Re: ping problem ...
- From: "Lew Pitcher" <lpitcher@xxxxxxxxxxxx>
- Date: 26 Sep 2006 05:25:11 -0700
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Lew Pitcher wrote:[snip]
I am configuring ADSL connection on my Linux box[snip]
every thing goes fine - network activated but ...
$ ping 192.168.1.1
PING 192.168.1.1 (192.168.1.1) 56(84) bytes of data.
-----no response ----
Let's see the results of
Give us both, from before and after the ping problem shows up. That is
to say, give us the ifconfig and route output when ping works and the
ifconfig and route output when ping fails.
Also, tell us a bit about your network. Where, for instance, is
192.168.1.1 in relation to the system you issue the ping on? Is it the
same system, or a different system. If it is on a different system,
does ping to it work when your DSL is disabled? If not, let's see the
routing tables for the 192.168.1.1 system as well.
Maybe you can explain me something.
Ping works with the ICMP protocol, right?
Could it happen that a firewall blocks ping but not ftp or telnet?
Also there are 2 parts in a ping, the sending and the echoing.
Could a firewall accept the sending but forbids the echoing?
And what about the ifconfig command: which protocol does it use?
None. It prints out the settings of the local network devices. It does
not generate network traffic, so it doesn't use any protocol.
The purpose of having the OP run ifconfig and route was to establish
/where/ the ping packets are being sent to.
route will tell us which local IP address they should go out on, and
ifconfig will tell us which local interfaces (devices) are connected to
which local IP addresses.
If 192.168.1.1 isn't a local IP address, then ifconfig won't show an
interface with that address.
If 192.168.1.1 is a remote IP address, then ifconfig will either show
us an interface on the same 192.168.x.y network, or not. If there is no
local interface on the 192.168.x.y network, then any traffic to
192.168.1.1 /must/ go through some other interface. But /which/
route will tell us which local IP address and interface will be used to
send the 192.168.1.1 traffic through. There are three possibilities:
1) an implicit route through a local interface on the 192.168.x.y
2) an explicit route through a local interface /not/ on the 192.168.1.1
3) the default route through a local interface to the next router
We use route to determine which interface, network and route the
packets took. Then we start looking for breaks in the route (that could
drop packets), or other reasons why the packets would disappear while
on that route. Firewalls are one possibility, but also non-routable IP
addresses over the internet is another, along with a broken outbound or
The OP might also try running traceroute to see the route that the
packets are taking, but (from the route and ifconfig dumps he supplied)
this is unnecessary at this time.
Many thanks in advance
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