[isapros] Re: Array Member Failover

  • From: "Jason Jones" <Jason.Jones@xxxxxxxxxxxxxxxxx>
  • To: <isapros@xxxxxxxxxxxxx>
  • Date: Mon, 29 May 2006 01:02:03 +0100

TBH this is something I have never tested in great detail and would
normally use NLB if failover is the priority. However, this customer is
being very specific about failover and test plans :-\ 

-----Original Message-----
From: isapros-bounce@xxxxxxxxxxxxx [mailto:isapros-bounce@xxxxxxxxxxxxx]
On Behalf Of Thomas W Shinder
Sent: 27 May 2006 14:32
To: isapros@xxxxxxxxxxxxx
Subject: [isapros] Re: Array Member Failover

Jason,

I'm afraid Jim's right here. While the marketing materials and stories
make CARP appear to be a failover and back tech, we know from long
experience that it does work that way :\

Tom

Thomas W Shinder, M.D.
Site: www.isaserver.org
Blog: http://blogs.isaserver.org/shinder/
Book: http://tinyurl.com/3xqb7
MVP -- ISA Firewalls

 

> -----Original Message-----
> From: isapros-bounce@xxxxxxxxxxxxx
> [mailto:isapros-bounce@xxxxxxxxxxxxx] On Behalf Of Jim Harrison
> Sent: Friday, May 26, 2006 2:49 PM
> To: isapros@xxxxxxxxxxxxx
> Subject: [isapros] Re: Array Member Failover
> 
> WPAD is not designed to provide failover/back.
> As you've noticed, this is not going to work.
> WPAD is nothing more or less than a "load-spreading" mechanism that 
> allows the client to use a different ISA for different destinations.
> 
> If you want failover/back, use NLB or another traffic-management 
> system.
> 
> -----Original Message-----
> From: isapros-bounce@xxxxxxxxxxxxx
> [mailto:isapros-bounce@xxxxxxxxxxxxx]
> On Behalf Of Jason Jones
> Sent: Friday, May 26, 2006 12:42 PM
> To: isapros@xxxxxxxxxxxxx
> Subject: [isapros] Re: Array Member Failover
> 
> Cheers Tom - unfortunately closing the browser doesn't seem to fix the

> problem...IE still trys to connect to the primary autoconfig defined 
> server first then eventually use the other array members (after about 
> 20-30 seconds). This behaviour seems to happen repeatedly on all 
> clients fdor every new URL entered
>  
> The only way to fix it is to bring the failed server back online :-(
> 
> ________________________________
> 
> From: isapros-bounce@xxxxxxxxxxxxx
> [mailto:isapros-bounce@xxxxxxxxxxxxx]
> On Behalf Of Thomas W Shinder
> Sent: 26 May 2006 12:18
> To: isapros@xxxxxxxxxxxxx
> Subject: [isapros] Re: Array Member Failover
> 
> 
> Hi Jason,
>  
> Not too low brow for me :)  This is a common question with a common 
> non-answer in the public realm.
>  
> What you need to do is close all browser windows and open a new one.
> Then the client connects to a live server. I've never worked out in 
> detail why this happens, but it's related to the autoconfig script 
> processing [hand waving explanation]
>  
> Maybe somebody else can chime in with a more detailed explanation.
> Bottom line is that you're not going to get completely transparent 
> failover for Web proxy clients.
>  
> Tom
> Thomas W Shinder, M.D.
> Site: www.isaserver.org <http://www.isaserver.org/>
> Blog: http://blogs.isaserver.org/shinder/
> Book: http://tinyurl.com/3xqb7 <http://tinyurl.com/3xqb7> MVP -- ISA 
> Firewalls
> 
>  
> 
> 
> ________________________________
> 
>       From: isapros-bounce@xxxxxxxxxxxxx
> [mailto:isapros-bounce@xxxxxxxxxxxxx] On Behalf Of Jason Jones
>       Sent: Thursday, May 25, 2006 4:44 PM
>       To: isapros@xxxxxxxxxxxxx
>       Subject: [isapros] Array Member Failover
>       
>       
> 
>       Hope this question is not too low brow, if so, kick me and I
will 
> move it to isaserver.org for the masses to mull over ;-)
> 
>       Anyhow, has anything changed with array member failover behavior
in 
> EE with ISA2k4 SP2? I am sure I have never had problems with array 
> member failovers in the past...
> 
>       I have recently deployed an SP2 array with several members and
while 
> testing I have noticed that if the server listed as the first entry 
> defined within the wpad.dat file is unavailable then the browser 
> delays for quite some time before attempting to connect to other array

> members (e.g. working through the server list in the wpad.dat file). 
> It does seem to get there, but we're talking 20 seconds or so per 
> website.
> Once the website is loaded, performance is fine. When using a new URL,

> the delays appears again.
> 
>       Apart from failover, balancing and distr caching seems to be
working 
> well. I know I could be using NLB, but I believe the following to be 
> good practice:
> 
>       Web Proxy => Autoconfig script (client side CARP) 
>       FW Client => RR DNS
> 
>       I am using a generic name of customerarray.domain.com with RR
DNS 
> entries to balance autoconfig requests between array members. This is 
> the name used in the autoconfig URL.
> 
>       I know NLB may come to mind as a workaround, but it is hard to 
> implement as the customer is using NIC teaming at the hardware driver 
> level to aggregate NICS and provide NIC fault tolerance. NLB and NIC 
> teaming never play well from what I have experienced :-(
> 
>       Can someone please define normal behavior for a client that is
using 
> an autoconfig script when array members are unavailable? I kinda get 
> the feeling the problem is with the browser and not the array, but not

> totally sure when IE does with the script in terms of processing...
> 
>       I've tried looking at wpad.dat caching and caching of bad
proxies, 
> but neither seems to make much difference...
> 
>       Any ideas? 
> 
>       JJ
> 
> 
> All mail to and from this domain is GFI-scanned.
> 
> 
> 
> 




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