Re: simple ping; pinging 101

From: Jeff Vian (jvian10_at_charter.net)
Date: 07/06/05

  • Next message: Alexander Dalloz: "Re: Postifx and virtual users (user unknown)"
    To: THUFIR HAWAT <hawat.thufir@gmail.com>, For users of Fedora Core releases <fedora-list@redhat.com>
    Date: Wed, 06 Jul 2005 07:31:53 -0500
    
    

    On Wed, 2005-07-06 at 04:40 -0700, 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.
    >
    >
    Probably nothing is wrong except the configuration.

    You have 2 NICs on the same subnet. Only one can be the default and in
    most flavors of *nix when 2 NICs are on the same subnet the drivers
    often get confused and in some cases all communication is either lost or
    severely slowed down with this setup.

    You can check which the system is using as the default by running
    "netstat -r". The Iface column will tell which is the default interface
    for the line that starts with default. Your route output below does not
    list a default route, and it lists 2 routes to the 192.168.0.0 network.

    A very simple test to see which interface is having the problem ( I
    don't suspect either) would be to do the following

    1. ifdown eth0
    2. ping 192.168.0.102
    3. ifup eth0
    4. ifdown eth1
    5. ping 192.168.0.102
    6. ifup eth1
    7. ping 192.168.0.102

    then compare the results of the pings.

    I suspect the only one that may have a problem is step 7 when both
    interfaces are active.

    > arrakis eth0 192.168.0.100
    > arrakis eth1 192.168.0.101
    > caladan eth0 192.168.0.102
    >
    > terminal stuff from arrakis:
    >
    > [root@arrakis init.d]# echo "arrakis eth0 pinging caladan eth0"
    > arrakis eth0 pinging caladan eth0
    > [root@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@arrakis init.d]# ping 192.168.0.102
    > PING 192.168.0.102 (192.168.0.102) 56(84) bytes of data.
    > 64 bytes from 192.168.0.102: icmp_seq=0 ttl=128 time=1.33 ms
    > 64 bytes from 192.168.0.102: icmp_seq=1 ttl=128 time=0.465 ms
    > 64 bytes from 192.168.0.102: icmp_seq=2 ttl=128 time=0.464 ms
    > 64 bytes from 192.168.0.102: icmp_seq=3 ttl=128 time=0.472 ms
    > 64 bytes from 192.168.0.102: icmp_seq=4 ttl=128 time=0.466 ms
    >
    > --- 192.168.0.102 ping statistics ---
    > 5 packets transmitted, 5 received, 0% packet loss, time 4028ms
    > rtt min/avg/max/mdev = 0.464/0.641/1.339/0.349 ms, pipe 2

    You do not know which interface this went through from this output

    > [root@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@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@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
    >

    The only one showing a received count is eth0

    > 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@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
    > 169.254.0.0 * 255.255.0.0 U 0 0 0
    > eth1

    No default route? It would have a UG flag

    > [root@arrakis init.d]#
    >
    > [root@arrakis init.d]# echo "arrakis eth1 pinging caladan eth0"
    > arrakis eth1 pinging caladan eth0
    > [root@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@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

    Now you have done a restart on both interfaces, and eth0 is not seeing
    the other machine

    > [root@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@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@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 MULTICAST MTU:1500 Metric:1
    > RX packets:123 errors:6 dropped:0 overruns:0 frame:6
    > TX packets:76 errors:0 dropped:0 overruns:0 carrier:0
    > collisions:21 txqueuelen:1000
    > RX bytes:15378 (15.0 KiB) TX bytes:4900 (4.7 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 RUNNING MULTICAST MTU:1500 Metric:1
    > RX packets:0 errors:0 dropped:0 overruns:0 frame:0
    > TX packets:54 errors:0 dropped:0 overruns:0 carrier:0
    > collisions:0 txqueuelen:1000
    > RX bytes:0 (0.0 b) TX bytes:3708 (3.6 KiB)
    > Interrupt:5 Base address:0xd000
    >

    eth0 still has the only received count. Eth1 has not received a single
    packet.

    Both show an increase in transmitted, but neither show a change in the
    received from the earlier listing.

    > 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:114 errors:0 dropped:0 overruns:0 frame:0
    > TX packets:114 errors:0 dropped:0 overruns:0 carrier:0
    > collisions:0 txqueuelen:0
    > RX bytes:9200 (8.9 KiB) TX bytes:9200 (8.9 KiB)
    >
    > [root@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
    > 169.254.0.0 * 255.255.0.0 U 0 0 0
    > eth1
    > [root@arrakis init.d]#
    >
    >
    > links:
    >
    > arrakis mother board:
    > <http://www.ecsusa.com/downloads/manual_k7s.html>
    >
    > eth1 NIC on arrakis:
    > <http://www.dlink.ca/product.php?PID=124>
    >
    >
    >
    > thanks,
    >
    > Thufir
    >

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  • Next message: Alexander Dalloz: "Re: Postifx and virtual users (user unknown)"

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