folkert/simh-testsetgenerator
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

Fixed MAC Address Conflict detection support.

Browse source 
VMS engineers designed the address conflict strategy when essentially all LANs were single collision domains (i.e. ALL nodes which might be affected by an address conflict were physically present on a single Ethernet cable which might have been extended by a couple of repeaters).  Since that time, essentially no networks are single collision domains.  Thick and thinwire Ethernet cables don’t exist and very few networks even have hubs.  Today, essentially all LANs are deployed using one or more layers of network switches.  In a switched LAN environment, the switches on the LAN ‘learn’ which ports on the LAN source traffic from which MAC addresses and then forward traffic destined for particular MAC address to the appropriate ports.  If a particular MAC address is already in use somewhere on the LAN, then the switches ‘know’ where it is.  The host based test using the loopback protocol is poorly designed to detect this condition.  This test is performed by the host first changing the device’s Physical MAC address to the address which is to be tested, and then sending a loopback packet FROM AND TO this MAC address with a loopback reply to be sent by a system which may be currently using the MAC address.  If no reply is received, then the MAC address is presumed to be unused.  The sending of this packet will result in its delivery to the right system since the switch port/MAC address tables know where to deliver packets destined to this MAC address, however the response it generates won’t be delivered to the system performing the test since the switches on the LAN won’t know about the local port being the right target for packets with this MAC address.  A better test design to detect these conflicts would be for the testing system to send a loopback packet FROM the current physical MAC address (BEFORE changing it) TO the MAC address being tested with the loopback response coming to the current physical MAC address of the device.  If a response is received, then the address is in use and the attempt to change the device’s MAC address should fail.  Since we can’t change the software running in these simulators to implement this better conflict detection approach, we can still ‘do the right thing’ in the sim_ether layer.  We’re already handling the loopback test packets specially since we always had to avoid receiving the packets which were being sent, but needed to allow for the incoming loopback packets to be properly dealt with.  We can extend this current special handling to change outgoing ‘loopback to self’ packets to have source AND loopback destination addresses in the packets to be the host NIC’s physical address.  The switch network will already know the correct MAC/port relationship for the host NIC’s physical address, so loopback response packets will be delivered as needed.
This commit is contained in:
Mark Pizzolato 2012-02-28 14:10:08 -08:00
parent 4ab52659be
commit 4f6ad32395
2 changed files with 115 additions and 14 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

100
sim_ether.c
View file

@ -1721,6 +1721,66 @@ char mac_string[32];
eth_mac_fmt(mac, mac_string);
sim_debug(dev->dbit, dev->dptr, "Determining Address Conflict for MAC address: %s\n", mac_string);
/* The process of checking address conflicts is used in two ways:
1) to determine the behavior of the currently running packet
delivery facility regarding whether it may receive copies
of every packet sent (and how many).
2) to verify if a MAC address which this facility is planning
to use as the source address of packets is already in use
by some other node on the local network
Case #1, doesn't require (and explicitly doesn't want) any
interaction or response from other systems on the LAN so
therefore no considerations regarding switch packet forwarding
are important. Meanwhile, Case #2 does require responses from
other components on the LAN to provide useful functionality.
The original designers of this mechanism did this when essentially
all LANs were single collision domains (i.e. ALL nodes which might
be affected by an address conflict were physically present on a single
Ethernet cable which might have been extended by a couple of repeaters).
Since that time, essentially no networks are single collision domains.
Thick and thinwire Ethernet cables don’t exist and very few networks
even have hubs. Today, essentially all LANs are deployed using one
or more layers of network switches. In a switched LAN environment, the
switches on the LAN ‘learn’ which ports on the LAN source traffic from
which MAC addresses and then forward traffic destined for particular
MAC address to the appropriate ports. If a particular MAC address is
already in use somewhere on the LAN, then the switches ‘know’ where
it is. The host based test using the loopback protocol is poorly
designed to detect this condition. This test is performed by the host
first changing the device’s Physical MAC address to the address which
is to be tested, and then sending a loopback packet FROM AND TO this
MAC address with a loopback reply to be sent by a system which may be
currently using the MAC address. If no reply is received, then the
MAC address is presumed to be unused. The sending of this packet will
result in its delivery to the right system since the switch port/MAC
address tables know where to deliver packets destined to this MAC
address, however the response it generates won’t be delivered to the
system performing the test since the switches on the LAN won’t know
about the local port being the right target for packets with this MAC
address. A better test design to detect these conflicts would be for
the testing system to send a loopback packet FROM the current physical
MAC address (BEFORE changing it) TO the MAC address being tested with
the loopback response coming to the current physical MAC address of
the device. If a response is received, then the address is in use and
the attempt to change the device’s MAC address should fail. Since we
can’t change the software running in these simulators to implement this
better conflict detection approach, we can still ‘do the right thing’
in the sim_ether layer. We’re already handling the loopback test
packets specially since we always had to avoid receiving the packets
which were being sent, but needed to allow for the incoming loopback
packets to be properly dealt with. We can extend this current special
handling to change outgoing ‘loopback to self’ packets to have source
AND loopback destination addresses in the packets to be the host NIC’s
physical address. The switch network will already know the correct
MAC/port relationship for the host NIC’s physical address, so loopback
response packets will be delivered as needed.
Code in _eth_write and _eth_callback provide the special handling to
perform the described loopback packet adjustments, and code in
eth_filter_hash makes sure that the loopback response packets are received.
*/
/* build a loopback forward request packet */
memset (&send, 0, sizeof(ETH_PACK));
send.len = ETH_MIN_PACKET; /* minimum packet size */
@ -1740,7 +1800,7 @@ if (status != SCPE_OK) {
char *msg;
msg = "Eth: Error Transmitting packet: %s\r\n"
"You may need to run as root, or install a libpcap version\r\n"
"which is at least 0.9 from www.tcpdump.org\r\n";
"which is at least 0.9 from your OS vendor or www.tcpdump.org\r\n";
printf(msg, strerror(errno));
if (sim_log) fprintf (sim_log, msg, strerror(errno));
return status;
@ -1752,7 +1812,10 @@ sim_os_ms_sleep (300); /* time for a conflicting host to respond */
do {
memset (&recv, 0, sizeof(ETH_PACK));
status = eth_read (dev, &recv, NULL);
if (memcmp(send.msg, recv.msg, 14)== 0)
if (((0 == memcmp(send.msg+12, recv.msg+12, 2)) && /* Protocol Match */
(0 == memcmp(send.msg, recv.msg+6, 6)) && /* Source Match */
(0 == memcmp(send.msg+6, recv.msg, 6))) || /* Destination Match */
(0 == memcmp(send.msg, recv.msg, 14))) /* Packet Match (Reflection) */
responses++;
} while (recv.len > 0);
@ -1789,12 +1852,16 @@ if (!packet) return SCPE_ARG;
/* make sure packet is acceptable length */
if ((packet->len >= ETH_MIN_PACKET) && (packet->len <= ETH_MAX_PACKET)) {
int loopback_self_frame = LOOPBACK_SELF_FRAME(dev->physical_addr, packet->msg);
int loopback_self_frame = LOOPBACK_SELF_FRAME(packet->msg, packet->msg);
eth_packet_trace (dev, packet->msg, packet->len, "writing");
/* record sending of loopback packet (done before actual send to avoid race conditions with receiver) */
if (loopback_self_frame) {
if (dev->have_host_nic_phy_addr) {
memcpy(&packet->msg[6], dev->host_nic_phy_hw_addr, sizeof(ETH_MAC));
memcpy(&packet->msg[18], dev->host_nic_phy_hw_addr, sizeof(ETH_MAC));
}
#ifdef USE_READER_THREAD
pthread_mutex_lock (&dev->self_lock);
#endif
@ -2343,6 +2410,17 @@ int from_me = 0;
int i;
int bpf_used;
if ((dev->have_host_nic_phy_addr) &&
(LOOPBACK_PHYSICAL_RESPONSE(dev->host_nic_phy_hw_addr, dev->physical_addr, data))) {
u_char *datacopy = malloc(header->len);
memcpy(datacopy, data, header->len);
memcpy(datacopy, dev->physical_addr, sizeof(ETH_MAC));
memcpy(datacopy+18, dev->physical_addr, sizeof(ETH_MAC));
_eth_callback(info, header, datacopy);
free(datacopy);
return;
}
switch (dev->eth_api) {
case ETH_API_PCAP:
#ifdef USE_BPF
@ -2377,7 +2455,9 @@ switch (dev->eth_api) {
}
/* detect reception of loopback packet to our physical address */
if (LOOPBACK_SELF_FRAME(dev->physical_addr, data)) {
if ((LOOPBACK_SELF_FRAME(dev->physical_addr, data)) ||
(dev->have_host_nic_phy_addr &&
LOOPBACK_PHYSICAL_REFLECTION(dev->host_nic_phy_hw_addr, data))) {
#ifdef USE_READER_THREAD
pthread_mutex_lock (&dev->self_lock);
#endif
@ -2394,7 +2474,7 @@ if (LOOPBACK_SELF_FRAME(dev->physical_addr, data)) {
#ifdef USE_READER_THREAD
pthread_mutex_unlock (&dev->self_lock);
#endif
}
}
if (bpf_used ? to_me : (to_me && !from_me)) {
if (header->len > ETH_MIN_JUMBO_FRAME) {
@ -2686,6 +2766,10 @@ if ((addr_count) && (dev->reflections > 0)) {
memcpy(dev->physical_addr, &dev->filter_address[i], sizeof(ETH_MAC));
/* let packets through where dst and src are the same as our physical address */
sprintf (&buf[strlen(buf)], " or ((ether dst %s) and (ether src %s))", mac, mac);
if (dev->have_host_nic_phy_addr) {
eth_mac_fmt(&dev->host_nic_phy_hw_addr, mac);
sprintf(&buf[strlen(buf)], "or ((ether dst %s) and (ether proto 0x9000))", mac);
}
break;
}
}
@ -2694,9 +2778,9 @@ if ((0 == strlen(buf)) && (!dev->promiscuous)) /* Empty filter means match nothi
strcpy(buf, "ether host fe:ff:ff:ff:ff:ff"); /* this should be a good match nothing filter */
sim_debug(dev->dbit, dev->dptr, "BPF string is: |%s|\n", buf);
/* get netmask, which is a required argument for compiling, the value, in our
case isn't actually interesting since the filters we generate aren't
referencing IP fields, networks or values */
/* get netmask, which is a required argument for compiling. The value,
in our case isn't actually interesting since the filters we generate
aren't referencing IP fields, networks or values */
if ((dev->eth_api == ETH_API_PCAP) && (pcap_lookupnet(dev->name, &bpf_subnet, &bpf_netmask, errbuf)<0))
bpf_netmask = 0;

27
sim_ether.h
View file

@ -136,13 +136,30 @@
#define ETH_MIN_JUMBO_FRAME ETH_MAX_PACKET /* Threshold size for Jumbo Frame Processing */
#define LOOPBACK_SELF_FRAME(phy_mac, msg) \
((memcmp(phy_mac, msg , 6) == 0) && \
(memcmp(phy_mac, msg+6, 6) == 0) && \
((msg)[12] == 0x90) && ((msg)[13] == 0x00) && \
(((msg)[12] == 0x90) && ((msg)[13] == 0x00) && \
((msg)[14] == 0x00) && ((msg)[15] == 0x00) && \
((msg)[16] == 0x02) && ((msg)[17] == 0x00) && \
(memcmp(phy_mac, msg+18, 6) == 0) && \
((msg)[24] == 0x01) && ((msg)[25] == 0x00))
((msg)[24] == 0x01) && ((msg)[25] == 0x00) && \
(memcmp(phy_mac, (msg), 6) == 0) && \
(memcmp(phy_mac, (msg)+6, 6) == 0) && \
(memcmp(phy_mac, (msg)+18, 6) == 0))
#define LOOPBACK_PHYSICAL_RESPONSE(host_phy, phy_mac, msg) \
(((msg)[12] == 0x90) && ((msg)[13] == 0x00) && \
((msg)[14] == 0x08) && ((msg)[15] == 0x00) && \
((msg)[16] == 0x02) && ((msg)[17] == 0x00) && \
((msg)[24] == 0x01) && ((msg)[25] == 0x00) && \
(memcmp(host_phy, (msg)+18, 6) == 0) && \
(memcmp(host_phy, (msg), 6) == 0) && \
(memcmp(phy_mac, (msg)+6, 6) == 0))
#define LOOPBACK_PHYSICAL_REFLECTION(host_phy, msg) \
(((msg)[12] == 0x90) && ((msg)[13] == 0x00) && \
((msg)[14] == 0x00) && ((msg)[15] == 0x00) && \
((msg)[16] == 0x02) && ((msg)[17] == 0x00) && \
((msg)[24] == 0x01) && ((msg)[25] == 0x00) && \
(memcmp(host_phy, (msg)+6, 6) == 0) && \
(memcmp(host_phy, (msg)+18, 6) == 0))
struct eth_packet {
uint8 msg[ETH_FRAME_SIZE]; /* ethernet frame (message) */