Re: Make packets to localhost go through external loopback

Trevor Johnson (trevor@jpj.net)
Mon, 17 May 1999 03:22:32 -0400 (EDT)

> I'm trying to develop driver for network card. As I've only one
> computer (but two cards ;-) available, I'd like trafic for localhost
> to go through external link.
>
> I know this has been here before. Alan's response was that it is only
> good for testing. There was even patch around. Does anyone remember
> what needs to be patched?

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From: Brian Moyle <BMoyle@redcreek.com>
To: linux-kernel@vger.rutgers.edu
Subject: [PATCH] linux/net/ipv4/arp.c, kernel 2.0.36
Date: Fri, 29 Jan 1999 17:43:35 -0800
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2nd post (previous attempt was reformatted, courtesy of Microsoft Exchange)

Description: Fixes problem with external loopback, using crossed route
entries.
Version: 2.0.36
Testing: Connected two NICs together, using an extenal cross-over cable,
swapped route entries (to force packets out the opposite
interfaces),
and then issued pings to both addreseses. Unplugged cable to
verify
pings were appropriately halted.
Request: Please CC bmoyle@redcreek.com with any comments/feedback. Thanks!

-Brian
bmoyle@redcreek.com

Fix to arp.c for external loopback (Brian Moyle, bmoyle@redcreek.com):
--- linux-2.0.36/net/ipv4/arp.c Sun Nov 15 10:33:21 1998
+++ linux/net/ipv4/arp.c Wed Jan 27 16:59:21 1999
@@ -20,6 +20,8 @@
* 2 of the License, or (at your option) any later version.
*
* Fixes:
+ * Brian Moyle : Fixed arp_set_predefined() to work
with
+ * external loopback w/ crossed routing
* Alan Cox : Removed the ethernet assumptions in
* Florian's code
* Alan Cox : Fixed some small errors in the ARP
@@ -1287,9 +1289,15 @@
switch (addr_hint)
{
case IS_MYADDR:
+ {
+ struct device *dev_found=ip_dev_find(paddr);
printk(KERN_DEBUG "ARP: arp called for own IP
address\n");
- memcpy(haddr, dev->dev_addr, dev->addr_len);
+ if (dev_found)
+ memcpy(haddr, dev_found->dev_addr,
dev_found->addr_len);
+ else
+ memcpy(haddr, dev->dev_addr, dev->addr_len);
return 1;
+ }
#ifdef CONFIG_IP_MULTICAST
case IS_MULTICAST:
if(dev->type==ARPHRD_ETHER ||
dev->type==ARPHRD_IEEE802

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__
Trevor Johnson

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