Multiple OSPF adjacencies on same interface...

[Kveri]

Hello,

you cannot use LACP between 3 devices. That is only possible if two of 
those devices (Force10 routers/switches) are forming one logical device 
(Cisco VSS, MEC, virtual PortChannel, HP IRF), I don't know if Force10 
has something like that. If you do this however, those 2 routers will 
appear as one logical device (one OSPF neighbor) to the server, then you 
don't have a problem. This is preferred solution, because it takes the 
problem from OSPF to much faster technologies.

On the other hand you can do VRRP between the routers and do OSPF on the 
hypervisor with both of the routers, in this case just beware the 
asymetric routing (which may/may not be a problem, depending on the 
setup).

Regarding your setup, I assume you're using the same IP on both of the 
routers, this won't work because from the router perspective the links 
are UP and they're advertising the same /31 to the rest of the network, 
this will cause half of the packets/flows to be lost.

So, you can either use some virtualization switching technology (if 
Force10 provides that), or you can use VRRP with 2 OSPF neighborships 
(but in that case you need /29 subnet), or you can do some sort of 
script on the server and use master-slave bonding mode, but be sure to 
always shutdown the inactive interface (be sure to always have enabled 
only one of them physically), that way only one of the Force10 routers 
would advertise the subnet...

Martin

2013-12-16 10:24 odosielateľ napísal:
> Yes - the reason is that this router is a VM with two passthrough NICs.
> The hypervisor is connected to both Force10 routers/switches with
> LACP, so the VM needs to run linux bonding mode 2 to provide a bond0
> interface to the VM.
> Neighbourship then needs to be established to both routers on this
> bonded interface.
> 
> I tried to create neighbourship directly on the interfaces, but this
> does not work, I assume because the switches loadbalance traffic on
> the LACP portchannel.
> 
> I could create a neighbourship with a VRRP interface, but as I
> understand it this will not work due to different router-ids in case
> of failover.
> 
> So basically as I see it, this is the only way to make this work -
> unless you have another idea?
> 
> Thanks
> 
> Regards
> Kristoffer
> 
> 
> On 13/12/2013, at 17.37.29, Raphael Mazelier <raph at futomaki.net> wrote:
> 
>>> I?m trying to use a bonded interface on linux to connect to two 
>>> routers, one router on each physical link, each with a /31 subnet.
>>> Only one of the routers (Force10 S4810) forms adjacency with the 
>>> linux host (whichever comes first), the other gets stuck in EXSTART
>>> until I shut/no shut the link, then Bird creates adjacency with both 
>>> routers.
>> 
>> What are you trying to do with this design ? It's rather strange.
>> 
>> --
>> Raphael Mazelier
>>