I have had problems like this before. Probably there is something
important that I don't know about routing.
Let me introduce to you "Lasso2", a CentOS 4 www server that has been
working perfectly well for years.
Now I added a second nw card (eth1), automatically using kudzu. I cannot
get this dual nw setup to work. The first nw card (eth0) stopped at once
working properly, when I added the second card. Hw failure is probably
outruled - the connection via eth0 works normally again if I remove the
eth1 card and its settings (on reboot with kudzu).
There are several symptoms with the dual nw card setup, and I cannot
really get to diagnosis.
1) if you ping lasso2 (the problem machine) with the eth0 ip, the ping
requests come in ok, but the ping responses leave the machine via eth2 -
not good. I don't really know how to analyze routing and how to use ip
(the program) to fix it, so please tell me about it.
The "ip route show" output looks perfectly normal to me, it is similar
to another 2-card machine I have running (though that is Centos v5)
[root@lasso2 ~]# ip route show
62.236.221.64/28 dev eth1 proto kernel scope link src 62.236.221.75
62.220.237.96/27 dev eth0 proto kernel scope link src 62.220.237.114
169.254.0.0/16 dev eth1 scope link
default via 62.236.221.65 dev eth1
2) if I ping _from_ lasso2 via eth0, it works ok, as long as the ping
target is inside the same network segment. I can ping the router. If I
try to ping anything beyond that, I get nothing back. This seems to be
problem with ARP resolution. It seems that the broadcast address cannot
return the ARP data. This is all I can get when I ping 84.20.154.60 via
eth0 (representative sample, I hope):
[root@lasso2 ~]# tcpdump -i eth0 -n ! port ssh
listening on eth0, link-type EN10MB (Ethernet), capture size 96 bytes
00:01:36.296651 IP 80.221.171.198.2113 > 62.220.237.114.http: S
803184933:803184933(0) win 65535 <mss 1460,nop,wscale 1,nop,nop,sackOK>
00:01:36.654963 IP 65.55.37.179.36910 > 62.220.237.114.http: S
1372599588:1372599588(0) win 8192 <mss 1460,nop,nop,sackOK>
00:01:36.690083 arp who-has 84.20.154.60 tell 62.220.237.114
00:01:37.690145 arp who-has 84.20.154.60 tell 62.220.237.114
The ping itself says: "Destination Host Unreachable".
3) incoming http requests via eth0 do not work at all. I can post
tcpdump results, if someone asks me to.
This is a production machine, so I cannot really experiment very much.
Now I will go and remove the eth1 card for now.
- Jussi
--
Jussi Hirvi * Green Spot
Topeliuksenkatu 15 C * 00250 Helsinki * Finland
Tel. +358 9 493 981 * Mobile +358 40 771 2098 (only sms)
jussi.hirvi@xxxxxxxxxxxx * http://www.greenspot.fi
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