Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!uunet!husc6!rutgers!sri-spam!ames!elroy!cit-vax!ucla-cs!zen!ucbvax!UIAMVS.BITNET!JNFORDPB From: JNFORDPB@UIAMVS.BITNET (Jay Ford, U of Iowa) Newsgroups: comp.protocols.tcp-ip Subject: help Message-ID: <8711210311.AA10698@ucbvax.Berkeley.EDU> Date: Fri, 20-Nov-87 22:46:56 EST Article-I.D.: ucbvax.8711210311.AA10698 Posted: Fri Nov 20 22:46:56 1987 Date-Received: Sun, 22-Nov-87 22:10:26 EST Sender: daemon@ucbvax.BERKELEY.EDU Organization: The ARPA Internet Lines: 137 This is a request for network configuration suggestions. Any responses should be sent to me rather than to the list. Questions How have other sites approached and/or solved the problems associated with establishing and administering large campus networks? Is the topology outlined below feasible without having static, manually-entered routes for the entire campus? Will an ARP (or any) ethernet-level broadcast from a host on one ethernet make it through a gateway to a host on another ethernet? Will the ARP reply make it back to the broadcaster? Is it necessary to have something along the lines of proxy-ARP to make this work? Does existing software support proxy-ARP? Does anyone have suggestions addressing problems at any level which would alleviate some of the routing complexity? Notes We are new at this, and very well might have incorrect interpretations of the problems we face. By the same reasoning, we certainly are not aware of all the possible solutions to our problems. Any help would be appreciated. Thank you. Background The University of Iowa is in the process of establishing a campus network consisting of departmental LANs hung off of a broadband backbone. The departmental nets use various technologies including Ethernet/IEEE 802.3, proprietary token rings, and fiber. Some departments have multi-level networks (see figure below). Access to the broadband backbone is provided through ethernet bridges (Bridge IB/1 boxes), with each department having one IB/1. The IB/1 is a MAC-level bridge, so that a host on a baseband ethernet connected to an IB/1 in one department appears to be on the same physical cable as a host on a baseband ethernet connected to an IB/1 in another department. We have a mixture of machines and OSs, including VAXes running 4.2 & 4.3 BSD, VAXes running VMS, Encores running UMAX 4.2, Apollos, Suns, PCs, Primes, and IBMs running MVS; we also have a handful of Encore Annex terminal servers. The U of Iowa has been granted a class B Internet number of 128.255. We will soon activate a connection to MIDnet -> NSFnet -> world. Topology The current network topology (with only two departments connected) is: || Annex1 ---| || +------+ | ||---| IB/1 |-----(ethernet1)-----| || +------+ | || Encore1 ---| || |--- Encore2 (broadband) | || |--- Alliant || | +------+ || |-----(ethernet2)-----| IB/1 |---|| | +------+ || |--- VMSVax1 || +---------+ | ||---| Proteon |----> (MIDnet) |--- Apollo1 || +---------+ | --- / \ / \ (Apollo-ring) \ / \ / |--- BSDVax1 --- | | |--- BSDVax2 Apollo2 ----(ethernet3)----| |--- BSDVax3 We would like to assign a subnet number to each physical network. For example: network internet subnet ------- --------------- ethernet1 128.255.32 ethernet2 128.255.22 ethernet3 128.255.20 Apollo ring 128.255.21 Problems The presence of independently administered networks within the campus lends itself to a subnetting scheme, with each department receiving a block of subnet numbers from which to allocate numbers for the networks under the control of the department. We have encountered some routing problems which may be attributable to the coexistence of IP implementations which do support subnetting and those which do not. The broadband bridging makes ethernet1 and ethernet2 appear to be one physical network, so we end up with one network having more than one subnet number. This seems to cause problems with routing for the hosts which understand subnetting. They think the hosts on the other subnet should be on a different physical network and expect to have a gateway to get there. Since there is no gateway, they don't see a path to the other subnet. Disabling subnetting (by changing the netmask to 255.255.0.0 in the subnetting hosts) makes everybody think that the entire campus is one big physical (class B) network. This solves the problem just described, but it defeats the subnet-based routing required to access the networks which are actually subnetted, such as Apollo-ring and ethernet3. One proposed solution is to place a router between the IB/1 and the networks within each department. This has the advantage of making the broadband a separate subnet and providing the gateways (arguably) needed for subnet-based routing as described above. Disadvantages include the decrease in throughput (compared to just the bridge), the added cost of the router (or an additional ethernet interface for a host acting as a router), and the restriction on the protocols which may then cross the broadband. Furthermore, I am not convinced that such a configuration would solve all our problems without introducing new ones. Jay Ford Weeg Computing Center University of Iowa Iowa City, IA 52242 (319) 335-5555