Subject: Re: Max number of caches supported by one router

From: michael rabinovich <[email-masked]>
Date: Mon, 22 Nov 1999 11:29:38 -0500 (EST)

One has to be careful to make sure the whole system is balanced.
A modern cache can service in the order of 100Mbps traffic, so you do not
want to hang too many of these off a single router.

But I also have a question to WCCP gurus.  What is the time 
granularity for detection of cache failures?  (How frequent can
the health checks be, and how many retries are done before 
the cache is considered dead)?  I realize these are probably
configurable parameters, but I would like to learn the default
values, the value range, and the issues to consider when choosing
the setting.

Thanks much,
Misha

> From [email-masked] Mon Nov 22 10:55 EST 1999
> 
> Juan,
> 
> WCCP can support 32 caches.
> 
> Dave
> 
> At 10:20 am 11/22/1999 -0500, Juan Romo wrote:
> >Using WCCP. What is the maximum number of caches that can be controlled
> >by one router?
> >Thanks,
> >--- Juan Romo ---
> >[email-masked]
> >"IPworX development"
> > 
>

---

From: [email-masked] (Raghu Mallena)
Date: Mon, 22 Nov 1999 10:50:26 -0800 (PST)

> values, the value range, and the issues to consider when choosing

The cache sends the router HERE_I_AM messages every 10 seconds,  which
is what the router uses as an indication of the cache's health.
If the router does not get one of these in 25 seconds,  it sends
the cache a REMOVAL_QUERY message (a WARNING of sorts).   If the
cache is still up at this point,  it is supposed to respond back
with 3 HERE_I_AM messages in quick succession.    If the cache
is really down and doesnt send these 3 here_i_ams,   the router waits 
for another 5 seconds before removing the cache from its service
group.    So,  you have a total of 30 seconds before the cache is
considered dead.

As far as I know,  these parameters are not configurable as per the
WCCPv2 spec.     I suspect that the router would not freak out if 
caches send HERE_I_AM's more often than 10 seconds and so individual
cache implementations might have some of these parameters as
configurable to a certain extent.

- raghu

Network Appiance Inc.