help on network config

[Mario Spinthiras]

Dear Tie,


 As I understand you have three machines of which each is in it's own
logical segment. That means that you require a router in each segment to
route packets from each subnet. Based on the networks you mentioned in your
email you problem probably lays with routing between each subnet. Of course
there is also the possibility of having rules locally on your machines
active with iptables which can hence block traffic. You can list them by
typing iptables -L and flush (empty) the rulesets by typing iptables -F.
 If you are not in charge of the routing between these segments then talk to
someone who is and see what goes bad there but before that I would suggest
checking the rules.
 In addition to that (as a plus) you can always run a tcpdump -i eth[X] and
start flowing traffic (tsclient , ftp , etc) and see if the other end does
indeed get the packets but simply can't route back to the originating
machine. This is a ncie way of doing some access-list reconnaissance.
 In conclusion your problem could possibly be the access given to route
between each of your three subnets.

Warm Regards,
Mario A. Spinthiras
Nicosia , Cyprus
Blog: http://www.spinthiras.net
Mail: mspinthiras at gmail.com
Skype: smario125



On Tue, Apr 1, 2008 at 5:46 AM, stin wang <stin.wang at gmail.com> wrote:

> I try to convert my work from windows to linux.
>
> first install Ubuntu is so easy , thanks god.
>
> now i can use Firefox, msn, and so on ,with proxy setting correctly
>
> but my question is
>
> my computer is used in subnet, configuration as follow
>
> pc1
> ip 172.18.20.87
> mask 255.255.255.224
> gate 172.18.20.94
>
> the problem is described as follow:
> there are other two pcs
>
> pc2
> 172.18.20.98
> 255.255.255.224
> 172.18.20.126
> pc3
> 172.18.20.225
> 255.255.255.224
> 172.18.20.253
>
> i can ping 172.18.20.98 172.18.20.225 in pc1 ,it's ok
> but i can't use ftp,vnc,or tsclient to pc2 or pc3, but it's ok for
> 172.18.20.88 which is in the same gateway as pc1,
>
>
> what's wrong with it? how to figure out.
>
> or just ubuntu have some problem with subnet??
>
> i use ubuntu 7.10
> --
> ----------------------------------------------
> Tie Wang
> TianJin Climate Center
> TianJin Meteorological Bureau
> Tianjin, China, 300074
> Email: stin.wang at gmail.com
> Tel:+86-22-23333559
> ----------------------------------------------
> --
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>
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