PPP works, but proxy ARP doesn't

PPP works, but proxy ARP doesn't

Post by Ramon F Herre » Thu, 17 Oct 2002 15:34:20



RedHat Linux 7.3 server
MS Windows XP client

I am trying to set up an universal dialup with support for
both traditional tty and PPP connections.  I am using the
instructions found here:

    http://www.hylafax.org/HylaFAQ/Q343.html

I placed the following line in the file /etc/ppp/options:

proxyarp

Therefore, the host server should use proxy ARP, since the pppd
man page reads:

proxyarp
    Add  an entry to this system's ARP [Address Resolu-
    tion Protocol] table with the  IP  address  of  the
    peer and the Ethernet address of this system.  This
    will have the effect of making the peer  appear  to
    other systems to be on the local ethernet.

However, every time I dial in I get an appropriate IP address,
and DNS server.  DNS works fine BUT from the PPP client PC I can
ping only one host: the PPP server.  I show below 2 lines from the
ARP cache, one is a regular entry and the other (with all zeros?)
is the PPP proxy ARP entry.

% cat /proc/net/arp
IP address       HW type     Flags       HW address            Mask     Device
xx.206.86.24     0x1         0x2         00:10:5A:0D:05:C4     *        eth0
xx.206.86.90     0x1         0xc         00:00:00:00:00:00     *        eth0

How can I make the proxy ARP feature work?

TIA,

-Ramon F. Herrera

 
 
 

PPP works, but proxy ARP doesn't

Post by Clifford Kit » Fri, 18 Oct 2002 02:58:02



Quote:> RedHat Linux 7.3 server
> MS Windows XP client
> I am trying to set up an universal dialup with support for
> both traditional tty and PPP connections.  I am using the
> instructions found here:
>     http://www.hylafax.org/HylaFAQ/Q343.html
> I placed the following line in the file /etc/ppp/options:
> proxyarp

...

Quote:> However, every time I dial in I get an appropriate IP address,
> and DNS server.  DNS works fine BUT from the PPP client PC I can
> ping only one host: the PPP server.  I show below 2 lines from the
> ARP cache, one is a regular entry and the other (with all zeros?)
> is the PPP proxy ARP entry.
> % cat /proc/net/arp
> IP address       HW type  Flags    HW address            Mask  Device
> xx.206.86.24     0x1      0x2      00:10:5A:0D:05:C4     *     eth0
> xx.206.86.90     0x1      0xc      00:00:00:00:00:00     *     eth0
> How can I make the proxy ARP feature work?

So it seems that the proxyarp feature is working.

Note that the PPP IP address of the host dialing in should belong to
the same subnet as does the LAN host's IP address.  The LAN host's
PPP IP address should also be the same as it's LAN IP address.

In addition, IP forwarding must be compiled into the kernel of the
LAN host and turned on.

cat /proc/sys/net/ipv4/ip_forward


PPP-Q&A links, downloads:    http://users3.ev1.net/~ckite/public_html/
/* ... packets usually cross many administrative boundaries on their way
   from a source to a destination and often the only point of agreement
   between those separate administrations is that all problems are someone
   else's fault.   --Van Jacobson, abstract of April 97 MSRI talk */

 
 
 

1. proxy ARP doesn't work?

I've read some news articles that people have problems with proxy arp
and linux. Unfortunately I have now the same problem. Doing the following
on a Linux 2.2.x (and a 2.4.x) kernel:

echo 1 > /proc/sys/net/ipv4/conf/eth0/proxy_arp
echo 1 > /proc/sys/net/ipv4/ip_forward
arp -s 21.21.161.50 00:00:B4:55:8B:13 pub -i eth0
route add -host 21.21.161.50 eth0

but nothing happens, no proxy arp... I am listening with tcpdump
on a host in the same subnet and see only "arp who-has" requests
but no "arp reply" packets. And looking in the arp cache with
'arp -a' I see only
212.21.161.50 (212.21.161.50) at <incomplete> on eth0

I am not sure but I am rough remembering that this works with
2.0.x kernels (I had a longer time ago a Axis WebCam which
couldn't propagate its MAC address, so I had enter a proxy
arp entry on 2.0.x server so I could connect the webcam).

Well, does anybody knows, why proxy ARP doesn't work? Or is
the really only solution to use ip aliases?

Regards,
Ralf

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