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Configuring InterVlan Routing

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Title: Configuring InterVlan Routing


1
Configuring InterVlan Routing
  • Presented By
  • Brian, Kevin, and John

2
Understanding How InterVLAN Routing Works
  • Network devices in different VLANs cannot
    communicate with one another without a router to
    route traffic between the VLANs. In most network
    environments, VLANs are associated with
    individual networks or subnetworks.

3
  • Configuring VLANs helps control the size of
    the broadcast domain and keeps local traffic
    local. However, when an end station in one VLAN
    needs to communicate with an end station in
    another VLAN, interVLAN communication is
    required. This communication is supported by
    interVLAN routing. You configure one or more
    routers to route traffic to the appropriate
    destination VLAN.

4
  • However, the real power of virtual networking
    comes from its ability to affect VLAN topologies
    that extend beyond single sites to combine
    multiple LANs across an organization's backbone
    network. Cisco Systems now offers a comprehensive
    VLAN solution that can bring together
    geographically dispersed users across an
    enterprise network to form VLAN workgroup
    topologies. Regardless of whether the network
    comprises Asynchronous Transfer Mode (ATM), Fiber
    Distributed Data Interface (FDDI), Ethernet/Fast
    Ethernet, Token Ring, or serial links, the Cisco
    product line now offers the advantages of
    virtualization.

5
  • The degree of flexibility and control that
    virtual networking offers is unprecedented.
    Regardless of physical location or interface
    type, network managers can define workgroups
    based on logical function rather than physical
    location through simple port configuration. Using
    switches and routers that have embedded VLAN
    intelligence obviates the need for expensive,
    time-consuming recabling to extend connectivity
    in switched LAN environments.

6
New Cisco IOS VLAN Services Make "Virtual" a
Reality
  • Virtual networking has rapidly become one of
    the major new areas in the internetworking
    industry. Virtual networking refers to the
    ability of switches and routers to configure
    logical topologies on top of the physical network
    infrastructure, allowing any arbitrary collection
    of LAN segments within a network to be combined
    into an autonomous user group, appearing as a
    single LAN.

7
  • Virtual LANs (VLANs) offer significant
    benefits in terms of efficient use of bandwidth,
    flexibility, performance, and security. VLAN
    technology functions by logically segmenting the
    network into different broadcast domains so that
    packets are only switched between ports that are
    designated for the same VLAN. Thus, by containing
    traffic originating on a particular LAN only to
    other LANs within the same VLAN, switched virtual
    networks avoid wasting bandwidth, a drawback
    inherent in traditional bridged/switched networks
    where packets are often forwarded to LANs that do
    not require them. This approach also improves
    scalability, particularly in LAN environments
    that support broadcast- or multicast-intensive
    protocols and applications that flood packets
    throughout the network. Figure 1 depicts a
    typical VLAN, where traffic is only switched
    between LAN interfaces that belong to the same
    VLAN. Here, the criteria for VLAN membership is
    departmental function however, users could also
    be combined in VLAN topologies based upon a
    common protocol or subnet address.

8
  • Figure 1 A Typical VLAN

9
Understanding VLANs
  • A VLAN is a switched network that is
    logically segmented by function, project team, or
    application, without regard to the physical
    locations of the users. VLANs have the same
    attributes as physical LANs, but you can group
    end stations even if they are not physically
    located on the same LAN segment. Any switch port
    can belong to a VLAN, and unicast, broadcast, and
    multicast packets are forwarded and flooded only
    to end stations in the VLAN. Each VLAN is
    considered a logical network, and packets
    destined for stations that do not belong to the
    VLAN must be forwarded through a router or bridge.

10
  • Because a VLAN is considered a separate
    logical network, it contains its own bridge
    Management Information Base (MIB) information and
    can support its own implementation of spanning
    tree.

11
Understanding How InterVLAN Routing Works
  • Network devices in different VLANs cannot
    communicate with one another without a router to
    route traffic between the VLANs. In most network
    environments, VLANs are associated with
    individual networks or subnetworks.

12
Subnets and VLANs
  • Cisco recommends that you maintain a
    one-to-one relationship between subnets and
    VLANs. This means that all stations residing in
    or ports configured on the same VLAN are assigned
    network addresses with the same subnet.
  • If you wish to configure your VLAN differently
    from the existing subnets, you must reassign the
    IP addresses on the subnets to match your
    intended VLAN configuration.

13
In order to create VLANs, you must decide how to
configure the following items
  • What VLAN Trunking Protocol (VTP) domain name and
    VTP mode will be used on this switch?
  • What ports on the switch will belong to which
    VLAN?
  • Will you need to have communication between
    VLANs, or will they be isolated? If you require
    communication between VLANs, you will need to use
    a L3 routing device, such as an external Cisco
    router or an internal router module such as a
    Route Switch Module (RSM) or a Multilayer Switch
    Feature Card (MSFC).

14
Recording the Plan
  • The table should contain the following
    information
  • VLAN name
  • Switch type, name, slot, port number and port
    type of the proposed VLAN
  • Subnet of each VLAN assignment
  • Location where you plan to connect a router(s)
  • User name and user location

15
Number of VLANs and Users
  • The maximum number of users that you can define
    per known network is 1000.
  • Cisco recommends that a VLAN contain no more than
    150 to 200 users.

16
Maximum Number of Supported VLANs
  • Switch Model Number of
    Supported VLANs
  • Catalyst 2950-12 64
  • Catalyst 2950-24 64
  • Catalyst 2950C-24 250
  • Catalyst 2950G-12-EI 250
  • Catalyst 2950G-24-EI 250
  • Catalyst 2950G-48-EI 250
  • Catalyst 2950G-24-EI-DC 250
  • Catalyst 2950T-24 250

17
Configuring VTP and VLANs on the Switch
  • To successfully configure a router for
    interVLAN routing, you must configure VTP and
    create and configure VLANs on the switch.

18
  • Because a trunk link carries traffic, or
    frames, from multiple VLANs, the switch must have
    a method of identifying which VLAN a frame
    belongs to. Cisco supports four methods of frame
    identification
  • Cisco Inter-Switch Link (ISL)The Cisco
    proprietary trunking method used over Fast
    Ethernet, Gigabit Ethernet, and EtherChannel
  • IEEE 802.1QThe IEEE industry standard trunking
    method, also used over Fast Ethernet, Gigabit
    Ethernet, and EtherChannel
  • 802.10The Cisco proprietary method of trunking
    over Fiber Distributed Data Interface (FDDI)
  • LAN Emulation (LANE)The IEEE standard for
    trunking over Asynchronous Transfer Mode (ATM)
    networks

19
Virtual LAN Standardization - IEEE 802.1Q
  • Cisco Systems pioneered the frame tagging
    technique for virtual LANs with both the ISL
    protocol and the use of the IEEE 802.10 Standard
    and has leveraged that experience to take a
    leadership role in defining the emerging,
    functionally equivalent IEEE 802.1Q virtual LAN
    Standard. It is anticipated that this standard
    with be ratified later in 1997 following which
    the Cisco IOS(tm) will offer the same
    comprehensive capabilities for IEEE 802.1Q based
    vLANs as are currently available with ISL, IEEE
    802.10 and LAN Emulation based virtual LANs.
    Support for IEEE 802.1Q will be delivered via a
    regular software upgrade available on Cisco
    IOS(tm) router and switch platforms.

20
  • While configuring 802.1Q trunking it is very
    important to match the native VLAN across the
    link. In the Cisco IOS software versions earlier
    than 12.1(3)T, you cannot define the native VLAN
    explicitly, as the encapsulation dot1Q 1 native
    command under the sub-interface is not
  • available.
  • In the earlier Cisco IOS versions, it is
    important not to configure VLAN1 interface as a
    sub-interface. The router then expects a tag
    dot1q frame on VLAN1 and the switch is not
    expecting a tag on VLAN1. As a result, no traffic
    will pass between VLAN1 on the switch and the
    router.

21
Using the VLAN Trunk Protocol
  • VTP is a Layer 2 messaging protocol that
    maintains VLAN configuration consistency by
    managing the addition, deletion, and renaming of
    VLANs on a network-wide basis. VTP minimizes
    misconfigurations and configuration
    inconsistencies that can cause several problems,
    such as duplicate VLAN names, incorrect VLAN-type
    specifications, and security violations.

22
  • By default, a Catalyst 2950, 2900 XL, or 3500
    XL switch is in the no-management-domain state
    until it receives an advertisement for a domain
    over a trunk link (a link that carries the
    traffic of multiple VLANs) or until you configure
    a domain name. The default VTP mode is server
    mode, but VLAN information is not propagated over
    the network until a domain name is specified or
    learned

23
VTP server
  • In this mode, you can create, modify, and delete
    VLANs and specify other configuration parameters
    (such as VTP version) for the entire VTP domain.
    VTP servers advertise their VLAN configurations
    to other switches in the same VTP domain and
    synchronize their VLAN configurations with other
    switches based on advertisements received over
    trunk links.
  • In VTP server mode, VLAN configurations are saved
    in nonvolatile RAM. VTP server is the default
    mode.

24
VTP client
  • In this mode, a VTP client behaves like a VTP
    server, but you cannot create, change, or delete
    VLANs on a VTP client.
  • In VTP client mode, VLAN configurations are saved
    in nonvolatile RAM.

25
VTP transparent
  • In this mode, VTP transparent switches do not
    participate in VTP. A VTP transparent switch does
    not advertise its VLAN configuration and does not
    synchronize its VLAN configuration based on
    received advertisements. However, transparent
    switches do forward VTP advertisements that they
    receive from other switches. You can create,
    modify, and delete VLANs on a switch in VTP
    transparent mode.
  • In VTP transparent mode, VLAN configurations are
    saved in nonvolatile RAM, but they are not
    advertised to other switches.

26
Communication Between VLANs
  • Communication between VLANs is accomplished
    through routing, and the traditional security and
    filtering functions of the router can be used.
    Cisco IOS software provides network services such
    as security filtering, quality of service (QoS),
    and accounting on a per VLAN basis. As switched
    networks evolve to distributed VLANs, Cisco IOS
    provides key inter-VLAN communications and allows
    the network to scale.

27
VLAN Colors
  • VLAN switching is accomplished through frame
    tagging where traffic originating and contained
    within a particular virtual topology carries a
    unique VLAN identifier (VLAN ID) as it traverses
    a common backbone or trunk link. The VLAN ID
    enables VLAN switching devices to make
    intelligent forwarding decisions based on the
    embedded VLAN ID. Each VLAN is differentiated by
    a color, or VLAN identifier. The unique VLAN ID
    determines the frame coloring for the VLAN.
    Packets originating and contained within a
    particular VLAN carry the identifier that
    uniquely defines that VLAN (by the VLAN ID).

28
  • The VLAN ID allows VLAN switches and routers
    to selectively forward packets to ports with the
    same VLAN ID. The switch that receives the frame
    from the source station inserts the VLAN ID and
    the packet is switched onto the shared backbone
    network. When the frame exits the switched LAN, a
    switch strips header and forwards the frame to
    interfaces that match the VLAN color. If you are
    using a Cisco network management product such as
    VlanDirector, you can actually color code the
    VLANs and monitor VLAN graphically.

29
Adding a Tag Recomputes the Frame Control
Sequence
30
Why Implement VLANs?
  • Network managers can group logically networks
    that span all major topologies, including
    high-speed technologies such as, ATM, FDDI, and
    Fast Ethernet. By creating virtual LANs, system
    and network administrators can control traffic
    patterns and react quickly to relocations and
    keep up with constant changes in the network due
    to moving requirements and node relocation just
    by changing the VLAN member list in the router
    configuration. They can add, remove, or move
    devices or make other changes to network
    configuration using software to make the changes.

31
  • Issues regarding benefits of creating VLANs
    should have been addressed when you developed
    your network design. Issues to consider include
  • Scalability
  • Performance improvements
  • Security
  • Network additions, moves, and changes
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