Multiple eth problem update

Multiple eth problem update

Post by Chris MacPhe » Wed, 21 Jun 2000 04:00:00



Hello all,

  I think I started my last thread off a bit on the wrong foot, so I'll
attempt to describe the purpose of this machine.  It has 6 NICs (5 x
3c905, 1 x 3c509), each of which are currently connected to a seperate
subnet of a class B network. eth0 works fine but eth1 thru eth5 are not able to communicate.  Linux
detects all six NICs, as modprobe eth5;dmesg states the correct
information.

  Now, if, for testing purposes, I put all the NICs on the same subnet,
they are able to retrieve the correct DHCP information.
ping -I eth1 www.yahoo.com  results in pings happenning perfectly fine if
eth0 is attached.  No communication happens if eth0 is not attached.  Not
even pings within the local subnet work.

  If the NICs are on seperate subnets, only eth0 is able to detect its
DHCP settings.  ifconfig shows no IP, netmask, or broadcast information
about eth1 thru eth5.

  What I would like is for each eth card to be able to run independantly
of one another...if eth3 wants to transfer data via TCP/IP, it should be
able to go through its subnets gateway and do so without the help of any
other cards.
  I realize that this may not be possible, perhaps due to the way Linux
handles routing.  If not, I would be content in having each card
communicate only with its local subnet, except for eth0 which would handle
all "outbound" traffic.

Thanks to all who've tried to help so far...hopefully this description
will better describe my problem.  Any ideas?

Thanks,
 - Chris

 
 
 

Multiple eth problem update

Post by Tom East » Wed, 21 Jun 2000 04:00:00



>Hello all,

>  I think I started my last thread off a bit on the wrong foot, so I'll
>attempt to describe the purpose of this machine.  It has 6 NICs (5 x
>3c905, 1 x 3c509), each of which are currently connected to a seperate
>subnet of a class B network. eth0 works fine but eth1 thru eth5 are not able to communicate.  Linux
>detects all six NICs, as modprobe eth5;dmesg states the correct
>information.

>  Now, if, for testing purposes, I put all the NICs on the same subnet,

Seems like people always do this then get hopelessly confused by the
result. Linux works in a very unintuitve way when configured in this
manner as it views all ip addresses as system attributes rather than as
attributes of a particular interface. Thus, you system is responding to
ARP requests for any of your interface attresses on ALL of your
interfaces. You can modify this behavior by:

        echo 1 > /proc/sys/net/ipv4/conf/all/hidden

they are able to retrieve the correct DHCP information.

Quote:>ping -I eth1 www.yahoo.com  results in pings happenning perfectly fine if
>eth0 is attached.  No communication happens if eth0 is not attached.  Not
>even pings within the local subnet work.

Of course -- look at your routing table (route -n); your default route is
out of eth0 so if eth0 is down, you are hosed.

Quote:

>  If the NICs are on seperate subnets, only eth0 is able to detect its
>DHCP settings.  ifconfig shows no IP, netmask, or broadcast information
>about eth1 thru eth5.

Something is fishy here -- how can the NICs "be on separate subnets" and
use DHCP? The NICs will be on the subnet determined by the DHCP server
attached to the interface's segment. Sounds like however you are setting
up your test, the other 5 NICs aren't successfully acquiring an address.

Quote:>  What I would like is for each eth card to be able to run independantly
>of one another...if eth3 wants to transfer data via TCP/IP, it should be
>able to go through its subnets gateway and do so without the help of any
>other cards.
>  I realize that this may not be possible, perhaps due to the way Linux
>handles routing.  If not, I would be content in having each card
>communicate only with its local subnet, except for eth0 which would handle
>all "outbound" traffic.

In the absence of additional static routes, whichever NIC has the default
hosts not in one of the subnets that your multi-homed system is connected
to. The above /proc modification (which must be done at each boot) may
make things less confusing.

-Tom
--
Tom Eastep             \  Eastep's First Principle of Computing:
ICQ #60745924           \  "Any sane computer will tell you how it

Shoreline, Washington USA \___________________________________________

 
 
 

Multiple eth problem update

Post by Ulrich Rot » Fri, 30 Jun 2000 04:00:00


Hello,

Quote:> >  If the NICs are on seperate subnets, only eth0 is able to detect its
> >DHCP settings.  ifconfig shows no IP, netmask, or broadcast information
> >about eth1 thru eth5.

> Something is fishy here -- how can the NICs "be on separate subnets" and
> use DHCP? The NICs will be on the subnet determined by the DHCP server
> attached to the interface's segment. Sounds like however you are setting
> up your test, the other 5 NICs aren't successfully acquiring an address.

And if you mean physically separated nets, you need a DHCP server (or relay
agent or so) on each subnet. DHCP is done via broadcast, and broadcast is not
routed, normally.
Ciao
        Uli
 
 
 

1. Multiple eth problem

Hello,
  I'm building a server with multiple network cards running on RedHat 6.2 - 5
3Com 3c905 and 1 3Com 3c509B, specifically.  The cards are recognised by Linux
and the modules load properly; modprobe gives the correct information.  The
cards even detect their DHCP IP addresses!
  The problem is that only eth0 seems to be able to communicate via TCP/IP (the
only protocol I care about at the moment).  For example,
      ping -I eth0 www.unb.ca
results in fine pings while
      ping -I eth1 www.unb.ca
results in a "Destination Host Unreachable" if eth0 is plugged in and produces
no output if eth0 is unplugged.

Any ideas?

Thanks,
- Chris

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