simple ping; pinging 101
Kevin J. Cummings
cummings at kjchome.homeip.net
Sat Jul 9 01:39:08 UTC 2005
THUFIR HAWAT wrote:
> two computers, arrakis and caladan, are
> connected with some standard RJ45 Cat 5e cable
> and a hub. arrakis can ping caladan from eth0.
> arrakis cannot ping caladan from eth1.
>
> what's wrong with arrakis eth1, please?
>
> I'm 99.999% sure it's not a hardware problem.
> eth0 is built-in to the motherboard,
> eth1 is a D-Link NIC.
>
>
> arrakis eth0 192.168.0.100
> arrakis eth1 192.168.0.101
Don't do this! It will give you more headaches than you want!
Use a *different* subnet for arrackis eth0. I suspect that the default
subnet for 192.168.0.0 network on arrakis is to use eth0, thus the
packets intended for caladan get sent on eth0.
> caladan eth0 192.168.0.102
> [root at arrakis init.d]# cat /etc/sysconfig/network-scripts/ifcfg-eth0
> # built-in
> DEVICE=eth0
> ONBOOT=yes
> BOOTPROTO=none
> HOSTNAME=arrakis
> #HWADDR=00:0D:88:37:FA:22
> NETMASK=255.255.255.0
> IPADDR=192.168.0.100
> USERCTL=yes
> PEERDNS=yes
> TYPE=Ethernet
> IPV6INIT=yes
> [root at arrakis init.d]# cat /etc/sysconfig/network-scripts/ifcfg-eth1
> # D-Link System Inc RTL8139 Ethernet
> DEVICE=eth1
> ONBOOT=yes
> BOOTPROTO=none
> HOSTNAME=arrakis
> HWADDR=00:0D:88:37:FA:22
> NETMASK=255.255.255.0
> IPADDR=192.168.0.101
> USERCTL=yes
> PEERDNS=yes
> TYPE=Ethernet
> IPV6INIT=yes
> [root at arrakis init.d]# ifconfig
> eth0 Link encap:Ethernet HWaddr 00:0A:E6:A0:24:27
> inet addr:192.168.0.100 Bcast:192.168.0.255
> Mask:255.255.255.0
> inet6 addr: fe80::20a:e6ff:fea0:2427/64 Scope:Link
> UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
> RX packets:123 errors:6 dropped:0 overruns:0 frame:6
> TX packets:62 errors:0 dropped:0 overruns:0 carrier:0
> collisions:21 txqueuelen:1000
> RX bytes:15378 (15.0 KiB) TX bytes:4144 (4.0 KiB)
> Interrupt:5 Base address:0xd400
>
> eth1 Link encap:Ethernet HWaddr 00:0D:88:37:FA:22
> inet addr:192.168.0.101 Bcast:192.168.0.255
> Mask:255.255.255.0
> inet6 addr: fe80::20d:88ff:fe37:fa22/64 Scope:Link
> UP BROADCAST MULTICAST MTU:1500 Metric:1
> RX packets:0 errors:0 dropped:0 overruns:0 frame:0
> TX packets:45 errors:0 dropped:0 overruns:0 carrier:0
> collisions:0 txqueuelen:1000
> RX bytes:0 (0.0 b) TX bytes:3090 (3.0 KiB)
> Interrupt:5 Base address:0xd000
>
> lo Link encap:Local Loopback
> inet addr:127.0.0.1 Mask:255.0.0.0
> inet6 addr: ::1/128 Scope:Host
> UP LOOPBACK RUNNING MTU:16436 Metric:1
> RX packets:108 errors:0 dropped:0 overruns:0 frame:0
> TX packets:108 errors:0 dropped:0 overruns:0 carrier:0
> collisions:0 txqueuelen:0
> RX bytes:8528 (8.3 KiB) TX bytes:8528 (8.3 KiB)
>
> [root at arrakis init.d]# route
> Kernel IP routing table
> Destination Gateway Genmask Flags Metric Ref Use
> Iface
> 192.168.0.0 * 255.255.255.0 U 0 0 0
> eth0
> 192.168.0.0 * 255.255.255.0 U 0 0 0
> eth1
Two routes for 192.168.0.0 is not what you want to see. If you instead
replace the second route with one directly to caladan, it *might* work.
192.168.0.102 * 255.255.255.0 UH 0 0
0 eth1
You would need to add the route via:
route -add 192.168.0.102 eth0
As you can see, this is complicated. Instead, use a different subnet
for arrakis eth0 (like 192.168.1.0). Then configure arrakis to forward
packets from caladan to the arrakis eth0 network (by setting a gateway
on caladan and configuring IP forwarding on arrakis).
> 169.254.0.0 * 255.255.0.0 U 0 0 0
> eth1
> [root at arrakis init.d]#
>
> [root at arrakis init.d]# echo "arrakis eth1 pinging caladan eth0"
> arrakis eth1 pinging caladan eth0
> [root at arrakis init.d]# ./network restart
> Shutting down interface eth0: [ OK ]
> Shutting down interface eth1: [ OK ]
> Shutting down loopback interface: [ OK ]
> Disabling IPv4 packet forwarding: [ OK ]
> Setting network parameters: [ OK ]
> Bringing up loopback interface: [ OK ]
> Bringing up interface eth0: [ OK ]
> Bringing up interface eth1: [ OK ]
> [root at arrakis init.d]# ping 192.168.0.102
> PING 192.168.0.102 (192.168.0.102) 56(84) bytes of data.
>
>>From 192.168.0.100 icmp_seq=1 Destination Host Unreachable
>>From 192.168.0.100 icmp_seq=2 Destination Host Unreachable
>>From 192.168.0.100 icmp_seq=3 Destination Host Unreachable
>>From 192.168.0.100 icmp_seq=5 Destination Host Unreachable
>>From 192.168.0.100 icmp_seq=6 Destination Host Unreachable
>>From 192.168.0.100 icmp_seq=7 Destination Host Unreachable
>
> --- 192.168.0.102 ping statistics ---
> 8 packets transmitted, 0 received, +6 errors, 100% packet loss, time
> 6999ms
> , pipe 4
I'm sure that a traceroute will indicate that you're going out through
eth0 instead of eth1.
--
Kevin J. Cummings
kjchome at rcn.com
cummings at kjchome.homeip.net
cummings at kjc386.framingham.ma.us
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