From b74d89bbbb6bee8b4b9f8395482b4acd8879dcad Mon Sep 17 00:00:00 2001
From: Andre Oppermann <andre@FreeBSD.org>
Date: Mon, 2 Feb 2004 22:53:16 +0000
Subject: [PATCH] Add sysctl net.inet.icmp.reply_src to specify the interface
 name used for the ICMP reply source in reponse to packets which are not
 directly addressed to us.  By default continue with with normal source
 selection.

Reviewed by:	bms
---
 sys/netinet/ip_icmp.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/sys/netinet/ip_icmp.c b/sys/netinet/ip_icmp.c
index 340efd4931b5..a157dd5f6ac1 100644
--- a/sys/netinet/ip_icmp.c
+++ b/sys/netinet/ip_icmp.c
@@ -110,6 +110,10 @@ static int	icmplim_output = 1;
 SYSCTL_INT(_net_inet_icmp, OID_AUTO, icmplim_output, CTLFLAG_RW,
 	&icmplim_output, 0, "");
 
+static char	reply_src[IFNAMSIZ+1];
+SYSCTL_STRING(_net_inet_icmp, OID_AUTO, reply_src, CTLFLAG_RW,
+	&reply_src, IFNAMSIZ, "icmp reply source for non-local packets.");
+
 /*
  * ICMP broadcast echo sysctl
  */
@@ -618,6 +622,7 @@ icmp_reflect(m)
 {
 	struct ip *ip = mtod(m, struct ip *);
 	struct ifaddr *ifa;
+	struct ifnet *ifn;
 	struct in_ifaddr *ia;
 	struct in_addr t;
 	struct mbuf *opts = 0;
@@ -658,6 +663,20 @@ icmp_reflect(m)
 				goto match;
 		}
 	}
+	/*
+	 * If the incoming packet was not addressed directly to us, use
+	 * designated interface for icmp replies specified by sysctl
+	 * net.inet.icmp.reply_src (default not set). Otherwise continue
+	 * with normal source selection.
+	 */
+	if (reply_src[0] != '\0' && (ifn = ifunit(reply_src))) {
+		TAILQ_FOREACH(ifa, &ifn->if_addrhead, ifa_link) {
+			if (ifa->ifa_addr->sa_family != AF_INET)
+				continue;
+			ia = ifatoia(ifa);
+			goto match;
+		}
+	}
 	/* 
 	 * If the packet was transiting through us, use the address of
 	 * the interface that is the closest to the packet source.