RE: [load balancing] Accessing VIP from the inside on Cisco CSM

Date: Mon Jan 05 2004 - 23:03:16 EST

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    Other than the SLB's documented approach (such as proxying the client
    IP) for dealing with this, you could try, if you're not happy with any
    other option, a "multi-VIP, host exclusion" approach (for want of a
    better term).

    This would be useful if you don't want to apply the Proxy method (i.e.
    if you need to maintain client IPs in frames as the original IPs so that
    they are recorded correctly in application/network logs - a
    troubleshooting comfort, and usually a necessity).

    What I mean by "multi-VIP, host exclusion" is as follows:

    For a connection coming from one host to another host on same subnet
    (via a VIP), ensure the VIP contains a grouping of only the other hosts.
    The host that initiates the connection should not be in the VIP (since
    in the response it is trying to return to an interface on itself it
    won't ever go through the loadbalancer for the required frame

    Once you set up a VIP for a given group of exclusive hosts, on each host
    under the VIP you need to add to the route table (of the server OS) a
    static route for the interface of all other hosts to enforce the frame
    return via the loadbalancer. This interface should be the one which the
    client connection is made from and the route should be the host gateway
    on your SLB.

    There are annoyances with scalability and maintenance for this approach,
    depending on your capacity outlook, since when you add a server:
    (i) it needs to be added to multiple VIPs/groups on the SLB
    (ii) you would also need to add a new VIP containing all the other
    servers for the new host to use
    (iii) you need to add a new host route on each server
    (iv) each webmail service would need to have a configurable, static
    reference to know which VIP it is supposed to talk to

    Not exactly an elegant solution, but it may be something you can
    entertain for your given implementation. However, I would recommend
    testing this thoroughly.

    Julian Herzel

    -----Original Message-----
    From: [] On Behalf Of
    Jan Chrillesen
    Sent: Tuesday, 6 January 2004 12:14 AM
    Subject: [load balancing] Accessing VIP from the inside on Cisco CSM


    We're running a pair of Cisco Catalyst 6509 switches with the CSM
    content blade. We loadbalance a setup of servers, each running several
    services, like smtp, pop3 and webmail. We have configured a VIP for each
    service and everything works fine. Now we need to access a VIP from the
    inside (the webmail servers needs to talk to the SMTP VIP). Since the
    request originates from the server VLAN, and not the client VLAN, the
    request just times out. Is there any way to make this work in a bridged

    Creating seperate VLAN's for each services is not an option since
    mean we can only run one service on each server.

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