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rc@die@you@!spammers.sandworm.demon.co.uk 09-07-2004 11:24 PM

CISCO 1600 Question
 
Hi

I have a 256 kilostream line between two of our sites

I am considering setting up a bridge rather than a routed network
using cisco 1600 routers

I have windows machine on both side of the network, will these machine
swamp the line with broadcast or can the router do some sort of
blocking to stop this

OR

Can I have a routed network with the same class C network on either
side (sorry if this a dumb question)

Can any one point me to url / advice etc or examples please

Thanks



Walter Roberson 09-08-2004 12:17 AM

Re: CISCO 1600 Question
 
In article <hegsj0hm5nfqk11a18p768hl4hgatsoicr@4ax.com>,
<rc@bhfshops.org.uk> wrote:
:I have a 256 kilostream line between two of our sites

:I am considering setting up a bridge rather than a routed network
:using cisco 1600 routers

:I have windows machine on both side of the network, will these machine
:swamp the line with broadcast or can the router do some sort of
:blocking to stop this

If you are not running NETBIOS over IP, then the Windows machines will
be broadcasting only for ARP, and DHCP, together with anything you
specifically turn on (e.g., some collaborative software uses broadcasts.)
Also, you might get the occassional broadcast from a program checking
to be sure that there aren't other copies of the program with the same
serial number running on the LAN [e.g., Norton Anti-Virus has some
manner of license-checking broadcast.]

But if you don't install anything unusual, and you aren't running
NETBIOS over IP, then you will find that your PCs don't do very much
broadcasting -- probably not enough to be an issue unless your sites
are large enough that you really should be going being 256 Kbps anyhow.

If you *are* running NETBIOS over IP, then it is important that
*all* NETBIOS-using Windows machines see those broadcasts, as NETBIOS
broadcasts are used to lock resources, hold elections, and a few other
fundamental features. You cannot filter out those NETBIOS broadcasts
without risking data corruption on any shared resource (e.g., disk
shares or printer shares.)

A bridge will usually filter out ARPs for IPs that it knows are on it's
local side, but you can't apply the same principle to NETBIOS, as
NETBIOS broadcasts are used to transfer control of resources over all
the machines in the entire subnet. If your subnet extends 1000 miles,
then the machines 1000 miles away -must- see those NETBIOS broadcasts
to protect the integrity of the protocol.

And if your sites are of radically different sizes (e.g., 10 hosts
at one, 300 hosts at the other), then watch out for the possibility
that the NETBIOS protocols may choose to elect a PDC or Master Browser
on the -other- side of the link, forcing a lot of unicast traffic
through the link that otherwise would stay local.


The obvious solution to this quandry is "Don't use NETBIOS" (or any
of the technologies that are layered on it, such as Windows shares.)
Or if you MUST use NETBIOS, then use routed networks and WINS.


:OR

:Can I have a routed network with the same class C network on either
:side (sorry if this a dumb question)

Only if you do address translation somewhere in the middle, or if
you do up a bunch of "host routes" that list explicitly which systems
are on which side of the link. That list of host routes would have
to be installed on every system at both sites, unless the circumstances
were such that you could *reliably* get proxy arp to work for you.
Bridging would probably be easier and more reliable to set up.
--
Is "meme" descriptive or perscriptive? Does the knowledge that
memes exist not subtly encourage the creation of more memes?
-- A Child's Garden Of Memes


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