Project ForgeComputer Networks
Transport Protocols & IP Addressing
GATE 2017
Medium
The maximum number of IPv4 router addresses that can be listed in the record route (RR) option field of an IPv4 header is ____.
9
Explanation
The IPv4 header's options area can be at most 40 bytes (60-byte max header − 20-byte fixed part). The RR option itself has 3 bytes of overhead (code, length, pointer), leaving 37 bytes for addresses. Each IPv4 address takes 4 bytes, so ⌊37/4⌋ = 9 addresses can be listed.
Source: GATE CS 2017 (Session 2) (2017)
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