Re: Networking Questions

I know your name from the old News/400 magazine.

I appreciate your rather generous explanation of
what you have done.

This entire tcp/ip networking thing has been a real
eye-opener for me. D.I.Y. networking is not my thing
but I will figure it out in time.

I much prefer the system side of things and I might also
say that SNA/SDLC makes tcp/ip look very crude in comparison.

Waaaay too many layers of obscurity, not to mention total
confusion.

When I think back to the S/34 and just setting an address and
the system handled it makes this look pretty sad.

I agree that TCP/IP is the new wave but what a giant leap
backward.

Thomas wrote:

Pat:

Looks like you'll be learning from experience like many of us did.

Comments added..

Pat Barber wrote:

Apparently the DSL connection uses DNS to get it's address.


Not exactly. DHCP (Dynamic Host Configuration Protocol) is what supplies the address. The DNS address is sent as a secondary element, mostly because there's no point for nearly all internet connections without DNS. Its address to the PC when it requests an address for the internet connection. The PC asks for an address by sending a DHCP request out the route to the DSL device which is either a modem or a router.

I did exactly what you said...

I enter the static address 192.168.1.1 ---> new PC
255.255.255.0

No DNS address.


No need for DNS until host names get involved and those hosts are on a different network segment. Hosts on the same segment can have their addresses resolved by a lookup in a local "hosts" table. DNS is mostly just a very glorified hosts table that includes addresses in all network address ranges. (Well, most address ranges. Some are reserved for local use only and a few other special purposes.)

Note that some address ranges are not allowed to communicate across the internet (at least, not without special handling).

I can access the Iseries with Access fine.
I close Iseries Access.

I start the internet connection on the PC(XP) and it
fires up a connection.

I go back and check IPCONFIG and my address is now:

192.168.17.64
255.255.255.0

It also shows a DNS address at this point.

gateway address is 192.168.17.254

It's like magic...(normal for MS products)


It's essentially unrelated to MS. That's how TCP/IP and related protocols work.

What I do at home is put a router for my house network between my DSL router and my network. My PCs and other devices don't communicate with the DSL router; only my personal router does. My router requests a dynamic address for itself. My PCs keep their addresses.

Also, my router does NAT; so it handles 'N'etwork 'A'ddress 'T'ranslation, translating my PC addresses to whatever addresses are handed out through the DSL router. My PCs don't even know that the addresses seen by the DSL are unrelated to the addresses known to them.

This PC I'm working on wants to talk to the internet, so it sends a request to an address that doesn't exist on my network out the wire. My local router is the default route, so it gets the request because there's no place on my network with that remote address. Because it's a router, it routes the request out through its uplink to the DSL router. It translates the PC address into the NAT address that it associated with my PC, so any replies that come back will be tagged with the NAT address. Replies come back tagged with the NAT address, and the router knows it should translate that back to the original PC address before putting the reply into my local network.

Technically, I don't need to know anything about what the DSL router does. I'm pretty sure that it's also doing its own NATting, so this PC has its address translated twice. But it's really irrelevant to me. I leave that up to the routers.

In any case, my local router is what keeps the internet/DSL connection alive. My PCs never "connect" to DSL. The DSL is always "on". From the PCs' viewpoints (or my AS/400's), that's simply another network segment.

As far as DNS goes, my ISP's DNS address gets inserted into my PCs right after one gets powered on and starts talking to the network. I don't really know what the real DNS address is; it's most likely NATted by the DSL anyway. My PCs are actually using DHCP, but the requests are handled by my local router and assigned within the local address range that I chose. So far, the address for my ISP's DNS has never changed, so AFAIK I could specify it as a static address.

Because I use DHCP and the dynamic addresses are assigned by my local router, the DNS address is also assigned by my router. However, it got the address from DSL when it was powered on because I configured the router to get its external address by DHCP from DSL.

I turn the router on; it asks the DSL router for an address to use for itself and an address for DNS. That DNS address gets copied to any PC when the PC powers up.

DNS and host tables have one particular use -- to allow you to use names instead of IP addresses. If you never refer to a remote system by name, you never need DNS nor host tables. A whole bunch of names get different addresses at regular (or irregular) intervals. Because addresses change, names are handy. DNS automates the association of name with address.

For a local network, addresses can work fine. You don't really need host tables on your PCs; they exist for convenience. I don't have a local DNS, but I do have my AS/400 at a fixed (static) local address. I usually store that name/address pair in a host table on my PCs, but that's generally the only address in the PC host table.

Well, that's not true. I actually have a bunch of addresses in this PC's host table. Here are some of them:

127.0.0.1 a.tribalfusion.com
127.0.0.1 ad.doubleclick.net
127.0.0.1 servedby.advertising.com
127.0.0.1 ad.targetingmarketplace.com
127.0.0.1 media.fastclick.net
127.0.0.1 adserver.00web.com
127.0.0.1 anad.tacoda.net
127.0.0.1 adopt.euroclick.com
127.0.0.1 c.casalemedia.com

You might recognize one or two.

I collect them. They're representative of host names for many junk ads that you see on lots of sites. When I find one that irritates me, I add the complete host name to my hosts table with the localhost address 127.0.0.1. When a web page refers to that host, the web browser looks at the hosts table first. Since it finds a match, it sends the request to the localhost address instead of whatever the real address is. The localhost address has no clue what's being requested, so the request gets rejected fairly quickly. Whatever image would have been sent never really gets requested. The web page just has a blank spot there. The pages show up a lot faster because there's less junk on it, and no images have to take my bandwidth and no image gets copied into my cache.

Sorry, for getting carried away with this response. The whole point is that your PCs shouldn't have to "open" a connection through DSL except when they're first turned on. The connection can simply "be there". It can simply be available at all times.

In my case, it's there because I kind of off-loaded that work to a fairly cheap piece of hardware -- a cheap Linksys router.

It's actually more complicated than that because (1) I have two local network routers, (2) the other one is a bit more expensive than the Linksys, (3) both of them are also wireless routers, (4) this PC has two ethernet ports, one of which actually connects direct to the DSL router and the other to my local router, (5) I have a KVM switch right here for a second PC that has an ethernet port to my local router and also connects via dialup to Earthlink, Netscape.com or Compuserve, (6) my home network includes segments that are switched through the power lines throughout my house, (7) four switches at different parts of the house handle some small collections of devices...

That is, once you get started experimenting, things just start sprouting up all over. As I started this post out, it's all just experimenting until it starts making sense. I'm hoping it'll make sense to me soon.

.

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