[nf-failover] Re: [RFC] ct_sync 0.15 (corrected)

Jamal Hadi Salim hadi at znyx.com
Wed Sep 29 13:13:10 CEST 2004

On Wed, 2004-09-29 at 04:12, Henrik Nordstrom wrote:
> On Wed, 28 Sep 2004, Jamal Hadi Salim wrote:

> > Unfortunately i am not sure if you can force current to always get
> > its port allocation from the allocated range _only_. Is this doable?
> iptables NAT allows you to specify the IP and port range acceptable.

My brain access is getting slow - I knew this. But does the machine then
only restrict itself to those ports for that IP defined?

> > Caveat: You just limited your active connections for your cluster to 64K
> > flows.
> Not really. But if you only have a single IP address then the port 
> allocation limits you to 64K flows per "other" IP. As already discussed 
> the tuple needs to be unique between different flows, not neccesarily the 
> port.

To clarify what you are saying: you will have (in the case of
masquareding single external realm IP) 64K possible flows per internal
realm _src_ IP?

> > I think we should make the issue of balancing a separate item.
> It is separate from the matter of syncronization. But the reason why the 
> syncronization protocol has not yet been designed for active-active is 
> because no load balancing scheme has been designed which would work. The 
> two goes hand in hand and both needs to be solved.

The cluster shouldnt care how the packet got there. Put LVS infront of
cluster or play ARP tricks - It doesnt matter.
Maybe iam missing something.

> Most likely the first load balancing method which will get implemented 
> (and forcing ct_sync to add the two minor pieces missing for active-active 
> syncronization) is the multicast balancing method in a no-NAT clused where 
> each firewall sees all traffic and selects what it looks closer at.

I am not saying this shouldnt be supported, but why the restiction
to _only_ this? 

>  This 
> is by far the easiest to implement. But even this is not entirely trivial 
> as there may be conflicts in flow key balance IDs depending on the 
> direction of the flow, but most likely this problem is more theoretical 
> than practical.

Thats what it seems to me. 
Maybe the piece i am missing is this "flow key balance IDs"...
If i have all the state of peer firewall, why should i not be able
to process packets you throw at me?

> > It shouldnt matter how the packet gets delivered to an active node
> > (pigeons, expensive loadbalancers, LVS, some routing tricks,
> > etc all is fine by me).
> > Assuming:
> >
> > - The state is already synced across all the nodes;
> >
> > - assuming theres no conflict and
> >
> > - assuming asymetry (ok, maybe thats too restrictive) but a good start.
> Allowing for assymetric flows is not something which is realistic to aim 
> for unless you also aim for absolute syncronization by delaying packets 
> until the firewalls have been syncronized. Such design will scale very 
> badly.

Sorry, I meant symetric setup .. i.e equal looking machines with same or
similar set of addresses. Two masquareding examples:

Machine A: internal IP:, external
Machine B: internal IP:, external

On failover, all addresses taken over by peer; state synced, things 
run as before.

Machine A: internal IP:, external
Machine B: internal IP:, external


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