route or ipforward problem

[John DeDourek]

Poul Moller wrote:

> Hi all,
> 
> I'm having a simple network but a strange problem that need some experts 
> eyes. My FC2 server that serves as a LTSP server has two "legs" in 
> different networks:
> 
> eth0: 10.0.0.1/24 (student network for thin clients)
> eth1: 192.168.1.10/24 (school network with Internet access router at 
> 192.168.1.1)
> 
> Here come the challege: On the server I can ping all hosts EXCEPT the 
> router 192.168.1.1 (the default gateway) ????????? The router is 
> perfectly alive and all hosts on the 192.168.1.0  net has Internet 
> access except the FC2 server. There must something I completely miss.
> NOTE: the last line (default gw) in the "netstat -r" command takes 10 
> sec to display !!!!!!!!!
> 
> Any hint is greatly appreciated
> Poul
> 

Any possibility that a firewall is configured?  Use
/sbin/iptables -L -v -n
to see the firewall rules.

Another debugging trick is to check whether the arp request for
the gateway is being comleted.  Run ping in one window (or on one
console, or in the background) while you check arp in another window.
Or, just check arp immediately after you stop ping.
/sbin/arp -a -n
You're looking for an entry giving the default router's IP and
MAC address.  An "incomplete" entry means that the trouble is
with arp...your server/router asked for the mac address of the
internet gateway but was not able to read a response successfully.
No entry at all would indicate that your server/router did not
even attempt to send a packet to the gateway and the difficulty
is with the routing tables.
> [root at odin root]# cat /proc/sys/net/ipv4/ip_forward
> 1
> 
> [root at odin root]# netstat -r
> Kernel IP routing table
> Destination     Gateway         Genmask         Flags   MSS Window  irtt 
> Iface
> 10.0.0.0        *               255.255.255.0   U         0 0          0 
> eth0
> 192.168.1.0     *               255.255.255.0   U         0 0          0 
> eth1
> 127.0.0.0       *               255.0.0.0       U         0 0          0 lo
> default         192.168.1.1     0.0.0.0         UG        0 0          0 
> eth1
>                                                                                              
> 
> [root at odin root]# cat /etc/sysconfig/network
> NETWORKING=yes
> HOSTNAME=odin
> FORWARD_IPV4=true
> NOZEROCONF=yes
> GATEWAY=192.168.1.1
> GATEWAYDEV=eth1
>                                                                                              
> 
> [root at odin root]# cat /etc/sysconfig/network-scripts/ifcfg-eth0
> # Intel Corp.|82547GI Gigabit Ethernet Controller
> DEVICE=eth0
> BOOTPROTO=none
> BROADCAST=10.0.0.255
> HWADDR=00:50:8D:E3:02:F4
> IPADDR=10.0.0.1
> NETMASK=255.255.255.0
> NETWORK=10.0.0.0
> ONBOOT=yes
> TYPE=Ethernet
> USERCTL=no
> PEERDNS=no
> IPV6INIT=no
> GATEWAY=192.168.1.1
>                                                                                              
> 
> [root at odin root]# cat /etc/sysconfig/network-scripts/ifcfg-eth1
> # 3Com Corporation|3c905C-TX/TX-M [Tornado]
> DEVICE=eth1
> ONBOOT=yes
> BOOTPROTO=none
> IPADDR=192.168.1.10
> NETMASK=255.255.255.0
> HWADDR=00:0A:5E:22:AE:D6
> USERCTL=no
> PEERDNS=no
> GATEWAY=192.168.1.1
> TYPE=Ethernet
> IPV6INIT=no
> GATEWAYDEV=eth1
>                                                                                              
> 
> [root at odin root]# ping 192.168.1.1
> PING 192.168.1.1 (192.168.1.1) 56(84) bytes of data.
>                                                                                              
> 
> --- 192.168.1.1 ping statistics ---
> 2 packets transmitted, 0 received, 100% packet loss, time 1000ms
>                                                                                              
> 
> [root at odin root]# ping 192.168.1.50
> PING 192.168.1.50 (192.168.1.50) 56(84) bytes of data.
> 64 bytes from 192.168.1.50: icmp_seq=0 ttl=127 time=0.525 ms
> 64 bytes from 192.168.1.50: icmp_seq=1 ttl=127 time=0.218 ms
>                                                                                              
> 
> --- 192.168.1.50 ping statistics ---
> 2 packets transmitted, 2 received, 0% packet loss, time 999ms
> rtt min/avg/max/mdev = 0.218/0.371/0.525/0.154 ms, pipe 2
>