dual-net problem

From: T. Horsnell (tsh_at_mrc-lmb.cam.ac.uk)
Date: 05/25/05

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To: fedora-list@redhat.com
Date: Wed, 25 May 2005 19:02:54 +0100 (BST)

Hi all,
I have a system with dual gigabit ethernet ports.
I've assigned them each an ip address, and am using
tcpdump and ping to check that they work as expected.
They dont.

If I ping, from another box, the address associated with eth1,
the traffic appears on eth0. This only happens when I ping from
another Linux box - if I ping from one of my Alpha boxes, everything
works as expected, i.e. pings addressed to the ipaddress
allocated to eth0 appear on eth0, and pings to the ipaddress
allocated to eth1 appear on eth1.

I'm running FC3 with kernel 2.6.10 on the dual-eth box, and I've
tried pinging from RH7.3, RH9 and FC3 boxes, all with the same
result.

It appears from the tcpdump output below, that ls1 is returing the
mac address of the eth1 interface *and* the address of the eth0
interface. Is this proper? What am I doing wrong?

Cheers,
Terry.

e.g.:

FC3 ping source:
[root@dev1 ~]# arp -d ls1
[root@dev1 ~]# arp -d ls1-2
[root@dev1 ~]# ping ls1-2
PING ls1-2.lmb.internal (10.1.0.11) 56(84) bytes of data.
64 bytes from ls1-2.lmb.internal (10.1.0.11): icmp_seq=0 ttl=64 time=0.322 ms
64 bytes from ls1-2.lmb.internal (10.1.0.11): icmp_seq=1 ttl=64 time=0.139 ms
64 bytes from ls1-2.lmb.internal (10.1.0.11): icmp_seq=2 ttl=64 time=0.140 ms
64 bytes from ls1-2.lmb.internal (10.1.0.11): icmp_seq=3 ttl=64 time=0.142 ms
64 bytes from ls1-2.lmb.internal (10.1.0.11): icmp_seq=4 ttl=64 time=0.140 ms
64 bytes from ls1-2.lmb.internal (10.1.0.11): icmp_seq=5 ttl=64 time=0.140 ms

--- ls1-2.lmb.internal ping statistics ---
6 packets transmitted, 6 received, 0% packet loss, time 5000ms
rtt min/avg/max/mdev = 0.139/0.170/0.322/0.069 ms, pipe 2
[root@dev1 ~]# arp ls1
Address HWtype HWaddress Flags Mask Iface
ls1.lmb.internal (incomplete) eth0
[root@dev1 ~]# arp ls1-2
Address HWtype HWaddress Flags Mask Iface
ls1-2.lmb.internal ether 00:E0:81:2B:AA:9A C eth0
[root@dev1 ~]#

dual-net target:

[root@ls1 ~]$ ifconfig
eth0 Link encap:Ethernet HWaddr 00:E0:81:2B:AA:9A
          inet addr:10.1.0.10 Bcast:10.127.255.255 Mask:255.128.0.0
          inet6 addr: fe80::2e0:81ff:fe2b:aa9a/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
          RX packets:376742 errors:0 dropped:0 overruns:0 frame:0
          TX packets:133194 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:179118055 (170.8 MiB) TX bytes:132633288 (126.4 MiB)
          Interrupt:177

eth1 Link encap:Ethernet HWaddr 00:E0:81:2B:AA:9B
          inet addr:10.1.0.11 Bcast:10.127.255.255 Mask:255.128.0.0
          inet6 addr: fe80::2e0:81ff:fe2b:aa9b/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
          RX packets:310052 errors:0 dropped:0 overruns:0 frame:0
          TX packets:7435 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:64100245 (61.1 MiB) TX bytes:9188440 (8.7 MiB)
          Interrupt:185

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:134 errors:0 dropped:0 overruns:0 frame:0
          TX packets:134 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:9620 (9.3 KiB) TX bytes:9620 (9.3 KiB)

[root@ls1 ~]$ netstat -r
Kernel IP routing table
Destination Gateway Genmask Flags MSS Window irtt Iface
169.254.0.0 * 255.255.0.0 U 0 0 0 eth1 (I dont know where this came from)
10.0.0.0 * 255.128.0.0 U 0 0 0 eth0
10.0.0.0 * 255.128.0.0 U 0 0 0 eth1
default fw.lmb.internal 0.0.0.0 UG 0 0 0 eth0
[root@ls1 ~]$

I've also tried fiddling with routes such that:
[root@ls1 ~]$ netstat -r
Kernel IP routing table
Destination Gateway Genmask Flags MSS Window irtt Iface
ls1-2.lmb.inter * 255.255.255.255 UH 0 0 0 eth1
169.254.0.0 * 255.255.0.0 U 0 0 0 eth1
10.0.0.0 * 255.128.0.0 U 0 0 0 eth0
default fw.lmb.internal 0.0.0.0 UG 0 0 0 eth0

[root@ls1 ~]$ tcpdump -i eth0 host dev1
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes
18:19:38.378486 arp who-has ls1-2.lmb.internal tell dev1.lmb.internal
18:19:38.386426 arp reply ls1-2.lmb.internal is-at 00:e0:81:2b:aa:9a
18:19:38.378591 IP dev1.lmb.internal > ls1-2.lmb.internal: icmp 64: echo request seq 0
18:19:38.378604 IP ls1-2.lmb.internal > dev1.lmb.internal: icmp 64: echo reply seq 0
18:19:39.379386 IP dev1.lmb.internal > ls1-2.lmb.internal: icmp 64: echo request seq 1
18:19:39.379391 IP ls1-2.lmb.internal > dev1.lmb.internal: icmp 64: echo reply seq 1
18:19:40.379251 IP dev1.lmb.internal > ls1-2.lmb.internal: icmp 64: echo request seq 2
18:19:40.379256 IP ls1-2.lmb.internal > dev1.lmb.internal: icmp 64: echo reply seq 2
18:19:41.379115 IP dev1.lmb.internal > ls1-2.lmb.internal: icmp 64: echo request seq 3
18:19:41.379120 IP ls1-2.lmb.internal > dev1.lmb.internal: icmp 64: echo reply seq 3
18:19:42.378979 IP dev1.lmb.internal > ls1-2.lmb.internal: icmp 64: echo request seq 4
18:19:42.378983 IP ls1-2.lmb.internal > dev1.lmb.internal: icmp 64: echo reply seq 4
18:19:43.378841 IP dev1.lmb.internal > ls1-2.lmb.internal: icmp 64: echo request seq 5
18:19:43.378845 IP ls1-2.lmb.internal > dev1.lmb.internal: icmp 64: echo reply seq 5
18:21:45.179131 arp who-has fw.lmb.internal tell dev1.lmb.internal

15 packets captured
19 packets received by filter
0 packets dropped by kernel
[root@ls1 ~]$

[root@ls1 ~]$ tcpdump -i eth1 host dev1
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth1, link-type EN10MB (Ethernet), capture size 96 bytes
18:19:38.378495 arp who-has ls1-2.lmb.internal tell dev1.lmb.internal
18:19:38.385104 arp reply ls1-2.lmb.internal is-at 00:e0:81:2b:aa:9b
18:21:45.179132 arp who-has fw.lmb.internal tell dev1.lmb.internal

3 packets captured
3 packets received by filter
0 packets dropped by kernel
[root@ls1 ~]$

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