Multiple OSPF adjacencies on same interface...

[Mikhail A. Grishin]

Kveri wrote, 16.12.2013 13:49:
> 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.

It has:

http://hasanmansur.com/2012/11/07/force10-s4810-vlt-quick-configuration-sample/

http://en.wikipedia.org/wiki/Virtual_Link_Trunking

> 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
>>>