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9059 Views 18 Replies Latest reply: Apr 19, 2010 9:50 AM by Conwyn RSS 1 2 Previous Next

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SVI

Apr 16, 2010 11:45 AM

Tim 57 posts since
Nov 9, 2009

Hello Everyone

I have some question about SVI (switch virtual interface)

Q: I have switch 2960 with VLAN 20 & VLAN 50

VLAN 10 : ip address 192.168.10.X 

VLAN 20 ip address 192.168.20.X

With no default gateway I am able to access the my server which is on different VLAN

Can some explain how is working without default gateway my studies you can ping between same VLAN without switch  default-gateway but if any thing going to the different VLAN then they need a default-gateway to route right I am confuse

Please help

  • Conwyn 7,914 posts since
    Sep 10, 2008
    Currently Being Moderated
    1. Apr 16, 2010 12:06 PM (in response to Tim)
    Re: SVI

    Hi Tim

     

    If you have more than one SVI active then you have a L3 switch.

     

    So inter vlan routing will automatically route between the SVI for vlan A and the SVI for vlan B.

     

    I never realised 2960 supported L3 switch. Are you sure you have not got a router on a stick hiding somewhere.

     

    Proxy arp on the router monitors traffic and if it sees a requested for a route it knows about it replies with his arp and the routes the traffic.

     

    Regards Conwyn

  • Keith Barker - CCIE RS/Security, CISSP 5,351 posts since
    Jul 3, 2009
    Currently Being Moderated
    2. Apr 16, 2010 12:09 PM (in response to Tim)
    Re: SVI

    Tim-

     

    To fully answer your question, (accurately), it would be helpful to know:

     

    VLANs on the switch (exactly)

    VLAN interfaces on the switch, including IP address

    Which port the server is connected to, and what VLAN is that port assigned

    What the IP address of the server is

     

    With that info, there is a better chance of getting a meaningful answer, that is also correct.

     

    Let us know.

     

    Keith

  • Conwyn 7,914 posts since
    Sep 10, 2008
    Currently Being Moderated
    Re: SVI

    Hi Keith

     

    2960 is a L2 switch.

     

    Regards Conwyn

  • Conwyn 7,914 posts since
    Sep 10, 2008
    Currently Being Moderated
    5. Apr 16, 2010 12:50 PM (in response to Tim)
    Re: SVI

    Hi Tim

     

    If you have a 3750 without ip routing then it is a L2 switch

     

    ip default-gateway simply allows you to telnet to the management vlan

     

    If you have a 3750 with ip routing then it is a L3 switch. default-gateway is ignored. Use ip route 0.0.0.0 0.0.0.0 a.b.c.d  or ip default-network or routing protocol. Inter-vlan routing will occur naturally as well as inter routed port.

     

    Regards Conwyn

  • Conwyn 7,914 posts since
    Sep 10, 2008
    Currently Being Moderated
    7. Apr 16, 2010 1:00 PM (in response to Tim)
    Re: SVI

    Hi Tim

     

    Please post your config

     

    Regards Conwyn

  • Conwyn 7,914 posts since
    Sep 10, 2008
    Currently Being Moderated
    9. Apr 16, 2010 1:52 PM (in response to Tim)
    Re: SVI

    Hi Tim

     

    2960 do support multiple SVI since 12.2 (something) but not routing. I think traffic is going down gi0/1 and the core is using proxy arp to do the routing for you.

     

    Regards Conwyn

  • Conwyn 7,914 posts since
    Sep 10, 2008
    Currently Being Moderated
    11. Apr 16, 2010 11:05 PM (in response to Tim)
    Re: SVI

    Hi Tim

     

    For a L2 switch such as the 2960 the int vlan x is used for switch management via telnet.

     

    default-gateway is used to allow the switch management output to get back to the person doing the telnet.

     

    It is nothing to do with inter-vlan routing.

     

    It is unfortuate that they call L2 switches SVI they should be called Management VI (MVI) to avoid confusion.

     

    I believe you have intervlan routing because your trunk to the core is using proxy-arp on the core. You could switch off g0/1 and see if you still have inter vlan traffic

     

    Regards Conwyn

  • Conwyn 7,914 posts since
    Sep 10, 2008
    Currently Being Moderated
    13. Apr 17, 2010 8:59 PM (in response to Tim)
    Re: SVI

    Hi Tim

     

    The proxy arp will be on your router or L3 switch. On the 2960 you have a trunk on 0/1 I assume there is router or L3 switch on the other end

     

    show ip int gi0/0

     

    GigabitEthernet0/0 is up, line protocol is up
      Internet address is /20
      Broadcast address is 255.255.255.255
      Helper address is not set
      Directed broadcast forwarding is disabled
        Proxy ARP is enabled

     

    Regards Conwyn

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