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Exam 300-410 topic 1 question 496 discussion

Actual exam question from Cisco's 300-410
Question #: 496
Topic #: 1
[All 300-410 Questions]

SIMULATION
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Guidelines
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This is a lab item in which tasks will be performed on virtual devices.

• Refer to the Tasks tab to view the tasks for this lab item.
• Refer to the Topology tab to access the device console(s) and perform the tasks.
• Console access is available for all required devices by clicking the device icon or using the tab(s) above the console window.
• All necessary preconfigurations have been applied.
• Do not change the enable password or hostname for any device.
• Save your configurations to NVRAM before moving to the next item.
• Click Next at the bottom of the screen to submit this lab and move to the next question.
• When Next is clicked, the lab closes and cannot be reopened.


Topology
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Tasks
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A company is connected to an ISP and some of the networks between the ISP and the company are not reachable. Troubleshoot and resolve the issues to achieve these goals:

1. A single /16 is advertised for all infrastructure-connected interfaces that belong to the 10.20.x.x network using BGP network commands from border routers connected to the ISP. Configuration modification is allowed in R4 and R5 to achieve the results. Do not use the BGP aggregate command.

2. R6 receives the ISP R2 Loopback2 from R4 and receives a summary address for both Loopbacks of ISP R2 from R4 or R5. Use BGP attribute local-preference, add , for example, for R6, use “default+6 = value to be used”. Use the existing prefix lists or route maps with the sequence numbering starting at 10 and added in increments of 10.

3. R6 receives the ISP R2 Loopback1 from R5 and receives a summary address for both Loopbacks of ISP R2 from R4 or R5 using the same guidelines.

4. R6 advertises its Loopback1 /24 address through BGP.

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[Removed]
Highly Voted 1 year, 2 months ago
Labbed as best I could without seeing the actual configs. Part 1 Router 4+5 Add static route to 10.20.0.0 255.255.0.0 null0 Advertise to BGP with network statement Part 2 Router 4 and 5. Match relevant R2 loopback using a standard access list. Create route map (question implies modification of existing). Permit 10 match access list and set LP to 100+routerID. Permit 20 match all/permit all (blank). Part3 Advertise Loopback on R6 using network statement.
upvoted 5 times
ExamNinja1
10 months, 4 weeks ago
I am a little lost on what might be going on under the hood on this one. Can someone explain why we would be installing a null0 route here.
upvoted 3 times
Gramterre
10 months, 2 weeks ago
Because we need the route to advertise it into bgp, as we are not allowed to use the aggregate command.
upvoted 3 times
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leipeG
3 months, 3 weeks ago
Using ip route 10.20.0.0 255.255.0.0 Null0 provides a simple and efficient way to summarize the 10.20.0.0/16 network for BGP advertisement without needing aggregate-address. It prevents "blackholing" by only advertising reachable subnets and drops traffic to unreachable subnets, thereby avoiding potential routing loops.
upvoted 3 times
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halil395
12 months ago
R4# ! ip route 10.20.0.0 255.255.0.0 Null0 ! router bgp 65000 network 10.20.0.0 mask 255.255.0.0 aggregate-address 192.168.2.0 255.255.254.0 neighbor 10.20.6.6 route-map BGP-R6 out ! ip prefix-list 65000-in seq 5 permit 192.168.2.0/24 ! route-map BGP-R6 permit 10 match ip address prefix-list 65000-in set local-preference 104 ! route-map BGP-R6 permit 20 #################### R5# ! ip route 10.20.0.0 255.255.0.0 Null0 ! router bgp 65000 network 10.20.0.0 mask 255.255.0.0 aggregate-address 192.168.2.0 255.255.254.0 neighbor 10.20.6.6 route-map BGP-R6 out ! ip prefix-list 65001-in seq 5 permit 192.168.3.0/24 ! route-map BGP-R6 permit 10 match ip address prefix-list 65001-in set local-preference 105 ! route-map BGP-R6 permit 20 ! #################### R6# ! router bgp 65000 network 172.16.6.0 mask 255.255.255.0 !
upvoted 3 times
AonDuine
5 months ago
It's not working with prefix-list, you need an ACL example for R4 R4(config)#access-list 10 permit 192.168.2.0 0.0.0.255 R4(config-route-map)#match ip address 10 R4(config-route-map)#set local-pref R4(config-route-map)#router bgp 65000 R4(config-router)#neighbor 10.20.6.6 route-map LOCAL out and you get on R6 R6#show ip bgp Network Next Hop Metric LocPrf Weight Path * i 10.20.0.0/16 10.20.5.5 0 100 0 i *>i 10.20.4.4 0 100 0 i *> 172.16.6.0/24 0.0.0.0 0 32768 i * i 192.168.2.0 10.20.5.5 0 100 0 65001 i *>i 10.20.4.4 0 106 0 65001 i *>i 192.168.3.0 10.20.5.5 0 106 0 65001 i * i 10.20.4.4 0 100 0 65001 i
upvoted 2 times
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IvAlAx
4 months, 2 weeks ago
Be careful because in point one it is clearly written that it is not possible to use the aggregate command.
upvoted 2 times
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Pietjeplukgeluk
8 months, 2 weeks ago
You really nailed the essence in my opinion.
upvoted 1 times
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CiscoTerminator
Most Recent 2 days, 10 hours ago
Can someone explain the requirement for me better here: " R6 receives the ISP R2 Loopback2 from R4 and receives a summary address for both Loopbacks of ISP R2 from R4 or R5. Use BGP attribute local-preference, add , for example, for R6," ?
upvoted 1 times
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leipeG
3 months, 3 weeks ago
There's discussion on prefix-list vs. ACL; both work in lab tests, but I'd choose a prefix-list for its flexibility with subnet masks and efficient route handling. Plus, the task suggests it: "Use the existing prefix lists or route maps." Here is my lab-setup: hostname R1 ! configure terminal ! interface Loopback0 ip address 10.10.1.1 255.255.255.255 ! interface GigabitEthernet0/0 ip address 10.41.14.1 255.255.255.248 no shutdown ! interface GigabitEthernet2/0 ip address 10.10.12.1 255.255.255.0 no shutdown ! interface GigabitEthernet3/0 ip address 10.10.13.1 255.255.255.0 no shutdown ! router bgp 65001 bgp log-neighbor-changes network 10.10.1.1 mask 255.255.255.255 neighbor 10.10.12.2 remote-as 65001 neighbor 10.10.13.3 remote-as 65001 neighbor 10.41.14.4 remote-as 65000
upvoted 2 times
leipeG
3 months, 3 weeks ago
hostname R2 ! configure terminal ! interface Loopback0 ip address 10.10.2.2 255.255.255.255 ! interface Loopback1 ip address 192.168.2.2 255.255.255.0 ! interface Loopback2 ip address 192.168.3.2 255.255.255.0 ! interface GigabitEthernet1/0 ip address 10.10.23.2 255.255.255.0 no shutdown ! interface GigabitEthernet2/0 ip address 10.10.12.2 255.255.255.0 no shutdown ! router bgp 65001 bgp log-neighbor-changes network 10.10.2.2 mask 255.255.255.255 network 192.168.2.0 mask 255.255.255.0 network 192.168.3.0 mask 255.255.255.0 neighbor 10.10.12.1 remote-as 65001 neighbor 10.10.23.3 remote-as 65001
upvoted 2 times
leipeG
3 months, 3 weeks ago
hostname R3 ! configure terminal ! interface Loopback0 ip address 10.10.3.3 255.255.255.255 ! interface GigabitEthernet0/0 ip address 10.53.35.3 255.255.255.248 no shutdown ! interface GigabitEthernet1/0 ip address 10.10.23.3 255.255.255.0 no shutdown ! interface GigabitEthernet3/0 ip address 10.10.13.3 255.255.255.0 no shutdown router bgp 65001 bgp log-neighbor-changes network 10.10.3.3 mask 255.255.255.255 neighbor 10.10.13.1 remote-as 65001 neighbor 10.10.23.2 remote-as 65001 neighbor 10.53.35.5 remote-as 65000
upvoted 2 times
leipeG
3 months, 3 weeks ago
hostname R4 ! configure terminal ! interface Loopback0 ip address 10.20.4.4 255.255.255.255 ! interface GigabitEthernet0/0 ip address 10.41.14.4 255.255.255.248 no shutdown ! interface GigabitEthernet1/0 ip address 10.20.45.4 255.255.255.0 no shutdown ! interface GigabitEthernet3/0 ip address 10.20.46.4 255.255.255.0 no shutdown ! router bgp 65000 bgp log-neighbor-changes network 10.20.0.0 mask 255.255.0.0 neighbor 10.41.14.1 remote-as 65001 neighbor 10.41.14.1 route-map LOCAL in neighbor 10.20.45.5 remote-as 65000 neighbor 10.20.46.6 remote-as 65000 ! ip route 10.20.0.0 255.255.0.0 Null0 ! do show ip bgp summary ! ip prefix-list R2_LOOPBACK seq 10 permit 192.168.3.0/24 ! route-map LOCAL permit 10 match ip address prefix-list R2_LOOPBACK set local-preference 104 ! route-map LOCAL permit 20
upvoted 2 times
leipeG
3 months, 3 weeks ago
hostname R5 ! configure terminal ! interface Loopback0 ip address 10.20.5.5 255.255.255.255 ! interface GigabitEthernet0/0 ip address 10.53.35.5 255.255.255.248 no shutdown ! interface GigabitEthernet1/0 ip address 10.20.45.5 255.255.255.0 no shutdown ! interface GigabitEthernet2/0 ip address 10.20.56.5 255.255.255.0 no shutdown ! router bgp 65000 bgp log-neighbor-changes network 10.20.0.0 mask 255.255.0.0 neighbor 10.53.35.3 remote-as 65001 neighbor 10.53.35.3 route-map LOCAL in neighbor 10.20.45.4 remote-as 65000 neighbor 10.20.56.6 remote-as 65000 ! ip route 10.20.0.0 255.255.0.0 Null0 ! ip prefix-list R2_LOOPBACK seq 10 permit 192.168.2.0/24 ! route-map LOCAL permit 10 match ip address prefix-list R2_LOOPBACK set local-preference 105 ! route-map LOCAL permit 20
upvoted 2 times
leipeG
3 months, 3 weeks ago
hostname R6 ! configure terminal ! interface Loopback0 ip address 10.20.6.6 255.255.255.255 ! interface Loopback1 ip address 172.16.6.6 255.255.255.0 ! interface GigabitEthernet2/0 ip address 10.20.56.6 255.255.255.0 no shutdown ! interface GigabitEthernet3/0 ip address 10.20.46.6 255.255.255.0 no shutdown ! router bgp 65000 bgp log-neighbor-changes network 10.20.6.6 mask 255.255.255.255 network 172.16.6.0 mask 255.255.255.0 neighbor 10.20.56.5 remote-as 65000 neighbor 10.20.46.4 remote-as 65000 ! do show ip bgp Network Next Hop Metric LocPrf Weight Path <..> * i 192.168.2.0 10.53.35.3 0 105 0 65001 i * i 10.41.14.1 0 100 0 65001 i * i 192.168.3.0 10.53.35.3 0 100 0 65001 i * i 10.41.14.1 0 104 0 65001 i Note: Local preference 100 is still visible, but the route with the highest local preference is preferred.
upvoted 2 times
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Ghauri777
1 year, 3 months ago
R4 router bgp 65000 bgp log-neighbor-changes network 10.20.0.0 mask 255.255.0.0 aggregate-address 192.168.0.0 255.255.252.0 as-set neighbor 10.10.1.1 remote-as 65001 neighbor 10.10.1.1 ebgp-multihop 2 neighbor 10.10.1.1 update-source Loopback0 neighbor 10.10.1.1 route-map R2-L2 in ip prefix-list 1 seq 5 permit 192.168.3.0/24 match ip address prefix-list 1 route-map R2-L2 permit 10 match ip address prefix-list 1 set local-preference 104 route-map R2-L2 permit 20 ----------------------------------- R5 router bgp 65000 bgp log-neighbor-changes network 10.20.0.0 mask 255.255.0.0 aggregate-address 192.168.0.0 255.255.252.0 as-set neighbor 10.10.3.3 remote-as 65001 neighbor 10.10.3.3 ebgp-multihop 2 neighbor 10.10.3.3 update-source Loopback0 neighbor 10.10.3.3 route-map R2-L1 in ip prefix-list 1 seq 5 permit 192.168.2.0/24 match ip address prefix-list 1 set local-preference 106 route-map R2-L1 permit 10 match ip address prefix-list 1 set local-preference 106 route-map R2-L1 permit 20 --------------- R6 router bgp 65000 bgp log-neighbor-changes network 172.16.6.0 mask 255.255.255.0
upvoted 1 times
[Removed]
1 year, 2 months ago
Its says you cannot use the aggregate command. As the published solution states - add a null static route and then advertise into BGP
upvoted 4 times
rgg
3 weeks, 4 days ago
As I understand we can't use aggregate command for the first task, but in the Ghauri777's solution its used for the tasks 2 and 3 which is fine
upvoted 1 times
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aqwsdfghjklp
1 year, 2 months ago
I don't know why you need the "as-set" command.
upvoted 1 times
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aqwsdfghjklp
1 year, 2 months ago
Is this a config?
upvoted 1 times
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