About the usage of a dual port card

t tlovie at pokey.mine.nu
Thu Oct 4 11:17:53 EDT 2001


Thomas:

If I understand channel bonding correctly, (and anybody feel free to
correct me) you could use that to accomplish something similar.  If your
switch would support trunking, and didn't mind multiple ports sharing
the same MAC address (many switches will freak out if you try this) you
have a random (round-robin based on outgoing packets) port respond to
the ping request.

But with the default set of OS tools, you cannot do what you are asking.
When an outgoing packet is ready to be sent, checked against (in order)
the routing table.  When a matching line is found, the packet is queued
for transmit on that interface.  I don't know what happens when a queue
gets beyond a certain length, but my understanding of it is that it
wouldn't overflow to another interface.  So I don't understand why the
packet counters are not 0 for the TX of the eth2 interface.

One alternative that you might have is to use policy based routing which
is available in the linux kernel.  I have never used it, or even
experimented with it, but I think that you can have more control over
the routing table and base outbound routing decisions on the source
interface/address.  You can find some brief information on it in the
/usr/src/linux/Documentation/networking/policy-routing.txt file in the
linux kernel.

Here is from the kernel config help file on policy routing:
If you are interested in this, please see the preliminary documentation
at http://www.compendium.com.ar/policy-routing.txt and
ftp://post.tepkom.ru/pub/vol2/Linux/docs/advanced-routing.tex. You will
need supporting software from ftp://ftp.inr.ac.ru/ip-routing/       

Another alternative to consider is to split the
192.168.200.0/255.255.255.0 subnet into two separate subnets like
192.168.200.0/255.255.255.128 and 192.168.200.128/255.255.255.128 then
packets routed to addresses less than 127 will fall out one interface
and packets to addresses greater than 128 will go out the other.

Good Luck,
Tom Lovie.

> -----Original Message-----
> From: beowulf-admin at beowulf.org 
> [mailto:beowulf-admin at beowulf.org] On Behalf Of Thomas Lorenzen
> Sent: Wednesday, October 03, 2001 7:51 AM
> To: beowulf at beowulf.org
> Subject: About the usage of a dual port card
> 
> 
>      Hi'
> 
>    In our linux cluster our server has a dual port intel
> nic. Both ports are configured to be on the same net as are
> all the clients of the cluster. The clients boot as diskless 
> clients using the server.
> 
>    My question is, if there is a way to make a specific 
> interface, to which a packet comes, also answer this request. 
> What happens at the moment is, that if one pings eth2, then 
> eth1 answers, and in general eth1 answers all requests unless 
> this line is saturated, in which case eth2 takes over. This 
> is immediately seen from the output of RX and TX records below.
> 
>    Below I present the relevant output of ifconfig.
> 
> eth1      Link encap:Ethernet  HWaddr 00:03:47:3B:27:EE  
>           inet addr:192.168.200.100  Bcast:192.168.200.255  
> Mask:255.255.255.0
>           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>           RX packets:399607 errors:0 dropped:0 overruns:0 frame:0
>           TX packets:1070472 errors:0 dropped:0 overruns:0 carrier:0
>           collisions:0 txqueuelen:100 
>           Interrupt:19 Base address:0x4000 
> eth2      Link encap:Ethernet  HWaddr 00:03:47:3B:27:EF  
>           inet addr:192.168.200.200  Bcast:192.168.200.255  
> Mask:255.255.255.0
>           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
>           RX packets:142634 errors:0 dropped:0 overruns:0 frame:0
>           TX packets:104 errors:0 dropped:0 overruns:0 carrier:0
>           collisions:0 txqueuelen:100 
>           Interrupt:16 Base address:0x6000 
> 
>    Below I present the relevant output of route.
> 
> 192.168.200.0   *               255.255.255.0   U     0 0 0 eth1
> 192.168.200.0   *               255.255.255.0   U     0 0 0 eth2
> 
>    In brief I would like, that if I contact an interface
> ethX using ping, say, then that particular interface ethX 
> should also answer the request. Would anybody know of the 
> possibility of doing so and what is in that case the trick to do.
> 
>    Thanks for any help in advance.
> 
>    Best Regards.
> 
>      Thomas.
> 
> ----------------------------------------------------------------------
> Cand. Scient. Thomas Lorenzen               Phone : (+ 45) 35 32 02 50
> Department of Chemistry                       Fax : (+ 45) 35 32 02 59
> University of Copenhagen                     Mail : tl at theory.ki.ku.dk
> DK, 2100 Copenhagen, Denmark   Homepage : http://theochem.ki.ku.dk/~tl
> ----------------------------------------------------------------------
> 
> 
> 
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