Cisco CCNA Study – Day 4 | Stuff that a middle age man is still learning

I was hoping to more than halfway done at this point, but there is a lot to learn and the labs are taking a little longer than I was hoping, but this is a good thing as the more I use the commands the better off I will be for the test and plus this will all be a reference for future review when I can’t remember commands 🙂

Section 20: OSPF – Open Shortest Path First

OSPF Adjacencies
- Focus on the first three steps in the OSPF Operations
  - OSPF Operations Review
    - Discover neighbors
    - Form adjacencies
    - Flood LSDB (Link State Database)
    - Compute the shortest path
    - Install best routes in the routing table
    - Respond to network changes
  - OSPF Packet Types Review
    - Hello – Used to find adjacent routers
    - DBD (DataBase Description) packets – Used for adjacent routers to tell each other the networks they know about.
    - LSR Link State Request – Used to populated missing info in the received DBD
    - LSA (Link State Advertisement) – Route Update
    - LSU (Link State Update) – List of LSA’s which should be updated, used during flooding
    - LSAck – LSA acknowledgment
- Hello Packets
  - OSPF routers discover each other and form adjacencies via Hello packets
  - Hello packets our sent out non-passive OSPF enabled interfaces.
  - Multicast on 224.0.0.5 every 10 seconds
  - Hello Packet Contents
    - Router ID
    - Hello Interval – Default 10 seconds
    - Dead Interval – Default 4x Hello Interval
    - Neighbors – list of adjacent OSPF routers that it has received Hello packets from
    - Area ID –
    - Router Priority – 8 bit number used to select DR (Designated Router) and BDR (Backup Designated Router)
    - DR and BDR IPv4 Address – If known
    - Authentication Flag – Auth details
    - Stub Area Flag – uses ABR to connect two OSPF areas
  - Routers must match for adjacency
    - Must be each other’s Neighbor list
    - Following must match
      - Hello and Dead Intervals
      - Area IDs
      - IP Subnet
      - Auth Flag
      - Stub Area Flag
- OSPF DR and BDR Designated Routers
  - When there are multiple routers in a multiaccess segment/subnet it is not effective for the routers to create a 1 to 1 link between each router to pass information.
  - DR (Designated Router)
    - Will control all replication for all routers on the segment
  - BDR (Backup Designated Router)
    - In place, if the DR goes down
  - The DR and BDR are elected
    - Router with the highest priority (0-255) becomes DR and the second-highest priority becomes BDR with the highest Router ID breaking a tie. Priority is set manually if not left at default which is 1.
      - Set Priority to zero if you wish the router to not become a DR or BDR
    - Ethernet interfaces will be considered a multiaccess segment and a DR/BDR will be designated, but serial connections are point to point and no DR/BDR will be advertised/elected.
  - OSPF Priority Command
    - (config#interface [interface]
    - (config-if)#ip ospf priority [0-255]
      - OSPF restart on the interface for change to take place
        
        Restart router
        
        Disable/Enable interface
        
        Clear OSPF
        
        command: #clear ip ospf process
        
        This does not cause a full election and the BDR will remain the same and the command would need to be restarted on the old BDR or the old DR for the BDR to change.
  - In the case of four routers on a segment, the DR and BDR will be in a full state communication with all the routers to pass information, the two routers that are not a DR or BDR, they will reside in a 2-way state to ensure each other are up and running but will not passing routing information.
    - If there is a link-state change an LSU packet is sent multicast over 224.0.0.6 to all designated routers
    - DR will multicast the update on 224.0.0.5 to all OSPF routers
- OSPF Areas
  - Potential issues
    - Too many routes can use up to much memory
    - Network changes on large networks can take a long time to reconverge and use a lot of CPU resources
  - Resolution for large networks
    - OSPF supports a hierarchical design, large networks into smaller areas
      - Transit area (backbone/area 0), generally does not contain users
      - Regular areas connect end-users to the transit area to connect to other areas
    - Routers maintains full info about its own area and summary info about other areas
  - Router types
    - Backbone contains all routes for area 0
    - ABR (Area Border Router) and contains multiple areas
      - Separates LSA flooding zones
      - Summarizes area address
      - Source for default routes
      - Maintains the LSDB for each area that is it connected to
      - Recommended that it is only connected to two areas
      - Summarisation is not automatic and needs to be configured manually
        
        (config-router)#area [area id] range [network address] [subnet]
  - Summary routes will show in the ‘#show ip route’ as ‘O IA’ which is OSPF inter area
  - ASBR (Autonomous System Boundry Router)
    - it is running OSPF but it is providing routes from another source
      - Example: RIP, EIGRP or static routes being distributed from another source
      - From “#show ip route’ it will show up as O*E1 or O*E2 route

Section 21: VLANs Virtual Local Area Networks

VLAN
- Operate at Layer 3
- Separate IP subnets and need a router to be able to communicate.
- Provide performance and security by splitting networks into smaller domains
- Layer 2 Switches broadcast traffic everywhere including between different IP subnets
VLAN Access Ports
- Where end hosts are plugged in.
- Have one VLAN
- end host is not VLAN aware
VLAN commands
- Create VLAN
  - (config)#vlan [vlan#]
  - (config-vlan)#name [text]
- Assign interface to VLAN
  - (config)#interface [interface] – Single interface
    - For multiple interfaces: (config)#interface range [interface range]
  - (config-if)#switchport mode access
  - (config-if)#switchport access vlan [vlan#]
- Trunk Ports
  - Dot1Q Trunk Port
    - Tags layer 2 Dot1Q header with correct VLAN
    - Receiving switch only forwards traffic out to requested VLAN ports
    - Dot1Q tad is removed from frame when it sends to the end host
  - Trunk Commands
    - (config)#interface [interface]
    - (config-interface)#description [text]
    - (config-interface)#switchport trunk encapsulation dot1q
    - (config-interface)#switchport mode trunk
  - Access Trunk Port
    - (config)#interface [interface]
    - (config-interface)#description [text]
    - (config-interface)#switchport mode access
    - (config-interface)#switchport access vlan 10
    - (config-interface)#switchport voice vlan 20
  - Native VLAN
    - Switch needs to know which VLAN to assign to any traffic which is untagged on a trunk port
    - Default VLAN is VLAN 1
      - It is recommended to change to a different VLAN then VLAN 1 for security concerns.
    - native VLAN must match on both sides of a trunk for it to come up
    - Native VLAN Configuration Command
      - Create VLAN
        
        (config)#vlan [vlan#]
        
        (config-vlan)#name [test description: Native]
      - Configure Trunk Port
        
        (config)#interface [interface]
        
        (config-interface)#description [text]
        
        (config-interface)#switchport trunk encapsulation dot1q
        
        (config-interface)#switchport mode trunk
        
        (config-interface)#switchport trunk native vlan 199
    - Allow VLAN over Trunk
      - (config)# interface [interface]
      - (config-interface)#switchport trunk allowed vlan [vlan#s separated by a comma]
  - DTP Dynamic Trunking Protocol
    - It is recommended not to use DTP and to manually configure the access and trunk ports
    - DTP configuration commands
      - #Switchport mode dynamic auto
        
        Will form a trunk if the neighbor switch port is set to trunk or desirable.
      - #Switchport mode dynamic desirable
        
        Will form a trunk if the neighbor switch port is set to trunk, desirable or auto
      - #Switchport nonegotiate
        
        disables DTP
  - VTP VLAN Trunking Protocol
    - Allows you to add, edit or delete VLANs on switches configured as VTP server
    - Switches configured as VTP clients synchronize their VLAN database with VTP servers
    - Good for large campus
    - If switch with a hight VLAN database revision number in the domain it can wipe out all your production VLANs
    - VTP domain name has to match on neighbor switches for DTP trunks to be formed.
    - VTP Modes
      - VTP Server
        
        Can add, edit or delete VLANs
        
        Sync VLAN database from another server with a higher revision number
      - VTP Client
        
        Cannot add, edit or delete VLANs
        
        Sync VLAN database from the server with the highest revision number
      - VTP Transparent
        
        Does not participate in the VTP domain
        
        Can add, edit or delete VLANs in its own local VLAN database
    - VTP Commands
      - Create a VTP domain
        
        (config)#vtp domain [Domain name]
      - Assign device VTP mode
        
        Server
        
        (config)#vtp mode server
        
        Client
        
        (config#vtp mode client
        
        Transpaent
        
        (config)#vtp mode transparent
      - Verification
        
        #show vtp status

Section 22: Inter-VLAN Routing

Router with separate Interfaces
- Config like it is a regular setup, no special setup.
Router on a Stick
- Create a sub interface on the router and use the same setting as a physical interface
- Commands
  - Enable router the interface that will be used
    - (config)#interface [interface: example: f0/1]
    - (config-interface)#no ip address
    - (config-interface)#no shutdown
  - Create VLAN interface
    - (config)#interface [interface: example: f0/1.10]
    - (config)#encapsulation dot1q 10
    - (config-interface)#ip address [ip address] [subnet]
    - (config)#interface [interface: example: f0/1.10]
    - (config)#encapsulation dot1q 20
    - (config-interface)#ip address [ip address] [subnet]
  - Set switch trunk
    - (config)#interface [interface]
    - (config-if)#switchport mode trunk
Layer 3 Switch
- Use SVI (Switched Virtual Interfaces) for the gateways interfaces
- Inter-VLAN Routing Configuration Commands
  - (config)#ip routing
  - (config)#interface vlan [vlan1#]
  - (config-if)#ip address [gateway ip address] [gateway subnet]
  - (config)#interface vlan [vlan2#]
  - (config-if)#ip address [gateway ip address] [gateway subnet]
- WAN Routing Configuration
  - Switch Example
    - (config)#interface F0/1
    - (config-if)#no switchport
    - (config-if#ip address 10.10.100.1 255.255.255.0
    - (config)#ip route 0.0.0.0 0.0.0.0 10.10.100.2
  - Router
    - (config)#interface f0/1
    - (config-interface)#ip address 10.10.100.2 255.255.255.0
    - (config)#interface f0/2
    - (config-interface)#ip address 203.0.113.1 255.255.255.0
    - (config)#ip route 0.0.0.0 0.0.0.0 203.0.113.2
    - (config)#ip route 10.10.0.0 255.255.0.0.10.10.100.1