This appears to be the closest to 'correct' forum to ask this in, I've been tasked with configuring our work network to allow another company to telnet one of our devices, I've forwarded port 23 to the device (which was already statically configured on the network), tested that the port is in fact open on the device (it's not a PC so I had to do this by scanning from within the network and seeing that in fact port 23 is responding), and yet none of the online port checking utilities I know of see port 23 as open.
Additionally I've tried bypassing the router entirely and plugging the device directly into the modem, with the same result. I've contacted the ISP and they claim to only block port 25 for the usual reasons (either to reduce spam, or upsell an unblocked service). also the router does successfully forward other ports with no difficulty.
Has anybody had any experience with a situation like this? or perhaps some theoretical knowledge?
N.B. There is no 'double router' issue in effect here.
Additionally I've tried bypassing the router entirely and plugging the device directly into the modem, with the same result. I've contacted the ISP and they claim to only block port 25 for the usual reasons (either to reduce spam, or upsell an unblocked service). also the router does successfully forward other ports with no difficulty.
Has anybody had any experience with a situation like this? or perhaps some theoretical knowledge?
N.B. There is no 'double router' issue in effect here.