300-320 · Question #556
A company must acquire register IP address space from a regional Internet authority and multihome the Internet connection to multiple Internet service providers Due to limited IPv4 address…
The correct answer is A. BGP: AS prepend at the secondary DC. BGP AS path prepending at the secondary DC is the correct method. By prepending extra AS numbers to BGP advertisements sent from the secondary data center, those routes appear to have a longer (less preferred) AS path. Internet peers will prefer the shorter AS path through the…
Question
A company must acquire register IP address space from a regional Internet authority and multihome the Internet connection to multiple Internet service providers Due to limited IPv4 address availability the company was able to allocate only a /24 address block Which method must be used to ensure that the primary data center receives all traffic unless it is offline?
Options
- ABGP: AS prepend at the secondary DC.
- BEIGRP: Advertise two 125 address blocks to each ISP at the primary DC and a /24 at the
- CBGP: Advertise two /25 address blocks to each ISP at the secondary DC and a 124 at the primary
- DOSPF: AS prepend at the secondary DC.
How the community answered
(41 responses)- A61% (25)
- B22% (9)
- C12% (5)
- D5% (2)
Explanation
BGP AS path prepending at the secondary DC is the correct method. By prepending extra AS numbers to BGP advertisements sent from the secondary data center, those routes appear to have a longer (less preferred) AS path. Internet peers will prefer the shorter AS path through the primary DC, sending all traffic there. If the primary DC goes offline, traffic automatically fails over to the secondary. OSPF and EIGRP are interior routing protocols not used for multihomed Internet BGP routing. Splitting the /24 into /25 blocks is not a valid approach with only a single /24 allocation and would cause many ISPs to filter those more-specific prefixes.
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