[CentOS] Redundant LAN routing possible?

Sun Jul 11 16:05:24 UTC 2010
Chan Chung Hang Christopher <christopher.chan at bradbury.edu.hk>

Emmanuel Noobadmin wrote:
> Thanks for the suggestion, I'll read up more about them. The
> bond0 and just works sounds simple which is a Good Thing!  The problem
> was the last time I tried to cross connect multiple switches,
> everything just died so there must be something a bit more involved?
> :D
> In the mean time since my post, I came across STP (spanning tree
> protocol) that seems to be designed to handle this sort of thing, i.e.
> figure out the shortest path and prevent network shortcircuit like
> what I had experienced with cross connecting multiple switches.

You only really need STP when you have switches that are connected 
together in such a way as to have multiple paths. For the setup you 
first posted, you could just have two physically separate networks. That 
does leave the question of what solution to use to get the boxes to use 
the other switch if the primary one goes down. So if you connect both 
networks to make say a big 'circular' network, then you need STP.

> But it apparently takes 50 seconds to reconfigure anytime sometime in
> the circuit fails. There is supposedly a Rapid STP that only takes 3
> seconds. Several couple-of-years old search results indicate that it
> was tested in 2.4 kernel and will be in 2.6 kernel. However, I cannot
> seem to find anything newer that confirms if such functionality is
> really in the current kernel. Anybody has any idea?

You probably want to inform the switch which ports are link ports and 
which ports are edge ports (that is, only hosts will use the port) to 
reduce the amount of work and therefore time needed.

> On 7/11/10, Jerry Franz <jfranz at freerun.com> wrote:
>> On 7/10/2010 2:21 PM, Emmanuel Noobadmin wrote:
>>> I've been reading that it's possible to set up a system with multiple
>>> NIC to provide redundant internet connectivity such that it will
>>> switch to a secondary connection if the primary ISP fails.
>>> Is it possible in a similar way to setup redundant LAN routing? I read
>>> that it is possible to aggregate/bond multiple NIC to stackable
>>> switches that support link aggregation and redundancy. But if only
>>> simple switches are available, is something like this possible?
>>> e.g.
>>> System A
>>> eth0 ->  lan switch/router 1
>>> eth1 ->  lan switch/router 2
>>> System B
>>> eth0 ->  lan switch 1
>>> eth1 ->  lan switch 2
>>> Then somehow specify that, if lan switch 1 fails, the two systems will
>>> switch to using switch 2 so that in case of a switch failure, the
>>> network continues to remain operational.
>> Yes. You can do it. I've done it before. All you need is the right
>> choice of bonding mode . You set up bond0 for eth0 and eth1 and it 'just
>> works'. To make it more robust, cross-connect the two switches as well.
>> --
>> Benjamin Franz
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