I have had some odd similar situations to this. Sometimes I have been but by the upstream ARP cache, but that is not a big deal.
Most recently I was replacing an MX84 and the link light on Internet 1 was dark for 20+ minutes after applying static IP info and waiting for it to come up. I knew the cable and upstream were good because all I did was move the cable. Only seconds before paper clip resetting it, it suddenly came on line and worked. Then Internet 2 was reporting problems and for some reason the perfectly valid ISP DNS (that had been used on the original MX) was not working properly and I had to change it to Google DNS and it started working.
The link light thing must be a bug but really bothered me. I know to patient and let the new MX come online, but seeing no link light makes me think L1 issue or bad port and how would anyone suspect it was fine by just waiting 25 minutes?
- Ex community all-star (⌐⊙_⊙)