Networking stuff, special IP's .. sort my confus-ed-ness out !

[confus-ed]

What's 0.0.0.0 really for .. I know its something to do with routing, but just what exactly ?

& why & what might you use it for .. somebody asked me this yesterday & I waffled a bit, but I didn't even convince me !

[NooNoo]

Well it's a class A address reserved by IANA...

RFC 1122 Section 3

(that should keep you busy for a while... )

[kato2274]

0.0.0.0 should be the first address in your routing table


it should show like this
Network Destination---Netmask----Gateway---------------Interface
0.0.0.0----------------0.0.0.0----your default gateway----Your IP address

this is the default destination which is why it's at the top of your routing table
your next line of your routing table if your on a lan should show your lan address and subnet masks with the gateway being your ip address

so with those two lines the way it basically works is that any traffic for your lan is sent through your LAN IP adress as a gateway and anything outside your LAN is sent through your default gateway address

do a "route print" on windows NT, 2K, or XP and check out your routing table. you'll see what I'm talking about.

[confus-ed]

So I got about as far as kato has gotten us, only not as well - [ Bev is obviously giving me a taste of my own with that huge link (which btw need's a fixin' )], quite a few more 'err umm' ah's included .. & then he stumped me & said how does that contrast against 'you' as 127.x.x.x ?

& that's where I got really stuck..

[NooNoo]

So I got about as far as kato has gotten us, only not as well - [ Bev is obviously giving me a taste of my own with that huge link (which btw need's a fixin' )], quite a few more 'err umm' ah's included .. & then he stumped me & said how does that contrast against 'you' as 127.x.x.x ?

& that's where I got really stuck..

127.0.0.1 is a loopback test - specifically designed to return from the nic

0.0.0.0 means "this" network but if you ping it
Pinging 0.0.0.0 with 32 bytes of data:

Destination specified is invalid.
Destination specified is invalid.
Destination specified is invalid.
Destination specified is invalid.

Ping statistics for 0.0.0.0:
Packets: Sent = 4, Received = 0, Lost = 4 (100% loss)

As I understand it - 0.0.0.0 is the equivalent of "me" in vb script - eg me.hide - meaning whatever window this routine has in focus, hide it.

[kato2274]

127.0.0.1 is a loopback test - specifically designed to return from the nic

0.0.0.0 means "this" network .

but I read it as "any" network as far as routing goes
lets assume that 192.168.0.2 is your IP and you have a consumer router which is 192.168.0.1

let's look at first three lines of the route table
Dest----------Netmask----------GW--------------Interface
0.0.0.0--------0.0.0.0-----------192.168.0.1------192.168.0.2
192.168.0.0---255.255.255.0-----192.168.0.2------192.168.0.2
192.168.0.2---255.255.255.255---127.0.0.1--------192.168.0.2

any address on the lan are routed through the 192.168.0.2 gateway (your IP address) -Line 2-

any request to your IP from your IP are sent through the loopback address
-line3-

all other requests are sent through the gateway 192.168.0.1 (the consumer router)


in cisco terms if you had one router at a remote office you would configure a default route and setup a "stub" network. meaning that all network requests through the router are sent through the same interface (either serial or CSU/DSU WIC depending on how you are hooked up to the outside world

The default route is the IP address of the next hop when no other routes are known.

Directions
To configure the default route to be 192.168.1.1:

</SPAN>config t
ip route 0.0.0.0 0.0.0.0 192.168.1.1

[confus-ed]

So if I'm translating one way around I might use 127.x.x.x (the whole range getting used as a loopback for some TCP transport or other?) or if I'm at it the other way, 0.0.0.0 ?

[NooNoo]

errr no

(g) { 127, <any> }

Internal host loopback address. Addresses of this form
MUST NOT appear outside a host.

(a) { 0, 0 }

This host on this network. MUST NOT be sent, except as
a source address as part of an initialization procedure
by which the host learns its own IP address.

See also Section 3.3.6 for a non-standard use of {0,0}.

[shanff]

I'll use this route as my example

let's look at first three lines of the route table
Dest----------Netmask----------GW--------------Interface
0.0.0.0--------0.0.0.0-----------192.168.0.1------192.168.0.2
192.168.0.0---255.255.255.0-----192.168.0.2------192.168.0.2
192.168.0.2---255.255.255.255---127.0.0.1--------192.168.0.2


first line, destination 0.0.0.0 = any host that doesn't match any other dest below

second line, dest. 192.168.0.0 = this NETWORK

third line, dest. 192.168.0.2 = this HOST

basically the routing table is saying, bottom up, if you're destination is localhost, your gateway is the loopback adapter, go no further.

if your destination is somwhere on the local network, use your NIC (192.168.0.2) as the gateway to get to the destination host.

if your destination doesn't match anything else, go through the door at 192.168.0.1 and look past that for your destination.

[kato2274]

I'll use this route as my example

let's look at first three lines of the route table
Dest----------Netmask----------GW--------------Interface
0.0.0.0--------0.0.0.0-----------192.168.0.1------192.168.0.2
192.168.0.0---255.255.255.0-----192.168.0.2------192.168.0.2
192.168.0.2---255.255.255.255---127.0.0.1--------192.168.0.2


first line, destination 0.0.0.0 = any host that doesn't match any other dest below

second line, dest. 192.168.0.0 = this NETWORK

third line, dest. 192.168.0.2 = this HOST

basically the routing table is saying, bottom up, if you're destination is localhost, your gateway is the loopback adapter, go no further.

if your destination is somwhere on the local network, use your NIC (192.168.0.2) as the gateway to get to the destination host.

if your destination doesn't match anything else, go through the door at 192.168.0.1 and look past that for your destination.

didn't I already make pretty much this exact post

[confus-ed]

errr no

I didn't mean physically, I meant conceptually - I don't want the mechanics of network translation explained, I just can't get the idea of what 0.0.0.0.0 is compared to 'this machine' (127.x.x.x) .. are you telling me its just 'this network' ? (well the current scope of the machine referencing it, so what 'this machine' can see ?).

[NooNoo]

That's what I see from the RFC... have you read it yet?

[confus-ed]

That's what I see from the RFC... have you read it yet?

You forgot the devil, no I haven't read it, its in 'mannual-ese' & 112 pages of that is too hard for me , but ta anyway !

[Six Eyed Smily]

you never know what random things you might learn from randomly browsing a forum....

now i know what 0.0.0.0 is for

.... now how to work that into my cv ....