Question

ECMP support for Overlay/RIOT/EVPN


Hi,

  • ECMP support for overlay networks on RIOT-capable Broadcom switches (Trident 3, Maverick, Trident 2+) in addition to Mellanox Spectrum-A1 and Tomahawk switches.
Can somebody please explain this feature as mentioned in https://docs.cumulusnetworks.com/display/DOCS/Ethernet+Virtual+Private+Network+-+EVPN.

I did not find any references to commands to enable this feature.

Thanks,
Sajish.

6 replies

Userlevel 2
Hi Sajish,

You don't have to enable it explicitly, it will just do ecmp in the overlay when there are multiple nexthops.
Hi Attilla,

Thanks for the quick response.

Could you please clarify regarding nexthops.

I was a bit confused about the scenarios/topology for ECMP in the overlay. Is this related to multihoming scenarios, where one host is connected to multiple VTEPs?

Thanks,
Sajish.
Userlevel 4
I'll clarify in the EVPN chapter that no configuration is needed for this.
Userlevel 2
Hi Sajish,

Overlay ECMP would occur when you have more than one VTEPs announcing the same route. This would be an example:

cumulus@leaf01:mgmt-vrf:~$ ip route sh vrf tenant1
10.201.1.0/24 proto bgp metric 20
nexthop via 10.10.40.2 dev dummysvi404001 weight 1 onlink
nexthop via 10.10.40.1 dev dummysvi404001 weight 1 onlink
10.203.1.0/24 proto bgp metric 20
nexthop via 10.10.40.2 dev dummysvi404001 weight 1 onlink
nexthop via 10.10.40.1 dev dummysvi404001 weight 1 onlink

In this case, VTEPs 10.10.40.1 and 10.10.40.2 are announcing two prefixes. Before this fix, traffic to these prefixes wouldn't be ecmp'ed to the two VTEPs, only one would be used.

I hope this explains it.
Could you please elaborate on how the synchronization between the VTEPs 10.10.40.1 and 10.10.40.2 are achieved when actual data flows through?
Userlevel 2
There is no synchronization between the VTEPs.

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