Anycast applicable to Radius Server Farm ?

Hugh Irvine hugh at
Mon May 8 07:13:24 UTC 2006

Hello Joe -

Can you indicate in more detail what the problems were with the L4  

If the loadbalancing is done by source/destination IP address pairs,  
then you can have problems when a target goes down, as all of the  
source/destination IP address pairs will get switched to another  
target which then gets into difficulty and you end up with a  
cascading failure. It is generally preferable to have the  
loadbalancing done on a weighted per-packet basis, ideally  
distributed according to round-trip times.

Also note that you can only do per-packet loadbalancing with simple  
RADIUS, things like EAP that require multiple exchanges of RADIUS  
requests typically require state to be maintained in the single  
RADIUS server that is processing the entire EAP sequence.



On 8 May 2006, at 14:07, Joe Shen wrote:

> Hi,
> we have a radius server farm. there is a L4 switch
> installed behind all servers. Incoming AAA packets are
> switched by L4 switch to different servers.
> In previous days we met a couple of problems with L4
> switch  which degraded our service a lot. Could it be
> possible to implement IPv4 Anycast architecture for
> radius server farm? Could it be any problem with AAA
> procedure?
> Any advice will be highly appreciated
> Joe
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Have you read the reference manual ("doc/ref.html")?
Have you searched the mailing list archive ( 
Have you had a quick look on Google (
Have you included a copy of your configuration file (no secrets),
together with a trace 4 debug showing what is happening?

Radiator: the most portable, flexible and configurable RADIUS server
anywhere. Available on *NIX, *BSD, Windows, MacOS X.
Nets: internetwork inventory and management - graphical, extensible,
flexible with hardware, software, platform and database independence.
CATool: Private Certificate Authority for Unix and Unix-like systems.

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