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[NO SUMMARY] R&S C5 : Inter-VLAN Routing (5.1 Inter-VLAN Routing…

- - - - forwarding network traffic from one VLAN to another VLAN using a router
    - - beginning : routers with multiple physical interfaces had to be connected to seperate network and configured with a distinct subnet
    - - router configuration in
        which a single
        physical interface routes traffic between
        multiple VLANs on a network
        
        internally routing between
        VLANs using subinterfaces
        
        subinterface
        
        software-based virtual interfaces
        associated
        with a single physical interface
    - - can perform layer 2
        and layer 3 functions
      - support dynamic routing
        and inter-VLAN routing
      - to enable : to perform routing functions : multilayer must have IP routing enabled
      - upgrade:r layer 2 device with upgrades
      - not replacement for
        router because router
        has extra security
      - sdm prefer lanbase-routing
  - - - legacy inter-VLAN routing requires rouers to have multiple physical interfaces
      - each one of the router's physical interfaces is connected to a uniquue VLAN
      - each interface is also configured with an IP address for the subnet associated with the particular vlan
      - network devices use the router as a gateway to access the devices connected to the other VLANs
    - - vlan 10
        vlan 30
        interface f0/11
        switchport access vlan 10
        interface f0/4
        switchport access vlan 10
        interface f0/6
        switchport access vlan 30
        interface f0/5
        switchport access vlan 30
        end
    - - interface g0/0
        ip address 172.17.10.1 255.255.255.0
        no shutdown
        interface g0/1
        ip address 172.17.30.1
        255.255.255.0
  - - - use VLAN trunking and subinterfaces
      - VLAN trunking allows a single physical router interface to route traffic for multiple VLANs
      - physical interface of the router must be connected to a trunk link on the adjacent switch
      - on the router, subinterfaces are created for each unique VLAN
      - each subinterface is assigned an IP address specific to its subnet or VLAN and is also configured to tag frames for that VLAN
    - - vlan 10
        vlan 30
        interface f0/5
        switchport mode trunk
        end
    - - interface g0/0.10
        encapsulation dot1q 10
        ip address 172.17.10.1 255.255.255.0
        interface g0/0.30
        encapsulation dot1q 30
        ip address 172.17.30.1 255.255.255.0
        interface g0/0
        no shutdown
    - - show vlans
      - show ip route
    - - access to devices on remote VLANs can be tested using the ping command.
      - the ping command sends an ICMP echo request to the destination address
      - when a host receives an ICMP echo request, it responds with an ICMP echo reply
      - Tracert is a useful utility for confirming the routed path taken between two devices
- - - - when using legacy routing model, ensure that the switch ports connect to the router interfaces and are configured with the correct VLANs
      - use switchport access vlan command to correct any erroneous VLAN port assignment
      - Ensure that the router is connected to the correct switch port
      - when using router-on-a-stick, ensure that the switch port connected to the router is configured as a trunk link
      - use the switchport mode trunk command to make the switch port a trunk
    - - show interfaces
        fastEthernet 0/4 switchport
        
        Administrative Mode: static access
        
        Access Mode VLAN: 1 (default)
    - - with router-on-a-stick configurations, a common problem i sassigning the wrong VLAN ID to the subinterface
      - the show interface command can help detect this problem
      - if this is the case, use the encapsulation dot1q <vlan_id> interface command to fix the problem
      - COMMAND
        
        show interfaces
        
        Encapsulation 802.1Q Virtual LAn, Vlan ID 100
        
        show run
        
        encapsulation dot1Q 100
  - - - when using legacy inter-VLAN routing, ensure that the router has the correct IP address and mask on the interfaces connection to the switch
      - ensure that the network devices are configured with the correct IP address and mask
      - in the router, use the ip address command to fix any erroneous IP assignments
      - in the PCs, refer to the installed operating system documentation to properly change IP information
    - - use the show ip interface command to verify the correct IP address is configured in the router
      - use the show running-ocnifg when troubleshooting router-related problems
      - when troubleshooting addressing issues , ensure that the subinterface is configured with the correct address for the VLAN
      - subinterface IDs are often configured to match the VLAN number, which makes it easier to manage inter-VLAN configuratoin, but this is not a requirement
- - - - catalyst multilayer switches support
        the following types of layer 3 interfaces
        
        Routed port
        
        pure layer 3 interface similar to a
        physical interface on a Cisco IOS Router
        
        Switch Virtual Interface (SVI)
        
        Virtual VLAN interface for inter-VLAN routing
    - - today's routing has become faster and cheaper
        and can be performed at hardware speed
      - routing can be transferred to core and distribution devices with little to no impact on network performance
      - many users are in separate VLANs , and each VLAN is usually a separate subnet.
        This implies that each distribution switch must have IP addresses matching each access switch VLAN
      - layer 3 (routed) ports are normally implemented between the distribution and the core layer. this model is less dependent on spanning tree, because there are no loop sin the layer 2 portion of the topology
    - - routed port
        
        physical port act similarly to
        an interface on router
    - - SVI is virtual interfac configured within multilayer switch,
      - for every vlan exist on switch
      - WHY CREATE SVI
        
        provide gateway for VLAN so traffic can
        be routed into or out of that VLAN
        
        provide layer 3 IP connectivity to switch
        
        support routing protocol and
        bridging configurations
      - ADVANTAGES OF SVI
        
        faster than router-on-a-stick
        (everything hardware switched/routed)
        
        no external links from switch to router
        
        no limit to one link
        
        latency lower (not leaving switch)
      - DISADVANTAGE OF SVI
        
        multilayer switches are
        more expensive
    - - SDM
        
        Cisco Switch Database Manager
        
        SDM lanbase-routing template that switch will route between VLANs and to support static routing
  - - - check this:
        
        VLANs
        
        VLANs defined
        across all switches
        
        Vlans must be enabled on the trunk ports
        
        Ports in the right VLANs
        
        SVIs (switch virtual interface)
        
        SVI need correct IP/ subnet mask
        
        SVI must be up
        
        SVI must match VLAN number
        
        Routing
        
        routing must be enabled
        
        each interface/network should
        be added to routing protocol
        
        Hosts
        
        hosts need correct IP
        
        hosts have default gateway
        associated with SVI or routed port