Manipulating the TTL of the Packet

Right now the TTL of the packet is not overwritten by Vrouter. It is
only decremented like a hop, for the required packets. But BGP packets
in VM (due to BGP as service), can come to Vrouter to with ttl of 1. In
a multi hop environment, we require this ttl to be more than 1. For this
purpose flow entry is added with another ttl field and if Agent sets
this, vrouter unconditionally sets this ttl in the packet and calculates
the checksum again.

Change-Id: I4619e81ad324827e29dc487857020ddd9e429f2c
partial-bug: #1567586

dp-core/vr_flow.c

@@ -225,6 +225,7 @@ __vr_flow_reset_entry(struct vrouter *router, struct vr_flow_entry *fe)
     fe->fe_flags &=
         (VR_FLOW_FLAG_ACTIVE | VR_FLOW_FLAG_EVICTED |
          VR_FLOW_FLAG_NEW_FLOW | VR_FLOW_FLAG_DELETE_MARKED);
+    fe->fe_ttl = 0;
 
     return;
 }
@@ -748,6 +749,8 @@ vr_flow_action(struct vrouter *router, struct vr_flow_entry *fe,
         struct vr_forwarding_md *fmd)
 {
     int valid_src;
+    unsigned int ip_inc_diff_cksum = 0;
+    struct vr_ip *ip;
 
     flow_result_t result;
 
@@ -829,6 +832,22 @@ vr_flow_action(struct vrouter *router, struct vr_flow_entry *fe,
         break;
     }
 
+    if (result == FLOW_FORWARD) {
+        if (pkt->vp_type == VP_TYPE_IP) {
+            ip = (struct vr_ip *)pkt_network_header(pkt);
+            if (ip) {
+                if (fe->fe_ttl && (fe->fe_ttl != ip->ip_ttl)) {
+                    vr_incremental_diff(ip->ip_ttl, fe->fe_ttl, &ip_inc_diff_cksum);
+                    ip->ip_ttl = fe->fe_ttl;
+
+                    if (ip_inc_diff_cksum)
+                        vr_ip_incremental_csum(ip, ip_inc_diff_cksum);
+                }
+            }
+        }
+    }
+
+
     if (fe->fe_tcp_flags & VR_FLOW_TCP_DEAD)
         vr_flow_mark_evict(router, fe, index);
 
@@ -1900,6 +1919,8 @@ vr_flow_set(struct vrouter *router, vr_flow_req *req)
         fe->fe_action = req->fr_action;
     }
 
+    fe->fe_ttl = req->fr_ttl;
+
     if (fe->fe_action == VR_FLOW_ACTION_DROP)
         fe->fe_drop_reason = (uint8_t)req->fr_drop_reason;
 

dp-core/vr_proto_ip.c

@@ -103,7 +103,8 @@ vr_ip_update_csum(struct vr_packet *pkt, unsigned int ip_inc, unsigned int inc)
     unsigned short *csump;
 
     ip = (struct vr_ip *)pkt_network_header(pkt);
-    ip->ip_csum = vr_ip_csum(ip);
+    if (ip_inc)
+        vr_ip_incremental_csum(ip, ip_inc);
 
     if (ip->ip_proto == VR_IP_PROTO_TCP) {
         tcp = (struct vr_tcp *)((unsigned char *)ip + ip->ip_hl * 4);

include/vr_flow.h

@@ -299,7 +299,8 @@ struct vr_flow_queue {
 
 struct vr_dummy_flow_entry {
     vr_hentry_t fe_hentry;
-    uint8_t fe_hentry_packing[3];
+    uint8_t fe_pack_hentry[2];
+    uint8_t fe_ttl;
     struct vr_flow fe_key;
     uint8_t fe_gen_id;
     uint16_t fe_tcp_flags;
@@ -326,7 +327,8 @@ struct vr_dummy_flow_entry {
 /* do not change. any field positions as it might lead to incompatibility */
 struct vr_flow_entry {
     vr_hentry_t fe_hentry;
-    uint8_t fe_hentry_packing[3];
+    uint8_t fe_pack_hentry[2];
+    uint8_t fe_ttl;
     struct vr_flow fe_key;
     uint8_t fe_gen_id;
     uint16_t fe_tcp_flags;

include/vr_packet.h

@@ -368,6 +368,44 @@ struct vr_ip {
     unsigned int ip_daddr;
 } __attribute__((packed));
 
+static inline void
+vr_incremental_diff(unsigned int oldval, unsigned int newval,
+        unsigned int *diff)
+{
+    unsigned int tmp;
+
+    tmp = ~oldval + newval;
+    if (tmp < newval)
+        tmp += 1;
+
+    *diff += tmp;
+    if (*diff < tmp)
+        *diff += 1;
+
+    return;
+}
+
+static inline void
+vr_ip_incremental_csum(struct vr_ip *ip, unsigned int diff)
+{
+    unsigned int csum;
+
+    diff = (diff >> 16) + (diff & 0xffff);
+    if (diff >> 16) {
+        diff &= 0xffff;
+        diff += 1;
+    }
+
+    csum = ~(ip->ip_csum) & 0xffff;
+    csum += diff;
+    csum = (csum >> 16) + (csum & 0xffff);
+    if (csum >> 16)
+        csum = (csum & 0xffff) + 1;
+
+    ip->ip_csum = (~csum & 0xffff);
+    return;
+}
+
 #define SOURCE_LINK_LAYER_ADDRESS_OPTION    1
 #define TARGET_LINK_LAYER_ADDRESS_OPTION    2
 
@@ -614,23 +652,6 @@ vr_ip_transport_header_valid(struct vr_ip *iph)
     return true;
 }
 
-static inline void
-vr_incremental_diff(unsigned int oldval, unsigned int newval,
-        unsigned int *diff)
-{
-    unsigned int tmp;
-
-    tmp = ~oldval + newval;
-    if (tmp < newval)
-        tmp += 1;
-
-    *diff += tmp;
-    if (*diff < tmp)
-        *diff += 1;
-
-    return;
-}
-
 #define VR_TCP_FLAG_FIN         0x0001
 #define VR_TCP_FLAG_SYN         0x0002
 #define VR_TCP_FLAG_RST         0x0004

sandesh/vr.sandesh

@@ -185,6 +185,7 @@ buffer sandesh vr_flow_req {
    35: u32          fr_flow_stats_oflow;
    36: i32          fr_oflow_entries;
    37: byte         fr_gen_id;
+   38: byte         fr_ttl;
 }
 
 buffer sandesh vr_vrf_assign_req {

utils/flow.c

@@ -534,6 +534,7 @@ dump_table(struct flow_table *ft)
                     printf(", %d, ", fe->fe_sec_mirror_id);
             }
             printf(" SPort %d", fe->fe_udp_src_port);
+            printf(" TTL %d", fe->fe_ttl);
             printf(")");
         }