FTP connection between AS400 and remote servers // TCP/IP Host table // DNS

[voicucosmin90]

Hi folks,
I have the following situation, the guys from network team which manage a remote server told that they will decommission a host for that remote server where we send data. but they will have other host which they told that will remain available.. my question is the following, the host to be decomissioned is something like this ftp.old_server_storage.com and the other which will still be available is similar ftp.new_server_storage.com but basically is the same box behind -- if we change in the TCP/IP Host table entries to have the same ip behind for both : ftp.old_server_storage.com and also for ftp.new_server_storage.com .. do we have any impact?
this decomission is related to the access through internet?
the name for host used on AS400 side in the internal programs which does ftp is important as long as in the TCP/IP Host table entries we can put the ip behind? I mean if the host will not be anymore available for the clients which use the website, for us will be if we have the link behind to the ip for this old host name?

I get a response like this from admin side which confused me a lot:
"If you're going to ftp.old_server_storage.com it's getting the address from DNS, not the host table. You shouldn't use this name, it is being decommissioned. If the IP address of ftp.new_server_storage.com changes we can update the host file so your program will still work"

Please give me some hints on this.. can this be handled form TCP/IP host table to avoid any impact or what it means that the address is getting from DNS? can be done some adjustment for this?

[jtaylor___]

I can't say how that would work on an antique AS/400. On IBMi I don't see why it wouldn't work.

My rule is "don't use host table entries". Of course, every rule has exceptions. If you add both hostnames to your hosts table, it shouldn't matter they both point to the same IP address.

[voicucosmin90]

Thanks for the answer, so no other weird deep stuff to be done by admin guy, only add into the TCP/IP host table the entry for this host which basically if I have a good understanding works as a symbolic name, or alias, and actually it points to the physical ip setup in TCP/IP host table

[jtaylor___]

That's it.

You don't phone "Mom", you phone 555-555-5555. Same thing here. "Mom" is like the hostname and 555-555-5555 like the IP address. IBMi has to convert the hostname to an IP address. It first checks the local hosts table. If it's not there, then it will check configured DNS servers.

[Scott Klement]

jtaylor is correct. Doing this in the host table will work.

However, it is a REALLY bad practice. You should always use DNS when connecting to another system besides your own, never use the host table or a hard-coded IP address.

People who run sites have the right to relocate them. Maybe they want to move them into the cloud, or to a different network within their organiztion, or change internet providers, etc, etc. They should be able to do this by changing their DNS server with no disruption to business. When you hard code their IP address into the host table (or worse, into your application) then they have to notify you, and you have to change your system. Or more likely, it'll start failing, and you'll have to call them and find out about the change that way after business has been disrupted. If all of the people they do transactions with do the same thing, they may have to hire staff to handle the call volume, costing them extra money in addition to the disruption. This is NOT okay.... use DNS.