# Radius LB DSR Mode

**URL:** <https://community.a10networks.com/t/radius-lb-dsr-mode/648>\
**Category:** ADC - Application Delivery\
**Tags:** load-balancing-method, slb-adc, a10-thunder\
**Created:** [February 26, 2021, 9:04am UTC](https://community.a10networks.com/t/radius-lb-dsr-mode/648 "2021-02-26T09:04:02Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Nathaneil0277](https://avatars.discourse-cdn.com/v4/letter/n/eada6e/32.png) [@Nathaneil0277](https://community.a10networks.com/u/Nathaneil0277)\
**Post date:** [February 26, 2021, 9:04am UTC](https://community.a10networks.com/t/radius-lb-dsr-mode/648/1 "2021-02-26T09:04:02Z")

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Hi Experts,  
Do you have a technical reference for load balancing Radius Server in DSR mode?  
The traffic flow will be something like this(see attached image). I am not really sure if this is the right behavior so I am asking if you can share some good references with regards to this deployment. Thank you.

 ![Traffic Flow Assumptions.PNG](https://us1.discourse-cdn.com/flex002/uploads/a10_community/original/1X/0068da423150d69f1ae1a804e4eef40b7b5d57bf.png)

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**Author:** ![jserrano](https://avatars.discourse-cdn.com/v4/letter/j/a9a28c/32.png) [@jserrano](https://community.a10networks.com/u/jserrano)\
**Post date:** [May 7, 2021, 8:38am UTC](https://community.a10networks.com/t/radius-lb-dsr-mode/648/2 "2021-05-07T08:38:53Z")

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Hi,  
You need to configure a loopback interface on each backend server with the Radius Cluster IP (2.2.2.1) to make sure the response is consistent with client request at ip level. Also make sure ARP proxy is disabled on servers to avoid any ip conflict with VIP presented at A10.  
I am attaching an small manual to configure it for Linux and Windows OS´s.

Configuration on the A10 side is straightforward, just create an L4 UDP vport with the “no-dest-nat” option preserve the original destination IP before forwarding packet to server-side:  
slb virtual-server vip1 192.0.2.99  
port 1812 udp  
service-group SG-RadiusSRVs  
no-dest-nat

Regards

[DSR Loopback Config.pdf](https://community.a10networks.com/uploads/short-url/ou5mwcSGwvTjQiOHi19CE0GwRLB.pdf) (1.42 MB)