If telnet sessions are tipping over, there's probably an address collision, or a routing error of some sort, that's been introduced here. There are some somewhat less likely triggers potentially lurking here, such as a screaming (failed) network controller, or a cable fault or such. And it's easy to miss an address collision on a secondary controller, too.
As for whether subnet mask and the broadcast address are the same, all nodes within a particular subnet typically share those values. The hosts will typically also share a default route and some other values.
If there's a VLAN and addresses are messed up, all bets are off; all sorts of weirdness can arise as the VLANs try to deal with the address collision.
That this subnet question is being asked could indicate some unfamiliarity with IP networking. For one form of that and as applied to OpenVMS, please see the introductory manual in the TCP/IP Services documentation.
If the second AlphaServer DS20e system disk was cloned from the first, then you may want to read this discussion on the various spots where the node name and node address can lurk:
http://64.223.189.234/node/589
