2 * INET An implementation of the TCP/IP protocol suite for the LINUX
3 * operating system. INET is implemented using the BSD Socket
4 * interface as the means of communication with the user level.
6 * The IP forwarding functionality.
8 * Version: $Id: ip_forward.c,v 1.48 2000/12/13 18:31:48 davem Exp $
13 * Many : Split from ip.c , see ip_input.c for
15 * Dave Gregorich : NULL ip_rt_put fix for multicast
17 * Jos Vos : Add call_out_firewall before sending,
18 * use output device for accounting.
19 * Jos Vos : Call forward firewall after routing
20 * (always use output device).
21 * Mike McLagan : Routing by source
24 #include <linux/types.h>
26 #include <linux/skbuff.h>
28 #include <linux/icmp.h>
29 #include <linux/netdevice.h>
35 #include <linux/tcp.h>
36 #include <linux/udp.h>
37 #include <linux/netfilter_ipv4.h>
38 #include <net/checksum.h>
39 #include <linux/route.h>
40 #include <net/route.h>
43 static int ip_forward_finish(struct sk_buff
*skb
)
45 struct ip_options
* opt
= &(IPCB(skb
)->opt
);
47 IP_INC_STATS_BH(IPSTATS_MIB_OUTFORWDATAGRAMS
);
49 if (unlikely(opt
->optlen
))
50 ip_forward_options(skb
);
52 return dst_output(skb
);
55 int ip_forward(struct sk_buff
*skb
)
57 struct iphdr
*iph
; /* Our header */
58 struct rtable
*rt
; /* Route we use */
59 struct ip_options
* opt
= &(IPCB(skb
)->opt
);
61 if (!xfrm4_policy_check(NULL
, XFRM_POLICY_FWD
, skb
))
64 if (IPCB(skb
)->opt
.router_alert
&& ip_call_ra_chain(skb
))
65 return NET_RX_SUCCESS
;
67 if (skb
->pkt_type
!= PACKET_HOST
)
70 skb_forward_csum(skb
);
73 * According to the RFC, we must first decrease the TTL field. If
74 * that reaches zero, we must reply an ICMP control message telling
75 * that the packet's lifetime expired.
77 if (ip_hdr(skb
)->ttl
<= 1)
80 if (!xfrm4_route_forward(skb
))
83 rt
= (struct rtable
*)skb
->dst
;
85 if (opt
->is_strictroute
&& rt
->rt_dst
!= rt
->rt_gateway
)
88 if (unlikely(skb
->len
> dst_mtu(&rt
->u
.dst
) &&
89 (ip_hdr(skb
)->frag_off
& htons(IP_DF
))) && !skb
->local_df
) {
90 IP_INC_STATS(IPSTATS_MIB_FRAGFAILS
);
91 icmp_send(skb
, ICMP_DEST_UNREACH
, ICMP_FRAG_NEEDED
,
92 htonl(dst_mtu(&rt
->u
.dst
)));
96 /* We are about to mangle packet. Copy it! */
97 if (skb_cow(skb
, LL_RESERVED_SPACE(rt
->u
.dst
.dev
)+rt
->u
.dst
.header_len
))
101 /* Decrease ttl after skb cow done */
102 ip_decrease_ttl(iph
);
105 * We now generate an ICMP HOST REDIRECT giving the route
108 if (rt
->rt_flags
&RTCF_DOREDIRECT
&& !opt
->srr
&& !skb
->sp
)
109 ip_rt_send_redirect(skb
);
111 skb
->priority
= rt_tos2priority(iph
->tos
);
113 return NF_HOOK(PF_INET
, NF_IP_FORWARD
, skb
, skb
->dev
, rt
->u
.dst
.dev
,
118 * Strict routing permits no gatewaying
120 icmp_send(skb
, ICMP_DEST_UNREACH
, ICMP_SR_FAILED
, 0);
124 /* Tell the sender its packet died... */
125 IP_INC_STATS_BH(IPSTATS_MIB_INHDRERRORS
);
126 icmp_send(skb
, ICMP_TIME_EXCEEDED
, ICMP_EXC_TTL
, 0);