I've got a pc with an SMC Elite Ultra ed0.
I've got a sun3/60 on the same thinnet cable.
I am running ip_filter which does not log any blocked packets during this
time.

I see this from tcpdump, over and over again:
04:00:38.384345 mysun ff:ff:ff:ff:ff:ff rarp 60: rarp who-is mysun tell mysun
04:00:38.385673 0:0:c0:92:44:96 mysun rarp 42: rarp reply mysun at mysun.my.net

sun3 list:

Can anyone think of a reason why the Sun3 won't recognize the rarp and get
on with the tftp?  I don't think it is the Sun since another one exhibits
the same behavior.

Another thing; one of the suns gives "le0: No Carrier" a lot while rarp
querying.  It sends out packets okay anyway.
The other sun (borrowed), gets VERY hot eventually and it's le0 cruds out.
No "No Carrier" messages though.

i386 list:

I thought my card might be sending the rarp replies back on the wrong
media (e.g. aui instead of transciever/coax).  I noticed at bootup:

ed0 at isa0 port 0x240-0x25f iomem 0xdc000-0xdffff irq 10 (transciever=50)
ed0: address 00:00:c0:92:44:96, type SMC8216/SMC8216C (16-bit) aui

The transciever=50 is the unsigned decimal representation I added:
        { u_char x;
          x = bus_io_read_1(bc, ioh, asicbase + ED_WD_IRR);
          printf("transciever=%u\n", (unsigned int)x);
          if ((x & ED_WD_IRR_OUT2) == 0)
                        ifp->if_flags |= IFF_LINK0;
        }

You see, the stored configuration is NOT for the AUI, and no matter what
I changed it to I could not influence the IRR's value.
I tried all combinations of {,-}link[0-2].
I tried for hours and hours.  At least six.
BUG: ed(4) doesn't document ANY of these flags!

Here's the debug output:
type=2b type_str=SMC8216/SMC8216C isa16bit=1 memsize=16384 id_msize=0
0 -> bd
1 -> fb
2 -> ba
3 -> ff
4 -> cc
5 -> ff
6 -> bd
7 -> 5b
...

$ ifconfig ed0
ed0: flags=9863<UP,BROADCAST,NOTRAILERS,RUNNING,SIMPLEX,LINK0,MULTICAST>
        inet 10.1.1.1 netmask 0xff000000 broadcast 10.255.255.255

What's up with this!  ARG!