[c-nsp] BGP multipath load balancing.. broken sessions upon hash change

[Adam Vitkovsky]

Another option would be to run GLBP on the 16 processing nodes.
Though that would require to connect them to a L2 segment and use 16 interfaces on the core router to connect to the L2 segment :).
But it would solve the hashing problem :)


adam
>

        Adam Vitkovsky
        IP Engineer

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-----Original Message-----
> From: cisco-nsp [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of
> Peter Kranz
> Sent: 03 September 2015 00:05
> To: 'Łukasz Bromirski' <lukasz at bromirski.net>
> Cc: cisco-nsp at puck.nether.net
> Subject: Re: [c-nsp] BGP multipath load balancing.. broken sessions upon
> hash change
>
> I am attempting to load balance ~100 Gbps of inbound traffic across several
> processing nodes. Each node advertising the same /32 back to the core
> router and CEF nicely divides the traffic so that 1/16th of it arrives at each
> node. The problem arises when a node is brought out of rotation, existing
> SSH sessions break since the source IP gets mapped to a new node after CEF
> re-computes. Given the large amount of traffic, it's not easily solvable with
> higher end load balancers for a reasonable cost.
>
> -PK
>
> -----Original Message-----
> From: Łukasz Bromirski [mailto:lukasz at bromirski.net]
> Sent: Wednesday, September 02, 2015 2:56 PM
> To: Peter Kranz <pkranz at unwiredltd.com>
> Cc: cisco-nsp at puck.nether.net
> Subject: Re: [c-nsp] BGP multipath load balancing.. broken sessions upon
> hash change
>
> Peter,
>
> > On 02 Sep 2015, at 22:49, Peter Kranz <pkranz at unwiredltd.com> wrote:
> >
> > I’m using bgp maximum-paths and several peers announcing the same /32
> > to create a poor man’s load balancer. This works well with up to 16
> > peers after which the CEF number of buckets is exceeded.
> >
> > However, if the number of connected peers change, all sessions break,
> > which I would like to avoid.
>
> That’s the way CEF works - it has to rebuild the hash every time new nexthop
> appears or vanishes.
>
> This is 6500 you’ve mentioned in different post, right? What is the overall
> architecture of the thing you’re trying to achieve here (remote terminal
> access?).
>
> —
> Łukasz Bromirski
>
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