What's happening

Discussion in 'Cisco' started by Seth, Dec 4, 2004.

  1. Seth

    Seth Guest

    Hi

    I have inherited a "non-standard" switching network that of course has some
    spotty problems. What are the negative effects of doing it this way? (if
    any)

    Core switch 6509 using vlans to segregate traffic. Access layer switches
    with NO trunking over the Etherchannel links (2xGigabit ports on 3500XL's).
    To make it more interesting, there are two networks on the same wire (not
    vlan'd). On top of that, all the ports on the access switch are added to a
    local vlan which just happens to match the VLAN number on the core switch.
    Usually one server at a time has trouble dropping packets for 3+ minutes at
    a time. Problem solved by moving server to the core switch.

    Is this common to use "transparent" VLANs like this? (The access switch is
    on a VLAN but doesn't know it.)

    I can see the horrible efficiency of 2 hosts on separate subnets on the same
    access vlan switch trying to talk. Traffic to the core switch , to the HA
    router/firewall w/VRRP, back to the same port on core switch and back out
    another port.

    Yuck! Any ideas on how to explain the pattern of one server after another
    having this problem (not all at once) and having to move to them to my core
    switch (and lose precious gigabit ports)??

    --Seth
    CCNA 4yrs about to upgrade to CCNP
     
    Seth, Dec 4, 2004
    #1
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  2. Seth,

    I came across a very similar network recently. It was in a prison for a
    Security company. I was quite shocked!!

    There was issues with servers dropping off line every so often, which
    was quite random. I put a sniffer on the lan just to listen to the
    background noise to see if anything might be causing the issues. (I used
    ethereal - www.ethereal.com - open source)

    There were 4 separate IP networks spanned across the site all on the
    same vlan. There were 1,000+ nodes and every so often browser elections
    would kick off, slowing the network down and taking out services.

    I put a plan together to redesign the network, putting the L3 switches
    in the core, trunking out to access switches. Set up a vtp domain and
    had it manage all the vlans, then I was able to build in security and
    QoS into the network.

    A big problem that I ran into was that some of the services were 24/7,
    but it was nothing a good plan couldn't sort out!

    To summerise: There is nothing technically wrong with having the
    different networks on the same flat segment, but it does defeat a lot of
    the reasons for having separate networks on a lan, i.e., security and QoS.

    Any problems or questions, get back to me at
    .

    LH



    Seth wrote:
    > Hi
    >
    > I have inherited a "non-standard" switching network that of course has some
    > spotty problems. What are the negative effects of doing it this way? (if
    > any)
    >
    > Core switch 6509 using vlans to segregate traffic. Access layer switches
    > with NO trunking over the Etherchannel links (2xGigabit ports on 3500XL's).
    > To make it more interesting, there are two networks on the same wire (not
    > vlan'd). On top of that, all the ports on the access switch are added to a
    > local vlan which just happens to match the VLAN number on the core switch.
    > Usually one server at a time has trouble dropping packets for 3+ minutes at
    > a time. Problem solved by moving server to the core switch.
    >
    > Is this common to use "transparent" VLANs like this? (The access switch is
    > on a VLAN but doesn't know it.)
    >
    > I can see the horrible efficiency of 2 hosts on separate subnets on the same
    > access vlan switch trying to talk. Traffic to the core switch , to the HA
    > router/firewall w/VRRP, back to the same port on core switch and back out
    > another port.
    >
    > Yuck! Any ideas on how to explain the pattern of one server after another
    > having this problem (not all at once) and having to move to them to my core
    > switch (and lose precious gigabit ports)??
    >
    > --Seth
    > CCNA 4yrs about to upgrade to CCNP
    >
    >
    >
     
    Leigh Harrison, Dec 5, 2004
    #2
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  3. Seth

    Seth Guest

    Thanks Leigh!
    I will try and sniff what's preceding the blackouts.
    --Seth
     
    Seth, Dec 6, 2004
    #3
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