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Re: Anycast applicable to Radius Server Farm ?

  • From: Hugh Irvine
  • Date: Tue May 09 19:05:08 2006


Hello Joe -

On 9 May 2006, at 01:23, Joe Shen wrote:

Can you indicate in more detail what the problems
were with the L4
switch?
We seperate our Radius servers into two farms, each
farm has a L4 switch in front. To our understanding,
radius authentication info. and accounting info. of a
PPPoE session should be processed by the same Radius
server. So, although L4 switch provides a single IP
for BRAS configuration  each BRAS is specified a real
server IP in L4 switch. So, there comes the problem:

Normal RADIUS does not require authentication and accounting for a single session to go to the same RADIUS server.

1) Load is not balanced automatically  but by human
estimation; there is server whose load is twice of
some other server.

You should use a loadbalancer that can distribute RADIUS requests on a per-request basis according to round-trip times which will be a reasonable indication of server load. Ie. the fastest round-trip time will be from the least-loaded server.

2) L4 switch becomes bottleneck of service
availability. In past years, L4 switch caused several
times of service failure. Just last friday, L4 switch
does not repond to any network packets while its
ethernet interface seems OK.

I suggest you find a better loadbalancer. Contact me off list if you need suggestions.

3) As L4 switch is the only entrance to a single
server farm, DoS attack or some other kind of software
bug  will surely degrade security level. While, a farm
using ECMP rely on server groups to resist DoS attack.

You should design your system with two loadbalancers, and configure your NAS equipment to use one as primary and the other as secondary. You should configure half of your NAS equipment to use loadbalancer A as primary, and the other half of your NAS equipment to use loadbalancer B as primary (and the converse for secondary).

4) Maintence is a little bit costy.  Any maintence ,
no matter on radius server or on L4 switch, need a
scheduled time window.

A design as above will have no single point of failure.

5) Service protection is hard ( as you mentioned as
'cascade' one). As there are two server farms, if one
farm failed it takes ten or more minute to migrate
those Radius traffic to the other farm. This is
unacceptable.

If you set your RADIUS timeouts and retries on the NAS equipment sensibly, depending on what end-user devices are being used (PC modems, DSL modems, GPRS WAP phones, mail servers, web servers ...) any outage should have almost imperceptible impact.

So, we consider to find a more scable, reliable,
secure and automatic  multi-farm radius solution.

hope that helps

regards

Hugh


Joe


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.

regards

Hugh


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


		
__________________________________
Do you Yahoo!?
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NB:

Have you read the reference manual ("doc/ref.html")?
Have you searched the mailing list archive
(www.open.com.au/archives/
radiator)?
Have you had a quick look on Google
(www.google.com)?
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.





		
__________________________________
Do you Yahoo!?
Yahoo! Movies - Search movie info and celeb profiles and photos.
http://sg.movies.yahoo.com/

NB:

Have you read the reference manual ("doc/ref.html")?
Have you searched the mailing list archive (www.open.com.au/archives/ radiator)?
Have you had a quick look on Google (www.google.com)?
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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