HELP! Windows and Netbios between 2 subnets - over a Cisco 2501

Discussion in 'Cisco' started by Simon Collins, Nov 9, 2003.

  1. Hi,

    Right I will try and keep this to the point. I have a client who needed more
    IP address space. Instead of NAT or a larger subnet (due to the fact they
    would have to renumber the existing 60ish machines), they were just given a
    /28 network to complement their /26. As the Cisco 2501 we provided had an
    address from the old /26 we added a secondary ethernet address from the new

    Customer setup is Cisco 2501 Router providing internet access - int
    Ethernet0 -->> Switch (Netgear non configurable) -->>Internal Win 2K

    The customer has re-numbered 3 machines that were working fine on the old
    subnet, to the new subnet. The new machines can ping machines on the old
    subnet. They have a default gateway of the routers ethernet (part of
    whichever subnet they are on) and the subnet masks are correct. However via
    Win 2K Network Neighborhood they cant see machines on the old subnet,
    logging on to a Novell Server times out as well. Both of these were working
    before when everything was on the same subnet.

    Using 'debug ip packet detail' I was seeing netbios (udp 137 ) being denied:

    (host .200 on new subnet, .130 on old subnet):
    02:39:29: IP: s=x.x.x.200 (Ethernet0), d=x.x.x.130 (Ethernet0), len
    78, access denied
    02:39:29: UDP src=137, dst=137

    I updated the ACL on e0 to allow udp 137-139 between the subnets. Now I see:

    (host .200 on new subnet, .138 on old):
    02:46:22: IP: ster=x.x.x.200 (Ethernet0), d=x.x.x.128 (Ethernet0),
    len 78, rcvd 5
    02:46:22: UDP src=137, dst=137

    I have removed the entire acl from e0 to make sure its not blocking anything
    useful. This makes no difference.

    Can any of you brainiacs think of something I can check as my windows skills
    leave a lot to be desired? The router side of things looks fine and
    obviously IP connectivity is fine between the subnets. Its just the windows
    setup which appears to need netbios.

    Some have suggested using an ip helper address on e0 - I have checked Cisco
    and am not sure what the ip helper address should be set as. Ive tried the
    broadcast address for each but no change.

    Others have suggested that the router needs to forward netbios between
    subnets (i.e. act as a bridge). ip forward-protocol udp 137 & 138 is enabled
    by default i.e. I can only add no ip forward-protocol udp 137 in the global

    Simon Collins, Nov 9, 2003
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  2. Simon Collins

    PES Guest

    If you ip helper to a broadcast adress x.x.x.255 you need to use the ip
    directed-broadcast on the destination interface.
    PES, Nov 9, 2003
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