tcp-ip@ucbvax.ARPA (06/25/85)
From: "J. Noel Chiappa" <JNC@MIT-XX.ARPA> We have recently noticed a problem with some 4.2 UNIX systems when a new gateway (which was a better route to large sections of the Internet) was installed on a network here. For most destinations, the old gateways sent ICMP Redirects to the new one. This was fine, except that apparently the 4.2 system had their routing tables fill up with the Redirect information as they tried to contact new sites. Apparently, when the tables filled up, they were unable to accept new entries, because the machines became unreachable from certain (random) destinations. I'm not sure why this happened, since the traffic should still have flowed (albeit generating floods of Redirects by taking a non-optimal path). Does this scenario make sense to any 4.2 network wizards? Certainly, it was something to do with routing, because when we went into the rc.local file and changed the 'default' route (i.e. in '/etc/route add') to be through the new gateway, and rebooted the machines, things started working. I'm pretty annoyed that all the 4.2 systems had to be hand tweaked when a new gateway started up. I guess this points up a general problem with IP layers, which is unfortunately not mentioned in Clark's 'IP Implementation guide'. You should time out old entries in the routing cache, and if you have a fixed size table and it fills up, you should be prepared to evict someone. Noel -------
tcp-ip@ucbvax.ARPA (06/25/85)
From: Bob Walsh <walsh@BBN-LABS-B.ARPA> The Berkeley 4.2 TCP does not reroute current connections when it receives an ICMP redirect. As a result, such a machine can receive a lot of redirects for the duration of those current connections. The UNIX host does not have a fixed size routing table; the table (at least in the kernel, I'm not sure about the routing demon) grows as needed and is implemented by an open chained hash table. This, and some other problems with the distributed 4.2 TCP are described in a paper I gave at the Salt Lake City USENIX in '84. bob walsh
tcp-ip@ucbvax.ARPA (06/30/85)
From: CERF@USC-ISI.ARPA Bob W - Are the problems acknowledged to be problems by our Berkeley friends and are they being resolved? I was in England last week at ONLINE 85 and found a surprising number of booths in the exhibition advertising LANs of all types and TCP/IP; mostly based on the BSD 4.2 version. Since it is that version which is getting the most play and exposure in Europe, it will prove important for us to clean up any serious bugs remaining. Vint