[lustre-discuss] multi-hop routing

[Horn, Chris]

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<mailto:172.18.2.5 at o2ib>
net              o2ib2 hops 2 gw                  172.18.2.6 at o2ib<mailto:172.18.2.6 at o2ib> up pri 0
----------------
router1
----------------
172.18.2.6 at o2ib<mailto:172.18.2.6 at o2ib>
172.18.2.2 at tcp<mailto:172.18.2.2 at tcp>
net              o2ib2 hops 1 gw                   172.18.2.3 at tcp<mailto:172.18.2.3 at tcp> up pri 0
----------------
router2
----------------
172.18.2.7 at o2ib2<mailto:172.18.2.7 at o2ib2>
172.18.2.3 at tcp<mailto:172.18.2.3 at tcp>
net               o2ib hops 1 gw                   172.18.2.2 at tcp<mailto:172.18.2.2 at tcp> up pri 0
----------------
client
----------------
172.18.2.8 at o2ib2<mailto:172.18.2.8 at o2ib2>
net               o2ib hops 2 gw                 172.18.2.7 at o2ib2<mailto: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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