May
05
This weekend while working on content updates for CCIE R&S Version 5, I ran into an interesting problem.  In order to test some nuances of routing protocol updates and packet fragmentation, I was trying to generate BGP UPDATE messages that would exceed the transit MTU.  To do this I manually created a bunch of Loopback interfaces and did a redistribute connected into BGP.  When I looked at the packet capture details, I started to realize how many routes I'd actually need in order to fill up the... Read More
May
02
A voice lab rack usually utilizes dedicated piece of hardware to simulate PSTN switch. Commonly, you can find a Cisco router in this role, with a number of E1/T1 cards set to emulate ISDN network side. It perfectly suits the function, switching ISDN connections between the endpoints. Additionally, it is often required to have an “independent” PSTN phone connected to the PSTN switch, in order to represent “outside” dialing patterns - such as 911, 999, 411 1-800/900 numbers. The most obvious way... Read More
Jan
28
Let's say you get a bunch of inexpensive (but a bit outdated) routers (36XX or 72Xx) and some really nice (maybe not so cheap) Cisco switches (e.g. 3550/3560) and you would like to provide a VPLS-like service to your customers. Since VPLS is a service available only on more powerful Cisco platforms, we have to figure a way to simulate Multipoint Ethernet L2 VPN over a packet switching network (PSN) using only "convenient" point-to-point L2 VPN services. Read More

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