Bgp

Front 1

syntax of ebgp-multihop command

Back 1

neighbor {ip-address | peer-group-name} ebgp-multihop [ttl]

Front 2

common reason to use ebgp-multihop

Back 2

allow routes to EBGP loopback address, which is considered more than 1 hop

Front 3

why to use next-hop-self command

Back 3

if a route points towards an address that is not being redistributed by any IGP

the source address will be replaced by the address of the border router which is directly connected to the other AS but is not advertising the network of the link between them via the IGP

Front 4

T/F: BGP "network" command specifies an interface and then advertises the network with the same subnet mask that is used on the ip address of that interface

Back 4

FALSE. it does not specify interfaces, just networks to advertise

Front 5

syntax of BGP "network" command

Back 5

network network-number [mask network-mask] [route-map map-tag]

Front 6

what is the default status of the bgp auto-summary setting

Back 6

no auto-summary (as of IOS 12.2(8)T)

Front 7

what is the BGP synchronization rule

Back 7

the BGP router should not use, or advertise to an external neighbor, a route that is learned from IBGP unless that route is local or the router learns it from the IGP

Front 8

T/F: by default, BGP synchronization is disabled

Back 8

TRUE (as of IOS 12.2(8)T)

Front 9

what happens if BGP synchronization is disabled

Back 9

routers are able to use and advertise routes that have been learned by IBGP and not an IGP

Front 10

when is it safe to disable BGP synchronization and what is the advantage

Back 10

if all routers in the transit path are running full mesh IBGP

advantage - router can carry fewer routes in the IGP and allows BGP to converge more quickly

Front 11

T/F: BGP synchronization is used when all external routes are to be imported into the IGP. this is difficult now because of the size of the internet routing table and is usually not used

Back 11

TRUE

Front 12

BGP states

Back 12

idle, connect, open sent, open confirm, established

Front 13

meaning of BGP states

Back 13

idle - searching the routing table to find a route to the neighbor
connect - found a route to the neighbor and has completed the TCP handshake
open sent - message sent
open confirm - received agreement on the parameters for the session
established - peering is established; routing begins

Front 14

why would a BGP router be stuck in idle state

Back 14

it is not able to find the specified IP address in its routing table

Front 15

why would a router be stuck in active or cycling between idle and active

Back 15

it has sent the open packet but does not get a response. this may be because the peer router does not have a way to send the response

Front 16

how to create a peer group

Back 16

neighbor peer-group-name peer-group

Front 17

benefit of peer group

Back 17

can apply policies to multiple neighbors without doing it over again for each one

Front 18

command for BGP authentication

Back 18

neighbor {ip-address | peer-group-name} password string

Front 19

ways to trigger a BGP update

Back 19

hard reset
soft reset
route refresh

Front 20

reset all BGP information

Back 20

clear ip bgp *

Front 21

reset BGP information for a single peer

Back 21

clear ip bgp [neighbor-address]

Front 22

clear ip bgp soft in

Back 22

soft reconfiguration of both inbound and outbound updates

Front 23

what are the common categories of BGP path attributes

Back 23

Well-known mandatory
Well-known discretionary
Optional transitive
Optional nontransitive

Front 24

only _________ attributes can be marked as partial

Back 24

optional transitive

Front 25

optional attributes are either _______ or _______

Back 25

transitive

non-transitive

Front 26

three well-known mandatory attributes

Back 26

autonomous system path
next hop
origin

Front 27

two well-known discretionary attributes

Back 27

local preference
atomic aggregate

Front 28

what is one optional transitive attribute

Back 28

aggregator

Front 29

what is one optional nontransitive attribute

Back 29

multi-exit discriminator (MED)

Front 30

what kind of attribute is weight

Back 30

it is a locally configured attribute and not propagated to other routers

Front 31

what information and what form does the AS path attribute have

Back 31

list of autonomous system numbers that a route has traversed to reach a destination, with the number of the autonomous system that originated the route at the end of the list

Front 32

what information does the next-hop attribute contain

Back 32

IP address of the border router that should be used as the next hop to the destination

Front 33

when an EBGP route is put into IBGP, what next-hop address is used

Back 33

the same as is used by EBGP, the IP of the border router of the other AS

Front 34

three values of the origin attribute

Back 34

IGP, EGP (no longer supported), incomplete (usually when a route is redistributed into BGP)

Front 35

local path attribute contains what information

Back 35

preferred path out of the AS

Front 36

MED value advertises what

Back 36

to tell EBGP neighbors how to exit their AS to reach networks owned by this AS

Front 37

routes with {higher | lower} weight are preferred when multiple routes exist to the same destination

Back 37

higher

Front 38

command to change the default local preference value

Back 38

bgp default local-preference value