Path: utzoo!attcan!uunet!husc6!think!ames!pasteur!ucbvax!HOGG.CC.UOREGON.EDU!jqj From: jqj@HOGG.CC.UOREGON.EDU Newsgroups: comp.protocols.tcp-ip Subject: Re: Brouters Message-ID: <8811232043.AA04821@hogg.cc.uoregon.edu> Date: 23 Nov 88 20:43:42 GMT Sender: daemon@ucbvax.BERKELEY.EDU Organization: The Internet Lines: 41 "Brouter" is not a well defined term. To a first approximation, it means some combination of MAC-level bridge and network-level router *functionality* in the same box. There are lots of possible schemes for mixing these two beasts, and all the schemes have some claim to the term "brouter". The industry hasn't made up its mind. Presumably, a "bridge" is a MAC layer product (more specifically an 802.3 product) that forwards packets, usually with filtering based on destination address. Most bridges these days support some spanning tree algorithm that takes a complex bridged topology and turns off enough forwarders to create a simple tree. Some remote bridges support parallel ptp links between two bridges, allowing limited load sharing (e.g. 2 56Kb circuits connecting a single pair of bridges and giving near-128Kb thruput). Some remote bridges allow filtering based on packet characteristics as well (e.g. type field). On of the first uses of the term "brouter" was in the product literature for the RAD "Remote Ethernet Bridge". RAD's bridge is a remote bridge that operates totally at the MAC layer connecting 802.3 segments (Ethernet, Starlan, etc.) but that allows multiple simultaneous paths between pieces with load balancing, loops, etc. Note that this is much more complex than redundant ptp links between a pair of bridges, but that it does not require a network-layer router. The cisco Systems "HyBridge" has also been called a "brouter". That product, like a similar product from Wellfleet, combines bridging and protocol-dependent routing in one box. One can route some protocols (as defined by the Ethernet type field) and not simply forward their packets, while bridging all other packets. Note that most protocol stacks involve special handling of several type fields (e.g. TCP/IP requires coordinated handling of IP and ARP packets, which I suspect means that if you route IP you can't bridge Chaos). Other vendors use "brouter" for mostly-MAC bridges that connect disparate media, e.g. Ethernet to 802.3+802.2 or 802.3 to 802.4, or for token ring "bridges" which should be quite a bit smarter than 802.3 bridges. See the January 1988 IEEE Networks magazine for more information. Note also that "bridge" is used in the Novell and LocalTalk worlds for what we TCP/IP types call a "gateway," i.e. a router.