Which one of the following protocols may need to broadcast some of its messages?

Question

A database has 25,000 fixed-length records of 100 bytes (primary key 15 bytes). The data file is block-aligned so each record is fully contained within a block. The file is indexed by a primary index file, also block-aligned and ordered. Block size is 1024 bytes and a block pointer is 5 bytes. Each index entry stores the block’s anchor key (15 bytes) and a pointer (5 bytes). Binary search on an index file of \(b\) blocks needs \(\lceil \log_2 b \rceil\) block accesses in the worst case. Given a key, the number of block accesses required to identify the data file block that may contain the record, in the worst case, is ____________.

Answer 1

The question is really asking which of these protocols can find itself needing to send a message without already knowing a specific destination IP address, since broadcasting is the fallback used exactly in that situation.

SMTP: used between mail servers that already know each other's address, found through a DNS MX lookup beforehand; it always talks point to point, never by broadcast.
FTP: the client must dial a known server IP to even open the control channel; there is no stage where FTP needs to reach whoever is listening on the network, so it is always unicast.
DHCP: a host joining a network for the first time typically has no IP address of its own and does not know the DHCP server's address either. Its opening message, DHCPDISCOVER, is sent as a local broadcast, to 255.255.255.255, so any DHCP server on the segment can pick it up and reply; later messages in the handshake are often broadcast too, until the client is fully configured.
HTTP: the client resolves the web server's IP through DNS before sending any request, so it always talks directly, unicast, to that one server.

Only DHCP has a genuine reason to broadcast: it operates at a point where the requesting host cannot yet address anyone directly. The other three protocols always have a specific, already known destination.

Let's summarize:

Broadcasting is needed when a host does not yet know who to talk to directly, exactly DHCP's situation when it first joins a network.
SMTP, FTP, and HTTP all run over connections to an already-known server address, so they stay unicast.

So the protocol that may need to broadcast its messages is DHCP, option (C).

Answer 2

The question is really asking which of these protocols can find itself needing to send a message without already knowing a specific destination IP address, since broadcasting is the fallback used exactly in that situation.

SMTP: used between mail servers that already know each other's address, found through a DNS MX lookup beforehand; it always talks point to point, never by broadcast.
FTP: the client must dial a known server IP to even open the control channel; there is no stage where FTP needs to reach whoever is listening on the network, so it is always unicast.
DHCP: a host joining a network for the first time typically has no IP address of its own and does not know the DHCP server's address either. Its opening message, DHCPDISCOVER, is sent as a local broadcast, to 255.255.255.255, so any DHCP server on the segment can pick it up and reply; later messages in the handshake are often broadcast too, until the client is fully configured.
HTTP: the client resolves the web server's IP through DNS before sending any request, so it always talks directly, unicast, to that one server.

Only DHCP has a genuine reason to broadcast: it operates at a point where the requesting host cannot yet address anyone directly. The other three protocols always have a specific, already known destination.

Let's summarize:

Broadcasting is needed when a host does not yet know who to talk to directly, exactly DHCP's situation when it first joins a network.
SMTP, FTP, and HTTP all run over connections to an already-known server address, so they stay unicast.

So the protocol that may need to broadcast its messages is DHCP, option (C).

Which one of the following protocols may need to broadcast some of its messages?

Show Hint

The Correct Option is C

Solution and Explanation

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