Ethernet ARP Request / Reply Packets
HardwareType: TYPE ~ Basics.HWORD;
ethernet: HardwareType ~ [00H, 01H];
HardwareAddressLength: TYPE ~ BYTE;
ethernetAddressLength: HardwareAddressLength ~ BYTE[06H]; -- 6 bytes = 48 bits
ProtocolType: TYPE ~ Basics.HWORD;
ipType: ProtocolType ~ [08H, 00H]; -- ARPA IP type from Assigned Numbers RFC
ProtocolAddressLength: TYPE ~ BYTE;
ipAddressLength: ProtocolAddressLength ~ BYTE[04H]; -- 4 bytes
TranslationType: TYPE ~ Basics.HWORD; -- opcode in RFC826
requestType: TranslationType ~ [00H, 01H];
replyType: TranslationType ~ [00H, 02H];
HostPair:
TYPE ~
MACHINE
DEPENDENT
RECORD [
nsHost: XNS.Host,
arpaHost: Arpa.Address];
TranslationPacketObject:
TYPE ~
MACHINE
DEPENDENT
RECORD [
hardwareType: Basics.HWORD,
protocolType: Basics.HWORD,
hardwareAddressLength: BYTE,
protocolAddressLength: BYTE,
translationType: TranslationType,
senderHostPair: HostPair,
targetHostPair: HostPair];
translationPacketBytes: CARDINAL ~ BYTES[TranslationPacketObject]; -- Must be even!
TranslationBuffer: TYPE ~ REF TranslationBufferObject;
TranslationBufferObject:
TYPE ~
MACHINE
DEPENDENT
RECORD [
ovh: CommBuffer.Overhead,
hardwareType: Basics.HWORD,
protocolType: Basics.HWORD,
hardwareAddressLength: BYTE,
protocolAddressLength: BYTE,
translationType: TranslationType,
senderHostPair: HostPair,
targetHostPair: HostPair];
Translation Entry Cache
For the Arpa world, the number of hash headers has been set to the maximum number of Pup hosts possible on an ethernet. The hash table chained overflow code is not exercised, and could be discarded. If you want to reduce the number of hash headers, replace the Identity hash function with something like the MOD function in the comment below.
numHashHeaders: CARDINAL ~ 256;
HashIndex: TYPE ~ [0..numHashHeaders);
Hash: PROC [arpaHost: Arpa.Address] RETURNS [HashIndex] ~ INLINE {
RETURN [arpaHost] };
Hash:
PROC [arpaHost: Arpa.Address]
RETURNS [HashIndex] ~
INLINE {
RETURN [ Basics.Card32FromF[LOOPHOLE[arpaHost]] MOD numHashHeaders ] };
Cache: TYPE ~ REF CacheObject;
CacheObject:
TYPE ~
MONITORED
RECORD [
daemon: PROCESS,
event: CONDITION,
newPendingEntry: BOOL ← FALSE,
sweepTime: Pulses,
sendHead, sendTail: Buffer,
broadcastHostEntry: CacheEntry,
thisHostEntry: CacheEntry,
pendingEntries: CacheEntry,
validEntries: ARRAY HashIndex OF CacheEntry];
CacheEntry: TYPE ~ REF CacheEntryObject;
CacheEntryObject:
TYPE ~
RECORD [
next: CacheEntry,
hosts: HostPair,
whenToSend: Pulses,
timeToLive: CARDINAL
];
UpToDate:
PROC [eH: CacheEntry]
RETURNS [
BOOL]
~ INLINE { RETURN [eH.timeToLive > 0] };
Timeouts
pulsesPerSweep: Pulses ← MSecsToPulses[19000];
sweepTimeout: Process.Ticks ← Process.SecondsToTicks[20];
sweepsToLive: CARDINAL ← 6;
pulsesPerResend: Pulses ~ MSecsToPulses[230];
resendTimeout: Process.Ticks ← Process.MsecToTicks[250];
sendsToLive: CARDINAL ← 8;
Encapsulating Arpa Packets
Statistics
noTranslation: INT ← 0;
notQuick: INT ← 0;
GetEncapsulation:
PROC [network: Network, arpaHost: Arpa.Address]
RETURNS [Encapsulation] ~ {
cH: Cache ← NARROW[ArpaTranslation.GetTranslationTable[network]];
eH: CacheEntry ← NIL;
subnetMask: Arpa.Address ← ArpaTranslation.GetSubnetMask[network];
hashIndex: HashIndex ~ Hash[arpaHost];
???? broadcastHost: Arpa.Address ← LOOPHOLE[Basics.DoubleOr[LOOPHOLE[ArpaTranslation.GetNet[network]], Basics.DoubleNot[LOOPHOLE[ArpaTranslation.GetSubnetMask[network]]]]]; ????
broadcastHost: Arpa.Address ← ArpaExtras.BroadcastAddressOnSubnetWithMask[network.arpa.host, subnetMask];
BEGIN
Quick check of first couple of entries without acquiring ML.
IF (eH ← cH.validEntries[hashIndex]) #
NIL
THEN {
IF (eH.hosts.arpaHost = arpaHost) AND UpToDate[eH] THEN GOTO Found;
IF (eH ← eH.next) #
NIL
THEN {
IF (eH.hosts.arpaHost = arpaHost) AND UpToDate[eH] THEN GOTO Found;
NULL; -- more checks would go here ...
};
};
IF ArpaExtras.IsBroadcastWithMask[arpaHost, subnetMask] THEN { eH ← cH.broadcastHostEntry; GOTO Found };
???? IF allHosts = LOOPHOLE[Basics.DoubleOr[LOOPHOLE[arpaHost], LOOPHOLE[ArpaTranslation.GetSubnetMask[network]]]] THEN { eH ← cH.broadcastHostEntry; GOTO Found }; ????
IF arpaHost = network.arpa.host THEN { eH ← cH.thisHostEntry; GOTO Found };
notQuick ← notQuick.SUCC;
IF (eH ← GetCacheEntry[cH, hashIndex, arpaHost]) # NIL THEN GOTO Found;
GOTO NotFound;
EXITS
Found => {
TRUSTED { RETURN[ [ethernet[ethernetDest~eH.hosts.nsHost, ethernetSource~thisHost, ethernetType~arpa]] ] }
};
NotFound => {
noTranslation ← noTranslation.SUCC;
TRUSTED { RETURN[ [ethernet[ethernetDest~XNS.unknownHost, ethernetSource~thisHost, ethernetType~translationFailed]] ] }
};
END;
};
GetCacheEntry:
ENTRY
PROC [cH: Cache, hashIndex: HashIndex, arpaHost: Arpa.Address]
RETURNS [CacheEntry] ~ {
Search for a valid cache entry for the given nsHost. If a valid entry is found, return it; otherwise return NIL and arrange for an entry to be added.
eH, prevH: CacheEntry;
eH ← cH.validEntries[hashIndex]; prevH ← NIL;
WHILE eH #
NIL
DO
IF eH.hosts.arpaHost = arpaHost
THEN {
IF UpToDate[eH]
THEN {
Move entry to head of list.
IF prevH #
NIL
THEN {
prevH.next ← eH.next;
eH.next ← cH.validEntries[hashIndex];
cH.validEntries[hashIndex] ← eH };
RETURN[eH] }
ELSE {
Entry needs to be refreshed — move it to pending list.
IF prevH #
NIL
THEN prevH.next ← eH.next
ELSE cH.validEntries[hashIndex] ← eH.next;
eH.timeToLive ← sendsToLive;
eH.whenToSend ← BasicTime.GetClockPulses[];
eH.next ← cH.pendingEntries;
cH.pendingEntries ← eH;
cH.newPendingEntry ← TRUE; NOTIFY cH.event;
RETURN[eH] };
};
prevH ← eH; eH ← eH.next
ENDLOOP;
Search for a pending entry.
FOR eH ← cH.pendingEntries, eH.next
WHILE eH #
NIL
DO
IF eH.hosts.arpaHost = arpaHost
THEN
RETURN[IF eH.hosts.nsHost # XNS.unknownHost THEN eH ELSE NIL];
ENDLOOP;
TRUSTED { cH.pendingEntries ← NEW[ CacheEntryObject ← [next~cH.pendingEntries, hosts~[nsHost~XNS.unknownHost, arpaHost~arpaHost], whenToSend~BasicTime.GetClockPulses[], timeToLive~sendsToLive] ] };
cH.newPendingEntry ← TRUE; NOTIFY cH.event;
RETURN[NIL] };
Building Request / Reply Packets
MakeRequest:
PROC [cH: Cache, arpaHost: Arpa.Address, sendTo:
XNS.Host ←
XNS.broadcastHost]
RETURNS [b: Buffer] ~ {
Allocate a buffer, build a request packet in it, and return it.
The sendTo parameter is the XNS Host to which the request packet will be sent. It should be broadcastHost for a normal request.
bH: TranslationBuffer;
b ← CommDriver.AllocBuffer[];
TRUSTED { bH ← LOOPHOLE[b] };
bH.hardwareType ← ethernet;
bH.protocolType ← ipType;
bH.hardwareAddressLength ← ethernetAddressLength;
bH.protocolAddressLength ← ipAddressLength;
bH.translationType ← requestType;
bH.targetHostPair ← [nsHost~XNS.unknownHost, arpaHost~arpaHost];
bH.senderHostPair ← cH.thisHostEntry.hosts;
TRUSTED { bH.ovh.encap ← Encapsulation[ethernet[ethernetDest~sendTo, ethernetSource~thisHost, ethernetType~arp]] };
};
ConvertToReply:
PROC [cH: Cache, bH: TranslationBuffer] ~ {
Given a request buffer, convert it to the corresponding reply.
Fill in the encapsulation part here, so the buffer can be sent using network.sendTranslate rather than network.return.
-- These 4 lines might not be needed but ...
bH.hardwareType ← ethernet;
bH.protocolType ← ipType;
bH.hardwareAddressLength ← ethernetAddressLength;
bH.protocolAddressLength ← ipAddressLength;
bH.translationType ← replyType;
bH.targetHostPair ← bH.senderHostPair;
bH.senderHostPair ← cH.thisHostEntry.hosts;
TRUSTED { bH.ovh.encap ← Encapsulation[ethernet[ethernetDest~bH.targetHostPair.nsHost, ethernetSource~thisHost, ethernetType~arp]] };
};
Processing Received Translation Packets
AddTranslation:
ENTRY
PROC [cH: Cache, hosts: HostPair] ~ {
eH, prevH: CacheEntry;
i: HashIndex ~ Hash[hosts.arpaHost];
Look for a pending entry.
eH ← cH.pendingEntries; prevH ← NIL;
WHILE eH #
NIL
DO
IF eH.hosts.arpaHost = hosts.arpaHost
THEN {
IF prevH = NIL THEN cH.pendingEntries ← eH.next ELSE prevH.next ← eH.next;
eH.hosts.nsHost ← hosts.nsHost;
EXIT };
prevH ← eH; eH ← eH.next
ENDLOOP;
If no pending entry, look for a valid one.
IF eH =
NIL
THEN {
eH ← cH.validEntries[i]; prevH ← NIL;
WHILE eH #
NIL
DO
IF eH.hosts.arpaHost = hosts.arpaHost
THEN {
IF prevH = NIL THEN cH.validEntries[i] ← eH.next ELSE prevH.next ← eH.next;
If existing entry is incorrect, drop it on the floor ...
IF eH.hosts.nsHost # hosts.nsHost THEN eH ← NIL;
EXIT };
prevH ← eH; eH ← eH.next
ENDLOOP;
};
IF eH =
NIL
THEN eH ← NEW[ CacheEntryObject ← [next~, hosts~hosts, whenToSend~, timeToLive~]];
eH.timeToLive ← sweepsToLive;
eH.next ← cH.validEntries[i];
cH.validEntries[i] ← eH;
};
Receive Statistics
requestsReceived: INT ← 0;
repliesReceived: INT ← 0;
tooShort: INT ← 0;
badProtocol: INT ← 0;
RecvTranslation: CommDriver.RecvProc
[network: Network, buffer: Buffer, bytes: NAT] RETURNS [Buffer]
~ {
cH: Cache ← NARROW[ArpaTranslation.GetTranslationTable[network]];
bH: TranslationBuffer;
IF bytes < translationPacketBytes
THEN {
tooShort ← tooShort.SUCC;
RETURN [buffer] };
TRUSTED { bH ← LOOPHOLE[buffer] };
SELECT
TRUE
FROM
bH.translationType = requestType => {
IF bH.targetHostPair.arpaHost = network.arpa.host
THEN {
requestsReceived ← requestsReceived.SUCC;
AddTranslation[cH, bH.senderHostPair];
ConvertToReply[cH, bH];
EnqueueForSending[cH, buffer];
buffer ← NIL;
};
};
bH.translationType = replyType => {
repliesReceived ← repliesReceived.SUCC;
AddTranslation[cH, bH.senderHostPair];
};
ENDCASE => {
badProtocol ← badProtocol.SUCC };
RETURN[buffer];
};
Daemon Process
EnqueueForSending:
ENTRY PROC [cH: Cache, b: Buffer] ~ {
IF cH.sendHead = NIL THEN cH.sendHead ← b ELSE cH.sendTail.ovh.next ← b;
cH.sendTail ← b;
b.ovh.next ← NIL;
NOTIFY cH.event };
InternalEnqueueForSending:
INTERNAL PROC [cH: Cache, b: Buffer] ~ {
IF cH.sendHead = NIL THEN cH.sendHead ← b ELSE cH.sendTail.ovh.next ← b;
cH.sendTail ← b;
b.ovh.next ← NIL;
NOTIFY cH.event };
DequeueForSending:
ENTRY
PROC [cH: Cache]
RETURNS [b: Buffer] ~ {
IF (b ← cH.sendHead) = NIL THEN RETURN;
IF (cH.sendHead ← NARROW[b.ovh.next]) = NIL THEN cH.sendTail ← NIL;
};
InternalSendQueueIsEmpty:
INTERNAL
PROC [cH: Cache]
RETURNS [
BOOL] ~
INLINE {
RETURN [cH.sendHead = NIL] };
sweepsInhibited: BOOL ← FALSE; -- DEBUG
WaitAndScanCache:
ENTRY
PROC [cH: Cache] ~ {
eH, prevH: CacheEntry;
IF InternalSendQueueIsEmpty[cH]
AND
NOT cH.newPendingEntry
THEN {
TRUSTED {
IF cH.pendingEntries #
NIL
THEN Process.SetTimeout[@cH.event, resendTimeout]
ELSE Process.SetTimeout[@cH.event, sweepTimeout] };
WAIT cH.event };
prevH ← NIL; eH ← cH.pendingEntries;
WHILE eH #
NIL
DO
IF PulsesSince[eH.whenToSend] >= 0
THEN {
IF eH.timeToLive = 0
THEN
{
Delete the entry.
eH ← eH.next;
IF prevH = NIL THEN cH.pendingEntries ← eH ELSE prevH.next ← eH;
LOOP };
{
Send the entry
destHost: XNS.Host ~ IF (eH.timeToLive > (sendsToLive/2)) AND (eH.hosts.nsHost # XNS.unknownHost) THEN eH.hosts.nsHost ELSE XNS.broadcastHost;
buffer: Buffer ~ MakeRequest[cH, eH.hosts.arpaHost, destHost];
InternalEnqueueForSending[cH, buffer];
eH.timeToLive ← eH.timeToLive - 1;
eH.whenToSend ← BasicTime.GetClockPulses[] + pulsesPerResend;
};
};
prevH ← eH; eH ← eH.next;
ENDLOOP;
cH.newPendingEntry ← FALSE;
IF (PulsesSince[cH.sweepTime] >= pulsesPerSweep)
AND (
NOT sweepsInhibited)
THEN {
Do a sweep ...
FOR i: HashIndex
IN [0..numHashHeaders)
DO
FOR eH ← cH.validEntries[i], eH.next
WHILE eH #
NIL
DO
IF eH.timeToLive > 0 THEN eH.timeToLive ← eH.timeToLive - 1;
ENDLOOP;
ENDLOOP;
cH.sweepTime ← BasicTime.GetClockPulses[];
};
};
Daemon:
PROC [network: Network] ~ {
cH: Cache ← NARROW[ArpaTranslation.GetTranslationTable[network]];
buffer: Buffer;
Process.SetPriority[Process.priorityForeground];
DO
WaitAndScanCache[cH];
WHILE (buffer ← DequeueForSending[cH]) #
NIL
DO
network.arpa.sendTranslate[network, buffer, translationPacketBytes];
CommDriver.FreeBuffer[buffer];
ENDLOOP;
ENDLOOP;
};