SDWAN IPsec preference weight command

[bradleyordner]

Looking for some more details on the weight command in relation to TLOCs. Documentation says the command allows configuration of 1 - 255. 

Is it correct to say - 

Primary Link Weight 1 

Secondary Link Weight 255 

So, for every 1 flow on the primary, 255 would be placed on the secondary? As there will be more than 256 flows going through the route then for flow number 2, another 255 flows would be placed on the secondary and so forth? Can this be represented as a percentage or traffic, or not due to not knowing how many flows? 

Also, is this inbound or outbound?

Thanks

[Kanan Huseynli]

Hi,

yes, if TLOC1 has weight of 1, TLOC2 has weight of 255 then traffic distribution ratio will be 1:255. It will be per flow, since per flow load-balancing happens in SD-WAN. If you have 1000 active traffic flow, then 3-4 will go over TLOC1 and rest of them will go over TLOC2 (approximately).

More interesting is router not only consider local weight, but also remote weight (per CVD document). So, seems it affects inbound traffic also. From normal logic point of view, if I understand correctly:

if cEDGE_A has T1 (w:10) and T2 (w:20) and cEDGE_B has T1 (w:10) and T2 (w:20) and the same route with no difference is received from both routers then for each 9N flow, then

cEDGE_A should send 3N flow over T1 ; 6N flow over T2 and since remote TLOCs' weight are different, then

(from 3N over local T1) N flow will go over T1 <> T1 ; 2N flow over T1 <> T2

(from 6N over local T2) 2N flow will go over T2 <> T1 ; 4N flow over T2 <> T2

Please, note that this may be in reality a bit different if differently implemented. In config guide/ CVD no details is given.

Below if from SD-WAN CVD (subsection: "Weight"):

"The weight parameter can be used to send traffic over weighted tunnels, where a higher value sends more traffic to a tunnel compared to another. Weight is often used when the bandwidth of the TLOCs vary and you cannot perform ECMP over the links. Weight can be set from 1 to 255, with a default value of 1. Traffic distribution takes into account the remote TLOC weight as well as the local TLOC weight."

https://www.cisco.com/c/en/us/td/docs/solutions/CVD/SDWAN/cisco-sdwan-design-guide.html

Regards, HTH,