nicolas@csi.forth.gr (Nicolas Chrissakis) (05/17/91)
Dear FDDI experts, We are planning to install 2 FDDI rings and we are looking for comments or experiences from users. Here are some questions: I have a host A connected to an ethernet segment. The ethernet segment is connected on an FDDI bridge and the bridge on an FDDI ring. I have a host B connected to an ethernet segment. The ethernet segment is connected on a FDDI ethernet router and the router on the ring. My question is: Will A talk to B? The bridge will be Dec compatible translation bridge. What can some one gain by having bridges mixed with routers? If routers are as fast as bridges why will some one use bridges? Do you have any experience with a router interfacing more than 2 ethernets and an FDDI? Did you notice or measure any performance degradation. I would like to have seperate measured filtering rates and forwarding rates for bridges and routers. Thank you for any pointers, I will summarize if I get any response. Regards Nicolas Chrissakis Office: +30 81 229368, 229302,221171,229346 Systems Analyst Fax : +30 81 229343, 229342 Foundation of Research Telex : 262389 CCI GR and Technology - Hellas E-mail: nicolas@csi.forth.gr Institute of Computer Science NICOLAS @ ARIADNE P.O.Box 1385, Heraklio, ariadne!nicolas Crete Greece 711 10
koning@koning.enet.dec.com (Paul Koning) (05/18/91)
|>Dear FDDI experts, |> |>We are planning to install 2 FDDI rings and we are looking for comments |>or experiences from users. |> |>Here are some questions: |> |>I have a host A connected to an ethernet segment. The ethernet segment is |>connected on an FDDI bridge and the bridge on an FDDI ring. I have a |>host B connected to an ethernet segment. The ethernet segment is connected |>on a FDDI ethernet router and the router on the ring. |> |>My question is: Will A talk to B? |> |>The bridge will be Dec compatible translation bridge. Yes. At the datalink level, A talks to the router's FDDI port; the router in turn forwards over its Ethernet port to B. Since you said that the bridge is a translating bridge, it will turn A's Ethernet packet into the corresponding FDDI packet, which the router will understand. This ONLY works with translating bridges -- not encapsulating bridges. |>... |>If routers are as fast as bridges why will some one use bridges? Not all protocols can be routed. Even if a protocol can be routed, it takes less (usually no) network management to set up bridges, while it always requires at least some network management to set up routers. Those are some reasons why you might select bridges. There are also reasons why you might prefer routers. You have to consider the strong and weak points of each and see which ones are important to your situation. The list of strong and weak points is subject to change over time as technology evolves, but today there is no "one best answer" and I would be surprised to see a single best answer soon if ever. |>... |>I would like to have seperate measured filtering rates and forwarding rates |>for bridges and routers. For the DEC bridge the simple answer is "as fast as the wire can possibly do it". The actual numbers are in the datasheets, but if you know the bitrates and minimum frame sizes you can compute them yourself... (Those are measured rates.) |> |>Thank you for any pointers, I will summarize if I get any response. |> |>Regards |>Nicolas Chrissakis Office: +30 81 229368, 229302,221171,229346 |>... paul
vjs@rhyolite.wpd.sgi.com (Vernon Schryver) (05/19/91)
In article <1779@ariadne.csi.forth.GR>, nicolas@csi.forth.gr (Nicolas Chrissakis) writes: > I have a host A connected to an ethernet segment. The ethernet segment is > connected on an FDDI bridge and the bridge on an FDDI ring. I have a > host B connected to an ethernet segment. The ethernet segment is connected > on a FDDI ethernet router and the router on the ring. > > My question is: Will A talk to B? > The bridge will be Dec compatible translation bridge. Ask DEC. I bet it will work, provided you get the IP network numbers right. > What can some one gain by having bridges mixed with routers? > If routers are as fast as bridges why will some one use bridges? It is impossible to build a "transparent FDDI to Ethernet" bridge. For one reason, the IP packet size on FDDI is 4352, which obviously cannot be "bridged" to ethernet. This means that any working FDDI<->ether "bridge" is capable of at least IP fragmentation. If you are bridging ether->FDDI->ether, this would not matter, but there are many fast servers that want to be on the dual ring itself, and with NFS/UDP/IP, cannot and should not avoid using 4KByte UDP/IP packets. Other reasons why DEC, for one, sells what some call "translucent bridges" involve differences in how data is encapsulated on ether and FDDI. This second problem tangles up older versions, at least, of Apple network protocols. The other side is that it takes fewer CPU cycles to bridge than to route a packet. It might take fewer cycles to IP fragment and then bridge than to do full routing. Some protocols are so stupid that bridging is the only reasonable solution. > Do you have any experience with a router interfacing more than 2 ethernets > and an FDDI? Did you notice or measure any performance degradation. > I would like to have seperate measured filtering rates and forwarding rates > for bridges and routers. Demand real measurements of real benchmarks, not just promises. There are sad rumors about current firmware or software for at least some current FDDI<->multiple-ether bridges. One vendor is making surprising claims that the MTU on FDDI is 1500, contrary to RFC-1188, perhaps because of performance problems. Vernon Schryver, vjs@sgi.com.
robelr@ucs.indiana.edu (Allen Robel) (05/24/91)
In article <1779@ariadne.csi.forth.GR> nicolas@csi.forth.gr (Nicolas Chrissakis) writes: > I have a host A connected to an ethernet segment. The ethernet segment is > connected on an FDDI bridge and the bridge on an FDDI ring. I have a > host B connected to an ethernet segment. The ethernet segment is connected > on a FDDI ethernet router and the router on the ring. > > My question is: Will A talk to B? > > The bridge will be Dec compatible translation bridge. If you are only concerned with protocols that a particular router routes, then there shouldn't be any problems if the bridge in front of A is indeed a *translation* bridge. If the router is a bridge/router however, and the bridge part is an encapsulation bridge, then host B's protocols that the router must *bridge* will be unintelligible to the translation bridge and it will not forward them to host A. In general, you can't mix encapsulation and translation bridges on an FDDI and you can't mix different vendor's encapsulation bridges and expect them to interoperate. regards, Allen Robel robelr@mythos.ucs.indiana.edu University Computing Services ROBELR@IUJADE.BITNET Network Research & Planning voice: (812)855-7171 Indiana University FAX: (812)855-8299
nicolas@csi.forth.gr (Nicolas Chrissakis) (05/25/91)
koning@koning.enet.dec.com (Paul Koning) writes: >|>Dear FDDI experts, >|> >|>We are planning to install 2 FDDI rings and we are looking for comments >|>or experiences from users. >|> >|>Here are some questions: >|> >|>I have a host A connected to an ethernet segment. The ethernet segment is >|>connected on an FDDI bridge and the bridge on an FDDI ring. I have a >|>host B connected to an ethernet segment. The ethernet segment is connected >|>on a FDDI ethernet router and the router on the ring. >|> >|>My question is: Will A talk to B? >|> >|>The bridge will be Dec compatible translation bridge. >Yes. At the datalink level, A talks to the router's FDDI port; the >router in turn forwards over its Ethernet port to B. Since you said >that the bridge is a translating bridge, it will turn A's Ethernet packet >into the corresponding FDDI packet, which the router will understand. >This ONLY works with translating bridges -- not encapsulating bridges. Dear Paul, Bridge vendors tell me that this works but router vendors tell me no it does not. The router acts like a router and there is no transilation function turned on. Have you SEEN this working. Where? So I contact them and find out my self because vendors answers confuse me more than enlighten me. Some router vendors say that only if the router has the ability to act as a translation bridge otherwise no. Some say if the protocol is TCP/IP then it will work for other protocols no. All bridge vendors say yes but most have not tested it. Anyone out there has installed FDDI bridges and FDDI routers (acting as routers only) and made them inoperate? >|>... >|>If routers are as fast as bridges why will some one use bridges? Are routers as fast as bridges? Any real experiences? Regards Nicolas Chrissakis Crete, Greece
nicolas@csi.forth.gr (Nicolas Chrissakis) (05/25/91)
robelr@ucs.indiana.edu (Allen Robel) writes: >In article <1779@ariadne.csi.forth.GR> nicolas@csi.forth.gr (Nicolas >Chrissakis) writes: >> I have a host A connected to an ethernet segment. The ethernet segment is >> connected on an FDDI bridge and the bridge on an FDDI ring. I have a >> host B connected to an ethernet segment. The ethernet segment is connected >> on a FDDI ethernet router and the router on the ring. >> >> My question is: Will A talk to B? >> >> The bridge will be Dec compatible translation bridge. >If you are only concerned with protocols that a particular >router routes, then there shouldn't be any problems if the >bridge in front of A is indeed a *translation* bridge. Have you seen this working? >If the router is a bridge/router however, and the >bridge part is an encapsulation bridge, then host B's >protocols that the router must *bridge* will be >unintelligible to the translation bridge and it will >not forward them to host A. The router is only a router and maybe in the future a transilation bridge . Encapsulation is out of the question seens it is not a standard. >In general, you can't mix encapsulation and translation >bridges on an FDDI and you can't mix different vendor's >encapsulation bridges and expect them to interoperate. I want to mix routers with bridges on the FDDI ring. Not routers with translation bridging capacity. Will they interoperate? Any sites have done that? >regards, Nicolas Chrissakis Office: +30 81 229368, 229302,221171,229346 Systems Analyst Fax : +30 81 229343, 229342 Foundation of Research Telex : 262389 CCI GR and Technology - Hellas E-mail: nicolas@csi.forth.gr Institute of Computer Science NICOLAS @ ARIADNE P.O.Box 1385, Heraklio, ariadne!nicolas Crete Greece 711 10
vjs@rhyolite.wpd.sgi.com (Vernon Schryver) (05/28/91)
In article <1793@ariadne.csi.forth.GR>, nicolas@csi.forth.gr (Nicolas Chrissakis) writes: > > Anyone out there has installed FDDI bridges and FDDI routers (acting as > routers only) and made them inoperate? Anyone who has found that such a combination does not work should get their money back. Any IP (as in TCP/IP, UDP/IP, or any-other/IP) router looks like a normal IP host to a bridge. Any "translating" or "translucent" bridge is invisible to any pair of IP hosts it connects. By definition the IP host on the FDDI ring cannot tell the other IP host is not also on the ring, and the ethernet IP host cannot tell that the other IP host is not also on the ethernet. I say again that there are rumors some bridge customers have found some bridges are not sufficently transparent. One brand is said to be unable to keep up while bridging the 4KByte NFS/UDP/IP packets generated by a brand of computer that I care about. Those of us who care about speed use up to the 4352 byte FDDI MTU defined in RFC-1188 and the familiar IP rules of local MTU for traffic on the LAN and 576 bytes other times. This requires FDDI-ether bridges to do IP-fragmenting. The possibly slow bridge vendor has not been named in this forum recently. I know no rumors about the performance of the bridges recently mentioned by name here, other than the statement of a very knowledgable employee that they run at media speed. Vernon Schryver, vjs@sgi.com Disclaimer: I'm of the router religion instead of the bridge faith.
koning@koning.enet.dec.com (Paul Koning) (05/29/91)
|>>|>I have a host A connected to an ethernet segment. The ethernet segment is |>>|>connected on an FDDI bridge and the bridge on an FDDI ring. I have a |>>|>host B connected to an ethernet segment. The ethernet segment is connected |>>|>on a FDDI ethernet router and the router on the ring. |>>|> |>>|>My question is: Will A talk to B? |>>|> |>>|>The bridge will be Dec compatible translation bridge. |> |>>Yes. At the datalink level, A talks to the router's FDDI port; the |>>router in turn forwards over its Ethernet port to B. Since you said |>>that the bridge is a translating bridge, it will turn A's Ethernet packet |>>into the corresponding FDDI packet, which the router will understand. |> |>>This ONLY works with translating bridges -- not encapsulating bridges. |> |>Dear Paul, |> |>Bridge vendors tell me that this works but router vendors tell me no it |>does not. The router acts like a router and there is no transilation |>function turned on. Have you SEEN this working. Where? So I contact them |>and find out my self because vendors answers confuse me more than enlighten me. |> |>Some router vendors say that only if the router has the ability to |>act as a translation bridge otherwise no. Some say if the protocol is TCP/IP |>then it will work for other protocols no. |> |>All bridge vendors say yes but most have not tested it. |> |>Anyone out there has installed FDDI bridges and FDDI routers (acting as |>routers only) and made them inoperate? Well, I didn't actually personally run the tests. But we make it our habit to claim something works only if we have actually tested it. And I definitely do know we ran a number of tests in this particular area. The final test is always your own... The set of potential bugs, whether our own or someone else's, is quite large. In spite of best effort of everyone involved there will always be strange cases (strange configurations, strange bugs, new bugs in previously working code, whatever) that cause trouble. But based on what I know we have done, I'm quite comfortable in saying that DEC bridges will do the right thing here. paul