UDP broadcast forwarding

[sharlino]

Hello!

I have: cisco 7606s router, RSP720-3C-GE , WS-X6704-10GE , c7600rsp72043_rp-ADVIPSERVICESK9-M, Version 12.2(33)SRB2.

Case: Server in LAN (192.168.1.8/29) connected to router's SVI 2 generates UDP broadcast (NetBIOS). Packet's headers are: SRC IP:192.168.1.12, DST IP:192.168.1.15 (broadcast in this case), SRC MAC: MAC of server, DST MAC:FFFF.FFFF.FFFF. Let's name this Packet-A.

Problem: the router, for some reason, forwards Packet-A (UDP broadcast) received on one VLAN to another (from SVI2 to SVI3).

Short question: why ?

Some show output:

sh ip int vl2 | i dcast|elper
  Broadcast address is 255.255.255.255
  Helper address is not set
  Directed broadcast forwarding is disabled

sh run | i ip for
no ip forward-protocol udp


Any help will be appreciated. Thank you for your time!

[Philip D'Ath]

It could be a mis-configured trunk between two devices.  For example, a native VLAN mismatch (so the packet moves from one VLAN to another at layer 2).  Or a trunk port connected to an access point.  Perhaps an unintentional network loop between access ports in different vlans.

It could also be a software bug (assuming the server has a single NIC and is not multi-homed).  Try moving your devices to "gold star" releases.