"No network provider accepted the given network path"

Discussion in 'Windows Server' started by Marlon D, Jan 24, 2005.

  1. Marlon D

    Marlon D Guest

    Hi all

    Config:
    - 2x W2k3 STD servers running IIS6.0 in NLB.

    Need:
    - The need has now arisen to run a script on one of the servers that
    connects to itself and the other server by means of UNC, so started enabling
    the services again and it has all gone pear-shaped.

    Problem:
    - I CAN access both servers using UNC from my pc
    - I CAN access OTHER servers using UNC from the webservers
    - However, when I connect to each of the servers from the other using UNC it
    doesn't connect - I can't even ping it - but it does resolve.
    - I've set all the services back to original, and even removed the group
    policy but no go.
    - What is strange is that it actually works for about 5 minutes if I
    restart both servers - and then just falls over .. nothing being reported in
    event viewer, etc at the time.
    - I've already rebuilt these servers once!

    Also, I've tried these solutions to no avail:
    http://www.jsiinc.com/SUBR/tip8500/rh8517.htm
    http://support.microsoft.com/?kbid=841570

    Marlon
     
    Marlon D, Jan 24, 2005
    #1
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  2. Marlon D

    Todd J Heron Guest

    NLB obfuscates the physical MAC address of each node in the cluster by
    default unless you take special steps to allow resolution of the physical
    MAC address on each node through a method known as

    The fact that node resolution worked for five minutes after server restarts
    is because it is occurring before convergence completes. After cluster
    convergence completes the switch doesn't know what to do when more than one
    switched port claims to own the same MAC address.

    http://support.microsoft.com/default.aspx?scid=/servicedesks/webcasts/wc032102/WCT032102.asp
     
    Todd J Heron, Jan 24, 2005
    #2
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  3. Marlon D

    Marlon D Guest

    I don't seem to recall the same thing happening when I had a couple of
    Windows 2000 servers running a while ago.

    Anyways .. I found this article too:

    http://www.microsoft.com/technet/prodtechnol/windowsserver2003/technologies/clustering/nlbbp.mspx

    and I quote:
    General Considerations
    . Some routers require a static ARP entry because they do not support
    the resolution of unicast IP addresses to multicast media access control
    addresses. For example, Cisco routers require an ARP (address resolution
    protocol) entry for every virtual IP address. While Network Load Balancing
    uses Level 2 Multicast for the delivery of packets, Cisco's interpretation
    of the RFCs is that Multicast is for IP Multicast. So, when the router
    doesn't see a Multicast IP address, it does not automatically create an ARP
    entry, and one has to manually have to add it on the router.



    . Network Load Balancing can operate in two modes: unicast and
    multicast. Unicast support is enabled by default, which ensures that it
    operates properly with all routers. You might elect to enable multicast mode
    so that a second network adapter is not required for communications within
    the cluster. If Network Load Balancing clients access a cluster (configured
    for multicast mode) through a router, be sure that the router accepts an
    Address Resolution Protocol (ARP) reply for the cluster's (unicast) IP
    addresses with a multicast media access control address in the payload of
    the ARP structure. ARP is a TCP/IP protocol that uses limited broadcast to
    the local network to resolve a logically assigned IP address. Verify that
    all cluster hosts are operating in unicast or multicast mode, one or the
    other, but not both.



    . If the cluster is operating in unicast mode (default setting),
    Network Load Balancing cannot distinguish between single adapters on each
    host. Therefore, any communication among cluster hosts is not possible
    unless each cluster host has at least two network adapters.



    Thanks Todd

    Marlon
     
    Marlon D, Jan 24, 2005
    #3
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