On Mon, Jun 06, 2005 at 03:50:43PM +0100, Paul Jakma wrote:
>> The most reliable way is to migrate the mac-address aswell, as part
>> of the resilience. We do this for all of our servers, and we have
>> 200ms failover with no problems. Though in our case we're using the
>> linux bonding driver.
>> Slightly different to L3 failover.
Yes, but it gets you very reliable L3 failover :) The end-result
is the same.
> For bonding you do want L2 to balance, hence you want a shared MAC.
Although we use the bonding driver, we are not doing channel-bonding. Our aim
is not to balance, but we do use it to team interfaces in order to have a
resilient MAC, which can operate on either interface (but only one at a time).
This is effectively exactly the same as the L3 failover, only a layer lower.
> For L3 failover, your choices are:
>> - failover the MAC from one port to another
> (ie update MAC<->port state in the switch)
>> - failover the IP
> (ie update IP<->MAC state in hosts)
>> I'd pick the latter: L2 doesnt need to know, gratuitous ARP is very
> commonly used and perfectly portable across different OSes and it's
> switch agnostic (think: what if the backup port is on a different
Our backup ports are on a different switch. You don't think we'd make our
servers resilient and then plug them into one switch do you? ;) Our services
network has multiple switches, as long as their in the same spanning-tree
mesh, it works out fine :)
There are other L3 failover options. Lately we're using OSPF as a L3
resilience mechanism to servers (Colin knows more about this), and it's
working out quite well (many thanks to your Quagga efforts). And for the next
iteration of ftp.heanet.ie we're planning to distribute 4Gb/sec of
connectivity via equal-cost static routes.
So, if the network really is expensive and shiny, there's always those kinds
of options also.
Colm MacCárthaigh Public Key: colm+pgp at stdlib.net
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