Octet

Scenarios

Switching and VLANs

  1. Users in VLAN 20 cannot reach their gatewayTroubleshootingCore
  2. Phones, printers and cameras drop on every floor at onceIncidentWorking

IPv6

  1. After a router swap, hosts get only link-local IPv6 addressesTroubleshootingCore
  2. Laptops get IPv6 on the new Wi-Fi VLAN but Android phones do notTroubleshootingWorking
  3. Large IPv6 downloads from HQ stall at the branch after a firewall changeTroubleshootingWorking
  4. Users on one floor get a strange IPv6 prefix and slow websitesSecurityWorking

Routing fundamentals

  1. Branch fails over to the backup tunnel, but HQ keeps replying over the dead linkTroubleshootingWorking
  2. Half the connections to one VLAN fail behind a summarizing distribution pairTroubleshootingWorking
  3. Bring an acquired company with overlapping addresses onto your routersDesignExpert
  4. Traffic to a RIP branch detours through the core after a reloadTroubleshootingExpert

EIGRP, RIP and IS-IS

  1. A new branch router will not become an EIGRP neighborTroubleshootingCore
  2. Move a six-router network from RIPv2 to EIGRP without an outageMigrationWorking
  3. Variance is configured but EIGRP still uses only one pathTroubleshootingWorking
  4. A data center VLAN flap resets EIGRP neighbors at dozens of branchesIncidentExpert

BGP

  1. iBGP session stuck in Active after moving to loopback peeringTroubleshootingCore
  2. A route map change leaks ISP1's routes to ISP2 and the session dropsIncidentWorking
  3. Internal routers learn the ISP routes but nobody can reach the internetTroubleshootingWorking
  4. Inbound traffic keeps arriving on the backup ISP despite AS path prependingTroubleshootingExpert
  5. Migrate an iBGP full mesh to route reflectors without an outageMigrationExpert

IP services

  1. A newly published server cannot be reached from the internetTroubleshootingWorking
  2. A security timeline breaks because one branch router's clock is 11 minutes offIncidentWorking
  3. DHCP stops working the morning after DHCP snooping was enabledTroubleshootingWorking
  4. Users still reach the old web server hours after a DNS cutoverMigrationWorking

TCP, UDP and applications

  1. Browsers load the shop after a certificate renewal, but API clients fail TLSTroubleshootingCore
  2. Branch users cannot load the intranet over the new GRE tunnel, but ping worksTroubleshootingWorking
  3. Orders service fails every few hours with thousands of sockets in CLOSE_WAITIncidentWorking
  4. Nightly backup crawls at 8.7 Mbit/s over an idle 1 Gbit/s circuitTroubleshootingExpert

Network security

  1. A one-line ACL meant for guests takes the whole branch offlineTroubleshootingCore
  2. Third floor users get 192.168.1.x addresses on Monday morningIncidentCore
  3. After 802.1X goes to closed mode, laptops work but printers stay offlineTroubleshootingWorking
  4. New laptops get no address the morning after DHCP snooping goes liveTroubleshootingWorking

VPNs and tunnels

  1. Branch VPN shows phase 1 up but no IPsec SAs after a re-addressingTroubleshootingWorking
  2. Downloads from HQ stall over the VPN after a firewall changeIncidentWorking
  3. GRE tunnel flaps every minute after OSPF replaced static routesTroubleshootingWorking
  4. Site-to-site VPN is up but traffic only flows one wayTroubleshootingWorking

Data center

  1. A vPC peer link outage takes down single-attached servers onlyIncidentWorking
  2. Load balancer health checks are green but clients time outTroubleshootingWorking
  3. Servers on a new leaf cannot reach their VLAN across the fabricTroubleshootingWorking
  4. Design a spine-leaf fabric for a new data hallDesignExpert

Automation and SDN

  1. The nightly Netmiko config backup fails on 9 of 120 devicesTroubleshootingCore
  2. A RESTCONF script fails on one router with 409, then 400TroubleshootingWorking
  3. An Ansible playbook reports changed on every runTroubleshootingWorking
  4. An automated vty ACL change locks the NOC out of 72 switchesIncidentExpert

Cloud networking

  1. A private EC2 instance cannot reach the internet through its NAT gatewayTroubleshootingCore
  2. An app in a peered VPC reaches the replica database but not the primaryTroubleshootingWorking
  3. Site-to-site VPN to AWS is up with BGP, but no traffic passesTroubleshootingWorking
  4. Redesign a sprawling multi-account AWS network with a data center linkDesignExpert

Linux networking

  1. A rebuilt Linux router answers pings but forwards nothingTroubleshootingCore
  2. A server reaches everything by IP but cannot resolve names after a DNS migrationTroubleshootingWorking
  3. Containers lose internet access after a host firewall reloadIncidentWorking
  4. Monitoring cannot reach a server's new management addressTroubleshootingExpert

Troubleshooting

  1. The internet is down, except it is notTroubleshootingCore
  2. A branch is dark the morning after a change windowIncidentWorking
  3. A printer that keeps dropping off and coming backTroubleshootingWorking
  4. A traceroute that bounces between two routersTroubleshootingWorking
  5. Intermittent loss and slow file copies from one wiring closetTroubleshootingWorking
  6. Ping works but every application fails after a backup WAN path is addedTroubleshootingExpert
  7. The network is slow, but only when saving documentsTroubleshootingExpert

Network design

  1. Design the network for a new 200-person officeDesignWorking
  2. Find the single points of failure after a site-wide outageDesignWorking
  3. Add a second ISP with tracked defaults or BGP multihomingDesignExpert
  4. Connect an acquired company that uses the same 10.1.0.0/16MigrationExpert
  5. Migrate a flat /16 network to routed VLANs without a big-bang outageMigrationExpert
  6. The company triples in two years, scale the networkDesignExpert