[TUHS] New patch for 2.11BSD on PDP-11: network DEUNA does not respond to ethernet broadcasts ... is SimH bug

Jörg Hoppe j_hoppe at t-online.de
Sun Aug 16 16:31:15 AEST 2009

False alert!
A few people reproduced this bug under SimH, but it is not present on
real PDP-11/44 or '84. So it must be a bug in SimH's DEUNA.

Jörg Hoppe schrieb:
> I found and patched an error in the network driver for UNIBUS ethernet 
> controllers
> DEUNA/DELUA in 2.11BSD for PDP-11.
> Error reproduction:
> --------------------------
> Build 2.11 BSD with ethernet/TCP/IP support over DEUNA/DELUA controller.
> Configure the network.
> Boot up 2.11 BSD, switch to multiuser mode.
> Wait for 15 Minutes, until all ARP caches in the system are aged out.
> Try to ping the PDP-11 from a network node, which is NOT listed 
> anywhere in the
> PDP-11's network configuration files. Ping will fail.
> Important: since arp requests are also arp responses, do not ping the 
> test node from your
> PDP-11. The test node may not be contacted by the PDP-11!
> Before testing, verify on the test node that the PDP-11 is unkown. The 
> command "arp -a" must not display the PDP-11 yet.
> You can clean the test node's arp cache by executing "arp -d *".
> This can also be reproduced in SimH,
> for example with the installation downloadable at
> /www.ak6dn.com/PDP-11/2.11BSD/
> Error explanation:
> --------------------
> The DEUNA/DELUA does not answer ARP requests, so other network nodes
> can not get the PDP-11's ethernet MACID and can not send anything to it.
> The DEUNA/DELUA does not answer ARP because it does not receive 
> ethernet broadcast packets
> (those addressed to MACID FF:FF:FF:FF:FF:FF).
> And it is not receiving broadcasts, because the DELUA driver in 
> /sys/pdpif/if_de.c
> did not set up the DELUA's packet filter to receive FF:FF:FF:FF:FF:FF.
> Error patch
> ---------------
> In /sys/pdpif/if_de.c , the DEUNA/DELUA must be programmed to receive 
> ethernet broadcast pakets.
> The good way would be to explicitly add MACID FF:FF:FF:FF:FF:FF to the 
> filter.
> The fast and dirty way was to program the DELUA to receive ALL 
> multicasts,
> by setting one more bit in the mode register:
> In /sys/pdpif/if_de.c, change line
>        ds->ds_pcbb.pcbb2 = MOD_TPAD|MOD_HDX;
> into
>        ds->ds_pcbb.pcbb2 = MOD_TPAD|MOD_HDX|MOD_ENAL;
> Status
> -----------------------------
> This is a major bug, as it prevents the PDP-11 under 2.11BSD to run as 
> a server.
> It's hard to believe that it is still there.
> In the typical quick "boot up and ping someone" test, it is almost 
> invisible.
> The bug is not present in the DELQA driver "if_qe.c".
> I did posted already to alt.sys.pdp11 newsgroup.
> The error has been acknowledeged by one other user.
> In the BSD patch archive, this bug seems not to be addressed.
> regards
> Joerg Hoppe
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