1.1.b Flash Cards

Here are the 1.1.b flash cards I created, I have uploaded the Anki package, and then I will be pasting them as text here if you do not use Anki.

Anki Package:
https://upw.io/u2/&1.1.b_CEF_v_1.1_(2).apkg

Flash cards in text:

 

What does CEF stand for? Cisco Express Forwarding

What does RIB stand for? Routing information base

What does FIB stand for? Forwarding information Base

What are the 3 methods for routing packets through a router, list in order of slowest to fastest. Process switching, Fast Switching, CEF switching

What part of the packet does fast switching cache? Fast switching caches the destination address.

How did fast switching build its route cache? Fast switching built its route cache by process switching the first packet in a flow (destination IP) and then storing the results in a cache for subsequent packets.

What load balancing was available for process switching? Only per packet load balancing was available for process switching.

What version of IOS was fast switching removed?  12.1

What two ways is CEF implemented? CEF can be implemented either in software (lower end ISR) or in hardware via TCAM in higher end routers or L3 switches.

is CEF turned on by default? Yes

What commands would you use to turn CEF back on for both IPv4 and IPv6?
conf t
ip cef
ipv6 unicast-routing
ipv6 cef

What command would you use to disable CEF in a per interface basis? no ip route-cache cef

What two steps in process switching were the most detrimental to the CPU? Route table lookup and L2 resolution

What command would you use to view the contents of the RIB for IPv4 and IPv6? sh ip route

sh ipv6 route

What command would you use to show the contents of the FIB for both IPv4 and IPv6? sh ip cef

sh ipv6 cef

What command would you use to show the adjacency table? show adjacency

What information does the adjacency table contain? Precomputed L2 header and L2 egress interface.

What tables does CEF utilize to route an IP packet? List in order with a short description. First CEF looks at the FIB to find the destination subnet, which points transparently points to the load-share table, then this table has 16 pointers to the adjacency table entries for the destination.

What load balancing is available on process switching? Only per packet load balancing is available on process switching.

What load balancing is available on fast switching? Per destination load balancing is available on fast switching.

What load balancing is available on CEF? per packet and per flow load balancing is available for CEF.

What is the load share table with respect to CEF? The loadshare table is the table in between the FIB and adjacency table. It has 16 pointers which determine how the flow is load balanced.

How many pointers does the CEF load share table have with 2 equal cost paths? What about with 3? The CEF loadshare table has 16 pointers available with 2 equal cost paths, each having 8 pointers. With  3 paths this changes to 15  pointers , each path having 5 pointers.

What concept was introduced to avoid CEF polarization? The universal ID was introduced.

How does the universal ID avoid CEF polarization? The universal ID introduced a bit of entropy into the hash algorithm for CEF such that each router produces a different hash for each flow.

What PER INTERFACE command can change CEF’s load balancing behavior to per packet on software based routers? ip load-share per-packet

How many algorithm iterations has CEF gone through? CEF has gone through 4 algorithm iterations.

Which CEF algorithm WAS vulnerable to CEF polarization? The original CEF algorithm was vulnerable to CEF polarization.

What did the universal CEF algorithm introduce? The universal ID.

What was the purpose of the Tunnel algorithm for CEF? This algorithm provided better load balancing for environments with a lot of tunnel interfaces.

What is the current CEF algorithm used and how does it work? The current CEF algorithm is the L4 port algorithm for CEF. It uses the universal ID, source and destination IPs, source and destination ports. This provided greater load balancing.

What global configuration command can change the CEF load balancing algorithm? What options are available?

ip cef load-sharing algorithm original
ip cef load-sharing algorithm universal
ip cef load-sharing algorithm tunnel

ip cef load-sharing algorithm included-ports