Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262138AbTEPVt1 (ORCPT ); Fri, 16 May 2003 17:49:27 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262148AbTEPVt0 (ORCPT ); Fri, 16 May 2003 17:49:26 -0400 Received: from ns.xdr.com ([209.48.37.1]:39892 "EHLO xdr.com") by vger.kernel.org with ESMTP id S262138AbTEPVtY (ORCPT ); Fri, 16 May 2003 17:49:24 -0400 Date: Fri, 16 May 2003 15:02:21 -0700 From: David Ashley Message-Id: <200305162202.h4GM2LGN024925@xdr.com> To: linux-kernel@vger.kernel.org Subject: Problem in ARP 2.4.20 kernel Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2234 Lines: 59 I'm working on a mechanism to load balance across multiple 100 mbit interfaces using the 2.4.20 linux kernel + custom server software. I have several interfaces all on the same subnet with different IP addresses. They are all connected to the same multi-port switch. The intent is that a client can connect to any of the IP addresses specifically and only burden that one. Some clients can connect to #1, others to #2, etc. The problem I ran into was the kernel's handling of ARP requests. What linux does is each interface receives the arp request, and every single one answers the request. So it becomes a race condition which response gets to the client, and the client will have usually an incorrect mac address/ip address arp entry. I fixed this problem by modifying net/ipv4/arp.c: //add to top of file in the #includes #include // (DA) 20030515 to fix arp problem //...then later in function arp_process() if (addr_type == RTN_LOCAL) { n = neigh_event_ns(&arp_tbl, sha, &sip, dev); if (n) { + struct in_device *ind; int dont_send = 0; if (IN_DEV_ARPFILTER(in_dev)) dont_send |= arp_filter(sip,tip,dev); +// (DA) 20030515 only send arp response if dev's IP address matches + if((ind=__in_dev_get(dev))) { + struct in_ifaddr *ifa; + ifa=ind->ifa_list; + while(ifa) + { + if(ifa->ifa_address==tip) break; + ifa=ifa->ifa_next; + } + if(!ifa) dont_send=1; + } if (!dont_send) arp_send(ARPOP_REPLY,ETH_P_ARP,sip,dev,tip,sha,dev->dev_addr,sha); neigh_release(n); } goto out; Before sending the arp response, the requested IP address is checked against the interface's configured IP address, and only if there is a match will an ARP response be sent. I think the the check is harmless in any case. It's not clear to me if you'd ever want each interface answering the ARP requests, and it is clear there is a valid reason for wanting to wire up a computer this way. Enjoy! -Dave - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/