CCNA 200 301 OSPF UPDATED ACTUAL
QUESTIONS AND CORRECT ANSWERS
COMPLETE STUDY GUIDE RESOURCE
●● What is fast switching?
Answer: *Fast switching* stores data in the "Fast Switching Cache" for
faster look-ups, thus allowing the CPU to have more breathing room.
●● What is the downside to fast switching compared to CEF?
Answer: *Fast switching* requires the first packet to be analyzed by the
CPU before entering the cache and does not actively monitor the routing
table so the cached entry aging out may take a bit of time.
●● What does CEF stand for?
Answer: *Cisco Express Forwarding.*
●● What is CEF?
Answer: *CEF* stores data in pre-populated cache and downloads
information from various tables as soon as available to reduce the strain
on the CPU.
●● What are some packets that cannot be CEF-switched?
,Answer: Some packets that cannot be CEF-switched are ARP requests
(Glean), packets requiring a response from the router CPU (MTU too
large, TTL expiring), routing protocol traffic, cdp, lldp, packets needing
encryption.
●● What does the FIB stand for?
Answer: *Forwarding Information Base.*
●● What is the FIB?
Answer: *FIB* is a shadow copy of the routing table used to assist in
CEF-switching.
●● What show command would verify CEF?
Answer: show ip cef [detail]
●● What is the adjacency table?
Answer: The adjacency table is pre-populated L2 tables (ARP, Frame-
Relay) used to assist in CEF-switching.
●● If FIB does not have a specific IP address, what occurs?
Answer: If FIB does not have a specific IP address, an ARP request is
sent out so that it can be seen in the FIB as 'attached', which means there
was a successful lookup.
,●● What is adjacency type Glean?
Answer: *Glean* in the adjacency table refers to the process of
determining the L2 information to forward the L3 packet. The request is
punted to the CPU to perform an ARP request, but if there is no reply,
entry stays as Glean until it ages out.
●● What is the adjacency type Null?
Answer: *Null* in the adjacency table refers to a valid packet that needs
to be dropped. This most commonly occurs because of a null0 route and
the switching is processed in hardware.
●● What is the adjacency type Drop?
Answer: *Drop* in the adjacency table refers to a valid packet that
needs to be dropped. This most commonly occurs because of no valid
route or something is wrong with the packet.
●● What is the adjacency type Discard?
Answer: *Discard* in the adjacency table refers to a valid that needs to
be dropped. This most commonly occurs because there are security
policies in place such as an ACL.
●● What is the adjacency type Punt?
Answer: *Punt* in the adjacency table is similar to Glean as packets will
be forwarded to the CPU. This occurs for packets that are destined for
the processor to begin with.
, ●● What show command would verify the adjacency table?
Answer: show adjacency
●● What is Unicast Flooding?
Answer: *Unicast Flooding* occurs when there is no entry in the L2
table (CAM) and packets are flooded out of all interfaces in the VLAN
besides the receiving interface.
●● How can you reduce Unicast Flooding?
Answer: *Unicast Flooding* can be reduced by making the ARP entry
expire earlier than the CAM entry, which enables the ARP entry to
repopulate before CAM entry expires.
●● What configuration command would block Unicast Flooding?
Answer: Router(config-if)# switchport block unicast
●● What are out-of-order packets?
Answer: *Out-of-order packets* are packets that arrive in a different
order than they were sent. This can be caused by asymmetric routing or
packet loss.
●● What does TCP do to alleviate issues caused by out-of-order
packets?
QUESTIONS AND CORRECT ANSWERS
COMPLETE STUDY GUIDE RESOURCE
●● What is fast switching?
Answer: *Fast switching* stores data in the "Fast Switching Cache" for
faster look-ups, thus allowing the CPU to have more breathing room.
●● What is the downside to fast switching compared to CEF?
Answer: *Fast switching* requires the first packet to be analyzed by the
CPU before entering the cache and does not actively monitor the routing
table so the cached entry aging out may take a bit of time.
●● What does CEF stand for?
Answer: *Cisco Express Forwarding.*
●● What is CEF?
Answer: *CEF* stores data in pre-populated cache and downloads
information from various tables as soon as available to reduce the strain
on the CPU.
●● What are some packets that cannot be CEF-switched?
,Answer: Some packets that cannot be CEF-switched are ARP requests
(Glean), packets requiring a response from the router CPU (MTU too
large, TTL expiring), routing protocol traffic, cdp, lldp, packets needing
encryption.
●● What does the FIB stand for?
Answer: *Forwarding Information Base.*
●● What is the FIB?
Answer: *FIB* is a shadow copy of the routing table used to assist in
CEF-switching.
●● What show command would verify CEF?
Answer: show ip cef [detail]
●● What is the adjacency table?
Answer: The adjacency table is pre-populated L2 tables (ARP, Frame-
Relay) used to assist in CEF-switching.
●● If FIB does not have a specific IP address, what occurs?
Answer: If FIB does not have a specific IP address, an ARP request is
sent out so that it can be seen in the FIB as 'attached', which means there
was a successful lookup.
,●● What is adjacency type Glean?
Answer: *Glean* in the adjacency table refers to the process of
determining the L2 information to forward the L3 packet. The request is
punted to the CPU to perform an ARP request, but if there is no reply,
entry stays as Glean until it ages out.
●● What is the adjacency type Null?
Answer: *Null* in the adjacency table refers to a valid packet that needs
to be dropped. This most commonly occurs because of a null0 route and
the switching is processed in hardware.
●● What is the adjacency type Drop?
Answer: *Drop* in the adjacency table refers to a valid packet that
needs to be dropped. This most commonly occurs because of no valid
route or something is wrong with the packet.
●● What is the adjacency type Discard?
Answer: *Discard* in the adjacency table refers to a valid that needs to
be dropped. This most commonly occurs because there are security
policies in place such as an ACL.
●● What is the adjacency type Punt?
Answer: *Punt* in the adjacency table is similar to Glean as packets will
be forwarded to the CPU. This occurs for packets that are destined for
the processor to begin with.
, ●● What show command would verify the adjacency table?
Answer: show adjacency
●● What is Unicast Flooding?
Answer: *Unicast Flooding* occurs when there is no entry in the L2
table (CAM) and packets are flooded out of all interfaces in the VLAN
besides the receiving interface.
●● How can you reduce Unicast Flooding?
Answer: *Unicast Flooding* can be reduced by making the ARP entry
expire earlier than the CAM entry, which enables the ARP entry to
repopulate before CAM entry expires.
●● What configuration command would block Unicast Flooding?
Answer: Router(config-if)# switchport block unicast
●● What are out-of-order packets?
Answer: *Out-of-order packets* are packets that arrive in a different
order than they were sent. This can be caused by asymmetric routing or
packet loss.
●● What does TCP do to alleviate issues caused by out-of-order
packets?
