Re: The PPP negotiation failed, coz serial loopback was detected
- From: ibuprofin@xxxxxxxxxxxxxxxxxxxxxx (Moe Trin)
- Date: Tue, 26 Jun 2007 15:07:20 -0500
On Tue, 26 Jun 2007, in the Usenet newsgroup alt.os.linux, in article
<f5qml9$kli$1@xxxxxxxxxxxxxxx>, Paul wrote:
Thanx Moe, I'll check the config and see if its got
0.0.0.0 etc in it.
Based on the fact that 'pon' works, I rather doubt this is your problem.
The "thing" that requires you to not have such a route is pppd itself,
not the helper programs.
If it does have 0.0.0.0 what should I change it to?
[compton ~]$ Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
192.168.195.11 0.0.0.0 255.255.255.255 UH 0 0 1 ppp0
192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 4198 eth0
127.0.0.0 0.0.0.0 255.0.0.0 U 0 0 20 lo
0.0.0.0 192.168.195.11 0.0.0.0 UG 0 0 5 ppp0
[compton ~]$
This is representative of a correct routing table. The routing table is
what the kernel uses to determine where to send packets for any
particular destination. Here, the first line shows a "host" route - a
route that reaches one specific IP address. In this case, it's the peer
on a ppp setup. The second line, shows the route to a different
network (the Genmask value indicates addresses in the range 192.168.1.0
to 192.168.1.255) that can be reached directly (gateway is empty), and
that these are on the 'eth0' interface. The third line shows another
network route - this time to 127.0.0.0 through 127.255.255.255 which is
located on the "lo" or "loopback" interface. The last one is the one
we are worrying about. This says that addresses 0.0.0.0 through
255.255.255.255 (determined by the genmask of 0.0.0.0) can be reached by
sending the packets to the gateway at 192.168.195.11. But if everyone
is reachable this way, why do we have the other three lines? The answer
is that we use the line that has the most bits in the genmask IF that
route leads to where we want to go. 255.255.255.255 has 32 'one' bits
(1111 1111 1111 1111 1111 1111 1111 1111) to it's the most specific
mask. 255.0.0.0 (1111 1111 0000 0000 0000 0000 0000 0000) has only
eight 'one' bits, so it's less specific, but it still has more 'ones'
than 0.0.0.0 (which has none). This last route is called the 'default'
route, and it the one to use if none of the others lead to where you want
to go. This is also called the way or route "to the world".
The problem that sometimes occurs (thanks to overly helpful installation
programs, and lack of knowledge by the person running that program_ is
that you have a bogus default route - often leading to a non-existent
host on your Ethernet interface. It may look like this:
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 4198 eth0
127.0.0.0 0.0.0.0 255.0.0.0 U 0 0 20 lo
0.0.0.0 192.168.1.254 0.0.0.0 UG 0 0 2673 eth0
Here, we are told that the way to the world is to send that packets to
192.168.1.254 (whether it exists or not) and hope that it works. The ppp
daemon recognizes this "pre-existing" default route, and will require
that any person you dial into (like your ISP) has to authenticate (give a
password) to you - and that ain't gonna happen. Second, pppd will refuse
to replace the pre-existing route as a security issue. Thus, if you are
going to be using ppp, you don't want a pre-existing default route (what
do you need a dialin for, you've already got a way to reach the world).
You said you are using 'Ubuntu Feisty' which is a Debian clone. The
bogus default route would be caused by a "gateway" entry in the file
/etc/network/interfaces.
Your problem with KPPP is some error in the configuration of _that_
program, not pppd, or not in the basic system setup. I can't see your
computer from here, so I can't tell what the error might be.
Old guy
.
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