Category Archives: Layer 3

The Route to Null0: How and Why it is There

So there you are looking over your routing table when you notice an entry that points to Null0 that leaves you wondering how it got there and what is represents. All you did was create a summary (or an aggregate in BGP-speak!) and it auto-magically appeared…but why?
In this supplemental video tutorial for the AACC CTS267 TSHOOT course, we take a deep dive look at using ‘manual summarization’ with BGP to create our own Null0 route entry and then dive into the aggregate-address command under the BGP global configuration section. In both cases we get the summary/aggregate RIB entry to Null0 to protect us against the perilous routing loop! Enjoy!
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