ly if other applications are required such as address learning based on multiple virtual private networks (VPNs) spanning more than one port. 6. Cascade had originally done this on their ATM switches. Then Ascend acquired Cascade, but was eventually acquired by Lucent. 7. The algorithm is described in depth in the book "Interconnections, 2nd Edition," by Radia Perlman, Addison-Wesley 2000. Downloaded from Digital Engineering Library McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. SYSTEMS ENGINEERING ISSUES SYSTEMS ENGINEERING ISSUES 353 Depending on the number and size of the VPNs as well as on the security policies in place, different approaches can be taken. It could be argued that the entire chassis is the customer's SO it is safe to leave everything on the software to do and wherever it could run. Others may say that in a specific customer context (a sensitive government agency), the MSR software cannot be allowed to propagate addresses of new VPN members to members of other VPNs that share physical ports. On the other hand, even if this is not the case, the address learning is a minor computational chore that can be seen as a minute nuisance when the network is operating at steady state. Therefore, it can always be safely sent to the system CPU. The counterargument states that the problem is acute precisely when the net- work starts up with many users at the same time. This dilemma cannot be avoided, SO for our purposes we will assume that the designer can live with the idea that his or her prospective users will be com- ing to work at random times during the day; therefore, this is not an issue. However, this shows how seemingly mundane events can drastically affect the design of such a complex product. In terms of network management, an approach such as using the Simple Network Management Protocol (SNMP) will be required. Locally produced statistics memory should be accessible by