# CEF Polarization **URL:** https://forum.networklessons.com/t/cef-polarization/1850 **Category:** Lessons Discussion **Created:** [June 26, 2017, 1:34pm UTC](https://forum.networklessons.com/t/cef-polarization/1850 "2017-06-26T13:34:43Z") **Posts on this page:** 1 **Showing post:** 8
### Author: ![samirkhair](https://cdn-forum.networklessons.com/letter_avatar_proxy/v4/letter/s/cdc98d/32.png) [@samirkhair](https://forum.networklessons.com/u/samirkhair) #### Post date: [March 22, 2021, 9:49am UTC](https://forum.networklessons.com/t/cef-polarization/1850/8 "2021-03-22T09:49:49Z")
Hi, I’m a little confused by how polarisation is avoided. I get that if you only use source and destination IP then all traffic between two hosts will take the same route, even if they are accessing different services (ports). And I understand that if you include ports then the above problem is mitigated in that the traffic is will be spread more evenly amongst exit interfaces. But, unless you use an algorithm that uses the random unique ID, wont polarisation always occur? Because the hash will always be the same. And the same exit interfaces will always be the same on all routers for all flows even if ports are used in decision making. So, your statement below about the 6500’s makes sense to me because Default is the only one using a unique ID > The full, simple and full simple variations are prone to CEF polarization. However, the statement before that has confused me > Only the original CEF variation is prone to CEF polarization, the other options avoid it by including other information besides the source/destination IP address. Because according to the list - original, universal, tunnel, l4 port - universal is the only one using a unique ID and thus the only one avoiding polarisation. Thanks, Sam --- _[View the full topic](https://forum.networklessons.com/t/cef-polarization/1850)._