Date: Sun, 18 Mar 2001 17:16:04 +0200 From: Ruslan Ermilov <ru@FreeBSD.org> To: net@FreeBSD.org, Garrett Wollman <wollman@FreeBSD.org> Subject: [PATCH] Re: Reading Stevens, playing routing games Message-ID: <20010318171604.D66563@sunbay.com> In-Reply-To: <20010316201916.A20185@sunbay.com>; from ru@FreeBSD.org on Fri, Mar 16, 2001 at 08:19:16PM %2B0200 References: <20010316201916.A20185@sunbay.com>
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--TB36FDmn/VVEgNH/ Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Fri, Mar 16, 2001 at 08:19:16PM +0200, Ruslan Ermilov wrote: > Hi! > > First of all, I would like to commit the attached patch; it removes > duplicate code. Please review. > This got already committed as part of another bugfix. See ip_input.c, revision 1.164. > Also, I found a nasty bug in IP routing. The new route added may not > take immediate effect for routing decisions, because ip_forward() may > use the cached route (rt_forwarding). > The attached patch fixes this. > DEMO (only relevant routes are shown). > > Step 1. On a router, add a route to the network (192.168.1). > > : # route add -net 192.168.1 gateway > : add net 192.168.1: gateway gateway > : > : # netstat -rn > : Routing tables > : > : Internet: > : Destination Gateway Flags Refs Use Netif Expire > : 192.168.1 gateway UGSc 0 0 rl0 > > Step 2. From some other host for which this machine is the default router, > run ``traceroute -m 2 -n 192.168.1.1''. Observe, on the router, > that the reference count grown on the 192.168.1 route. > > : # netstat -rn > : Routing tables > : > : Internet: > : Destination Gateway Flags Refs Use Netif Expire > : 192.168.1 gateway UGSc 1 3 rl0 > > Step 3. Add RTF_REJECT host route to the destination: > > : # route add 192.168.1.1 -iface lo0 -reject > : add host 192.168.1.1: gateway lo0 > : # netstat -rn > : Routing tables > : > : Internet: > : Destination Gateway Flags Refs Use Netif Expire > : 192.168.1 gateway UGSc 1 3 rl0 > : 192.168.1.1 lo0 UHRS 0 0 lo0 > > Step 4. The fun begins. What you would expect if you run traceroute to > 192.168.1.1 again? Obviously host route should take precedence > over network route, and I expected ICMP Destination Unreachable. > But... what's a hell? the new route did not take immediate effect, > traceroute succeeded (192.168.1.1 still has zero refcound and use): > > : # netstat -rn > : Routing tables > : > : Internet: > : Destination Gateway Flags Refs Use Netif Expire > : 192.168.1 gateway UGSc 1 6 rl0 > : 192.168.1.1 lo0 UHRS 0 0 lo0 > > Step 5. The fun continues. From another host, run traceroute to another > destination (to help router change rt_forward.ro_dst). > traceroute -m 2 -n 192.168.1.2: > > : # netstat -rn > : Routing tables > : > : Internet: > : Destination Gateway Flags Refs Use Netif Expire > : 192.168.1 gateway UGSc 1 9 rl0 > : 192.168.1.1 lo0 UHRS 0 0 lo0 > > Step 6. Run traceroute again to 192.168.1.1. The fun ends. > > > The solution I found so far is to unstaticize the ``rt_forward'', and > invalidate the rt_forward.ro_rt in in_addroute() (in_rmx.c). Any better > ideas? -- Ruslan Ermilov Oracle Developer/DBA, ru@sunbay.com Sunbay Software AG, ru@FreeBSD.org FreeBSD committer, +380.652.512.251 Simferopol, Ukraine http://www.FreeBSD.org The Power To Serve http://www.oracle.com Enabling The Information Age --TB36FDmn/VVEgNH/ Content-Type: text/plain; charset=us-ascii Content-Disposition: attachment; filename=p Index: in_rmx.c =================================================================== RCS file: /home/ncvs/src/sys/netinet/in_rmx.c,v retrieving revision 1.38 diff -u -p -r1.38 in_rmx.c --- in_rmx.c 2001/03/15 14:52:12 1.38 +++ in_rmx.c 2001/03/18 15:08:25 @@ -54,6 +54,7 @@ #include <net/route.h> #include <netinet/in.h> #include <netinet/in_var.h> +#include <netinet/ip_var.h> extern int in_inithead __P((void **head, int off)); @@ -137,6 +138,16 @@ in_addroute(void *v_arg, void *n_arg, st RTFREE(rt2); } } + + /* + * If the new route successfully added, and we are forwarding, + * and there is a cached route, free it. + */ + if (ret != NULL && ipforwarding && ipforward_rt.ro_rt) { + RTFREE(ipforward_rt.ro_rt); + ipforward_rt.ro_rt = 0; + } + return ret; } Index: ip_input.c =================================================================== RCS file: /home/ncvs/src/sys/netinet/ip_input.c,v retrieving revision 1.164 diff -u -p -r1.164 ip_input.c --- ip_input.c 2001/03/18 13:04:07 1.164 +++ ip_input.c 2001/03/18 15:08:26 @@ -257,7 +257,7 @@ ip_init() } static struct sockaddr_in ipaddr = { sizeof(ipaddr), AF_INET }; -static struct route ipforward_rt; +struct route ipforward_rt; /* * Ip input routine. Checksum and byte swap header. If fragmented Index: ip_var.h =================================================================== RCS file: /home/ncvs/src/sys/netinet/ip_var.h,v retrieving revision 1.53 diff -u -p -r1.53 ip_var.h --- ip_var.h 2001/03/16 20:00:53 1.53 +++ ip_var.h 2001/03/18 15:08:26 @@ -141,6 +141,7 @@ extern struct ipstat ipstat; extern u_short ip_id; /* ip packet ctr, for ids */ extern int ip_defttl; /* default IP ttl */ extern int ipforwarding; /* ip forwarding */ +extern struct route ipforward_rt; /* ip forwarding cached route */ extern u_char ip_protox[]; extern struct socket *ip_rsvpd; /* reservation protocol daemon */ extern struct socket *ip_mrouter; /* multicast routing daemon */ --TB36FDmn/VVEgNH/-- To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-net" in the body of the message
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