200-301 Cheat Sheet

Key concepts

• ✓VLAN creation, access port assignment, 802.1Q trunking, and inter-VLAN routing via SVIs or router subinterfaces
• ✓IPv4/IPv6 interface addressing, EUI-64, SLAAC, DHCP, DNS, and default gateway configuration on hosts
• ✓Static routes, OSPFv2/v3 neighbor adjacencies, and verifying the routing table with show ip route
• ✓Wireless 2.4/5 GHz behavior, channel overlap, and fiber versus copper media characteristics

Watch out for

• ⚠Forgetting that a host needs both an IP address and a default gateway to reach other subnets, or misconfiguring DNS server addresses.
• ⚠Assuming EUI-64 works without checking the interface MAC or that SLAAC alone provides DNS, when RDNSS or DHCPv6 may be required.
• ⚠Treating trunk ports as access ports, or forgetting to allow the needed VLANs on the 802.1Q trunk between switches.

Key concepts

• ✓Configuring access ports with data VLAN and voice VLAN using switchport commands
• ✓Trunk configuration and verifying allowed VLAN lists with show interfaces trunk
• ✓Rapid PVST+ operation, root bridge election, and port roles and states
• ✓EtherChannel negotiation with LACP or PAgP and verifying with show etherchannel summary

Watch out for

• ⚠Forgetting that a trunk's allowed VLAN list must match on both ends, so a missing VLAN blocks traffic even when the trunk is up.
• ⚠Mixing up access and trunk mode commands, or leaving a port in dynamic auto so no trunk forms with another dynamic auto port.
• ⚠Assuming a blocked spanning-tree port is a fault, when blocking is normal and expected on redundant links.

Key concepts

• ✓Interpreting show ip route codes, next-hop addresses, and outgoing interfaces
• ✓Longest-prefix match selection among connected, static, and OSPF routes
• ✓Administrative distance comparison, including static routes with modified distance
• ✓Static route configuration with ip route, including default and floating routes

Watch out for

• ⚠Assuming the lowest administrative distance always wins; longest prefix match is checked before administrative distance.
• ⚠Forgetting that a static route with distance 200 loses to OSPF (distance 110) while OSPF is up.
• ⚠Mixing up next-hop IP and exit interface in static routes, causing unresolved or recursive routing.

Key concepts

• ✓Ordering DHCP relay and DHCP snooping steps on a Cisco switch with a remote DHCP server
• ✓Diagnosing dynamic NAT failure where inside hosts reach outside but return replies never arrive
• ✓Comparing IPv4 and IPv6 ACL statements, implicit denies, and wildcard versus prefix matching
• ✓Troubleshooting DNS resolution failures for a VLAN despite working IP reachability

Watch out for

• ⚠Configuring ip helper-address on the wrong interface or forgetting it entirely, so DHCP broadcasts never reach the remote server.
• ⚠Mixing up NAT inside and outside interface designations, which breaks return traffic even when outbound translation works.
• ⚠Assuming IPv4 wildcard masks work like IPv6 prefix lengths, or forgetting that every ACL ends with an implicit deny.

Key concepts

• ✓Match REST methods GET, POST, PUT, PATCH, DELETE to read, create, replace, update, delete intents
• ✓Identify NETCONF as SSH-based, XML-encoded, using YANG models and RPC operations like get-config
• ✓Recognize RESTCONF as HTTPS-based, supporting JSON and XML, using HTTP verbs for CRUD on YANG data
• ✓Explain HTTPS preference over HTTP for controller APIs due to TLS encryption, authentication, and integrity

Watch out for

• ⚠Confusing PUT (full replace) with PATCH (partial update) when mapping REST methods to configuration changes.
• ⚠Assuming NETCONF uses HTTP or JSON; it runs over SSH and encodes data in XML, not JSON.
• ⚠Believing HTTPS only encrypts data but does not verify server identity; TLS also authenticates via certificates.