Networking Fundamentals
The Networking Fundamentals domain tests whether you can reason from the wire upward: the OSI and TCP/IP models, Ethernet framing, MAC addressing and ARP, IPv4/IPv6 addressing, and the transport layer. Expect short scenario puzzles - trace a frame across a switch, decide whether a host is local, size a subnet - rather than pure definitions.
Encapsulation and device roles
A Layer 2 switch forwards on the destination MAC within one broadcast domain; unknown unicast, broadcast and multicast frames are flooded. A router or L3 switch strips the L2 header, performs a longest-prefix lookup, decrements TTL and rewrites the header. ARP requests are broadcast and are never routed; the reply is unicast.
Ethernet facts
A frame is preamble/SFD, destination MAC, source MAC, EtherType/Length, payload, FCS. Standard MTU is 1500 bytes; PowerSwitch platforms typically support jumbo frames up to 9216 bytes, but only if every hop agrees. CRC and alignment errors point at cabling or optics; late collisions point at duplex mismatch. MAC table entries age out (OS10 default 300 seconds).
IPv4 and IPv6 addressing
Prefix length maps to a mask; the block size in the interesting octet is 256 minus the mask value. Network and broadcast addresses are reserved. Private space is 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16, plus 169.254.0.0/16 link-local. IPv6 replaces ARP with neighbour discovery and uses router advertisements/SLAAC for autoconfiguration; there is no broadcast in IPv6.
Transport layer
TCP opens with SYN, SYN-ACK, ACK; useful ports are 22 SSH, 67/68 DHCP, 161 SNMP, 443 HTTPS and 514 syslog. UDP is connectionless and carries DHCP, SNMP traps, RADIUS and VXLAN (4789).
Worked example
Is 192.168.10.100/26 in the same subnet as 192.168.10.70/26? The mask is 255.255.255.192, the block size is 256 − 192 = 64, so the subnets are .0, .64, .128 and .192, each with 62 usable hosts. Both .100 and .70 fall in 192.168.10.64–.127 (network .64, broadcast .127), so the host ARPs directly and the frame is switched, not routed.
Traps
Treating the broadcast address as usable; confusing /26 (255.255.255.192) with /27 (255.255.255.224); assuming ARP crosses a router; enabling jumbo frames on only one link; thinking a switch floods known unicast traffic.