Return-Path: william@bourbon.usc.edu Delivery-Date: Sun Oct 5 20:46:56 2008 X-Spam-Checker-Version: SpamAssassin 3.2.3 (2007-08-08) on merlot.usc.edu X-Spam-Level: X-Spam-Status: No, score=-2.3 required=5.0 tests=AWL,BAYES_00 autolearn=ham version=3.2.3 Received: from bourbon.usc.edu (bourbon.usc.edu [128.125.9.75]) by merlot.usc.edu (8.14.1/8.14.1) with ESMTP id m963ktwq015685 for ; Sun, 5 Oct 2008 20:46:55 -0700 Received: from bourbon.usc.edu (localhost.localdomain [127.0.0.1]) by bourbon.usc.edu (8.14.2/8.14.1) with ESMTP id m963qapL010581 for ; Sun, 5 Oct 2008 20:52:36 -0700 Message-Id: <200810060352.m963qapL010581@bourbon.usc.edu> To: cs551@merlot.usc.edu Subject: Re: E-BGP vs. I-BGP Date: Sun, 05 Oct 2008 20:52:36 -0700 From: Bill Cheng Someone wrote: > I was looking at the lecture 11 slides and was confused about the > distinction made between slides 63 amd 65 about being on the same network vs > different networks. Why is that distinction important? Good observation! Actually, I've added the first bullet on page 63 and the first bullet on page 65 after our lecture! On page 63, the two endpoints of the TCP connection are on the same network. When the link breaks, there is no way for a packet to reach from one endpoint to another due to shortest path routing! This is kind of a suttle point. If you imagine another router in the network, in order for it to reach the 138.39.1.1/30 network, it can only choose *one way* to deliver a packet. On page 63, the two endpoints of the TCP connection are on different networks. Then we don't have the problem described in the paragraph above. Again, this is a bit suttle, so you have to look pretty hard to see why this is the case! -- Bill Cheng // bill.cheng@usc.edu