03-23-2011, 09:13 AM
View the exhibit. Currently the two eBGP links between AS100 and AS200 have an average inbound load of 65% and 20% respectively. After further investigation, traffic to 10.10.1.16/28 accounts for 45%, and traffic to 10.10.1.32/28 and to 10.10.1.48/28 each account for 20% of the inbound load. The BGP attributes are currently set at their default values in both autonomous systems.
If you want to influence how AS200 sends traffic to AS100, which eBGP configurations would you configure in AS100 to influence AS200 to use the eBGP links more evenly? (Select two.)
Your Answer: route-map as_50 permit 10
match ip address 50
set metric 150
access-list 50 permit 10.10.1.32 0.0.0.240
neighbor 192.168.30.2 route-map as_50 out
Correct Answer: neighbor 192.168.20.2 route-map as_50 out
route-map as_50 permit 10
match ip address 50
set metric 150
access-list 50 permit 10.10.1.32 0.0.0.240
Explanation:
We want to reduce the incoming traffic on the 65% route and increase the traffic on the 20% route, by using mechanism that instructs EBGP neighbor in AS 200 to prefer more the path between routers F and B.
The MED is used to decide how to enter an AS. It is used when multiple pathways exist between two autonomous systems, and one AS is trying to influence the incoming path from the other AS. A lower MED value is preferred; the default set to 0 for Cisco routers. So what we want to do is raise the MED on a subnet on the 65% route in AS 100, that when advertised to EBGP neighbor in AS 200, it prefers the 20% route.
Since the 10.10.1.48 favors the 20% from router B route due to route cost, and 10.10.1.16 favors the 65% route from router A due to the same reasoning, the subnet we should try to manipulate is the 10.10.1.32 because it is traveling the 65% path (20% +45%=65%). So lets raise the MED on the 65% path from router A to 150 so the lower MED on the 20% path from router B is preferred.
Step 1: Define the neighbor that you want to raise the MED to and the route-map you will use to do this:
Neighbor 192.168.30.2 route-map AS_50 out
Step 2: Write the Route map to raise Med to 150 and define the traffic associated with this route-map via ACL:
route-map as_50 permit 10
match IP address 50
set metric 150
access-list 50 permit 10.10.1.32 0.0.0.240
Now you have raised the med of a 20% traffic across the Router A route to the AS200. This traffic will now switch to use router B route as the preferred route due to lower MED. This in turn raises the traffic on router B to 40% (from 20%) and lowers the traffic on router A to 45% (from 65%).
Based on the explanation, shouldn't my answer be correct? Also the access-list entry wildcard mask should be 0.0.0.7 and not 0.0.0.240
If you want to influence how AS200 sends traffic to AS100, which eBGP configurations would you configure in AS100 to influence AS200 to use the eBGP links more evenly? (Select two.)
Your Answer: route-map as_50 permit 10
match ip address 50
set metric 150
access-list 50 permit 10.10.1.32 0.0.0.240
neighbor 192.168.30.2 route-map as_50 out
Correct Answer: neighbor 192.168.20.2 route-map as_50 out
route-map as_50 permit 10
match ip address 50
set metric 150
access-list 50 permit 10.10.1.32 0.0.0.240
Explanation:
We want to reduce the incoming traffic on the 65% route and increase the traffic on the 20% route, by using mechanism that instructs EBGP neighbor in AS 200 to prefer more the path between routers F and B.
The MED is used to decide how to enter an AS. It is used when multiple pathways exist between two autonomous systems, and one AS is trying to influence the incoming path from the other AS. A lower MED value is preferred; the default set to 0 for Cisco routers. So what we want to do is raise the MED on a subnet on the 65% route in AS 100, that when advertised to EBGP neighbor in AS 200, it prefers the 20% route.
Since the 10.10.1.48 favors the 20% from router B route due to route cost, and 10.10.1.16 favors the 65% route from router A due to the same reasoning, the subnet we should try to manipulate is the 10.10.1.32 because it is traveling the 65% path (20% +45%=65%). So lets raise the MED on the 65% path from router A to 150 so the lower MED on the 20% path from router B is preferred.
Step 1: Define the neighbor that you want to raise the MED to and the route-map you will use to do this:
Neighbor 192.168.30.2 route-map AS_50 out
Step 2: Write the Route map to raise Med to 150 and define the traffic associated with this route-map via ACL:
route-map as_50 permit 10
match IP address 50
set metric 150
access-list 50 permit 10.10.1.32 0.0.0.240
Now you have raised the med of a 20% traffic across the Router A route to the AS200. This traffic will now switch to use router B route as the preferred route due to lower MED. This in turn raises the traffic on router B to 40% (from 20%) and lowers the traffic on router A to 45% (from 65%).
Based on the explanation, shouldn't my answer be correct? Also the access-list entry wildcard mask should be 0.0.0.7 and not 0.0.0.240