two nics to one lan

From: Hans Fugal (hfugal_at_wencor.com)
Date: 05/21/04

  • Next message: Greg: "connecting to cvs server" 
    Date: Thu, 20 May 2004 16:41:57 -0600

    I have two NICs, one LAN. eth0: 172.16.59.1, eth1: 172.16.59.17. This
    afternoon something odd happened (I'm not sure what), I see in the logs:

    May 20 13:08:37 x440 kernel: NETDEV WATCHDOG: eth1: transmit timed out
    May 20 13:08:40 x440 kernel: e1000: eth1 NIC Link is Up 1000 Mbps Full
    Duplex

    The link may have come back up, but all connectivity was hosed. No ping
    response on 172.16.59.17 _or_ 172.16.59.1. ifconfig claimed things were
    normal, and the routing table was also normal, which I believe is the
    problem. Whatever happened caused the eth1 route to be non-functional,
    but all traffic bound to 172.16.59.0/24 was being routed through eth1.

    Unfortunately I don't have the routing table from then, because I was
    frantically bringing interfaces down and up in hopes that connectivity
    would be restored (it was). But here is my current route config:

    # ip route show
    172.16.59.0/24 dev eth1 scope link
    172.16.59.0/24 dev eth1 proto kernel scope link src 172.16.59.17
    127.0.0.0/8 dev lo scope link
    default via 172.16.59.15 dev eth0

    # tcpdump -n -i eth0 src 172.16.59.1 and dst net 172.16.59.0/24

    That command gives no output at all, but s/eth0/eth1/ gives lots. All
    the traffic is being routed through eth1, as you would expect from that
    routing configuration. But I didn't ask for two 172.16.59.0/24 routes
    via eth1, and before I did ifup eth1 (after doing some forensics and it
    was down) there was one well-configured route via eth0 for that subnet.
    (This is RHEL AS 2.1)

    So the crux of my question is, is there a way to configure the routing
    such that the preferred interface for frames from 172.16.59.1 is eth0,
    and the preferred interface for frames from 172.16.59.17 is eth1?
    Preferably one that wouldn't preclude the alternate route if one route
    goes down, but the route isn't likely to go down unless the whole
    interface does and there's not likely going to be traffic to
    172.16.59.17 if eth1 is down...

    At least I'd like to have a route over eth0 if eth1 goes away, and the
    routing config above doesn't look like there is (although I could add
    one, right?) Note I'm not asking about load balancing, although that
    wouldn't be a bad side effect either.

    I'm just starting to feel very comfortable with routing stuff, so it's
    possible (likely) that I've made some bad assumptions in the above
    dialog; I'd appreciate it if you'd point them out to me!

  • Next message: Greg: "connecting to cvs server"

    Relevant Pages

    • Re: [opensuse] Suse 10.2 +two network cards (Not yet solved)
      ... then set the eth0 as it was default from the installation. ... set eth1 DNS servers etc. so DHCP would not update them. ... Also have figure out where to put the route command ...
      (SuSE)
    • Re: DNS or network problem
      ... UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 ... The first thing that leaps out at me is the fact that eth0 and eth1 ... Because all your routes passes through eth1, and not eth0, I ...
      (Fedora)
    • Re: Network Puzzle with 2 NICs
      ... Is that Your routing table? ... into that 192.168.0/24 subnet will be sent via eth1. ... So if one route matches the target, ...
      (comp.os.linux.networking)
    • Re: Cant send packets via WiFi (possibly route issue)
      ... which means that the gateway needs a host route. ... > With that you should be able to ping any 192.168.0.x address on ... the only IPs I could ping were IPs of eth0 and eth1. ...
      (comp.os.linux.networking)
    • Re: pppd kills eth0
      ... I have a new Palm TX which connects to the machine via bluetooth. ... the pppd connection with the Palm all eth0 activity resumes. ... That is the default route. ... consistent with the routes associated to eth0 in the routing table. ...
      (alt.os.linux)