Refer to 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 toAS100, which eBGP configurations
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 0.0.0.240
Explanation:
Note: The wildcard masks in the access-list are notcorrect, they should be 0.0.0.15 instead
of 0.0.0.240.
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: there is a “deny all” statement at
the end of each access-list. In other words, all the routes that do not match the accesslist used by the route-map will be filtered out. For example in answer C, only network
10.10.1.16/28 is matched by the access-list and allother networks will be dropped (not
advertised to EBGP).
Therefore in answer C, only traffic to 10.10.1.16/28 will be go through routerA (45%). All
other traffic must go through routerB (40%) -> links are used more evenly -> C is correct.
There are some debates saying D is correct but in fact it is not. 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, whichis lower than 150). The access-list will
also filter out network 10.10.1.16 -> router E can not send traffic for network 10.10.1.16 to
router A. Now all traffic must go through router B (85%).