[fw-wiz] Wayyy too many spoofed packets

From: Chris de Vidal (chris_at_devidal.tv)
Date: 11/21/03

  • Next message: Chris de Vidal: "Re: [fw-wiz] Wayyy too many spoofed packets"
    To: firewall-wizards@honor.icsalabs.com
    Date: Fri, 21 Nov 2003 10:27:36 -0500 (EST)

    I'm going to be installing firewalls on my internal servers (yes, I'm
    paranoid) and right now I'm testing in flag-only mode (don't drop any
    packets) on one server. So-far, so-good, except every day I get about 150
    "spoofed" packets; packets claiming to be my IP coming INTO the NIC card.
    Strangely, the destination is always my network's broadcast address.
    Perhaps even more strangely is I'm seeing it only on SMB (UDP 137:138) and
    backup traffic (UDP 20031) ports.

    Here is the rule:
    /sbin/iptables -A bad_packets \
        -i eth0 -s \
        --m limit --limit 3/minute \
        --j LOG --log-level INFO \
        --log-prefix "Spoofed packet type 1 (bad): "

    Here is the log:
    Logged 142 packets on interface eth0
      From - 142 packets
        To - 142 packets
          Service: netbios-ns (udp/137) (Spoofed packet type 1
    (bad):,eth0,none) - 19 packets
          Service: netbios-dgm (udp/138) (Spoofed packet type 1
    (bad):,eth0,none) - 103 packets
          (20031 is the backup port)
          Service: 20031 (udp/20031) (Spoofed packet type 1 (bad):,eth0,none)
    - 20 packets

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