Refer to the exhibit.
There are two eBGP links between AS100 and AS200. Currently the router A to router E link has
an average inbound load of 65% and the router B to router F link has an average inbound load of
20%. After further investigation, it is found that traffic to the 10.10.1.16/28 subnet is using 45% of
the bandwidth on the A to router E link and traffic to the 10.10.1.32/28 subnet is using 20% of the
bandwidth on the A to router E link. Traffic to the 10.10.1.48/28 subnet is using 20% of the
bandwidth on the B to router F link. If you want to influence how AS200 sends traffic to AS100,
which two commands would you configure in AS100 to influence AS200 to use the eBGP links
more evenly? (Choose two.)
A.
neighbor 192.168.30.2 route-map as_50 out
B.
neighbor 192.168.20.2 route-map as_50 out
C.
route-map as_50 permit 10
match ip address 50
set metric 150
access-list 50 permit 10.10.1.16 0.0.0.240
D.
route-map as_50 permit 10
match ip address 50
set metric 150
access-list 50 permit 10.10.1.32 0.0.0.15
B&D Are correct.
First let’s recall about MED. If you want to influence external neighbors about the path it sends traffic then MED, also called the metric, should be used. A lower MED value is preferred over a higher value. The default MED value is 0.
Also, an important point I wish to notice in this question is: for Policy-based routing, if no match is made, the packets are forwarded normally via the routing table.
In answer C & B (combined), the MED for prefix 10.10.1.16/28 through router A is set to 150. This would make traffic for this route (45%) go through router B (because the MED default value is 0, which is lower than 150). Since the access-list will also NOT match prefixes: 10.10.1.32/28 & 10.10.1.48/28 – traffic for these two prefixes will be forwarded just normally (via the routing table) ->
Traffic for prefix: 10.10.1.32/28 will continue to go via the upper E-A link (now just 20% total load), while traffic for prefixes 10.10.1.16/28 and 10.10.1.48/28 will be going through the lower F-B link (now 65% total load) -> Original unbalanced (65/20) load is maintained, although it has been reversed between the upper (A-E) and lower (B-F) link -> C is not correct.
For more information about Policy-based routing matches you can read this article: http://www.ciscopress.com/articles/article.asp?p=426637&seqNum=2
If answer D is applied for router A, the MED for 10.10.1.32 set to 150 would make traffic for this route go through router B (because the MED default value is 0, which is lower than 150). So router A will be responsible for 45% traffic and router B will receive 40% traffic -> D is correct.
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