Add ARP Responder module

bessctl/conf/samples/arp.bess

@@ -0,0 +1,11 @@
+import scapy.all as scapy
+
+eth_header = scapy.Ether(src='02:1e:67:9f:4d:ae', dst='ff:ff:ff:ff:ff:ff')
+arp_header = scapy.ARP(op=1, pdst='1.2.3.4')
+pkt = eth_header/arp_header
+packets = [str(pkt)]
+
+arp::ArpResponder()
+arp.add(ip='1.2.3.4', mac_addr='A0:22:33:44:55:66')
+
+Source() -> Rewrite(templates=packets) -> arp -> Sink()

core/modules/arp_responder.cc

@@ -0,0 +1,84 @@
+#include "arp_responder.h"
+
+#include "../utils/arp.h"
+
+using bess::utils::Arp;
+using bess::utils::be16_t;
+
+const Commands ArpResponder::cmds = {
+    {"add", "ArpResponderArg", MODULE_CMD_FUNC(&ArpResponder::CommandAdd), 0}};
+
+CommandResponse ArpResponder::CommandAdd(const bess::pb::ArpResponderArg &arg) {
+  be32_t ip_addr;
+  arp_entry entry;
+
+  if (!arg.ip().length()) {
+    return CommandFailure(EINVAL, "IP address is missing");
+  }
+  if (!bess::utils::ParseIpv4Address(arg.ip(), &ip_addr)) {
+    return CommandFailure(EINVAL, "Invalid IP Address: %s", arg.ip().c_str());
+  }
+
+  if (!entry.mac_addr.FromString(arg.mac_addr())) {
+    return CommandFailure(EINVAL, "Invalid MAC Address: %s",
+                          arg.mac_addr().c_str());
+  }
+
+  entry.ip_addr = ip_addr;
+  entries_[ip_addr] = entry;
+  return CommandSuccess();
+}
+
+void ArpResponder::ProcessBatch(bess::PacketBatch *batch) {
+  gate_idx_t out_gates[bess::PacketBatch::kMaxBurst];
+
+  int cnt = batch->cnt();
+  for (int i = 0; i < cnt; i++) {
+    bess::Packet *pkt = batch->pkts()[i];
+
+    out_gates[i] = 0;
+
+    Ethernet *eth = pkt->head_data<Ethernet *>();
+    if (eth->ether_type != be16_t(Ethernet::Type::kArp)) {
+      // Currently drop all non ARP packets, but can also just continue
+      out_gates[i] = DROP_GATE;
+      continue;
+    }
+
+    Arp *arp = reinterpret_cast<Arp *>(eth + 1);
+    if (arp->opcode == be16_t(Arp::Opcode::kRequest)) {
+      // TODO(galsagie) When learn is added, learn SRC MAC here
+
+      // Try to find target IP in cache, if exists convert request to reply
+      auto it = entries_.find(arp->target_ip_addr);
+      if (it != entries_.end()) {
+        const struct arp_entry &entry = it->second;
+        arp->opcode = be16_t(Arp::Opcode::kReply);
+
+        eth->dst_addr = eth->src_addr;
+        eth->src_addr = entry.mac_addr;
+
+        arp->target_hw_addr = arp->sender_hw_addr;
+        arp->sender_hw_addr = entry.mac_addr;
+
+        arp->target_ip_addr = arp->sender_ip_addr;
+        arp->sender_ip_addr = entry.ip_addr;
+      } else {
+        // Did not find an ARP entry in cache, drop packet
+        // TODO(galsagie) Optinally continue packet to next module here
+        out_gates[i] = DROP_GATE;
+      }
+    } else if (arp->opcode == be16_t(Arp::Opcode::kReply)) {
+      // TODO(galsagie) When learn is added, learn SRC MAC here
+      out_gates[i] = DROP_GATE;
+    } else {
+      // TODO(galsagie) Other opcodes are not handled yet.
+      out_gates[i] = DROP_GATE;
+    }
+  }
+
+  RunSplit(out_gates, batch);
+}
+
+ADD_MODULE(ArpResponder, "arp_responder",
+           "Respond to ARP requests and learns new MAC's")

core/modules/arp_responder.h

@@ -0,0 +1,41 @@
+#ifndef BESS_MODULES_ARP_RESPONDER_H_
+#define BESS_MODULES_ARP_RESPONDER_H_
+
+#include <map>
+
+#include "../module.h"
+#include "../module_msg.pb.h"
+#include "../utils/endian.h"
+#include "../utils/ether.h"
+#include "../utils/ip.h"
+
+using bess::utils::Ethernet;
+using bess::utils::be32_t;
+
+// ARP cache entry struct which keeps mapping between IP and MAC
+struct arp_entry {
+  Ethernet::Address mac_addr;
+  be32_t ip_addr;
+  uint64_t time; // timestamp used to expire cache entries (in milliseconds)
+};
+
+// ARP Responder module
+// Answer ARP requests from an internal configurable cache
+// Currently drops non ARP packets
+class ArpResponder final : public Module {
+ public:
+  static const gate_idx_t kNumIGates = 1;
+  static const gate_idx_t kNumOGates = 1;
+
+  static const Commands cmds;
+
+  void ProcessBatch(bess::PacketBatch *batch) override;
+
+  CommandResponse CommandAdd(const bess::pb::ArpResponderArg &arg);
+
+ private:
+  // Mapping between IP (key) and its ARP entry (MAC Address)
+  std::map<be32_t, struct arp_entry> entries_;
+};
+
+#endif  // BESS_MODULES_ARP_RESPONDER_H_

protobuf/module_msg.proto

@@ -972,3 +972,18 @@ message VXLANEncapArg {
 message WildcardMatchArg {
   repeated WildcardMatchField fields = 1; /// A list of WildcardMatch fields.
 }
+
+/**
+ * The ARP Responder module is responding to ARP requests
+ * TODO: Dynamic learn new MAC's-IP's mapping
+ *
+ * __Input Gates__: 1
+ * __Output Gates__: 1
+ */
+message ArpResponderArg {
+  /**
+   * One ARP IP-MAC mapping
+   */
+   string ip = 1; // The IP
+   string mac_addr = 2; /// The MAC address
+}