Re: Cannot ping host in another subnet

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$ii6.121285690@newssvr11.news.prodig y.com...
]> As you say yourself, and as your routing table clearly shows, there is no
]> route to the 192.168.100.N network.
]> This includes both the interface (eth1) on B and the host A.
]>
]> man route
]>
]> You'll need to add the route to that specific network. Note that your
]> "default" is eth1. IOW, if the router
]> doesn't know where a network is, it's going to use eth1 and hope for the
]> best (which in this case
]> didn't work).
]>
]> mas
]>
]> "spade" <kieneckb@web.de> wrote in message
]> news:bd7jtq$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

]> >
]> >
]>
]>