Multipath support?

[Vasu M]

On Thu, May 25, 2017 at 12:05 AM, Vasu M <vasu.kernel at gmail.com> wrote:

> I would like to know from which version of Linux, ECMP is supported? I am
> trying to add a route with two next hops. Only one path gets added. And for
> the other path, the route says "RTNETLINK answers: File exists". I am not
> able to understand what's going on. The route prefix is not pointing to
> ecmp because metric is not given for static routes? How can I test
> multipath for a prefix that goes over 2 links?
>
> I tried "echo 7 > /proc/sys/kernel/printk" and dmesg but I don't see
> anything related to route add events. Just wondering how I should approach
> this problem.
>
> I am running the following versions on two devices running ONL.
>
> *Linux localhost 3.16.43-OpenNetworkLinux #1 SMP Thu May 11 18:37:48 UTC
> 2017 x86_64 GNU/Linux*
> I tried the following :-
>
> root at localhost:~# route -n
>
> Kernel IP routing table
>
> Destination     Gateway         Genmask         Flags Metric Ref    Use
> Iface
>
> 0.0.0.0         192.168.100.1   0.0.0.0         UG    0      0        0 ma1
>
> 10.10.10.0      0.0.0.0         255.255.255.0   U     0      0        0
> fpPort2
>
> 20.20.20.0      0.0.0.0         255.255.255.0   U     0      0        0
> fpPort13
>
> 192.168.100.0   0.0.0.0         255.255.255.0   U     0      0        0 ma1
>
> root at localhost:~# arp -a
>
> ? *(20.20.20.2) at 00:a0:c9:00:00:01 [ether] on fpPort13 *
>
> ? (192.168.100.100) at f0:7f:06:1d:56:ff [ether] on ma1
>
> ? (192.168.100.1) at 18:b1:69:33:88:a4 [ether] on ma1
>
> ? (192.168.100.52) at cc:37:ab:7c:ca:16 [ether] on ma1
>
> ? (192.168.100.3) at c8:1f:66:f6:ea:07 [ether] on ma1
>
> ? *(10.10.10.2) at 00:a0:c9:00:00:01 [ether] on fpPort2*
>
>
> ip route add 100.100.100.0/24  via 10.10.10.2
>
> root at localhost:~# route -n
>
> Kernel IP routing table
>
> Destination     Gateway         Genmask         Flags Metric Ref    Use
> Iface
>
> 0.0.0.0         192.168.100.1   0.0.0.0         UG    0      0        0 ma1
>
> 10.10.10.0      0.0.0.0         255.255.255.0   U     0      0        0
> fpPort2
>
> 20.20.20.0      0.0.0.0         255.255.255.0   U     0      0        0
> fpPort13
>
> 100.100.100.0   10.10.10.2      255.255.255.0   UG    0      0        0
> fpPort2
>
> 192.168.100.0   0.0.0.0         255.255.255.0   U     0      0        0 ma1
>
> root at localhost:~# ip route add 100.100.100.0/24  via 20.20.20.2
>
> *RTNETLINK answers: File exists*
>


Figured "ip route append" is used to add ECMP. I am, however, seeing some
ECMP paths getting added to the rt table which seems to be a bug although
the behavior is not consistent.
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