Network not working correctly without promiscuous mode being set?

David habeeb at cfl.rr.com
Thu Jul 10 13:29:55 PDT 2003


my setup is basically like this: I have a freebsd machine that is supposed
to act as a gateway, it has 2 ethernet cards xl0 (local network) and xl1
(internet).  xl1 is plugged directly into the cable modem and off it goes,
and xl0 is plugged into a switch where all the other machines are plugged
into locally.  xl1 is 65.35.123.123 for example and internally xl0 is
172.16.16.1.

If i attempt to ping 172.16.16.10 from .1 it does not work/go through.  if I
run tcpdump -i xl0, then try to ping again it will go through just fine and
i see the packets going both ways now.  Without tcpdump in promisc it wasn't
working?  Now when i try to get a DHCP lease on xl1 it sits there and sends
requests with no replies, then when i run tcpdump -i xl1 it will get a lease
and the internet will work fine.  This is as best I can describe the issue
and below is some included information.

damn# ifconfig -a
xl0: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> mtu 1500
        options=3<RXCSUM,TXCSUM>
        inet 172.16.16.1 netmask 0xffffff00 broadcast 172.16.16.255
        ether 00:01:03:c1:ac:19
        media: Ethernet autoselect (100baseTX <full-duplex>)
        status: active
xl1: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> mtu 1500
        options=3<RXCSUM,TXCSUM>
        inet 65.35.126.31 netmask 0xfffff800 broadcast 255.255.255.255
        ether 00:01:03:c1:4a:b9
        media: Ethernet autoselect (10baseT/UTP)
        status: active
lp0: flags=8810<POINTOPOINT,SIMPLEX,MULTICAST> mtu 1500
lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384
        inet 127.0.0.1 netmask 0xff000000

damn# grep nat /etc/rc.conf
natd_program="/sbin/natd"       # path to natd, if you want a different one.
natd_enable="YES"               # Enable natd (if firewall_enable == YES).
natd_interface="xl1"            # Public interface or IPaddress to use.
natd_flags=""                   # Additional flags for natd.

damn# grep ifconfig /etc/rc.conf
ifconfig_xl1="DHCP"
ifconfig_xl0="inet 172.16.16.1  netmask 255.255.255.0"

damn# ipfw show
00100 34686  5360662 divert 8668 ip from any to any via xl1
65535 70033 10711879 allow ip from any to any

damn# arp -a
1.120.35.65.cfl.rr.com (65.35.120.1) at 00:06:2a:ce:64:54 on xl1 [ethernet]
? (172.16.16.1) at 00:01:03:c1:ac:19 on xl0 permanent [ethernet]
? (172.16.16.10) at 00:01:03:c1:89:1a on xl0 [ethernet]









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