chapter 8

Question 1

what is route summerization and why use it?

Answer 1

allows a group of networks to be lumped together and advertised as one address. summerization reduces the router updates required and the size of the neighbor/ border router tables.

Question 2

what is the benifit or why would one disable automatic summerization on a border router when using eigrp?

Answer 2

when automatic summerization is disabled, updatees include subnet information and this allows the best possible path to each subnet on the enterprise network. summerization does not include subnet information for each subnet and therfore the best path is not always chosen.

Question 3

is automatic summerization desabled or enabled by default on cisco 15.01 routers (todays routers)? how and when is summerization used.?

Answer 3

cisco 15.01 does not have automatic summerization turned on by default. earlier cisco versions did and everytime the eigrp topology crossed a border between 2 diff. major class networks the auto-summerization took place. (border routers)

Question 4

NSF aware means what?

Answer 4

means that in your switch/router you have non-stop forwarding enabled, which prevents any disruption in traffic even in case of a reload as it segregates the control plane with the data plane

Question 5

what command is used to enable auto summerization on a router?

Answer 5

#router eigrp 'attonomous number, like 1'
#auto-summary

Question 6

what command is entered to disable auto summerization on a router once u are in the eigrp sub configuration?

Answer 6

sub-configuration = #router eigrp 'AS number like 1'
#no auto-summary

Question 7

what decides which interfaces send out network summerizations?

Answer 7

Summarized updates are only sent out interfaces on different classful networks, so if the summerization is of a 172.16 network then the update will be sent out an interfce with the classful network other than 172.16, like 192.168.

Question 8

what command is used to verify that the auto-summerization is disabled/ enabled?

Answer 8

show ip route eigrp

this displays many ip addresses that are within the same class but are separate subnets = summerization is disabled.
-if only one network address for a class is displayed and is labeled as summary then the summerization is enabled.

Question 9

is automatic summerization available for eigrp ipv6?

Answer 9

no, b/c ipv6 is not a classful addressing, no need for it in ipv6

Question 10

what is the Null0 interface and y is it used?

Answer 10

it is a virtual interface that goes nowhere. (bit bucket) packets that match a route with a null0 exit interface are discarded.
The purpose of the Null0 summary route is to prevent routing loops for destinations that are included in the summary, but do not actually exist in the routing table.
aka the subnet does not exist as a destination address and the packet is then discarded.

Question 11

if the auto-summary is configured on a router that only has one interface ip that it needs to advertise to a neighbor router… how is the route summarized?

Answer 11

it is kept as is and is not summarized. no need to summarize the route.

Question 12

what is a supernet route?

Answer 12

a collection of major classful network addresses.

*classful = subnet mask info is not included in advertisements.

Question 13

what command is used to manually set a summary route?

Answer 13

interface serial'serial number'
#ip summary-address eigrp '#' 'summary address and subnet mask num.'
example: ip summary-address eigrp 1  192.168.0.0 255.255.252.0

Question 14

is auto-summerization and manual summerization available for eigrp ipv6?

Answer 14

only manual summerization is available for ipv6.

Question 15

what is the purpose and how does it work- the static default route?

Answer 15

it is quad zero or 0.0.0.0/0 this is set on the boarder edge router and is not protocol-dependent. this route is the connection to the isp or other network outside the main eigrp network. this default route is propagated to all routers on the network.

Question 16

redistribute static -command does what?

Answer 16

The redistribute static command tells EIGRP to include static routes in its EIGRP updates to other routers

Question 17

default static route is also known as the ?

Answer 17

gateway of last resort.

Question 18

when u see the letter (D) in the ‘show ip route’ output?

Answer 18

D - This route was learned from an EIGRP routing update.

Question 19

when u see the letter (*) in the ‘show ip route’ output?

Answer 19

• • The route is a candidate for a default route.

Question 20

when u see the letter (EX) in the ‘show ip route’ output?

Answer 20

EX - The route is an external EIGRP route, in this case a static route outside of the EIGRP routing domain.

Question 21

what does the ‘passive-interface’ command do?

Answer 21

stops that interface from sending or receiving routing updates. for security and bandwidth saving reasons. access interfaces are set as passive.