SD-WAN cEdge Source TLOC Selection

[millsy2000]

Hi Team,

Quick question which I have been unable to find a definitive answer for online.

I understand the concept of TLOC and OMP Route preference when selecting the destination TLOC for forwarding traffic, however I don't quite understand how the router makes a decision on source TLOC if there are multiple tunnel paths to the same destination TLOC. 

Example

Branch router has two public TLOC's: public-internet and LTE. It is trying to reach destination 10.15.200.0/24, from the OMP output the chosen OMP route is via TLOC 172.18.255.2 public-internet. There are two active BFD sessions to this TLOC, one via public-internet and the other LTE. How can I determine what the chose source TLOC or interface is used, because there could be significant performance implications choosing one over the other. Also is there a way to influence this locally without using a central data policy?

BRANCH-ROUTER#show sdwan omp routes vpn 10 10.15.200.0/24

PATH ATTRIBUTE
FROM PEER ID LABEL STATUS TYPE TLOC IP COLOR ENCAP PREFERENCE
-----------------------------------------------------------------------------------------------------------

10.97.193.132 4407 1003 C,I,R installed 172.18.255.2 public-internet ipsec - (vSmart1)
10.97.195.132 4292 1003 C,R installed 172.18.255.2 public-internet ipsec - (vSmart2)

BRANCH-ROUTER#show sdwan bfd sessions

SYSTEM IP SITE ID STATE COLOR COLOR SOURCE IP IP PORT ENCAP MULTIPLIER INTERVAL(msec) UPTIME TRANSITIONS
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

172.18.255.2 11101 up lte public-internet 10.91.78.111 150.207.167.13 12406 ipsec 7 1000 0:21:03:52 0
172.18.255.2 11101 up biz-internet public-internet 192.168.1.11 150.207.167.13 12406 ipsec 7 1000 0:06:50:12 1

Appreciate any help.

Cheers!

[Kanan Huseynli · Accepted solution]

Hi,

Normally, ECMP happens based on hashing result and result will be 50-50% traffic distribution, but you can use interface parameter "IPSec weight" to send more traffic over one interface. You should configure higher value for public-internet color, in your case.

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

HTH,

[millsy2000]

Thanks Kanan thats great, 

Cheers