Date: Tue, 27 Mar 2007 23:15:14 +0200 From: Andrea Venturoli <ml@netfence.it> To: Jordan Gordeev <jgordeev@dir.bg> Cc: freebsd-net@freebsd.org, Ross Draper <Ross.Draper@gcapmedia.com> Subject: Re: Vrrp/CARP/ucarp Problems Message-ID: <46098962.3040707@netfence.it> In-Reply-To: <46092E46.4090502@dir.bg> References: <3DDDCC38D00FA545A6C012475EF2DC0302AF8F55@LQEVS1.gcapmedia.com> <46092E46.4090502@dir.bg>
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Jordan Gordeev wrote:
> The only load balancing that CARP supports, to my knowledge, is ARP
> level load balancing. From carp(4):
> The ARP load balancing has some limitations. First, ARP balancing only
> works on the local network segment. It cannot balance traffic that
> crosses a router, because the router itself will always be balanced to
> the same virtual host.
Forgive me for stepping in, but I had read the above statement over and
over trying to figure what it meant; perhaps it's not so clear...
If I understood it correctly it's not saying you should not use CARP on
routers. Instead it's meaning that load-balancing won't cross a third
router which is on cascade of the two CARP routers.
An image might help to clarify:
+------+ +------+ +------+ .... +------+
|host I| |host J| |host K| .... |host Z|
+------+ +------+ +------+ .... +------+
| | | |
\--------+--------+-------------+---------\
|
+------+ +------+ +------+ .... +------+ +--------+
|host A| |host B| |host C| .... |host H| |Router 3|
+------+ +------+ +------+ .... +------+ +--------+
| | | | |
\--------+-----+--+-------+-----+---------/
| |
+--------+ +--------+
|Router 1| |Router 2|
+--------+ +--------+
Suppose you are arp-balancing with CARP on Router 1 & 2, hosts A-H will
get balanced, but hosts I-Z will all go to the same router (wether
Router 1 or Router 2). This is because all their incoming packets will
bear Router 3's MAC address.
Is this interpretation correct?
bye & Thanks
av.
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