From: Simon Wunderlich simon@open-mesh.com
When a packet is received from another node first and later from the best next hop, this packet is dropped. However the first OGM was sent with the BATADV_NOT_BEST_NEXT_HOP flag and thus dropped by neighbors. The late OGM from the best neighbor is then dropped because it is a duplicate.
If this situation happens constantly, a node might end up not forwarding the "valid" OGMs anymore, and nodes behind will starve from not getting valid OGMs.
Fix this by refining the duplicate checking behaviour: The actions should depend on whether it was a duplicate for a neighbor only or for the originator. OGMs which are not duplicates for a specific neighbor will now be considered in batadv_iv_ogm_forward(), but only actually forwarded for the best next hop. Therefore, late OGMs from the best next hop are forwarded now and not dropped as duplicates anymore.
Signed-off-by: Simon Wunderlich simon@open-mesh.com
--- Changes to PATCHv1: * use enum to distinguish different duplicate states * fix typo "is_simlar -> is_similar" * remove antonios sign off (the patch changed, feel free to add it if he is ok with it, it was his idea originally ...) --- bat_iv_ogm.c | 86 +++++++++++++++++++++++++++++++++++++--------------------- 1 file changed, 55 insertions(+), 31 deletions(-)
diff --git a/bat_iv_ogm.c b/bat_iv_ogm.c index 8d87f87..2b94fdd 100644 --- a/bat_iv_ogm.c +++ b/bat_iv_ogm.c @@ -701,6 +701,21 @@ static void batadv_iv_ogm_schedule(struct batadv_hard_iface *hard_iface) batadv_hardif_free_ref(primary_if); }
+/** + * batadv_dup_status - duplicate status + * @BATADV_NO_DUP: the packet is a duplicate + * @BATADV_ORIG_DUP: OGM is a duplicate in the originator (but not for the + * neighbor) + * @BATADV_NEIGH_DUP: OGM is a duplicate for the neighbor + * @BATADV_PROTECTED: originator is currently protected (after reboot) + */ +enum batadv_dup_status { + BATADV_NO_DUP = 0, + BATADV_ORIG_DUP, + BATADV_NEIGH_DUP, + BATADV_PROTECTED, +}; + static void batadv_iv_ogm_orig_update(struct batadv_priv *bat_priv, struct batadv_orig_node *orig_node, @@ -708,7 +723,7 @@ batadv_iv_ogm_orig_update(struct batadv_priv *bat_priv, const struct batadv_ogm_packet *batadv_ogm_packet, struct batadv_hard_iface *if_incoming, const unsigned char *tt_buff, - int is_duplicate) + enum batadv_dup_status dup_status) { struct batadv_neigh_node *neigh_node = NULL, *tmp_neigh_node = NULL; struct batadv_neigh_node *router = NULL; @@ -734,7 +749,7 @@ batadv_iv_ogm_orig_update(struct batadv_priv *bat_priv, continue; }
- if (is_duplicate) + if (dup_status != BATADV_NO_DUP) continue;
spin_lock_bh(&tmp_neigh_node->lq_update_lock); @@ -774,7 +789,7 @@ batadv_iv_ogm_orig_update(struct batadv_priv *bat_priv, neigh_node->tq_avg = batadv_ring_buffer_avg(neigh_node->tq_recv); spin_unlock_bh(&neigh_node->lq_update_lock);
- if (!is_duplicate) { + if (dup_status == BATADV_NO_DUP) { orig_node->last_ttl = batadv_ogm_packet->header.ttl; neigh_node->last_ttl = batadv_ogm_packet->header.ttl; } @@ -932,15 +947,16 @@ out: return ret; }
-/* processes a batman packet for all interfaces, adjusts the sequence number and - * finds out whether it is a duplicate. +/** + * batadv_iv_ogm_update_seqnos - processes a batman packet for all interfaces, + * adjusts the sequence number and finds out whether it is a duplicate. + * @ethhdr: Ethernet header of the packet + * @batadv_ogm_packet: OGM packet to be considered + * @if_incoming: interface where the OGM packet was received + * Returns: duplicate status as enum batadv_dup_status * returns: - * 1 the packet is a duplicate - * 0 the packet has not yet been received - * -1 the packet is old and has been received while the seqno window - * was protected. Caller should drop it. - */ -static int + */ +enum batadv_dup_status batadv_iv_ogm_update_seqnos(const struct ethhdr *ethhdr, const struct batadv_ogm_packet *batadv_ogm_packet, const struct batadv_hard_iface *if_incoming) @@ -948,17 +964,18 @@ batadv_iv_ogm_update_seqnos(const struct ethhdr *ethhdr, struct batadv_priv *bat_priv = netdev_priv(if_incoming->soft_iface); struct batadv_orig_node *orig_node; struct batadv_neigh_node *tmp_neigh_node; - int is_duplicate = 0; + int is_dup; int32_t seq_diff; int need_update = 0; - int set_mark, ret = -1; + int set_mark; + enum batadv_dup_status ret = BATADV_NO_DUP; uint32_t seqno = ntohl(batadv_ogm_packet->seqno); uint8_t *neigh_addr; uint8_t packet_count;
orig_node = batadv_get_orig_node(bat_priv, batadv_ogm_packet->orig); if (!orig_node) - return 0; + return BATADV_NO_DUP;
spin_lock_bh(&orig_node->ogm_cnt_lock); seq_diff = seqno - orig_node->last_real_seqno; @@ -966,22 +983,29 @@ batadv_iv_ogm_update_seqnos(const struct ethhdr *ethhdr, /* signalize caller that the packet is to be dropped. */ if (!hlist_empty(&orig_node->neigh_list) && batadv_window_protected(bat_priv, seq_diff, - &orig_node->batman_seqno_reset)) + &orig_node->batman_seqno_reset)) { + ret = BATADV_PROTECTED; goto out; + }
rcu_read_lock(); hlist_for_each_entry_rcu(tmp_neigh_node, &orig_node->neigh_list, list) { - is_duplicate |= batadv_test_bit(tmp_neigh_node->real_bits, - orig_node->last_real_seqno, - seqno); - neigh_addr = tmp_neigh_node->addr; + is_dup = batadv_test_bit(tmp_neigh_node->real_bits, + orig_node->last_real_seqno, + seqno); + if (batadv_compare_eth(neigh_addr, ethhdr->h_source) && - tmp_neigh_node->if_incoming == if_incoming) + tmp_neigh_node->if_incoming == if_incoming) { set_mark = 1; - else + if (is_dup) + ret = BATADV_NEIGH_DUP; + } else { set_mark = 0; + if (is_dup && (ret != BATADV_NEIGH_DUP)) + ret = BATADV_ORIG_DUP; + }
/* if the window moved, set the update flag. */ need_update |= batadv_bit_get_packet(bat_priv, @@ -1001,8 +1025,6 @@ batadv_iv_ogm_update_seqnos(const struct ethhdr *ethhdr, orig_node->last_real_seqno = seqno; }
- ret = is_duplicate; - out: spin_unlock_bh(&orig_node->ogm_cnt_lock); batadv_orig_node_free_ref(orig_node); @@ -1024,7 +1046,8 @@ static void batadv_iv_ogm_process(const struct ethhdr *ethhdr, int is_bidirect; bool is_single_hop_neigh = false; bool is_from_best_next_hop = false; - int is_duplicate, sameseq, simlar_ttl; + int sameseq, similar_ttl; + enum batadv_dup_status dup_status; uint32_t if_incoming_seqno; uint8_t *prev_sender;
@@ -1149,10 +1172,10 @@ static void batadv_iv_ogm_process(const struct ethhdr *ethhdr, if (!orig_node) return;
- is_duplicate = batadv_iv_ogm_update_seqnos(ethhdr, batadv_ogm_packet, - if_incoming); + dup_status = batadv_iv_ogm_update_seqnos(ethhdr, batadv_ogm_packet, + if_incoming);
- if (is_duplicate == -1) { + if (dup_status == BATADV_PROTECTED) { batadv_dbg(BATADV_DBG_BATMAN, bat_priv, "Drop packet: packet within seqno protection time (sender: %pM)\n", ethhdr->h_source); @@ -1224,11 +1247,12 @@ static void batadv_iv_ogm_process(const struct ethhdr *ethhdr, * seqno and similar ttl as the non-duplicate */ sameseq = orig_node->last_real_seqno == ntohl(batadv_ogm_packet->seqno); - simlar_ttl = orig_node->last_ttl - 3 <= batadv_ogm_packet->header.ttl; - if (is_bidirect && (!is_duplicate || (sameseq && simlar_ttl))) + similar_ttl = orig_node->last_ttl - 3 <= batadv_ogm_packet->header.ttl; + if (is_bidirect && ((dup_status == BATADV_NO_DUP) || + (sameseq && similar_ttl))) batadv_iv_ogm_orig_update(bat_priv, orig_node, ethhdr, batadv_ogm_packet, if_incoming, - tt_buff, is_duplicate); + tt_buff, dup_status);
/* is single hop (direct) neighbor */ if (is_single_hop_neigh) { @@ -1249,7 +1273,7 @@ static void batadv_iv_ogm_process(const struct ethhdr *ethhdr, goto out_neigh; }
- if (is_duplicate) { + if (dup_status == BATADV_NEIGH_DUP) { batadv_dbg(BATADV_DBG_BATMAN, bat_priv, "Drop packet: duplicate packet received\n"); goto out_neigh;
On Thu, May 23, 2013 at 01:07:42PM +0200, Simon Wunderlich wrote:
Changes to PATCHv1:
- use enum to distinguish different duplicate states
- fix typo "is_simlar -> is_similar"
- remove antonios sign off (the patch changed, feel free to add it if he is ok with it, it was his idea originally ...)
no, it's ok as it is :)
bat_iv_ogm.c | 86 +++++++++++++++++++++++++++++++++++++--------------------- 1 file changed, 55 insertions(+), 31 deletions(-)
diff --git a/bat_iv_ogm.c b/bat_iv_ogm.c index 8d87f87..2b94fdd 100644 --- a/bat_iv_ogm.c +++ b/bat_iv_ogm.c @@ -701,6 +701,21 @@ static void batadv_iv_ogm_schedule(struct batadv_hard_iface *hard_iface) batadv_hardif_free_ref(primary_if); }
+/**
- batadv_dup_status - duplicate status
- @BATADV_NO_DUP: the packet is a duplicate
- @BATADV_ORIG_DUP: OGM is a duplicate in the originator (but not for the
- neighbor)
- @BATADV_NEIGH_DUP: OGM is a duplicate for the neighbor
- @BATADV_PROTECTED: originator is currently protected (after reboot)
- */
+enum batadv_dup_status {
- BATADV_NO_DUP = 0,
- BATADV_ORIG_DUP,
- BATADV_NEIGH_DUP,
- BATADV_PROTECTED,
+};
Very nice! splitting the "simple boolean" into an enum is a very good idea imho.
-/* processes a batman packet for all interfaces, adjusts the sequence number and
- finds out whether it is a duplicate.
+/**
- batadv_iv_ogm_update_seqnos - processes a batman packet for all interfaces,
- adjusts the sequence number and finds out whether it is a duplicate.
- @ethhdr: Ethernet header of the packet
- @batadv_ogm_packet: OGM packet to be considered
- @if_incoming: interface where the OGM packet was received
A blank line is needed here. Maybe who's going to merge this patch can add it? :)
- Returns: duplicate status as enum batadv_dup_status
- returns:
- 1 the packet is a duplicate
- 0 the packet has not yet been received
- -1 the packet is old and has been received while the seqno window
was protected. Caller should drop it.- */
-static int
- */
+enum batadv_dup_status batadv_iv_ogm_update_seqnos(const struct ethhdr *ethhdr, const struct batadv_ogm_packet *batadv_ogm_packet, const struct batadv_hard_iface *if_incoming)
The rest looks good! Thanks Simon.
Cheers,
Hi Simon,
I'm currently wondering whether changing the protocol in the way you described is sufficient.
I think it still has the problem of not converging to the optimal solution in various scenarios, for instance:
----------
B1 --------- / \ A C1 ---- D \ / / B2 - C2 ----
A-B1: 10%, 0ms A-B2: 100%, 0ms B2-C1: 5%, 0ms B2-C2: 100%, 5ms B1-D: 100%, 0ms C1-D: 100%, 0ms C2-D: 100%, 0ms ('link': 'link-quality', 'link-delay')
Obviously, here the path A-B2-C2 is the best, having a 100% link quality. However with this patch, it will select A-B1-D, having only a 10% link quality (I'm not considering asym/hop-penalty or that 0ms delay is unrealistic, and I'm not considering that the link quality will cause lost OGMs - just to keep things simple):
The OGM from D gets forwarded to B1 and then to A instantly; A notes a path quality of 10% towards D via B1.
The OGM from D reaches B2 via C1 first, so B2 first forwards an OGM with a path quality of 5% to A first. A notes a path quality of 5% towards D via B2.
Then the OGM from D reaches B2 via C2, too. Now, with this patch B2 will correctly choose the path via C2, B2 notes a 100% path quality towards D via C2 instead of ignoring this OGM. And B2 will also rebroadcast this OGM.
However, A will ignore this second OGM from D via B2 because it came from the same neighbor even though it came from the best, optimal, 100% link-quality path.
----------
While converging to a path after applying this patch is obviously better than the starvation which can currently happen I'm still wondering whether the issue could be solved better.
What if we were always rebroadcasting/forwarding an OGM even from the same neighbor, too, if the sequence number is the same but the TQ better (so similar to what is specified for BATMAN V)?
Cheers, Linus
On Thu, May 23, 2013 at 01:07:42PM +0200, Simon Wunderlich wrote:
From: Simon Wunderlich simon@open-mesh.com
When a packet is received from another node first and later from the best next hop, this packet is dropped. However the first OGM was sent with the BATADV_NOT_BEST_NEXT_HOP flag and thus dropped by neighbors. The late OGM from the best neighbor is then dropped because it is a duplicate.
If this situation happens constantly, a node might end up not forwarding the "valid" OGMs anymore, and nodes behind will starve from not getting valid OGMs.
Fix this by refining the duplicate checking behaviour: The actions should depend on whether it was a duplicate for a neighbor only or for the originator. OGMs which are not duplicates for a specific neighbor will now be considered in batadv_iv_ogm_forward(), but only actually forwarded for the best next hop. Therefore, late OGMs from the best next hop are forwarded now and not dropped as duplicates anymore.
Signed-off-by: Simon Wunderlich simon@open-mesh.com
Changes to PATCHv1:
- use enum to distinguish different duplicate states
- fix typo "is_simlar -> is_similar"
- remove antonios sign off (the patch changed, feel free to add it if he is ok with it, it was his idea originally ...)
bat_iv_ogm.c | 86 +++++++++++++++++++++++++++++++++++++--------------------- 1 file changed, 55 insertions(+), 31 deletions(-)
diff --git a/bat_iv_ogm.c b/bat_iv_ogm.c index 8d87f87..2b94fdd 100644 --- a/bat_iv_ogm.c +++ b/bat_iv_ogm.c @@ -701,6 +701,21 @@ static void batadv_iv_ogm_schedule(struct batadv_hard_iface *hard_iface) batadv_hardif_free_ref(primary_if); }
+/**
- batadv_dup_status - duplicate status
- @BATADV_NO_DUP: the packet is a duplicate
- @BATADV_ORIG_DUP: OGM is a duplicate in the originator (but not for the
- neighbor)
- @BATADV_NEIGH_DUP: OGM is a duplicate for the neighbor
- @BATADV_PROTECTED: originator is currently protected (after reboot)
- */
+enum batadv_dup_status {
- BATADV_NO_DUP = 0,
- BATADV_ORIG_DUP,
- BATADV_NEIGH_DUP,
- BATADV_PROTECTED,
+};
static void batadv_iv_ogm_orig_update(struct batadv_priv *bat_priv, struct batadv_orig_node *orig_node, @@ -708,7 +723,7 @@ batadv_iv_ogm_orig_update(struct batadv_priv *bat_priv, const struct batadv_ogm_packet *batadv_ogm_packet, struct batadv_hard_iface *if_incoming, const unsigned char *tt_buff,
int is_duplicate)
enum batadv_dup_status dup_status){ struct batadv_neigh_node *neigh_node = NULL, *tmp_neigh_node = NULL; struct batadv_neigh_node *router = NULL; @@ -734,7 +749,7 @@ batadv_iv_ogm_orig_update(struct batadv_priv *bat_priv, continue; }
if (is_duplicate)
if (dup_status != BATADV_NO_DUP) continue;spin_lock_bh(&tmp_neigh_node->lq_update_lock);
@@ -774,7 +789,7 @@ batadv_iv_ogm_orig_update(struct batadv_priv *bat_priv, neigh_node->tq_avg = batadv_ring_buffer_avg(neigh_node->tq_recv); spin_unlock_bh(&neigh_node->lq_update_lock);
- if (!is_duplicate) {
- if (dup_status == BATADV_NO_DUP) { orig_node->last_ttl = batadv_ogm_packet->header.ttl; neigh_node->last_ttl = batadv_ogm_packet->header.ttl; }
@@ -932,15 +947,16 @@ out: return ret; }
-/* processes a batman packet for all interfaces, adjusts the sequence number and
- finds out whether it is a duplicate.
+/**
- batadv_iv_ogm_update_seqnos - processes a batman packet for all interfaces,
- adjusts the sequence number and finds out whether it is a duplicate.
- @ethhdr: Ethernet header of the packet
- @batadv_ogm_packet: OGM packet to be considered
- @if_incoming: interface where the OGM packet was received
- Returns: duplicate status as enum batadv_dup_status
- returns:
- 1 the packet is a duplicate
- 0 the packet has not yet been received
- -1 the packet is old and has been received while the seqno window
was protected. Caller should drop it.- */
-static int
- */
+enum batadv_dup_status batadv_iv_ogm_update_seqnos(const struct ethhdr *ethhdr, const struct batadv_ogm_packet *batadv_ogm_packet, const struct batadv_hard_iface *if_incoming) @@ -948,17 +964,18 @@ batadv_iv_ogm_update_seqnos(const struct ethhdr *ethhdr, struct batadv_priv *bat_priv = netdev_priv(if_incoming->soft_iface); struct batadv_orig_node *orig_node; struct batadv_neigh_node *tmp_neigh_node;
- int is_duplicate = 0;
- int is_dup; int32_t seq_diff; int need_update = 0;
- int set_mark, ret = -1;
int set_mark;
enum batadv_dup_status ret = BATADV_NO_DUP; uint32_t seqno = ntohl(batadv_ogm_packet->seqno); uint8_t *neigh_addr; uint8_t packet_count;
orig_node = batadv_get_orig_node(bat_priv, batadv_ogm_packet->orig); if (!orig_node)
return 0;
return BATADV_NO_DUP;spin_lock_bh(&orig_node->ogm_cnt_lock); seq_diff = seqno - orig_node->last_real_seqno;
@@ -966,22 +983,29 @@ batadv_iv_ogm_update_seqnos(const struct ethhdr *ethhdr, /* signalize caller that the packet is to be dropped. */ if (!hlist_empty(&orig_node->neigh_list) && batadv_window_protected(bat_priv, seq_diff,
&orig_node->batman_seqno_reset))
&orig_node->batman_seqno_reset)) {ret = BATADV_PROTECTED;goto out;
}
rcu_read_lock(); hlist_for_each_entry_rcu(tmp_neigh_node, &orig_node->neigh_list, list) {
is_duplicate |= batadv_test_bit(tmp_neigh_node->real_bits,orig_node->last_real_seqno,seqno);- neigh_addr = tmp_neigh_node->addr;
is_dup = batadv_test_bit(tmp_neigh_node->real_bits,orig_node->last_real_seqno,seqno);- if (batadv_compare_eth(neigh_addr, ethhdr->h_source) &&
tmp_neigh_node->if_incoming == if_incoming)
tmp_neigh_node->if_incoming == if_incoming) { set_mark = 1;
else
if (is_dup)ret = BATADV_NEIGH_DUP;} else { set_mark = 0;if (is_dup && (ret != BATADV_NEIGH_DUP))ret = BATADV_ORIG_DUP;}/* if the window moved, set the update flag. */ need_update |= batadv_bit_get_packet(bat_priv,
@@ -1001,8 +1025,6 @@ batadv_iv_ogm_update_seqnos(const struct ethhdr *ethhdr, orig_node->last_real_seqno = seqno; }
- ret = is_duplicate;
out: spin_unlock_bh(&orig_node->ogm_cnt_lock); batadv_orig_node_free_ref(orig_node); @@ -1024,7 +1046,8 @@ static void batadv_iv_ogm_process(const struct ethhdr *ethhdr, int is_bidirect; bool is_single_hop_neigh = false; bool is_from_best_next_hop = false;
- int is_duplicate, sameseq, simlar_ttl;
- int sameseq, similar_ttl;
- enum batadv_dup_status dup_status; uint32_t if_incoming_seqno; uint8_t *prev_sender;
@@ -1149,10 +1172,10 @@ static void batadv_iv_ogm_process(const struct ethhdr *ethhdr, if (!orig_node) return;
- is_duplicate = batadv_iv_ogm_update_seqnos(ethhdr, batadv_ogm_packet,
if_incoming);
- dup_status = batadv_iv_ogm_update_seqnos(ethhdr, batadv_ogm_packet,
if_incoming);
- if (is_duplicate == -1) {
- if (dup_status == BATADV_PROTECTED) { batadv_dbg(BATADV_DBG_BATMAN, bat_priv, "Drop packet: packet within seqno protection time (sender: %pM)\n", ethhdr->h_source);
@@ -1224,11 +1247,12 @@ static void batadv_iv_ogm_process(const struct ethhdr *ethhdr, * seqno and similar ttl as the non-duplicate */ sameseq = orig_node->last_real_seqno == ntohl(batadv_ogm_packet->seqno);
- simlar_ttl = orig_node->last_ttl - 3 <= batadv_ogm_packet->header.ttl;
- if (is_bidirect && (!is_duplicate || (sameseq && simlar_ttl)))
- similar_ttl = orig_node->last_ttl - 3 <= batadv_ogm_packet->header.ttl;
- if (is_bidirect && ((dup_status == BATADV_NO_DUP) ||
(sameseq && similar_ttl)))
tt_buff, is_duplicate);
tt_buff, dup_status);/* is single hop (direct) neighbor */ if (is_single_hop_neigh) {
@@ -1249,7 +1273,7 @@ static void batadv_iv_ogm_process(const struct ethhdr *ethhdr, goto out_neigh; }
- if (is_duplicate) {
- if (dup_status == BATADV_NEIGH_DUP) { batadv_dbg(BATADV_DBG_BATMAN, bat_priv, "Drop packet: duplicate packet received\n"); goto out_neigh;
-- 1.7.10.4
On Sat, May 25, 2013 at 11:07:48PM +0200, Linus Lüssing wrote:
Hi Simon,
I'm currently wondering whether changing the protocol in the way you described is sufficient.
I think it still has the problem of not converging to the optimal solution in various scenarios, for instance:
B1 ---------/ \ A C1 ---- D \ / / B2 - C2 ----
A-B1: 10%, 0ms A-B2: 100%, 0ms B2-C1: 5%, 0ms B2-C2: 100%, 5ms B1-D: 100%, 0ms C1-D: 100%, 0ms C2-D: 100%, 0ms ('link': 'link-quality', 'link-delay')
Obviously, here the path A-B2-C2 is the best, having a 100% link quality. However with this patch, it will select A-B1-D, having only a 10% link quality (I'm not considering asym/hop-penalty or that 0ms delay is unrealistic, and I'm not considering that the link quality will cause lost OGMs - just to keep things simple):
The OGM from D gets forwarded to B1 and then to A instantly; A notes a path quality of 10% towards D via B1.
The OGM from D reaches B2 via C1 first, so B2 first forwards an OGM with a path quality of 5% to A first. A notes a path quality of 5% towards D via B2.
Then the OGM from D reaches B2 via C2, too. Now, with this patch B2 will correctly choose the path via C2, B2 notes a 100% path quality towards D via C2 instead of ignoring this OGM.
This was true also before this patch.
And B2 will also rebroadcast this OGM.
However, A will ignore this second OGM from D via B2 because it came from the same neighbor even though it came from the best, optimal, 100% link-quality path.
While converging to a path after applying this patch is obviously better than the starvation which can currently happen I'm still wondering whether the issue could be solved better.
What if we were always rebroadcasting/forwarding an OGM even from the same neighbor, too, if the sequence number is the same but the TQ better (so similar to what is specified for BATMAN V)?
If I am not wrong this is what is going to happen, but with one originator interval of delay.
If I correctly got your example, this happens the first time only, but from the next originator interval B2 will only rebroadcast the OGM coming from C2 since this is the best next hop for it. So yes, this can happen but only the first time. As soon as B2 learns the best route via C2.
What this patch is changing is to make B2 rebroadcast the OGM coming from C2 (best next hop) in case the latter arrived after the OGM coming from C1 (which is not rebroadcasted because C1 is not best next hop). Actually the fix is only acting on the duplicate detection only (which affect forwarding).
So, without this patch, in this case I described, we were having a real "block". There is no change in the route selection. The routes are still selected the same way as before.
Cheers,
Hey Linus & Antonio,
On Sat, May 25, 2013 at 11:42:19PM +0200, Antonio Quartulli wrote:
On Sat, May 25, 2013 at 11:07:48PM +0200, Linus Lüssing wrote:
Hi Simon,
I'm currently wondering whether changing the protocol in the way you described is sufficient.
I think it still has the problem of not converging to the optimal solution in various scenarios, for instance:
B1 ---------/ \ A C1 ---- D \ / / B2 - C2 ----
A-B1: 10%, 0ms A-B2: 100%, 0ms B2-C1: 5%, 0ms B2-C2: 100%, 5ms B1-D: 100%, 0ms C1-D: 100%, 0ms C2-D: 100%, 0ms ('link': 'link-quality', 'link-delay')
Obviously, here the path A-B2-C2 is the best, having a 100% link quality. However with this patch, it will select A-B1-D, having only a 10% link quality (I'm not considering asym/hop-penalty or that 0ms delay is unrealistic, and I'm not considering that the link quality will cause lost OGMs - just to keep things simple):
The OGM from D gets forwarded to B1 and then to A instantly; A notes a path quality of 10% towards D via B1.
The OGM from D reaches B2 via C1 first, so B2 first forwards an OGM with a path quality of 5% to A first. A notes a path quality of 5% towards D via B2.
Then the OGM from D reaches B2 via C2, too. Now, with this patch B2 will correctly choose the path via C2, B2 notes a 100% path quality towards D via C2 instead of ignoring this OGM.
This was true also before this patch.
I agree - actually A would have not gotten any (valid) packets from B2 because B2 would got the packets first from C1, discard them (not best nexthop), and then from C2 (best nexthop) but don't forward it because it was a duplicate. Antonio pointed out the same thing below ...
Then A would always have to choose B1 because it gets no valid OGMs via B2. The patch actually solves this situation, even not in optimal time as Antonio pointed out ...
And B2 will also rebroadcast this OGM.
However, A will ignore this second OGM from D via B2 because it came from the same neighbor even though it came from the best, optimal, 100% link-quality path.
While converging to a path after applying this patch is obviously better than the starvation which can currently happen I'm still wondering whether the issue could be solved better.
What if we were always rebroadcasting/forwarding an OGM even from the same neighbor, too, if the sequence number is the same but the TQ better (so similar to what is specified for BATMAN V)?
If I am not wrong this is what is going to happen, but with one originator interval of delay.
If I correctly got your example, this happens the first time only, but from the next originator interval B2 will only rebroadcast the OGM coming from C2 since this is the best next hop for it. So yes, this can happen but only the first time. As soon as B2 learns the best route via C2.
Agreed here too - B2 should select C2 "soon" as the best nexthop and then only forward Ds OGMs via C2, but not via C1. Then A will get the good OGMs via C2-B2 and - voila - will select it as best route.
The situation you describe happens for the first "few" OGMs (not sure if it's only the first), when only OGMs from C1 have been received at B2 but not from C2.
Regarding your suggestion to forward multiple packets with the same seqno, but better TQ: We currently would ignore them in A for beeing a duplicate. If we were to change that, we would have to change the TQ ring buffer as well. However this ring buffer currently has no specific order, so it's not so easy to update a specific value in this ring buffer because we don't know which TQ value belongs to which seqno. If packets arrive out of order, they will be saved in the ring buffer in the order they come in, regardless of the seqno. Have a look at batadv_iv_ogm_orig_update(), maybe you can find a decent solution for that. :)
Apart from this technical issue, I don't think it's that critical to save a single OGM cycle by sending (many) more OGMs, that's pretty much an overhead vs speed discussion.
What this patch is changing is to make B2 rebroadcast the OGM coming from C2 (best next hop) in case the latter arrived after the OGM coming from C1 (which is not rebroadcasted because C1 is not best next hop). Actually the fix is only acting on the duplicate detection only (which affect forwarding).
So, without this patch, in this case I described, we were having a real "block". There is no change in the route selection. The routes are still selected the same way as before.
Yup, see above.
Thanks for you comments and thoughts, Simon
Hey guys,
On Sun, May 26, 2013 at 05:14:43PM +0200, Simon Wunderlich wrote: [cut...]
Regarding your suggestion to forward multiple packets with the same seqno, but better TQ: We currently would ignore them in A for beeing a duplicate. If we were to change that, we would have to change the TQ ring buffer as well. However this ring buffer currently has no specific order, so it's not so easy to update a specific value in this ring buffer because we don't know which TQ value belongs to which seqno. If packets arrive out of order, they will be saved in the ring buffer in the order they come in, regardless of the seqno. Have a look at batadv_iv_ogm_orig_update(), maybe you can find a decent solution for that. :)
Honestly, I think that we should avoid adding features to batman iv any longer (this is my point of view) and rather concentrate the effort in pushing them into batman v (which is going to come soonish[tm]).
Therefore, if you think there is something which we can do better, I'd prefer to push such improvement into the new version of the protocol, which is going to be "simpler" (to some extends) and since it is still under development it would be easier to change/improve/modify.
batman iv already has many "patches and corner cases" which I think is better to do not change too much to avoid introducing some new nice bugs :)
these were just my 2 cents
Cheers!
On Thursday, May 23, 2013 19:07:42 Simon Wunderlich wrote:
From: Simon Wunderlich simon@open-mesh.com
When a packet is received from another node first and later from the best next hop, this packet is dropped. However the first OGM was sent with the BATADV_NOT_BEST_NEXT_HOP flag and thus dropped by neighbors. The late OGM from the best neighbor is then dropped because it is a duplicate.
If this situation happens constantly, a node might end up not forwarding the "valid" OGMs anymore, and nodes behind will starve from not getting valid OGMs.
Fix this by refining the duplicate checking behaviour: The actions should depend on whether it was a duplicate for a neighbor only or for the originator. OGMs which are not duplicates for a specific neighbor will now be considered in batadv_iv_ogm_forward(), but only actually forwarded for the best next hop. Therefore, late OGMs from the best next hop are forwarded now and not dropped as duplicates anymore.
Signed-off-by: Simon Wunderlich simon@open-mesh.com
Changes to PATCHv1:
- use enum to distinguish different duplicate states
- fix typo "is_simlar -> is_similar"
- remove antonios sign off (the patch changed, feel free to add it if he is ok with it, it was his idea originally ...)
bat_iv_ogm.c | 86 +++++++++++++++++++++++++++++++++++++--------------------- 1 file changed, 55 insertions(+), 31 deletions(-)
Applied in revision 3d999e5.
Thanks, Marek
b.a.t.m.a.n@lists.open-mesh.org
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Antonio Quartulli -
Linus Lüssing -
Marek Lindner -
Simon Wunderlich