[LARTC] Enabling Proxy Arp

[LARTC] Enabling Proxy Arp

[nkef]

I have read the section  http://lartc.org/howto/lartc.bridging.proxy-arp.html .
I configured my two ethernet devices with the same ip address .
Should i configure them with a specific command ?

I used : ifconfig eth0 192.168.47.104 netmask 255.255.255.0
	     ifconfig eth1 192.168.47.104 netmask 255.255.255.0

I tried to configure them with ip also .

eth0      Link encap:Ethernet  HWaddr 00:90:27:72:B8:1D
          inet addr:192.168.47.104  Bcast:192.168.47.255  Mask:255.255.255.0
          UP BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:100
          RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)
          Interrupt:9

eth1      Link encap:Ethernet  HWaddr 00:00:E8:8D:0C:DC
          inet addr:192.168.47.104  Bcast:192.168.47.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:100
          RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)
          Interrupt:9 Base address:0x2000

I checked for support in kernel 
# dmesg |grep ip_
ip_conntrack version 2.1 (4095 buckets, 32760 max) - 292 bytes per conntrack
ip_tables: (C) 2000-2002 Netfilter core team
Is there any specific kernel option for proxy-arp ?

then i tried to enable proxy arp with :
echo 1 > /proc/sys/net/ipv4/conf/eth0/proxy_arp
echo 1 > /proc/sys/net/ipv4/conf/eth1/proxy_arp
but proxy_arp remains 0 , whatever i do .

Thank you for your help
Nikolaos Kefalas


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Re: [LARTC] Enabling Proxy Arp

[Martin A. Brown]

Nikolaos,

 : I have read the section
 : http://lartc.org/howto/lartc.bridging.proxy-arp.html . I configured my
 : two ethernet devices with the same ip address . Should i configure them
 : with a specific command ?
 :
 : I used : ifconfig eth0 192.168.47.104 netmask 255.255.255.0
 : 	     ifconfig eth1 192.168.47.104 netmask 255.255.255.0
 :
 : I tried to configure them with ip also .

You don't need to use the same IP on both interfaces, but I don't see a
problem if you do so.

<snip/>

 : I checked for support in kernel
 : # dmesg |grep ip_
 : ip_conntrack version 2.1 (4095 buckets, 32760 max) - 292 bytes per conntrack
 : ip_tables: (C) 2000-2002 Netfilter core team
 : Is there any specific kernel option for proxy-arp ?

OK, so there's not much here, but you may find the tidbit you seek here:

  http://linux-ip.net/html/ether-arp.html#ether-arp-proxy

See also Julian's remarks (this includes comments on medium_id, which you
don't need), which should give you a good idea of how to perform proxy ARP
with the kernel.

  http://www.ssi.bg/~julian/#medium_id

Or, if you don't want the kernel to perform proxy ARP, you can use this
technique, which employs /sbin/arp directly to add proxy ARP entries:

  http://linux-ip.net/html/adv-proxy-arp.html

The benefit of manual proxy ARP entries is a very fine-grained control
over which machines are visible to each side of your proxy ARP'ing router.

 : then i tried to enable proxy arp with :
 : echo 1 > /proc/sys/net/ipv4/conf/eth0/proxy_arp
 : echo 1 > /proc/sys/net/ipv4/conf/eth1/proxy_arp
 : but proxy_arp remains 0 , whatever i do .

This is exactly what you wish to do, but you forgot one other sysctl:

echo 1 > /proc/sys/net/ipv4/conf/all/proxy_arp

See Oskar Andreasson's sysctl tutorial for some more details on how to use
the net/ipv4/conf sysctl variables.

  http://ipsysctl-tutorial.frozentux.net/

Best of luck,

-Martin

-- 
Martin A. Brown --- SecurePipe, Inc. --- mabrown@securepipe.com

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