three layered hierarchical network design - BSCI

Can you quote a book or a pdf?

I agree. Answer should be A. Access lists are implemented on Access Layer most of the times.

I think it should be the answer A. Not B. Doing any access control checks at the distribute level is a bad mistake and security concern. Remote access layer connections are aggregated by the address aggregation. Regards, Andrew

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B. Access-lists

The distribution layer also aggregates multiple access layer remote connections but doesn't aggregate addresses.

Peter

I still think B. is the correct answer, I did this test last week, and did pass but dont take my word for it, here's what the text books say.

The clue is also that the answer A just is not true... the distribution layer doesn't have anything to do with address aggregation, that is done with good network design using a hierarchial addressing plan, vlsm and using summarization etc.

Address Aggregation is done by border routers doing summarization eg. ABR's is OSPF, EIGRP summary routes etc. the distribution layer is the consolidation (aggregation) point for access-layer devices.

Yes, you can have firewalls, vlans and access-lists at the access-layer but, you can also have access-lists for policy-based connectivity at the distribution layer.

CCNP BSCI Exam Certification Guide (Third Edition) by Clare Gough

Page 91 - 92

The Distribution Layer

----------------------

"The distribution layer provides connectivity between several parts of the access-layer. The distribution layer is responsible for determining access across the campus backbone by filtering out unnecessary resource updates and by selectively granting specific access to users and departments.

Access-lists are used not just as traffic filters, but as the first level of rudimentary security.

Access to the Internet is implemented here, requiring a more sophisticated security or firewall system".

Also from: CCNP Self Study Building Scalable Cisco Internetworks (BSCI) Second Edition by Catherine Paquet and Diane Teare - Page 6

Distribution Layer

- Provides policy-based connectivity and is the consolidation point for access layer devices and corporate services.

Hope this helps, Peter.