jgd@pollux.UUCP (Dr. James George Dunham) (07/29/87)
We are beginning to create local ethernet networks and are considering connecting them together. We have four seperate groups and each group is afraid that if we simply hook them all together that the ethernet will become overloaded. I have heard that there are bridges that can be used to connect ethernets togethers which keep local traffic local and pass other messages over the bridge. What is such a bridge called and what vendors make reliable products. Is there some vendor who makes a single bridge that will connect 4 ethernets together in one box? Any help would be appreciated. -Jim Dunham jgd@pollux
ron@topaz.rutgers.edu (Ron Natalie) (08/03/87)
There are several ways to interconnect two ETHERNET cable segments.
REPEATER:
The first is via a repeater. A repeater is theoretically the fastest
and easiest. In essentially transfers all the bits in real time from
one cable to the other. The distance requirements remain and no packet
filtering occurs. The ETHERNET specification permits only two repeaters
in the path between any two stations. No cycles are permitted in the
topology. An example is the DEC DEREP.
DATA LINK BRIDGE:
A data link bridge copies an entire packet into it's memory and then
repeats it on the other segment. The bridge may learn from examining
traffic which stations are on which segment and avoid passing datagrams
for local traffic to the other segment. However, broadcast and multicast
datagrams must be sent accross all segments. Since the bridge acts as
a station rather than a repeater the cable length and maximum number
requirements are removed, however, no cycles may be present in the
topology. Examples of data link bridges are the DEC LANBridge 100,
the Bridge Communications IB/2, and the Ungermann/Bass DL1.
PROTOCOL ROUTERS:
Routers or gateways are similar to the data link bridges in that they
read in the entire packet and resend it on the other segment but they
actually examine the protocol dependent data in the packet to decide
where and when to forward the packets. These routers can function to
the limit of the protocol and the topology can get quite complex with
cycles and redundant paths. The disadvantage is that the router must
know about every protocol it intends to route. Some routers can deal
with more than one protocol, many only one. Each segment must be
interconnected with routers for each protocol in use. IP routers
include CISCO and Proteon, DEC also sells DECNET routers.
-Rongeoffb@trwind.TRW.COM (G. Geoffrey Baehr) (08/05/87)
In article <323@pollux.UUCP> jgd@pollux.UUCP (Dr. James George Dunham) writes: > >What is such a bridge called and what vendors make reliable products. Is there >some vendor who makes a single bridge that will connect 4 ethernets together in >one box? Any help would be appreciated. > -Jim Dunham > jgd@pollux We have used the DEC LanBridge 100 with good results. Our configuration includes multiple Ethernets, separated by bridges from a "backbone" segment. The backbone is used for a preferred link between computer center hosts with the bridges isolating traffic from hosts on other segments. The only hosts on the other segments connected by the bridges are those hosts who cannot understand IP subnet addressing and therefore require "direct" connection to the network on which they send their traffic; all other Ethernets are connected through Cisco and Proteon IP routers/gateways to the backbone. We separated SUN diskless traffic with a DEC Lanbridge from other traffic on a local Ethernet, the diskless traffic was chewing up net capacity. With the SUN disk server on the same side of the bridge as the diskless nodes, the traffic is almost non-existant to the rest of the world. Also, we have tried Bridge GS/3's as remote ( via 56kb ) bridges between buildings successfully. Summary: Dec Lanbridge - ~ $8k, high performance, inscrutable Bridge Management System methodology. MAC level bridge. Two Ethernets only. option for remote bridge via Fiber. Hmmm, now about that March 1988 100mbit Fiber net DEC will introduce .... Shades of FDDI ! We have pushed it above 4000 pkts /sec at the MAC level. Cisco AGS1-E - IP router, high performance ( >1200 pkts/sec net to net). Can be made into a gateway easily (buy interface boards !) Very reliable, high quality code/product. About $9k. Also can be remote bridge, via serial lines with serial intf board. If operated as remote bridge via serial lines, only device available which does load balancing across multiple serial lines. Can have up to 5 Ethernets installed in one box. Bridge GS/3 - IP router, can be remote bridge via serial lines. The usual bridge product,it works fine and does not break. About $9k (may be wrong here ). Proteon p4200 - Very similar to Cisco box, of course has option for ProNET 80 mbit or 10mbit interfaces in addition to Ethernet. Speed tops out at ~ 1000 pkts sec net to net. Can have more than 3 Ethernets installed (4 ? 5 ?) depends on card cage etc. Can handle XNS, DecNET protocols also. Before I receive flames about my use of terminology, notice that the only MAC level bridge is the DEC Lanbridge, while all others are IP routers (is this a bridge !). Hope this helps . -- Geoffrey Baehr "Book 'em, Dano !" TRW Information Networks Division 23800 Hawthorne Blvd, Torrance CA 90505 ATT: 1 213.373.9161 (+10db Noise/Signal Ratio Usually) ARPA: geoffb@trwind.TRW.COM USENET: ..trwrb!trwind!geoffb