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Explanation: The BGP next-hop attribute is a well-known mandatory attribute that indicates the
next hop IP address that is to be used to reach a destination. For EBGP, the next hop is the IP
address of the neighbor specified who sent the update, Router CK2 in this scenario. However,
since Router CK2 learned this route through IBGP with the next-hop of 40.1.1.2, this value will
be used instead. This avoids an unnecessary hop.
Incorrect Anss
A: Router CK2 learned this route through IBGP with the next-hop of 40.1.1.2, this value will be
used instead of 40.1.1.1.. This avoids an unnecessary hop.
C: This is the local interface on Router CK1 itself.
D: The advertisement is accepted.
E: The route is advertised.
Q7
Exhibit:
o all routers are using BGP
o synchronization is OFF in AS 647000
Regarding the route to 198.12.1.0; to which routers will this route propagate to?A. Router CK6B. Routers CK2 and CK6C. Routers CK2 , CK4 , and CK6D. Routers CK2 , CK3 , CK4 , and CK6E. Routers CK1 , CK2 , CK3 , CK4 , and CK6F. Routers CK1 , CK2 , CK3 , CK4 , CK5 , and CK6
Ans: F
Explanation: Router CK 6 will advertise the 192.12.1.0 route to Router CK2 using EBGP. This
route would propagate to Router CK1 , CK3 , and CK4 through IGBP. And since synchronization
is turned off Router CK1 will advertise the internally learned route to Router CK5 using EGBP.
Q8
Exhibit:
o synchronization is OFF
o NO IGP is running in AS 65500
Which router in AS 65500 is going to end up advertising a route to network 172.16.0.0?A. B onlyB. E onlyC. B and E onlyD. B, C and D onlyE. B, C, D, and E
Ans: E
Explanation: We need to run IGP on AS 65500 to control the exit points from the AS. All
routers in AS 65500 will advertise the route.
Reference: Using the Border Gateway Protocol for Interdomain Routing
http://www.cisco.com/univercd/cc/td/doc/cisintwk/ics/icsbgp4.htm
Q9
The numbers below are all AS (autonomous system) numbers. However, one of them is a
private AS umber; which one is it?A. 10080B. 48512C. 64128D. 64524
Ans: D
Explanation:
This autonomous system designator is a 16-bit number, with a range of 1 to 65535. RFC 1930
provides guidelines for the use of AS numbers. A range of AS number, 64512 through 65535, is
reserved for private use, much like the private Internet Protocol (IP) addresses.
Reference: Building Scalable Cisco Networks (Ciscopress) page 312
Q20
On the presumption that your router is limited in memory, how would Cisco recommend
you connect multiple ISP's with BGP?A. receive only default routes.B. receive only partial BGP routes.C. receive only internal BGP routes.D. receive only redistributed routes.
Ans: A
Explanation: By only accepting default routes from the ISPs ensures a minimal impact on the
system. There is no risk of having your autonomous system (AS) becoming a transit AS.
Note: One recommendation of Cisco, not listed here, is to use AS_PATH filters for accepting
only routes originated from an ISP and its directly connected Autonomous Systems (AS), instead
of receiving the full BGP routing table from an ISP.
Reference: Achieve Optimal Routing and Reduce BGP Memory Consumption
http://www.cisco.com/warp/public/459/41.shtml
Q21
Why should iBGP sessions be fully meshed within a Transit AS?A. BGP requires redundant TCP sessions between iBGP peers.B. A full mesh allows for optimal routing within the Transit AS.C. Routes learned via iBGP are never propagated to other eBGP peers.D. Routes learned via iBGP are never propagated to other iBGP peers.E. Routes learned via eBGP are never propagated to other iBGP peers.
Ans: D
BSCI CCNP Self-Study Guide on pages 564 and 566 and the Cisco Press BGP-4 Command and
Configuration Handbook (2001 version)
Q22
You are the network engineer at CertKing . The CertKing network is shown in the following
graphic:
Router B advertises network 172.30.0.0 to Router A using BGP.
What is the default value of the next-hop attribute?A. 10.1.1.1B. 10.1.1.2C. 10.1.1.3D. Router A does not accept the advertisement from Router B because Router A is not
peering with Router C via BGP.E. Router B does not advertise network 172.30.0.0 to Router A because the network is not
directly connected to Router B.
Ans: A
Explanation:
Ans should be "A" = 10.1.1.1 as the default next-hop attribute.
Reference: Cisco Press's BSCI 2nd Edition pg 529
Section 16: Explain how BGP policy-based routing functions within an
autonomous system (6 questions)
Q 1
Hypothetically speaking, what would happen if you're using BGP policy-based routing on
your system, the next hop router goes down, and there's no alternative path?A. If the next-hop router goes down and no alternative path is in place, policy routing will
route to null 0.B. If the next-hop router goes down and no alternative path is in place, policy routing will
default to another BGP path.C. If the next-hop router goes down and no alternative path is in place, policy routing will
deny all traffic to that destination.D. If the next-hop router goes down and no alternative path is in place, policy routing will
default to dynamic routing decisions.
Ans: D
Explanation:
In Cisco Press ISBN: 1-58720-078-3 CCNP Self-Study CCNP BSCI Exam Certification Guide
by Clare Gough, it states in page 499: "Disadvantages of Policy Routing - Some things should be
considered before arbitrarily
deciding to implement policy routing:
. A backup path should be in place in case the defined next-hop router goes down. If there is no
alternative defined, policy routing will default to dynamic routing decisions."
Q2
Which of the following statements are true about BGP policy-based routing? (Select two)A. Policy routing is configure on the inbound interface.B. Policy routing can be used to alter the final destination of the packet.C. Policy routing can be used to alter the next hop in the path to the destination.D. Policy routing does not allow traffic to be directed based on the source address.
Ans: B, C
Explanation: Policy routing can alter the final destination of a packet and alter the next hop in
the path to the destination.
Incorrect Anss
A: Policy routing can be configure both on the inbound and on outbound interfaces.
D: Policy routing allows traffic to be directed based on the source address.
Q3
In regard to BGP policy-based routing, what is true?A. If the next-hop router goes down and no alternative path is in place, policy routing will
route to null 0.B. If the next-hop router goes down and no alternative path is in place, policy routing will
default to another BGP path.C. If the next-hop router goes down and no alternative path is in place, policy routing will
deny all traffic to that destination.D. If the next-hop router goes down and no alternative path is in place, policy routing will
default to dynamic routing decisions.
Ans: D
Explanation: If no alternate path is specified and the next hop router fails, policy based routing
will default to dynamic routing decisions.
Q4
Which one of the following BGP prefix lists would you use if you wanted to deny the
default route 0.0.0.0?A. ip prefix-list abc deny 0.0.0.0/0B. ip prefix-list abc permit 0.0.0.0/32C. ip prefix-list abc deny 255.255.255.255/0D. ip prefix-list abc permit 255.255.255.255/32
Ans: A
Explanation: To deny the default route 0.0.0.0/0 use the following command:
ip prefix-list abc deny 0.0.0.0/0
Incorrect Anss
B, D: We are required to deny it, not permit it.
C: We should simply list the route. Not the opposite of the route.
Q5
Which of the following prefix-list statements would you enter if you wanted to permit all
prefixes that fall between /8 and /24 on the 192.0.0.0 network?A. ip prefix-list 192.0.0.0/8 ge 8 le 24B. ip prefix-list 192.0.0.0/8 ge 24 le 8C. ip prefix-list 192.0.0.0/24 ge 24 le 8D. ip prefix-list 192.0.0.0/24 ge 8 le 24
Ans: A
Explanation: Greater than (ge) 8 and less than (le) 24. Furthermore we must specify an 8 bit
network mask, not a 24 bit network mask.
Reference: Cisco, BGP Commands
Q6
With regard to BGP policy-based routing, which two of the statements are true? (Choose
two)A. Policy routing is configured on the inbound interface.B. Policy routing can be used to alter the final destination of the packet.C. Policy routing can be used to alter the next hop in the path of the destinationD. Policy routing does not allow traffic to be directed based on the source address.
Ans: A, C
Explanation:
Rules of Policy-Based Routing
BGP can implement any of the following rules associated with the hop-by-hop paradigm. This
paradigm is the capability to influence which router will be the next-hop router, potentially dictating it at every
router and thus influencing the entire path of the traffic, hop by hop. The following rules associated with
policybased
routing seem repetitive, but, in fact, each point raises a subtly different nuance:
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