From 1ad6ecd556423c12ffe6c1dabacff9b5c1adafb2 Mon Sep 17 00:00:00 2001
From: Onur Filiz <onfiliz@amazon.com>
Date: Fri, 2 Aug 2019 13:54:10 -0700
Subject: [PATCH] vpc-shared-eni: Enable IP forwarding and ARP proxy when using
 L3 mode

---
 network/ipcfg/ip.go                           | 49 +++++++++++++++++++
 .../vpc-shared-eni/network/bridge_linux.go    | 32 +++++++++++-
 2 files changed, 80 insertions(+), 1 deletion(-)
 create mode 100644 network/ipcfg/ip.go

diff --git a/network/ipcfg/ip.go b/network/ipcfg/ip.go
new file mode 100644
index 00000000..a1d04545
--- /dev/null
+++ b/network/ipcfg/ip.go
@@ -0,0 +1,49 @@
+// Copyright 2019 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License"). You may
+// not use this file except in compliance with the License. A copy of the
+// License is located at
+//
+//     http://aws.amazon.com/apache2.0/
+//
+// or in the "license" file accompanying this file. This file is distributed
+// on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
+// express or implied. See the License for the specific language governing
+// permissions and limitations under the License.
+
+package ipcfg
+
+import (
+	"bytes"
+	"fmt"
+	"io/ioutil"
+	"strconv"
+)
+
+const (
+	ipv4Forwarding = "/proc/sys/net/ipv4/conf/%s/forwarding"
+	ipv4ProxyARP   = "/proc/sys/net/ipv4/conf/%s/proxy_arp"
+)
+
+// SetIPv4Forwarding sets the IPv4 forwarding property of an interface to the given value.
+func SetIPv4Forwarding(ifName string, value int) error {
+	return set(fmt.Sprintf(ipv4Forwarding, ifName), value)
+}
+
+// SetIPv4ProxyARP sets the IPv4 proxy ARP property of an interface to the given value.
+func SetIPv4ProxyARP(ifName string, value int) error {
+	return set(fmt.Sprintf(ipv4ProxyARP, ifName), value)
+}
+
+// Set sets a system variable to the given value.
+func set(name string, value int) error {
+	valueStr := strconv.Itoa(value)
+
+	// Do not rewrite if the value is already set.
+	currValue, err := ioutil.ReadFile(name)
+	if err == nil && bytes.Equal(bytes.TrimSpace(currValue), []byte(valueStr)) {
+		return nil
+	}
+
+	return ioutil.WriteFile(name, []byte(valueStr), 0644)
+}
diff --git a/plugins/vpc-shared-eni/network/bridge_linux.go b/plugins/vpc-shared-eni/network/bridge_linux.go
index 32c74d42..39778438 100644
--- a/plugins/vpc-shared-eni/network/bridge_linux.go
+++ b/plugins/vpc-shared-eni/network/bridge_linux.go
@@ -20,6 +20,7 @@ import (
 
 	"github.com/aws/amazon-vpc-cni-plugins/network/ebtables"
 	"github.com/aws/amazon-vpc-cni-plugins/network/eni"
+	"github.com/aws/amazon-vpc-cni-plugins/network/ipcfg"
 	"github.com/aws/amazon-vpc-cni-plugins/network/netns"
 	"github.com/aws/amazon-vpc-cni-plugins/network/vpc"
 	"github.com/aws/amazon-vpc-cni-plugins/plugins/vpc-shared-eni/config"
@@ -456,8 +457,10 @@ func (nb *BridgeBuilder) createBridge(
 		return 0, err
 	}
 
-	// Setup bridge layer2 configuration.
 	if bridgeType == config.BridgeTypeL2 {
+		// In layer2 configuration, the bridge inherits shared ENI's IP address and default route.
+		// Frames are switched between veth pairs and the shared ENI.
+
 		// Assign IP address to bridge.
 		log.Infof("Assigning IP address %v to bridge link %s.", ipAddress, bridgeName)
 		address := &netlink.Addr{IPNet: ipAddress}
@@ -485,6 +488,33 @@ func (nb *BridgeBuilder) createBridge(
 			log.Errorf("Failed to add IP route %+v: %v.", route, err)
 			return 0, err
 		}
+	} else {
+		// In layer3 configuration, the IP address and default route remain on the shared ENI.
+		// IP datagrams are routed between the bridge and the shared ENI.
+
+		// Bridge proxies ARP requests originating from veth pairs to the VPC.
+		log.Infof("Enabling IPv4 proxy ARP on %s.", bridgeName)
+		err = ipcfg.SetIPv4ProxyARP(bridgeName, 1)
+		if err != nil {
+			log.Errorf("Failed to enable IPv4 proxy ARP on %s: %v.", bridgeName, err)
+			return 0, err
+		}
+
+		// Enable IPv4 forwarding on the bridge and shared ENI, so that IP datagrams can be
+		// routed between them.
+		log.Infof("Enabling IPv4 forwarding on %s.", bridgeName)
+		err = ipcfg.SetIPv4Forwarding(bridgeName, 1)
+		if err != nil {
+			log.Errorf("Failed to enable IPv4 forwarding on %s: %v.", bridgeName, err)
+			return 0, err
+		}
+
+		log.Infof("Enabling IPv4 forwarding on %s.", sharedENI.GetLinkName())
+		err = ipcfg.SetIPv4Forwarding(sharedENI.GetLinkName(), 1)
+		if err != nil {
+			log.Errorf("Failed to enable IPv4 forwarding on %s: %v.", sharedENI.GetLinkName(), err)
+			return 0, err
+		}
 	}
 
 	return bridgeLink.Attrs().Index, nil