// makes a room for a new entry, get rid of
// the least recently used entry (LRU)
public void PurgeLRUEntry()
{
if (arpEntries.Count == 0)
{
return;
}
// can use a LRU list to avoid O(n)
// but this is a kind of a small table...
IDictionaryEnumerator dicEnum = arpEntries.GetEnumerator();
dicEnum.MoveNext(); // get the first entry
ArpEntry lruElement = (ArpEntry)dicEnum.Value;
while (dicEnum.MoveNext())
{
ArpEntry current = (ArpEntry)dicEnum.Value;
if (current.EntryAge < lruElement.EntryAge)
{
lruElement = current;
}
}
RemoveEntry(lruElement);
}
// add a new entry
// return false if there is no more room
public bool AddEntry(ArpEntry e)
{
// if no more room, make one
if (arpEntries.Count >= maxEntries)
{
PurgeLRUEntry();
}
e.EntryAge = this.defaultAge;
arpEntries.Add(e.IPAddress, e);
DebugPrint("Added entry {0}\n", e);
return(true);
}
// an upper layer interface to get the mac
// to a target IP. The upper protocol must
// provide the Mux for the target IP.
// if we have it then we return true + macAddress
// and refresh the age to create a LRU list
public bool Lookup(IPv4 targetIP, out EthernetAddress macAddress)
{
ArpEntry e = arpEntries[targetIP] as ArpEntry;
if (e != null)
{
e.EntryAge = Age;
macAddress = e.MacAddress;
return(true);
}
macAddress = EthernetAddress.Zero;
return(false);
}
private void RemoveEntry(ArpEntry e)
{
arpEntries.Remove(e.IPAddress);
DebugPrint("Removed entry for {0}\n", e);
}
// Original note from Yaron:
// ARP logic: see RFC 826 http://www.faqs.org/rfcs/rfc826.html
//
public void ProcessIncomingPacket(Bytes packet, IAdapter adapter)
{
//Get the ARP packet info located after the ethernet header
ArpHeader arpHeader = new ArpHeader(packet, 14);
DebugPrint("ARP: ProcessIncomingPacket\n");
//do some checks to make sure the packet is copacetic
if (arpHeader.htype != 0x1)
{
DebugPrint("ARP: ProcessIncomingPacket got wrong hardware type? 0x{0,8:x}\n",
arpHeader.htype);
//delete packet;
return;
}
if (arpHeader.ptype != 0x0800)
{
DebugPrint("ARP: ProcessIncomingPacket got wrong protocol? 0x{0,8:x}\n",
arpHeader.ptype);
//delete packet;
return;
}
//ethernet address should be 6 bytes
if (arpHeader.hlen != 6)
{
DebugPrint("ARP: ProcessIncomingPacket got wrong hw length? 0x{0,8:x}\n",
arpHeader.hlen);
//delete packet;
return;
}
if (arpHeader.plen != 4)
{
DebugPrint("ARP: ProcessIncomingPacket got wrong protocol address length? 0x{0,8:x}\n",
arpHeader.plen);
//delete packet;
return;
}
DebugPrint("Incoming packet\n");
bool merged = false;
bool updated = false;
ArpEntry target = arpTable.Lookup(arpHeader.senderIPAddr);
if (target != null && target.Dynamic == true)
{
DebugPrint("ARP UPDATE\n");
// we have it already - just update the details...
target.MacAddress = arpHeader.senderEthernetAddr;
target.EntryAge = arpTable.Age;
merged = true;
updated = true;
}
if (merged == false)
{
DebugPrint("ARP ADDITION\n");
arpTable.AddEntry(new ArpEntry(arpHeader.senderIPAddr,
arpHeader.senderEthernetAddr, true));
merged = true;
UpdatePendingRequests(arpHeader.senderIPAddr, arpHeader.senderEthernetAddr);
}
//Is this a local address
bool forSelf = IP.IsLocalAddress(arpHeader.destIPAddr);
if (forSelf == false)
{
//delete packet;
return;
}
// now figure out the opcode
if (arpHeader.op == ARP_REQUEST)
{
DebugPrint("Handling request ({0},{1}) ---> ({2},{3} \npkt dest {4} {5})\n",
arpHeader.senderIPAddr, arpHeader.senderEthernetAddr,
arpHeader.destIPAddr, adapter.HardwareAddress,
arpHeader.destIPAddr, arpHeader.destEthernetAddr
);
int dataLength = EthernetHeader.Size + ArpHeader.Size;
VTable.Assert(packet.Length >= dataLength);
Bytes data = Bitter.SplitOff(ref packet, EthernetHeader.Size);
EthernetHeader.Write(packet,
adapter.HardwareAddress,
arpHeader.senderEthernetAddr,
EthernetHeader.PROTOCOL_ARP);
//use arp header to format reply
ArpHeader.Write(data, adapter.HardwareAddress,
arpHeader.destIPAddr, ArpHeader.ARP_REPLY,
arpHeader.senderEthernetAddr, arpHeader.senderIPAddr);
adapter.PopulateTxRing(packet, data);
}
else
{
// otherwise we are done
DebugPrint(
"Handling reply ({2},{3}) <--- ({0},{1})\n",
arpHeader.senderIPAddr, arpHeader.senderEthernetAddr,
arpHeader.destIPAddr, arpHeader.destEthernetAddr
);
//delete packet;
}
if (merged && !updated)
{
DebugPrint(arpTable.ToString());
}
}
