randall@uvaarpa.virginia.edu (Randall Atkinson) (08/18/89)
% 1) using subnets for remote networks and limiting my connections % in the future % or 2) getting distinct network numbers to leave me flexibility in the % future In article <164@jove.dec.com> mogul@decwrl.dec.com (Jeffrey Mogul) writes: >The most basic rule of subnetting is that, if you go with option #1, >the subnets must be connected to each other via a path that doesn't >ever leave your class B network. If you cannot arrange internal links >between the home office and the branch offices, then you are not really >allowed to use option #1. > >If you can use option #1, there are two potential problems: > (a) Except for sites with hand-crafted routes into your network, it > will nearly impossible to say "use gateway X between the Internet > and the home office, but use gateway Y between the Internet and the > Amsterdam office." This means that there may be some packets that > go around the world when they only need to travel a few miles. For > example, if your primary Internet gateway is in California, and a > customer in Amsterdam tries to send a packet to the Amsterdam office, > the packet will flow via California. I imagine that most of the traffic would be mail and with mail it is simple to set up MX records so that mail to a site in Europe would go via European gateways and mail destined for the US would go via US gateways. In short, I'm not sure that the above is all that overriding a concern. > (b) Nasty people in Amsterdam, if they know that Adobe is paying > for an internal IP link between their city and California, could > try to save money on their own phone bills by routing their > packets through your network. This should not happen with normal > routing protocols; anyway, it is a simple matter to provide access > control mechanisms in your routers to deny forwarding of such > "transit" packets. Again, this really isn't much of a problem because as noted above, you can configure things so that such improper forwarding would be prevented. >If you use option #2, then neither of these two problems exists. >On the other hand, the size of the Internet routing tables is >growing at a frightening rate, and I'm sure people would rather that >you kept the number of networks as low as possible. Although >option #2 may be better for some specific situations, for the >community as a whole, the fewer networks the better. Really neither of these is much of a "problem" even for option 1 and if I were in the position of trying to manage an internal network of this size, I'd make sure it was all internally connected and go with option 1 because I'd find that easier to manage. In the case of GE, all of our sites interconnect and are setup such that we always use the internal connections to pass traffic rather than sending data over someone else's network. In most cases, this kind of setup is preferable both for the firm and for the network community as a whole.