[SUMMARY] Multiple NICs on a subnet

From: Swan, Laurie (SwanL@logica.com)
Date: Tue Sep 05 2000 - 11:30:56 CDT

Thanks to Kent Perrier (Kent.Perrier@Oneco.net) and Danny (dannyc@pcs.co.uk)
for their suggestions. And hello (!?) to Mark who couldn't help me, but he
did like my name. I should warn you Mark that, outside the US and Canada,
Laurie is predominantly a male name...

But, big thanks to Hans Schaechl (schaechl@bigfoot.com) who explained the
problem. Sadly a simple solution was not to be, but at least I understand
what is going on now. Hans pointed out that I had a routing problem. He

> Assuming you have an IP subnet like where both interfaces
> hme0 and qfe0 are connected with IP addresses like this: hme0 =
> / qfe0 =
> When your machine boots up it initializes the interfaces order of first
> hme0 and then qfe0 (and so on). This leads to a routing
> table like this:
> U (bla) hme0
> U (bla) qfe0
> Now if an IP packet has to leave the machine (due to a request coming in
> from outside like your ICMP echo requests) it checks against its routing
> table to find the correct way out. First match wins! It will always route
> packets to over the hme0 interface (as long as it is up)
> even if the request came in on qfe0.
> If you perform an 'ifconfig hme0 down' the first line from the routing
> table is being dropped and qfe0 is the new default route to your local
> subnet. After 'ifconfig hme0 up' it is added after qfe0 so that your new
> table now looks like this:
> U (bla) qfe0
> U (bla) hme0
> Since you seem to want to have load-sharing enabled for your machine while
> talking to your clients, this is not what you
> want - obviously. BTW: you have a sort-of-load sharing since on the MAC
> level all incoming packets are distributed to either
> the hme or the qfe interface but all the outgoing traffic accumulates on
> one of them.
Both Hans and Kent Perrier suggested that SUN trunking software may be the
only solution. Hans also suggested enabling IP interface groups via 'ndd
-set /dev/ip ip_enable_group_ifs 1' may work too. However this did not,
sadly, solve the problem.


My original question:

> >First attempt at a question on this forum. Be gentle!
> >
> >We have an E450 and some E420Rs running Solaris 7 with a primary hme
> >interface and a QFE card. hme0 and qfe0 are connected to the same subnet.
> >On most machine we only use the two interfaces.
> >
> >I have set the following to enable the card MAC addresses:
> >
> >eeprom local-mac-address?=true
> >ndd /dev/ip ip_forwarding=0
> >ndd /dev/ip ip_strict_dst_multihoming=1
> >
> >All good so far. Now when I began testing...
> >
> >When I disconnect the line to qfe0, the IP address for hme0 still
> responds
> >correctly and the IP for qfe0 doesn't. All well and good.
> >
> >However, (after both lines are again connected and happily ping'ed) if I
> >disconnect the line to hme0, neither interface's IP address will respond
> >until I do:
> >
> >ipconfig hme0 down
> >ipconfig hme0 up
> >
> >after which the qfe0 address responds correctly. The hme0 interface still
> >(correctly) does not respond.
> >
> >It's not quite the behaviour I'd expect. I suspect this has something to
> do
> >with hme0 being the primary interface. Anyone seen this before? Can I be
> >sure that when they're both connected one interface isn't taking all the
> >load? Is there any way of stopping all interfaces from doing down when
> the
> >primary has problems?
> >
> >It does manifest itself on both the E450 and the E420R.

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