Actually I've seen the arp problem as well. What arp entry do you have for them? We have: mae-west.netcom.net (198.32.136.15) at 0:0:c:61:b:0 If yours is different, you could try deleting it and if it still comes back wrong, you could try temporarily adding a static entry. Are either you or netcom connected through a netedge?

ps. At this point, we still can't see Netcom... problem has lasted for 1 day, 8 hours. From my interface (198.32.136.18) I cannot ping Netcom at 198.32.136.15, but I can ping Alternet at 198.32.136.42. That points to a layer 2 discontinuity.