[lustre-discuss] multi-hop routing

[John White]

Oh, so don’t even tell the client about tcp!  That seems to have immediately kicked things into place!
I owe you a beverage of your choice if we ever meet up!

Seriously, the imposter syndrome was getting _bad_ the last few days here.

> On Mar 5, 2025, at 12:05 PM, Horn, Chris <chris.horn at hpe.com> wrote:
> 
> You need LNet routes configured on all nodes. It should look something like this:
> 
> # pdsh -w n0[0-3] 'lctl list_nids; lctl show_route' | dshbak -c
> ----------------
> server
> ----------------
> 172.18.2.5 at o2ib
> net              o2ib2 hops 2 gw                  172.18.2.6 at o2ib up pri 0
> ----------------
> router1
> ----------------
> 172.18.2.6 at o2ib
> 172.18.2.2 at tcp
> net              o2ib2 hops 1 gw                   172.18.2.3 at tcp up pri 0
> ----------------
> router2
> ----------------
> 172.18.2.7 at o2ib2
> 172.18.2.3 at tcp
> net               o2ib hops 1 gw                   172.18.2.2 at tcp up pri 0
> ----------------
> client
> ----------------
> 172.18.2.8 at o2ib2
> net               o2ib hops 2 gw                 172.18.2.7 at o2ib2 up pri 0
> #
>  Chris Horn
>  From: lustre-discuss <lustre-discuss-bounces at lists.lustre.org> on behalf of John White via lustre-discuss <lustre-discuss at lists.lustre.org>
> Date: Wednesday, March 5, 2025 at 1:17 PM
> To: lustre-discuss at lists.lustre.org <lustre-discuss at lists.lustre.org>
> Subject: [lustre-discuss] multi-hop routing
> Hello folks.  I have a rare situation that I’m told some centers are successfully pulling off and am looking for guidance - multi-hop lnet routing.
> In short, I have 2 distinct o2ib fabrics at disparate geo sites joined by a routed ethernet fabric.  I’m looking to use a 2-lnet-router chain to plumb the two o2ib fabrics together.
> 
> servers on the left, clients on the right
> o2ib0(10.5.0.0/16) <-> router(o2ib0,tcp0) <-> routed eth (10.37.0.0/16, 10.38.0.0/16) <-> router(tcp0,o2ib2) <-> o2ib2(10.6.0.0/16)
> 
> I have both sets of routers up but traffic absolutely fails the 2nd hop in either direction (I can `lctl ping` tcp0 from o2ib2 and o2ib0 but no further).
> 
> I’ve tried adding a route ON the routers, that didn’t help. 
> 
> I’ve tried defining the 2nd hop on the client:
> options lnet routes="tcp0 10.6.0.[250-251]@o2ib2;\
> o2ib0 10.37.250.[162-163]@tcp0”
> 
> but that failed with the following kern message on lnet load:
> 74067:0:(router.c:644:lnet_add_route()) Cannot add route with gateway 10.37.250.162 at tcp. There is no local interface configured on LNet tcp
> 
> Does anyone have any hints here?  It feels like I’m a syntax change or a routing hint away from getting this working.
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