When bridging on OpenBSD, OpenBSD-bridge have problem about arp....

When bridging on OpenBSD, OpenBSD-bridge have problem about arp....

Post by deja » Sat, 03 Feb 2001 00:08:12

My hardware platform :

    CPU -  Intel Pentium III - 933MHz
    NIC -  fxp0 , fxp1 ( 100baseTX full-duplex)

What I already done :


   #net.inet.ip.forwarding=1 --> net.inet.ip.forwarding=1


   ipfilter=NO  -->  ipfilter=YES
   ipnat=NO     -->  ipnat=YES


   inet NONE media 100baseTX mediaopt full-duplex


   inet NONE media 100baseTX mediaopt full-duplex

   add fxp0 add fxp1 up

   /usr/src/sys/conf/GENERIC add following two lines

   option GATEWAY

   rebuild kernel.

   reboot finally.

My First Network Topology :


/ (

                                                            |------ -------|
                                                    Win2000 --|  OpenBSD
2.8 |----- HUB
    |------- ------|                \
fxp1               \
(               Win2000

  As you see above , we are in NAT environment.

  We bridge fxp0 and fxp1.

  But when we ftp-download from or to ,
we can almost get full speed, says 100Mbps.

My Second Network Topology :

RedHat 7.0

/ (

                                                            |------ -------|
                                                    Win2000 --|  OpenBSD
2.8 |----- HUB
    |------- ------|                \
fxp1               \
(               RedHat 7.0

  What makes me crazy is .....

  In this topology,  we cannot get no more performance than 10Mbps....

My Suspection :

  As far as I know, Linux has problems about arp.

  OpenBSD-Bridge is assumed to be influenced by Linux's arp problem.

  Is there anyone to answer this problem???

  Please email to me....


1. I'm Desperate: Proxy ARP and Bridging without the Bridge

Hi everyone! I have a quick question about Proxy ARP. I've been trying
to get this thing working for days, and I can't seem to find any
documentation on this matter what so ever, so I'm hoping somebody out
there who knows a lot about networking (which isn't me!) can answer my

I have some computers on a network, with a netmask of (/22 I think?). The router is at I wanted to
setup a "transparent firewall" with proxy arp and iptables and
friends. Naturally, I made a box with two network interfaces (It has
two IPs, .68, and .69.), and put my laptop on one side for testing,
and the public network is on the other side. I setup a static route
for my laptop on the firewall, and I can ping it from the firewall,
and can ping outside nodes from the firewall. The problem is - when I
enable proxy arp and IP forwarding, it only works for nodes in my
subnet (! I can ping outside hosts (still in
my subnet) from my laptop, and from machines in my subnet, I can ping
my laptop, too, so proxy ARP seems to be working. When I try to ping a
host on the Internet (not even on the rest of the
network, it doesn't work! Neither do any nodes outside It's like everytime it needs the router to
route traffic, it doesn't work! I placed a protocol analyzer on the
outside, and I see the replies come back from the external test hosts,
but they never reach the other side of my firewall - they are
addressed to the computer on the other side (with a destination mac
address of 0:0:0:0:0:1?), but shouldn't the firewall "proxy" (i.e. act
as it) and accept those packets and forward them on? I even tried
putting the outside interface in promiscious mode! Nothing seems to
work! Do I need to put a route on the router, telling it
about my firewall? But isn't this a "pseudo bridge?" Or is it the
router's ARP cache? I can't force it to expire (I don't have access to
it), so I can't verify that unfortunately. A route isn't an option,
either, so I hope I don't need one. Somebody in the CS department here
has done it, but they have their own CS router, so maybe he added a
route for his firewall on it... I'm lost!

Thanks for any reply and your time,


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