Segment Routing WECMP

[dundient]

Good day everyone,

I am interested in Segment Routing WECMP. I've searched about load balancing in Segment Routing and found that there is a formula by which load balancing calculates. But i didn't find the logic that on which information it load balances the packets. For. example, if there are 2 segment-lists within the same candidate-path preference 10. Segment-list #1's weight is 2, Segment-list #2's weight is 3. Somehow it load balances the packets by these 2 explicit paths. I wonder based on what it load balances them?

Is there any  criteria that router chooses packets to load balance?

Like source-ip, destination-ip, mac-address or port?

Any thoughts, thank you in advance

[Harold Ritter · Accepted solution]

Hi @dundient ,

Load balancing is based on hashing different components of the packet, such as source IP, destination IP, source port, destination port, mpls label(s), IPv6 flow label, etc. 

The specific combination depends on the platform and the NOS you use.

Regards,

[dundient]

Thank you for your response!

[Harold Ritter]

You are very welcome @dundient and thanks for the feedback

[dundient]

Good day @Harold Ritter 

I've been searching the document about the WECMP load balancing criteria but couldn't find. We're going to try configure Segment Routing WECMP packets by various components . 

Could you share, please, the document, if you have, of course, that confirms load-balancing criteria and how to configure it?

Thank you in advance.

[Harold Ritter]

Hi @dundient ,

Here's a good document covering several ECMP components on the ASR9k platform.  The implementation on other platforms may vary.

https://community.cisco.com/t5/service-providers-knowledge-base/asr9000-xr-load-balancing-architecture-and-characteristics/ta-p/3124809#field

Let me know if you need something more specific.

Regards,

[dundient]

Good day @Harold Ritter , Thank you for your response

Does IOS-XE work based on the same logic? I'm using specifically ESR6300 IOS-XE(17.09.5a) and c8000v IOS-XE(17.09.5a).

I've tried configure the commands that explained there but i guess it doesn't work for IOS-XE platform. I'm wondering where I can find the document for IOS-XE Segment-Routing Explicit-list weighted load-balancing configuration. 

Could you briefly explain me about SR-TE explicit-list weighted load-balancing and how it works, briefly. I'm little bit confused because as I understand: 

explicit segment-list sr_333 weight 5
explicit segment-list sr_555 weight 3

work based on policy and do not apply on interface specifically. 

Could you explain little bit about this case, please? Thank you very much in advance.