retrieve the upstream MTU

Signed-off-by: Bjørn Mork <bjorn@mork.no>

1 files changed, 21 insertions, 4 deletions

diff --git a/ldra.c b/ldra.c
index 30954e2..723d189 100644
--- a/ldra.c
+++ b/ldra.c
@@ -42,6 +42,18 @@
   code sample:
 http://aschauf.landshut.org/fh/linux/udp_vs_raw/ch01s03.html
 
+
+
+TODO:
+
+ = collect input:
+
+   - upstream interface
+   - enterprisenumber for remote ID
+   - client interface mappings (if, vlan, remoteid, subscriberid, trusted)
+
+ = use mmap packet interface
+
  */
 
 #include <arpa/inet.h>
@@ -134,11 +146,11 @@ u_int32_t chksum(char *buf, size_t n)
 	return sum;
 }
 
-/* calculate IPv6 udp chksum, blindly assuming that there are no other headers in the packet */
+/* calculate IPv6 udp chksum, blindly assuming that the UDP header follows immediately after the IP header */
 u_int16_t udp6chksum(struct ip6_hdr *ip6)
 {
-	int len = ntohs(ip6->ip6_plen);
 	struct udphdr *udp = (struct udphdr *)((char *)ip6 + sizeof(struct ip6_hdr));
+	int len = ntohs(udp->len);
 	u_int32_t sum = chksum((char *)udp, len);	/* udp header + packet data */
 
 	/* add the pseudo header: src + dst + nxtheader + length */
@@ -302,6 +314,7 @@ int main(int argc, char *argv[]) {
 	int idx_up, idx_down;
 
 	struct in6_addr all_dhcp_servers_and_relays;
+	int mtu;		/* get this from the upstream interface? */
 
 
 	/* prepare for comparing later on */
@@ -323,13 +336,18 @@ int main(int argc, char *argv[]) {
 		
 	idx_up = ifr.ifr_ifindex;
 
+	/* it's the upstream MTU that will be a problem */
+	if (ioctl(s, SIOCGIFMTU, &ifr, sizeof(ifr)))
+		fprintf(stderr, "%s(): SIOCGIFMTU failed: %m\n", __FUNCTION__);
+	mtu = ifr.ifr_mtu;
+
 	strncpy((char *)&ifr.ifr_name, downstream, IFNAMSIZ);
 	if (ioctl(s, SIOCGIFINDEX, &ifr, sizeof(ifr)))
 		fprintf(stderr, "%s(): SIOCGIFINDEX failed: %m\n", __FUNCTION__);
 		
 	idx_down = ifr.ifr_ifindex;
 
-	fprintf(stderr,"idx_down=%d, idx_up=%d\n", idx_down, idx_up);
+	fprintf(stderr,"idx_down=%d, idx_up=%d, mtu=%d\n", idx_down, idx_up, mtu);
 
 	/* Maybe bind to exactly two interfaces - one upstream and one downstream,
 	   using a specifically crated filter for each socket? */
@@ -539,7 +557,6 @@ Steven McCanne and Van Jacobson of Lawrence Berkeley Laboratory.
 		int *val;
 		int hopcount = 0;
 		int trusted = 1;	/* FIMXE: allow setting this per interface */
-		int mtu = 1500;		/* FIMXE: get this from the upstream interface? */
 
 
 		/* FIMXE: We receive three(!) copies of the same frame in the common case: