Section 3 – Implement an eBGP based solution, given a network design and a set of requirements
QUESTION NO: 26
Refer to the exhibit. Routing updates for the 192.168.1.0 network are being received from all three neighbors. Which statement is correct regarding the result of the configuration shown? Select the best response.
A. The router will prefer the next hop of 172.16.1.1 for packets destined for the 192.168.1.0 network.
B. The router will prefer the next hop of 172.26.1.1 for packets destined for the 192.168.1.0 network.
C. The router will advertise the 192.168.1.0 network only to 172.30.1.1.
D. The router will advertise the 192.168.1.0 network only to 172.26.1.1.
E. The router will prefer the next hop of 172.26.1.1 for packets except those destined for the
QUESTION NO: 27
Refer to the exhibit. It is desired to set up a BGP neighbor relationship between routers R1 and R4. BGP packets between them could travel through R2 or R3. What is the simplest configuration that will allow for failover? Select the best response.
A. Configure BGP neighbor relationships between all interfaces on R1 and R4.
B. Install a direct connection between R1 and R4.
C. Configure loopback interfaces on R1 and R4 to provide the update source address for BGP packets.
D. Configure only one neighbor relationship between R1’s 192.168.1.2 interface and R4’s
The point of this question is about using lookback interface establish neighbor.
You can use two ways to configure IBGP neighbor. First is use physical address, and the second is use loopback interface. In this picture, you find that there are two way to each other, if you use physical address for failover, you need to establish two connection, and you will receive two route, this is no good. If you use loopback interface, there are only one connection, but if one way is down, it also can failover. So answer C is the best.
QUESTION NO: 28
Which two methods advertise internal networks to external ISPs via BGP? (Choose two.)
A. using aggregate routes
B. disabling synchronization
C. forcing the next-hop address
D. defining routes via the network statement
In BGP, the network command tells the BGP process what locally learned networks to advertise.
The networks can be connected routes, static routes, or routes learned by way of a dynamic routing protocol, such as RIP. These networks must also exist in the routing table of the local router or they will not be sent out in updates. The mask keyword can be used with the network command to specify individual subnets. Routes learned by the BGP process are propagated by default but are often filtered by a routing policy.
Router(config-router)# network network-number [ mask network-mask ]
QUESTION NO: 29
Refer to the exhibit. The neighbor 10.1.1.1 weight 200 BGP configuration command has been configured on router A. What will be the result of this configuration?
A. Router A will prefer the path through router B for network 172.20.0.0
B. Router A will prefer the path through router C for network 172.20.0.0
C. Packets from router D will prefer the path through router B for networks advertised by router A
D. Packets from router D will prefer the path through router C for networks advertised by router A
The weight attribute is a special Cisco attribute that is used in the path selection process when there is more than one route to the same destination. The higher the weight value, the bettwe the path. The default weight is 0. Therefore, by configuring weight 200 to the neighbor 10.1.1.1, router A will prefer the path through router B for network 172.20.0.0 then the path through router C.
The weight attribute is local to the router and not propagated to other routers. In this case the weight is local to router A so it has no effect on the decision of transferring packets from router D.
QUESTION NO: 30
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.
Any two routers that have formed a TCP connection in order to exchange BGP routing information are called peers or neighbors. It is important to remember that the BGP peers will never become established unless there is IP connectivity between the two peers.
BGP does not advertise routes learned by way of IBGP peers to other IBGP peers. If BGP did,
BGP routing inside the AS would present a dangerous potential for routing loops. For IBGP routers to learn about all BGP routes inside the AS, they must connect to every other IBGP router in a full IBGP mesh. This full mesh needs to be only logical, not physical. In other words, as long as the
IBGP peers can connect to each other using TCP/IP, a logical full mesh can be created even if the routers are not directly connected.
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