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**bryce4president** · June 2, 2008, 12:20 PM

Re: Which server is the AS400 using for DNS?

The iSeries does not determine the DNS server. From what I've learned messing with our IP tables when setting up our Disaster Recovery/High Availability system is this....

The IP tables are used to direct traffic out of the box to the first hop (default gateway). Once the packets get to the LAN is your network guy's job to figure out how to make it get to where it wants to go. You have no control once it leaves the box for the first hop. If your traffic is destined for a specific server then you can use the IP tables to route that traffic out a particular NIC card as well.

Once it leaves your box there is nothing you can do. Your network guy should know this. The only thing that can screw you up is if he starts changing your first hop. Once that is set it is his job to route the traffic and resolve DNS.

**ADMobius** · June 2, 2008, 12:59 PM

Re: Which server is the AS400 using for DNS?

Thanks Bryce. That answer makes sense to me.

**bryce4president** · June 2, 2008, 01:01 PM

Re: Which server is the AS400 using for DNS?

I hope it makes sense to your network guy as well, or you are in for some headaches and he will be in the bread line.

**jtemple** · June 2, 2008, 01:30 PM

Re: Which server is the AS400 using for DNS?

Um....maybe I'm misunderstanding the question, but the DNS servers can be set on the AS/400. The command CHGTCPDMN allows you to set the DNS servers used during IP lookup. AAMOF, my machine at home has entries for the two DNS used by my IP.

**bryce4president** · June 2, 2008, 01:56 PM

Re: Which server is the AS400 using for DNS?

You can set them, but on a typical network that has its own DNS servers I would think that the network guys would handle that. If you set your first hop to be your router, then the router would send its traffic to your modem, then to the ISP and the ISP should be able to resolve without any problems. I can't think of any great reasons to set these manually on modern network infrastructures. If someone can enlighten me with a good example of why you would want to do this I'd like to know.

From his first post it sounds like they have a couple of LANs set up that should have an over arching WAN to connect them. Depending on the size of the LANs, each one might have its own DNS server. If the AS400 is hardwired to look for a DNS then yea, it would mess it up, but the gateway(switch) should be the device that is configured for routing to DNS. Thats just my opinion when it comes to network architecture. Network settings like that should be left to the network when possible. That way the network guys and build in redundancy, so if one DNS goes down they can have their routers and switches flip you over to a different one automagically. If you hard code it into the AS400, you lose that.
/End-Sermon

Check the table, if there is nothing in there then you have no control at this point.

**arrow483** · June 2, 2008, 02:06 PM

Re: Which server is the AS400 using for DNS?

I've never set an iSeries up for DHCP. I set the DNS the way Jonas does - usually pointing to a local DNS server. I suggest you check that setting, change it if you need to. If the entry is missing, you probably aren't using it anyway.

**bryce4president** · June 2, 2008, 02:21 PM

Re: Which server is the AS400 using for DNS?

Setting the DNS doesn't make the setup non-DHCP. DHCP just allows the network to set the address of your iSeries. I've never heard of an iSeries being set up as DHCP. Setting a DNS server on the iSeries has nothing to do with how the network sees the iSeries...

**ADMobius** · June 2, 2008, 02:23 PM

Re: Which server is the AS400 using for DNS?

Jonas & Arrow,

So, you are saying that the information in CFGTCP, option 10 Work with TCP/IP host table entries is the correct place to look for the DNS servers/names/IP addresses? CFGTCP, option 12 Change TCP/IP domain information is the same command that Jonas is referring to.

I don't want to change anything, I just wanted to know where to find the information.

**jtemple** · June 2, 2008, 03:01 PM

Re: Which server is the AS400 using for DNS?

Think of "Work with TCP/IP Host Table Entries" as a place to set host name to IP address translations for things that are NOT handled by DNS. For example, I once wrote an IP application for a client that dumped information to a hot site. This hot site was configured in their LAN but the address of the machine was not resolvable via DNS. I could've hard-coded the IP address in the program but instead I put an entry in option 10 that resolved the name in my program to the machine's IP address. That way if the IP address of the machine changed, I didn't have to change my program.

If you want to see if you AS/400 has DNS servers specified, use option 12. Look under "Domain name server". If you see IP addresses listed then it has been specified on your machine.

**arrow483** · June 2, 2008, 03:05 PM

Re: Which server is the AS400 using for DNS?

Originally posted by bryce4president View Post

Setting the DNS doesn't make the setup non-DHCP. DHCP just allows the network to set the address of your iSeries. I've never heard of an iSeries being set up as DHCP. Setting a DNS server on the iSeries has nothing to do with how the network sees the iSeries...

Maybe I misunderstood. I thought he was looking for which DNS the AS400 was using, not using the AS400 as a DNS server. And DHCP usually does provide the DNS servers when it provides an IP address. Normally servers do not use DHCP.

**bryce4president** · June 2, 2008, 03:16 PM

Re: Which server is the AS400 using for DNS?

He is looking for which DNS the AS400 is using. You understand that correctly. But DHCP is not mutually exclusive to this subject. If I have two iSeries servers and one of them is entered into my DNS server so that the address is static it is not DHCP. If, however, your routers or switches assign IP address on the fly then it is DHCP. This is regardless of whether the iSeries has a DNS entered into its hosts table.

With today's network hardware it takes a special case like Jonas' to formulate a reason to have a DNS manually entered in the IP tables and not just have the first hop configured to handle it. You lose redundancy, and you don't have to maintain information in more than one place because there is likely more than device connected to your switch. So let the switch handle DNS and IP forwarding instead of configuring each device on that switch manually. Because like now, if the DNS changes IP you have to change each machine that it is hardcoded into. In a normal network this would make no sense at all.

my $.02. /End-Monday

**tomholden** · June 3, 2008, 07:47 AM

Re: Which server is the AS400 using for DNS?

FWIW the iSeries can be a DHCP server...but not a DHCP client...why? ask IBM /shrug

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Which server is the AS400 using for DNS?

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