Mike Gerdts wrote: > On Mon, May 11, 2009 at 5:14 PM, Dave Miner <Dave.Miner at sun.com> wrote: >> Mike Gerdts wrote: >>> On Sun, May 10, 2009 at 12:47 PM, Sarah Jelinek <Sarah.Jelinek at sun.com> >>> wrote: >> ... >>>> -You want to query network information >>> In particular, I want to be able to use protocols that are already >>> present on my network. That is, EIGRP, CDP, LLDP, etc. can be helpful >>> protocols to understand network topology. >>> >> I haven't looked deeply at those protocols' details, but I would be >> concerned in some cases about determinism of results. Dynamic discovery of >> network topology based on passive listening can be fairly unreliable in my >> experience, and having flakiness of network infrastructure turn into >> unanticipated deployment results seems like a bad path to head down. > > Agreed. The same problem exists to a certain degree for DHCP and mdns, right? > > I actually worry more about mdns doing the wrong thing (I can > accidentally install from the wrong server) than having automatic > network discovery doing the wrong thing. If I don't have really > careful post-installation verification, I may not realize that I > installed from the wrong server until I'm running the wrong bits in > production. If the network discovery goes wrong, the applications > just don't work. If applications don't work, it is hard to miss this > in the pre-production time of a server's life. Non-deterministic > behavior that leads to a defect that isn't detected before a server > goes live is a very bad thing in certain regulated environments. >
Sure, anytime you're using DHCP there's a degree of non-determinism, since there's no authentication associated with the protocol; anyone can drop a DHCP server in that disrupts things. mDNS represents only a minor additional risk, in that the service name is acquired from DHCP and it's just a matter of whether someone "steals" your service name. At least in most environments we've been dealing with DHCP quite some time and understand the issues. Providing greater determinism than that means going to media installs or getting the updated equivalent of S10 WAN installation implemented, which is a ways out yet. Dave
