[179837] in North American Network Operators' Group
Re: Thousands of hosts on a gigabit LAN, maybe not
daemon@ATHENA.MIT.EDU (Blake Hudson)
Fri May 8 15:56:48 2015
X-Original-To: nanog@nanog.org
Date: Fri, 08 May 2015 14:54:16 -0500
From: Blake Hudson <blake@ispn.net>
To: nanog@nanog.org
In-Reply-To: <20150508185303.55159.qmail@ary.lan>
Errors-To: nanog-bounces@nanog.org
Linux has a (configurable) limit on the neighbor table. I know in RHEL
variants, the default has been 1024 neighbors for a while.
net.ipv4.neigh.default.gc_thresh3
net.ipv4.neigh.default.gc_thresh2
net.ipv4.neigh.default.gc_thresh1
net.ipv6.neigh.default.gc_thresh3
net.ipv6.neigh.default.gc_thresh2
net.ipv6.neigh.default.gc_thresh1
These may be rough guidelines for performance or arbitrary limits
someone thought would be a good idea. Either way, you'll need to
increase the number if you're using IP on Linux.
Although not explicitly stated, I would assume that these computers may
be virtualized or inside some sort of blade chassis (which reduces the
number of physical cables to a switch). Strictly speaking, I see no
hardware limitation in your way, as most top of rack switches will
easily do a few thousand or 10's of thousands of MAC entries and a few
thousand hosts can fit inside a single IP4 or IP6 subnet. There are some
pretty dense switches if you actually do need 1000 ports, but as others
have stated, you'll utilize a good portion of the rack in cable and
connectors.
--Blake
