Xref: utzoo comp.dcom.sys.cisco:984 comp.protocols.appletalk:5560
Newsgroups: comp.dcom.sys.cisco,comp.protocols.appletalk
Path: utzoo!utgpu!cunews!bnrgate!bwdls61!bnr.ca!bschmidt
From: bschmidt@bnr.ca (Ben Schmidt (BNR))
Subject: Re: Problem with ciscos and Public Folder
Message-ID: <1991Mar25.212405.28514@bwdls61.bnr.ca>
Sender: usenet@bwdls61.bnr.ca (Use Net)
Organization: Bell-Northern Research
References: <9293@castle.ed.ac.uk>
Date: Mon, 25 Mar 1991 21:24:05 GMT

Sam, I didn't see your original posting, but I wonder if there might be 
another source for incorrect DDP checksums in packets from Public Folder.

Certain LocalTalk-to-Ethernet routers have an intermittent problem whereby 
they sometimes incorrectly calculate the DDP checksum, and place otherwise 
perfectly formed packets onto Ethernet with invalid DDP checksums.  
Packets which are thus mangled by them on their way from a LocalTalk Mac
to a cisco on Ethernet, are thus correctly discarded by the cisco.

What cisco has done to provide a "work-around" to this problem, is to 
provide a way to optionally just ignore DDP checksums.  (If the packet is 
*really* incorrectly formed, a higher-level protocol will then have to detect
this.) 

Is one of your Public Folder users in the above example a 
LocalTalk-to-Ethernet gateway?  Which kind are you using?

Ben Schmidt       Information Technology,   Bell-Northern Research
bschmidt@bnr.ca   FAX:(613) 763-3283  /* My opinions, not BNR's */