Network with 15 bridges – certain bridges are falling over regularly

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Networking Equipment
Hi, I have a network with 450 PCs in total on the same broadcast domain. About 200 of these PCs are located on 15 remote sites that have been bridged into the main network. Eleven of these bridged are working fine, and the links stay up 99% of the time. BUT, the other four links, which are all using Blackbox MDS-921AE network extenders working over telephone line in bridge mode, crash every few hours. After a reboot they work fine again for a few more hours then crash again. I have tried them with different telephone lines, different configs (suggested by blackbox), everything. The only thing that hasnt changed is the fact that they are all conected to the same large network. I have these devices on many other (smaller) networks and they work fine, so it's not a problem with the device either. Is it possible that the memory of the bridge devices are filling up with MAC address tables and crashing? This is baffling, any ideas???? regards, Jonathan
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I haven’t touched a BlackBox box in quite some years, but if memory serves, there’s not much good to say about them.

I’m sorry that I don’t have much to offer other than my advice to stop bridging a network that size across phone lines.

If you’re stuck with this design because your boss implemented it and you can’t afford to make him/her look bad, then you have my sympathy, but certainly not my envy.

If you go to routers, your performance overall should pick up significantly.

If it’s a political difficulty, perhaps (I don’t know your employer’s history) you could bring up the point that the network has grown beyond the ability of a bridged network.

Even Microsoft finally dropped their bridged network 5-10 years ago.

Please go to routing! Please go to routing!

This is a recording!

Bob

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  • DrillO
    Hi Jonathan.... Sorry to tell you this, but Bob's right. I know this is a difficult thing to do, but the network really needs to be on routers. A tough thing to tell the boss..... Also, don't discount the fact that these things can screw up and breakdown.....have you tried switching one of the troubled devices with a known good one? Good luck, Paul
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  • JonathanAnon
    Hi guys thanks for your help. There is politics, but there's also the fact that the router should not be crashing - not matter what the configuration. I would subnet right now if it were up to me, but it's up to management (and accounts :-) ). Regarding swapping out the devices, we have 4 links (8 routers) and all are displaying the same characteristics, so it's definitely an issue with the device itself. But the manufacturers say they have the router on loads of sites and they dont fail.
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  • DrillO
    Hi Jonathan..... First, let me begin by saying that I know exactly what you mean. The toughest job we face other than supporting end users is educating Management. "I have "X" number of degrees, I know what is going on". I have heard it all. The truth is, they don't want to look like they don't know what they are talking about, so they fake it. I have found that me best defence is to bring in an outsider to say the same things that I have said and then things get done. It stings like crazy, but it works. As far as the vendour is concerned, I can't begin to tell you how many times I've heard that one. Everything from RAM to modems to routers to firewall appliances, to inventory security systems. In every case, when the faulty equipement was replaced by a "brand name" piece, success was observed. My mantra for such occasions is "just because you haven't seen it before, doesn't mean that it isn't happening to me". Words to live by in this business. Does the vendour have any firmware or software updates? A shot in the dark, but possible. Best of luck to you. Paul
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  • JonathanAnon
    Hi Paul, Firware was the first thing I tried, bit worried that the latest update was from three years ago, but it's been confirmed as the latest firware by a number of people. I like the mantra. I've just invented my own. It goes like "Either you find me a solution for the problem, or I'm taking every one of these damned devices out of the network and shipping them straight back to you". I need them to at least tell me WHY the device is crashing - at least then I can have a reason to subnet, but they keep giving me suggestions to try to fix it, which dont work. But dont worry, I'll get there in the end.
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  • TIMWATSON
    IS LATENCY A FACTOR ? WHEN IT COMES TO DEALING WITH HIGHER (?) UPs (MANAGEMENT..., IF THATS THE CORRECT TERM), ASK THEM IF IT IS WORTH THE TIME (READ MONEY) THAT IS BEING WASTED TROUBLESHOOTING, V. THE COST OF DOING THE RIGHT THING. THE OTHER REPLIES PUT IT NICELY, I AM UNABLE TO UNGRIT MY OWN TEETH, IN THE FACE OF BAD DECSIONS, BY THOSE WHO SHOULD HAVE LEARNED GOOD MANAGEMENT IN SCHOOLS OF 'HIGHER LEARNING'. TIM.
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  • DrillO
    Hi Jonathan... These types of issues with vendours drive me nuts too.....why not just admit there is a problem and go forward. I'm with you, I would be very concerned about three year old firmware updates. I have seen these products in the past and never had the guts to try any of them...lucky me I guess. I hope that you keep us posted on your progress.... Best, Paul
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  • JonathanAnon
    UPDATE Hey guys here's the update. The devices are still crashing, we have spoken to blackbox on a number of occassions with no success. They are saying to me the following - "We have these devices all over the world and only on your network are they behaving like this". But they cannot provide a reason why the device is crashing. My point of view is the following: The network is a mess through years of neglect and taking the easy option of bridging all remote sites, instead of thinking about it and subnetting the network properly. BUT, my main point is that blackbox should be able to provide me with a reason why their device is crashing. The problem definitely lies with their device, because when any particular link is down, a reboot of the COE end bridge brings the link back up. I was saying before that I thought it was a traffic issue, so I got a person on one of the remote sites to run Ethereal (what a brilliant program) and take a packet capture. Here's what I found: An average of 340 packets on the network per second. An average of 240 ARP broadcasts per second, all from about six or seven different IP addresses (bridges, I assume). An average of 50 IPX SAP (Novell Service Advertisement protocol) broadcasts per second. Sound like it's been flooded with broadcasts. I guess I've found the source of the problem, but I would appreciate your opinions anyway. Thanks once again for all of your help.
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  • Sonotsky
    Boy, it's been a LOOOONG time since I had to use a bridge, so some of my information may be inaccurate. Please get a grain of salt ready.... IIRC, bridges have next to no RAM/cache for storing packets, they would typically just direct-forward the packet from one interface to the other. If there are a flood of packets coming into the bridge, I suppose it's poossible that eventually the memory fills to capacity, and overflows, causing it to crash. In theory, bridges should only be used to segregate a small number of network hosts into separate broadcast domains. It sounds to my rusty ear that you have too many hosts, with too many bridges, for a bridging solution to work efficiently. IMHO, you need to start replacing some of the busier bridges with routers. Cheers
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  • ItDefPat1
    Everyone is right about the bridges. Several reasons that bridges went away was that they passed everything and couldn't deal with a lot it. They could kill the core network. And then switched came around - which turned them into the network "Model T". And then cam layer 3 switching/routing, which turned them into the equivalent of a horse-drawn carriage. then came switches . . . dinosaurs (switches are just very fast IP bridges). Bridges are like three generations past. anyways, sorry about the history lesson. Routers would be good; You could probably get some low-end routers like cisco 2621 (or other vendor equivalent) that would do great. There are also some remote VPN appliances that would do great. Actually, there are probably a few other types of similar appliances, even some firewalls, that would be good here. Do a quick search on Ebay for a 26xx. I've seen some there for a few hundred bucks each (but you might not get service, warranty, etc.). There are a lot of vendors selling remote office routers with a few i/f on inside, 1 i/f on outside. Most are only a few hundred dollars. You could sell the VPN or firewall as a necessity for protecting the data. You might even get better performance. manageability and/or security. Oh, I don't buy the vendor "we have a million of these and you are the only one with a problem". I'd tell them if they don't fix it, Cisco (or 3com, or nortel, or. . . ) would love to.
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