braden@VENERA.ISI.EDU (03/17/88)
There is a bridge that is about 70% of a router. It is called REB (Remote Ethernet Bridge). The designer has taken a small number of the fields in the IP header and has done a similar implementation at level II. For example, REB can close loops. I can assign a weight to each line (i.e. one line is 9.6kb, another is T1, another is X.25, and another should hardly ever be used) and based on the weight and the network load, the REB will determine the routing the packet should take. In addition, it has implemented a TTL type of field so that packets that loop around between REBs get removed. You can configure in each REB what the maximum TTL should be and each outgoing packet gets assigned that number. As the packet passes thru other REBs, the number is decremented. When it hits zero, the packet is thrown away. There are many other functions that was designed via 802.3 D - Managament specs. What it cannot do is ARP or ICMP but if you are looking for a bridge replacement, you should seriously evaluate the RAD REB. Hank I would describe this as a level-2 router, essentially an IMP for Ethernets. Seems like a reasonable concept. The bridge guys work very hard to keep the overhead low enough to handle back-to-back Ethernet packets; can the REB guys do as well, with the extra protocol processing? Bob Braden
satz@CLASH.CISCO.COM (03/17/88)
>> In addition, it has implemented a TTL type >> of field so that packets that loop around between REBs get >> removed. You can configure in each REB what the maximum TTL >> should be and each outgoing packet gets assigned that number. >> As the packet passes thru other REBs, the number is decremented. >> When it hits zero, the packet is thrown away. If it is acting as a router it should use the TTL field in the IP header. It seems, from your message, that another field may be used possibly from a REB-REB protocol.
HANK@BARILVM.BITNET (Henry Nussbacher) (03/20/88)
>Seems like a reasonable concept. The bridge guys work very hard to >keep the overhead low enough to handle back-to-back Ethernet packets; >can the REB guys do as well, with the extra protocol processing? The stated rate is 2500 packets per second (forwarding). Falls between a bridge (10,000 pps) and a router (1000 pps). Hank
HANK@BARILVM.BITNET (Henry Nussbacher) (03/20/88)
>If it is acting as a router it should use the TTL field in the IP >header. It seems, from your message, that another field may be used >possibly from a REB-REB protocol. It is not acting as a router. It is a bridge which has adopted "router concepts" at the level II. It does not look at the protocol so it can't possibly use TTL. It uses its own concept of stopping packets from travelling in the network forever, all within the definition of 803.2 D - Management specs. Hank