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Re: [LUG] Mulithomed server - how?



On 17-Jan-2003 at 23:36:33 Simon Waters wrote:
> John Horne wrote:
>> Ther problem is how to configure this?? At startup both nic's
>> are seen but the routing table only shows one. If I add a static route
>> for the gateway using the missing nic, and a default to the gateway
>> using that nic, then I can get access to/from the server. However,
>> ifconfig seems to indicate that most traffic goes to/from one nic far
>> more often that the other nic. Also each server cannot ping the other
>> one, despite the fact that they are on the same subnet.
>>
> The LARTC HOW-TO discusses some ideas, mainly aimed at routing
> other boxes traffic, but well worth a read IMHO. It is not
> uncommon approach to create a virtual address, and pretend you
> are routing from it to the router, with redundant routes.
> 
Yes I have looked at the LARTC. Some of it seems a bit beyond me, other bits
just confusing. Unfortunately there seems to be no 'if you want a multihomed
server with resilience and load-balancing all on the same network...then do
this' :-)

> Another pragmatic but "dumb" approach is just to run different
> traffic to/from each, and alias the address to the other if one
> interfaces can't ping the router.
> 
No, we want all services on all nic's :-)

> The "smart" way is to bind them at level 2, but this requires
> compatible switch hardware I believe, but I think "config" tells
> you about this option when your building a kernel ;-)
> 
I assume this is part of the virtual server stuff. It seems possible but
will probably take me longer to work out :-)

Current thoughts, taken from the lartc, are to mark traffic inbound on each
nic; one outgoing to send traffic to the correct nic depending on the mark.
For new outbound traffic from the server - i.e. with no mark - setup
multiple default gateways with load-balancing - ala iptables with '-m random
--average 50', which should send out traffic 50% of the time to one nic, and
the rest to the other nic. That's the theory...:-)

OT: odd thing - does 'multihomed' actually mean a machine with more than one
IP address (possibly on one nic), or a machine with more than one nic and
hence more than one IP address. (I assume no-one would put the same IP
address on different nic's?)


John.

------------------------------------------------------------------------
John Horne, University of Plymouth, UK           Tel: +44 (0)1752 233914
E-mail: jhorne@xxxxxxxxxxxxxx
PGP key available from public key servers

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