Generate a PDP11 emulation test-set using simh.
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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. |
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| ALTAIR | ||
| AltairZ80 | ||
| GRI | ||
| H316 | ||
| HP2100 | ||
| I1401 | ||
| I1620 | ||
| I7094 | ||
| Ibm1130 | ||
| Interdata | ||
| LGP | ||
| NOVA | ||
| PDP1 | ||
| PDP8 | ||
| PDP10 | ||
| PDP11 | ||
| PDP18B | ||
| S3 | ||
| SDS | ||
| swtp | ||
| VAX | ||
| Visual Studio Projects | ||
| .gitattributes | ||
| .gitignore | ||
| 0readme_38.txt | ||
| 0readme_ethernet.txt | ||
| 0readmeAsynchIO.txt | ||
| build_mingw.bat | ||
| build_mingw_ether.bat | ||
| build_mingw_noasync.bat | ||
| descrip.mms | ||
| makefile | ||
| scp.c | ||
| scp.h | ||
| sim_BuildROMs.c | ||
| sim_console.c | ||
| sim_console.h | ||
| sim_defs.h | ||
| sim_disk.c | ||
| sim_disk.h | ||
| sim_ether.c | ||
| sim_ether.h | ||
| sim_fio.c | ||
| sim_fio.h | ||
| sim_rev.h | ||
| sim_sock.c | ||
| sim_sock.h | ||
| sim_tape.c | ||
| sim_tape.h | ||
| sim_timer.c | ||
| sim_timer.h | ||
| sim_tmxr.c | ||
| sim_tmxr.h | ||