CCIE R&S 400-101 V5.1 WRITTEN EXAM ESSENTIALS – Layer 3 Technologies

CCIE R&S 400-101 V5.1 WRITTEN EXAM ESSENTIALS – Layer 3 Technologies

time for exam


In a series of blog posts, I will go over each of the Cisco’s official blueprint sections for CCIE R&S 400-101 V5.1 written exam and call out the very essential topics and knowledge base that are must-know for passing the exam. Please note that all of our CCIE Written Exam Cert Study Guides include similar exam essentials at the end of each chapter to reinforce key concepts for our readers.

I hope that you find them useful!

  • Administrative distance is a measure of the trustworthiness of the source of the routing information. Administrative distance has only local significance, and is not advertised in routing updates. The smaller the administrative distance value, the more reliable the protocol
  • In order to control the advertising and processing of routes in routing updates, use the distribute-list command
  • When you are redistributing between two routing protocol eg. OSPF/EIGRP, if you don’t configure filters or administrative distance modification then suboptimal routing may occur
  • One BFD session is established per interface regardless of the actual number of routing protocols that are being used
  • Holddown is also a loop-prevention mechanism employed by distance vector routing protocol
  • Key chains consist of two necessary and two are optional components. The necessary components are key number and key string. Optionally it also include an accept-lifetime and a send-lifetime parameter
  • Under key chain we need to configure key number. Key number must be match on both side of router and should be active. If multiple key numbers are configured on a router, the router will select the lowest key ID number for outbound authentication however will accept any matching valid keys in the keychain upon receipt
  • OSPFv3 uses the IPsec secure to add authentication (using AH and/or ESP header) and encryption (using ESP header) to OSPFv3 packets.
  • Asynchronous BFD mode uses half as many packets for failure detection compared to demand mode and periodic hello packets do not necessitate using echo function
  • Bellman-ford algorithm is the basis of mechanism used by path vector protocols
  • Passive-interface command allows admins to exclude an interface from becoming a peer during routing protocol bring up
  • The BGP conditional advertisement feature uses the non-exist-map and the advertise-map keywords of the neighbor advertise-map command in order to track routes by the route prefix. If a route prefix is not present in output of the non-exist-map command, then the route specified by the advertise-map command is announced. This feature is useful for multihomed networks, in which some prefixes are advertised to one of the providers only if information from the other provider is not present (this indicates a failure in the peering session or partial reachability).

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