Subnet.String(), knftables.IPv4Family)
err := nftm.addMasqRules(ctx, tx, flannelIPv4Net.String(), currentlease.Subnet.String(), knftables.IPv4Family, ipMasqRandomFullyDisable)
if err != nil {
return fmt.Errorf("nftables: couldn't setup masq rules: %v", err)
}
Expand All @@ -191,7 +192,7 @@ func (nftm *NFTablesManager) SetupAndEnsureMasqRules(ctx context.Context, flanne
tx.Flush(&knftables.Chain{
Name: postrtgChain,
})
err := nftm.addMasqRules(ctx, tx, flannelIPv6Net.String(), currentlease.IPv6Subnet.String(), knftables.IPv6Family)
err := nftm.addMasqRules(ctx, tx, flannelIPv6Net.String(), currentlease.IPv6Subnet.String(), knftables.IPv6Family, ipMasqRandomFullyDisable)
if err != nil {
return fmt.Errorf("nftables: couldn't setup masq rules: %v", err)
}
Expand All @@ -207,9 +208,10 @@ func (nftm *NFTablesManager) SetupAndEnsureMasqRules(ctx context.Context, flanne
func (nftm *NFTablesManager) addMasqRules(ctx context.Context,
tx *knftables.Transaction,
clusterCidr, podCidr string,
family knftables.Family) error {
family knftables.Family,
ipMasqRandomFullyDisable bool) error {
masquerade := "masquerade fully-random"
if !nftm.checkRandomfully(ctx) {
if !nftm.checkRandomfully(ctx) || ipMasqRandomFullyDisable {
masquerade = "masquerade"
}

Expand Down
3 changes: 2 additions & 1 deletion pkg/trafficmngr/nftables/nftables_windows.go
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Original file line number Diff line number Diff line change
Expand Up @@ -43,7 +43,8 @@ func (nftm *NFTablesManager) SetupAndEnsureForwardRules(ctx context.Context,
func (nftm *NFTablesManager) SetupAndEnsureMasqRules(ctx context.Context, flannelIPv4Net, prevSubnet, prevNetwork ip.IP4Net,
flannelIPv6Net, prevIPv6Subnet, prevIPv6Network ip.IP6Net,
currentlease *lease.Lease,
resyncPeriod int) error {
resyncPeriod int,
ipMasqRandomFullyDisable bool) error {
log.Warning(trafficmngr.ErrUnimplemented)
return nil
}
3 changes: 2 additions & 1 deletion pkg/trafficmngr/trafficmngr.go
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Original file line number Diff line number Diff line change
Expand Up @@ -55,5 +55,6 @@ type TrafficManager interface {
flannelIPv4Net, prevSubnet, prevNetwork ip.IP4Net,
flannelIPv6Net, prevIPv6Subnet, prevIPv6Network ip.IP6Net,
currentlease *lease.Lease,
resyncPeriod int) error
resyncPeriod int,
ipMasqRandomFullyDisable bool) error
}
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