As you say yourself, and as your routing table clearly shows, there is no
route to the 192.168.100.N network.
This includes both the interface (eth1) on B and the host A.

man route

You'll need to add the route to that specific network. Note that your
"default" is eth1. IOW, if the router
doesn't know where a network is, it's going to use eth1 and hope for the
best (which in this case
didn't work).

mas

"spade" <kieneckb@web.de> wrote in message
news:bd7jtq$r40$05$1@news.t-online.com...
> Hi,
> I have the following configuration
>
> Hostname IP address device
> -----------------------------------------
> A 192.168.100.21 eth0
> B 192.168.100.3 eth0
> B 192.168.101.99 eth1
> C 192.168.101.20 eth0
>
>
> the Network Address is 192.168.100 or 192.168.101 and the netmask
> 255.255.255.0.
>
> Host C is connected via LAN with B and B is also connected with A.
>
> Routing table of C:
>
> dest gateway address iface
> 192.168.101.0 192.168.101.20 eth0
> default 192.168.101.99 eth0
>
> Now I try to ping from host C to 192.168.101.99 on host B. This works
fine!
> However, when I try to ping from host C to 192.168.100.3 on host B or to
> 192.168.100.21 on host A
> then there is no route!
>
> Any idea what is wrong :-)
>
>

"spade" <kieneckb@web.de> writes:

]Hi,
]I was fiddling around but I was not successful yet! Maybe I have to repeat
]my understanding:

]The Routing table an host B is as follows:

]Kernel IP routing table
]Destination Gateway Genmask Flags Metric Ref Use
]Iface
]192.168.100.0 * 255.255.255.0 U 0 0 0
]eth1
]192.168.101.0 * 255.255.255.0 U 0 0 0 eth0
]default 192.168.100.21 0.0.0.0 UG 0 0 0 eth1

This says send anything addressed to teh 192.169.100.x to eth1 (meaning
eth 1 must be directly connected to all computers with those addresses,
so that it can request and arp and get the ethernet numbers
corresponding to each of those addresses. )
for any address 192.168.101.x send it to eth1 (with the same caveate)
For any other address send it to 192.168.100.21 which must be connected
directly via ethernet cable 1 to this machine so that it can arp the
ethernet card number.



]The Routing table on host C is as follows:
]Kernel IP routing table
]Destination Gateway Genmask Flags Metric Ref Use
]Iface
]192.168.101.0 * 255.255.255.0 U 0 0 0 eth0
]default 192.168.101.99 0.0.0.0 UG 0 0 0 eth0

Here there is only one ethernet. Note that eth0 need not be the same
ethernet cable as eth0 on B.
I have no idea which machine is 192.168.101.99 Is that Machine B?



]The Routing table on host A is as follows:
]Kernel IP routing table
]Destination Gateway Genmask Flags Metric Ref Use
]Iface
]192.168.100.0 * 255.255.255.0 U 0 0 0 eth0
]default xxx.xxx.xxx.xxx 0.0.0.0 UG 0 0 0
]eth1

What is xxx.xxx.xxx.xxx? There seems no route to that number anywhere on
A? How does this machine know how to send a packet to that address?
(unless it is on the 192.168.100.0 subnet and is directly connected to A
via that ethernet cable connected to eth0)




]If I am sending now a package with the address 192.168.100.21 from host C
]then my understanding of the
]routing table is as follows: I have to send 192.168.100.21, ok, I have to
]take the default route through
]the gateway 192.168.101.99. There is no ther way. Now this pacage is
]received on host B. Now I have to

Is B the machine 192.168.101.99? If not then there is no way C knows to
send it to B. The address of B must be the gateway for C.

]apply the routing table of B. The routing table of B says whenever there is
]a package belonging to the
]subnet 192.168.100 send it via eth1 across the line, i.e. host A is
]listening on eth0 to so packages.

Is A 192.168.100.21?


]If this understanding is true, then it might be, that I have to activate
]something on host B (IP forwarding ??).

Yes, you certainly need to enable ip forwarding.


]However, in general are my routing tables and my understanding wrong??

Given the right answer to the questions above, yes.


]Spade

]"M. Swope" <mswope@nowhere.com> schrieb im Newsbeitrag
]news:pzIJa.161$ii6.121285690@newssvr11.news.prodigy.com...
]> As you say yourself, and as your routing table clearly shows, there is no
]> route to the 192.168.100.N network.
]> This includes both the interface (eth1) on B and the host A.
]>
]> man route
]>
]> You'll need to add the route to that specific network. Note that your
]> "default" is eth1. IOW, if the router
]> doesn't know where a network is, it's going to use eth1 and hope for the
]> best (which in this case
]> didn't work).
]>
]> mas
]>
]> "spade" <kieneckb@web.de> wrote in message
]> news:bd7jtq$r40$05$1@news.t-online.com...
]> > Hi,
]> > I have the following configuration
]> >
]> > Hostname IP address device
]> > -----------------------------------------
]> > A 192.168.100.21 eth0
]> > B 192.168.100.3 eth0
]> > B 192.168.101.99 eth1
]> > C 192.168.101.20 eth0
]> >
]> >
]> > the Network Address is 192.168.100 or 192.168.101 and the netmask
]> > 255.255.255.0.
]> >
]> > Host C is connected via LAN with B and B is also connected with A.
]> >
]> > Routing table of C:
]> >
]> > dest gateway address iface
]> > 192.168.101.0 192.168.101.20 eth0
]> > default 192.168.101.99 eth0
]> >
]> > Now I try to ping from host C to 192.168.101.99 on host B. This works
]> fine!
]> > However, when I try to ping from host C to 192.168.100.3 on host B or to
]> > 192.168.100.21 on host A
]> > then there is no route!
]> >
]> > Any idea what is wrong :-)

Sounds like IP forwarding is not set up on B.

/etc/sysctl.conf
and/or /etc/sysconfig/network

]> >
]> >
]>
]>