CCIE RS – Written – Network Principles – Evaluate Proposed Changes to a network

Evaluate Proposed Changes to a network

Before making changes to the network you’ll want to know what the current state is. Capture appropriate show output depending on the type of change being made. Ensure network diagrams are up to date (physical and logical). Backup configurations. 

If possible test the changes in a lab environment that directly mimics the production network. Write out a plan for the flow of changes and validations after the change is made to ensure the expected result occurred.

Changes to routing protocol parameters

Each routing protocol has a set of parameters can be changed depending on a technical or business requirement. The parameters for each routing protocol will be gone into in depth in future blog posts.

Before making the changes, check the routing table (show route), and check specifics about the routing protocol your about to change.

Migrate parts of a network to IPv6

IPv4 and IPv6 can exist in the network at the same time (as long as the device supports IPv6). IPv6 has it’s own routing table and if a device has both IPv4 and IPv6 addressing, the IPv6 address will be preferred.

  • Dual Stack
    • Requires infrastructure to support IPv4 and IPv6
    • Applications choose between IPv4 and IPv6 based on response to DNS requests
  • Tunneling
    • Encapsulates IPv6 traffic within an IPv4 packet
    • Used between IPv6 sites over an IPv4 backbone
    • Tunneling Techniques
      • ISATAP
      • Teredo
      • 6PE
      • 6VPE
      • mGRE v6 over v4
    • Manual or automatically configured
  • Translation
    • NAT between v4 to v6, v6 to v4

Details about configurations will be in future blog posts 

Routing protocol migration

Moving between routing protocols can be done in a couple ways

  1. Modify administrative distance
  2. Redistribution 

Multiple routing protocols can be running at the same time, but only 1 route to the destination will be put into the routing table (disregarding multiple paths). Administrative distance is one of the criteria that says which routing protocol is more trustworthy than another.

Redistribution will be explained in future blog posts

Adding multicast support

To add IPv4 multicast support to a router you’ll need to configure multicast routing and enable PIM on interfaces that will be participating in the multicast routing path. 


Configuration of multicast will be covered in future blog posts

Migrate spanning tree protocol

Specifics of the different STP types will be explained in future blog posts.

PVST+ to Rapid-PVST+

  • Rapid uses the same BPDU format as PVST+
  • BackboneFast and UplinkFast get disabled when Rapid-PVST+ is configured
  • Start at the access switches and work your way up to the core
  • Clean up configuration
  • Do these changes during a maintenance window because a disruption will occur
  • Verify changes and make sure STP is behaving the way you intended

Rapid-PVST+ to MST

  • Identify p2p and edge ports (portfast)
  • Map vlans to instances
  • Place as many switches as possible into a single region
  • Start at core and work your way to the access

Evaluate impact of new traffic on existing QoS design

Before adding more traffic to an existing QOS queue you’ll want to know the behavior of the traffic and how it needs to be treated. Is the traffic UDP or TCP based? Is the existing queue policed or shaped? Is bandwidth over utilized? 

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