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General software and network General OS-independent software and network questions, X11, MTA, routing, etc.

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Old 29th September 2008
PatrickBaer PatrickBaer is offline
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Default Funny network behaviour :)

A little riddle for everyone. I am really stumped and have no idea why that happens.

So here we go:

I have a Wifi setup with five APs without authentication. They are connected to the WAN via an SMC gateway, which does web-based password authentication. so the procedure is: Customer connects to an SSID and gets an IP-adress via DHCP, enters some URL and gets forwarded to the login-page, enters his personal login-data, can browse the web.

The internal setup is like this:

Gateway and default router is 172.16.0.1
Static IPs are ranged from 172.16.0.2 through 172.16.0.127
DHCP adress range is from .128
APs have a static IP-adress from 172.16.0.11 for AP1 .12 for AP2 and so on.
All devices have netmask 255.255.0.0!

As the IP range is obviously not routed outside the internal network, the administration-machine is connected via LAN to the internal network. When plugging in, the admin-machine gets an IP-adress via the gateway, e.g. 172.16.0.130 netmask 255.255.0.0 default gateway 172.16.0.1. The machine can login via web-interface and then access the external net. So far so good.

Now I want to connect to the other APs and configure them via http. And this is where the fun begins:

A simple ping results in a timeout to all devices except the gateway itself. So I thought about some setup failure and used a static IP-adress like 172.16.0.4.

Still, no responses to pings. Now, I did a broadcast ping to 172.16.255.255 and voila, APs 1 through 4 came responded! Number 5 remained silent. From that point on, I could access the APs via http also, even AP5, although it still did not respond to any ping.

Suddenly, AP5 stopped responding to http requests. So I did another broadcast ping. AP5 still not responded to the ping, but came back answering http-requests! Actually, as long as i kept pinging, the AP5 was ok, without the ping it remained silent.

After some minutes, the authentication on the APs timed out and I needed to reauthenticate. But when entering the IP into the browser bar, it did not connect, but instead forward to an adress like http://http.172.16.0.11

I think this has something to do with my internal network setting switching from the class B network to a class D and hence passing the IP to the router instead of staying in his own range.

Can someone explain this?

BTW, I also connected another laptop with ubuntu And did a broadcast ping, which showed some APs as well, but not all, like BSD did!

Oh, and if I connect to the APs with a direct connection, they work just fine.
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Old 29th September 2008
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Quote:
Originally Posted by PatrickBaer
I think this has something to do with my internal network setting switching from the class B network to a class D and hence passing the IP to the router instead of staying in his own range.
I was with you up until this point. Can you expand upon what you mean? Are you capturing packets that demonstrate this?

The way you're describing this, it sounds more like a physical layer problem. (Weak signal, lots of interference perhaps...)

Quote:
Oh, and if I connect to the APs with a direct connection, they work just fine.
Direct connection as in an ethernet cable?
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Old 30th September 2008
PatrickBaer PatrickBaer is offline
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Good morning amonie,

I try to explain both:

I ping broadcast to the network and the devices show up. Pinging directly, nothing happens. That goes beyond my knowledge, honestly.

The part I was referring is the last part, when the browser begins to rewrite the url. I assume, the gateway does that rewriting stuff. But why does my pc connect to the gateway anyway? It is connecting to the same subnet, no need to pass the URL through a router?

BTW, the connection goes through the buildings wiring of course, from the patch panel to a small 8 port switch where all devices are connected. One uplink to the gateway, which is connected to the external lan.
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Old 30th September 2008
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Quote:
Originally Posted by PatrickBaer
I ping broadcast to the network and the devices show up. Pinging directly, nothing happens. That goes beyond my knowledge, honestly.
With the caveat that I don't know anything about your network (apart from what you've described here), is it possible that you have some sort of filtering rules at the switch level, host level or elsewhere?

It almost sounds like icmp echo requests to the broadcast address are being allowed and (some) other icmp echo requests are being filtered.

Quote:
But why does my pc connect to the gateway anyway? It is connecting to the same subnet, no need to pass the URL through a router
No idea. What if you traceroute from your pc to said box on the same subnet? Is it still going to the gateway?
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Old 2nd October 2008
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Confirm the subnet masks of the AP's that only respond when pung on the broadcast.

For giggles, since your network doesn't seem so large that it would need THAT much address space anyways (a class B's worth), cut your subnet mask down to 255.255.255.0 on your whole network... anything change?
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Old 9th October 2008
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It's actually not possible to switch to a class c, as some of the APs use an internal dhcp with their own class c range, while some others rely on the gateways DHCP. Meanwhile mr supervisor handles it himself, I am quite thrilled for the result
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