Implementing and Operating Cisco Service Provider Network Core Technologies
Question
You are writing an RPL script to accept routes only from certain autonomous systems.
Consider this code: RP/0/RP0/CPU0:router(config-rpl)# if as-path in (ios-regex '.*77$') RP/0/RP0/CPU0:router(config-rpl-if)# pass RP/0/RP0/CPU0:router(config-rpl-if)# endif If you apply this code to BGP filters, which effect does the code have on your router?
Answers
Explanations
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A. B. C. D.B.
The given RPL script is used to filter incoming routes from specific Autonomous Systems (AS) in BGP. The script is checking for the AS-path attribute of the BGP route and filtering out routes that do not match the specified regular expression.
The regular expression used in the script is .*77$. This regular expression matches any string that ends with "77". Therefore, if a BGP route's AS-path ends with "77", the route will be allowed. Otherwise, it will be denied.
Now, let's consider the options given in the question:
A. denies routes from AS 7070: This option is incorrect because the regular expression in the RPL script does not match AS 7070. The regular expression only matches AS numbers that end with "77".
B. allows routes from AS 7077: This option is correct because the regular expression in the RPL script matches AS numbers that end with "77". AS 7077 ends with "77", so the script allows routes from this AS.
C. denies routes from AS 7007: This option is incorrect because the regular expression in the RPL script does not match AS 7007. The regular expression only matches AS numbers that end with "77".
D. allows routes from AS 770: This option is incorrect because the regular expression in the RPL script does not match AS 770. The regular expression matches AS numbers that end with "77", but AS 770 does not end with "77".
Therefore, the correct answer is option B: allows routes from AS 7077.
