dunigan@MSR.EPM.ORNL.GOV (Tom Dunigan 576-2522) (10/19/88)
>We have a multi-segment ethernet connected by supposedly transparent >filtering bridges. Recently we were unable to reach the lone node, a >Sun4/260 on the far side of a DEC LANBRIDGE 100. Upon investigation we >found that the problem was due to the DEC bridge filtering out broadcast >packets, thus preventing arp requests from reaching the Sun4. If the >Sun4's physical ethernet address was entered by hand there was no problem. >Monitoring the Sun4 side of the bridge revealed a bunch of packets that >the network analyser called "Lanbridge Management Packets". Toggling >power to the Lanbridge fixed things. Newer models of DEC's LANBRIDGE 100 apparently will "learn" the broadcast address if there is a sick engine on the Ether that emits packets with a source addresss of all 1's (broadcast). Having stashed the broadcast address in its filter table, the LANBRIDGE will no longer pass broadcast packets, so engines behind the LANBRIDGE that require broadcast (e.g. ARP) no longer work! (We had a sick microvax 2000 that would issue the bogus packets with broadcast source address occasionally and gum up three or four of our LAN100s) Older LAN 100s survive. I think DEC may have a ROM patch or some such, but the only recourse is to restart the LAN100 (can be done remotely however) AND, of course, see if you can "catch" the engine that is sending packets with a broadcast source address -- a challenge!