Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.3 alpha 4/15/85; site ucbvax.ARPA Path: utzoo!watmath!clyde!cbosgd!ihnp4!ucbvax!tcp-ip From: tcp-ip@ucbvax.ARPA Newsgroups: fa.tcp-ip Subject: Apparent problem with ICMP Redirects on 4.2 systems Message-ID: <8448@ucbvax.ARPA> Date: Mon, 24-Jun-85 19:15:40 EDT Article-I.D.: ucbvax.8448 Posted: Mon Jun 24 19:15:40 1985 Date-Received: Tue, 25-Jun-85 03:46:06 EDT Sender: daemon@ucbvax.ARPA Organization: University of California at Berkeley Lines: 29 From: "J. Noel Chiappa"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 -------