ip helper-address confusion

Discussion in 'Cisco' started by Northern Lights, Jul 24, 2003.

  1. I am relatively inexperienced with Cisco routing, so this is probably a
    simple question. Here's the hardware:

    Location A
    Cisco 2621 Router
    IOS 12.0
    Interfaces - e0 to local LAN 192.168.48.55/24
    s0/0.100-s0/0.105 to WAN (IP 192.168.100.1/24 -
    192.168.106.1/24)

    Locations B-H
    Cisco 1720 or 1750
    IOS 12.0
    Interfaces - e0 to local LANs on each router 192.169.41.55/24-
    192.168.47.55/24)
    s0/0.1 to WAN on each router (IP 192.168.100.2/24 -
    192.168.106.2/24)

    This network is running 3DES on frame relay.

    Here's the problem:
    I am attempting to use a PC remote control software package (NetSupport) to
    control PCs on the network.
    The software resides at location A above. I am unable to see the PCs on the
    subnets at locations B thru H
    with the NetSupport software when browsing, but can see them using the
    client's IP address.

    NetSupport looks at the network broadcast address to find available clients.
    My thinking is that an ip helper-address
    command is needed for each subnet B-H on the router at location A. Also, I
    would need to use the
    ip forward-protocol 5405 command as the software uses udp port 5405 to talk
    to the clients.

    My questions:
    First, is my thinking correct on using the ip helper-address/ip
    forward-protocol commands?
    Next, would I use the ip helper-address command on e0 at location A? or
    another interface?
    Am I missing something else?

    As a test, I have tried using ip helper-address 192.168.41.255 and
    192.168.42.255 on e0 at location A
    in conjunction with ip forward-protocol 5405 with no success.

    Can anyone help?

    -Phil

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    Northern Lights, Jul 24, 2003
    #1
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  2. On Thu, 24 Jul 2003 14:09:33 -0400, Northern Lights wrote:

    [Snip]

    >
    > As a test, I have tried using ip helper-address 192.168.41.255 and
    > 192.168.42.255 on e0 at location A
    > in conjunction with ip forward-protocol 5405 with no success.
    >


    192.168.41.255 and 192.168.42.255 are the subnet broadcast addresses at
    locations B and C, I guess, so you need to ensure that you have "ip
    directed-broadcast" on inteface E0 at locations B and C.

    Without "ip directed-broadcast" the router will drop the packet when it
    sees that the destination address is the broadcast address.

    You can use "debug ip udp" at A to check the router is forwarding the
    packets as you expect.

    Rgds,
    Martin
     
    Martin Gallagher, Jul 25, 2003
    #2
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