Vieri Di Paola wrote: >However, a tech from the remote network has stated (without >explaining why) that having a /16 netmask in 'loc' instead of a more >narrow mask would generate too many broadcasts in his network (net2). >I'd like to know: >1) if this statement is correct given the above setup description.
I can't see how >2) if a higher broadcast is a "significant" network load. It might be, it might not be ! It all depends on the nature of the network and the volume of broadcasts. Bear in mind that ethernet used to be a purely broadcast medium (where every station saw all traffic from every other station - the downside being that this severely limited throughput. On a fast network that's lightly loaded, a bit of broadcast traffic won't be noticed. On a slow network that's heavily loaded, it may make a different if there's a lot of it. Back to your situation. You have a router between your network and the foreign network - this means no broadcast traffic from your network will be seen on the foreign network - if the tech believes otherwise then he's an idiot (sadly, there are lots of idiots running networks). With the right settings, it is possible for a device on your network to send a directed broadcast. Ie, you would send a packet from one of your devices to 10.215.0.255, and the router would broadcast it on the foreign network. This is usually blocked for what should be obvious reasons - but can be a useful network tool. For example, Retrospect (a backup tool) uses broadcasts to find clients. If you network supports directed broadcasts then it can use this to find clients in remote networks - one directed broadcast packet will elicit responses from all clients in that remote network. Without directed broadcasts, the server must try every possible address in the remote network to find clients - thus 254 packets sent instead of one for a /24. This is both irrelevant to you (I assume you aren't using them) and is also completely unconnected with the size of your network. The only possible reason I can see for making the statement is that if you have a lot of devices on a network then there will naturally be a lot more broadcast traffic than if you have only a few devices. This is independent of length of subnet mask - ie 2 devices will create the same broadcast traffic on a /16 as they would on a /24. Though if you have something trying to contact lots of IP addresses, it will do more ARP lookups rather than directing the packets via the default gateway when they aren't on the same subnet. This is still invisible to a network the other side of a router. Perhaps you should ask the tech what sort of broadcast traffic he expects to see from your network - bearing in mind there is a router in between and you aren't on the same broadcast domain. -- Simon Hobson Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed author Gladys Hobson. Novels - poetry - short stories - ideal as Christmas stocking fillers. Some available as e-books. ------------------------------------------------------------------------------ Monitor your physical, virtual and cloud infrastructure from a single web console. Get in-depth insight into apps, servers, databases, vmware, SAP, cloud infrastructure, etc. Download 30-day Free Trial. Pricing starts from $795 for 25 servers or applications! http://p.sf.net/sfu/zoho_dev2dev_nov _______________________________________________ Shorewall-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/shorewall-users
