Commit 1c78efa8 authored by Robert Shearman's avatar Robert Shearman Committed by David S. Miller
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mpls: flow-based multipath selection

Change the selection of a multipath route to use a flow-based
hash. This more suitable for traffic sensitive to reordering within a
flow (e.g. TCP, L2VPN) and whilst still allowing a good distribution
of traffic given enough flows.

Selection of the path for a multipath route is done using a hash of:
1. Label stack up to MAX_MP_SELECT_LABELS labels or up to and
   including entropy label, whichever is first.
2. 3-tuple of (L3 src, L3 dst, proto) from IPv4/IPv6 header in MPLS
   payload, if present.

Naturally, a 5-tuple hash using L4 information in addition would be
possible and be better in some scenarios, but there is a tradeoff
between looking deeper into the packet to achieve good distribution,
and packet forwarding performance, and I have erred on the side of the
latter as the default.

Signed-off-by: default avatarRobert Shearman <>
Signed-off-by: default avatarRoopa Prabhu <>
Signed-off-by: default avatarDavid S. Miller <>
parent f8efb73c
......@@ -22,6 +22,11 @@
#include <net/nexthop.h>
#include "internal.h"
/* Maximum number of labels to look ahead at when selecting a path of
* a multipath route
static int zero = 0;
static int label_limit = (1 << 20) - 1;
......@@ -77,10 +82,78 @@ bool mpls_pkt_too_big(const struct sk_buff *skb, unsigned int mtu)
static struct mpls_nh *mpls_select_multipath(struct mpls_route *rt)
static struct mpls_nh *mpls_select_multipath(struct mpls_route *rt,
struct sk_buff *skb, bool bos)
/* assume single nexthop for now */
return &rt->rt_nh[0];
struct mpls_entry_decoded dec;
struct mpls_shim_hdr *hdr;
bool eli_seen = false;
int label_index;
int nh_index = 0;
u32 hash = 0;
/* No need to look further into packet if there's only
* one path
if (rt->rt_nhn == 1)
goto out;
for (label_index = 0; label_index < MAX_MP_SELECT_LABELS && !bos;
label_index++) {
if (!pskb_may_pull(skb, sizeof(*hdr) * label_index))
/* Read and decode the current label */
hdr = mpls_hdr(skb) + label_index;
dec = mpls_entry_decode(hdr);
/* RFC6790 - reserved labels MUST NOT be used as keys
* for the load-balancing function
if (likely(dec.label >= MPLS_LABEL_FIRST_UNRESERVED)) {
hash = jhash_1word(dec.label, hash);
/* The entropy label follows the entropy label
* indicator, so this means that the entropy
* label was just added to the hash - no need to
* go any deeper either in the label stack or in the
* payload
if (eli_seen)
} else if (dec.label == MPLS_LABEL_ENTROPY) {
eli_seen = true;
bos = dec.bos;
if (bos && pskb_may_pull(skb, sizeof(*hdr) * label_index +
sizeof(struct iphdr))) {
const struct iphdr *v4hdr;
v4hdr = (const struct iphdr *)(mpls_hdr(skb) +
if (v4hdr->version == 4) {
hash = jhash_3words(ntohl(v4hdr->saddr),
v4hdr->protocol, hash);
} else if (v4hdr->version == 6 &&
pskb_may_pull(skb, sizeof(*hdr) * label_index +
sizeof(struct ipv6hdr))) {
const struct ipv6hdr *v6hdr;
v6hdr = (const struct ipv6hdr *)(mpls_hdr(skb) +
hash = __ipv6_addr_jhash(&v6hdr->saddr, hash);
hash = __ipv6_addr_jhash(&v6hdr->daddr, hash);
hash = jhash_1word(v6hdr->nexthdr, hash);
nh_index = hash % rt->rt_nhn;
return &rt->rt_nh[nh_index];
static bool mpls_egress(struct mpls_route *rt, struct sk_buff *skb,
......@@ -175,7 +248,7 @@ static int mpls_forward(struct sk_buff *skb, struct net_device *dev,
if (!rt)
goto drop;
nh = mpls_select_multipath(rt);
nh = mpls_select_multipath(rt, skb, dec.bos);
if (!nh)
goto drop;
......@@ -541,6 +614,12 @@ static int mpls_nh_build_multi(struct mpls_route_config *cfg,
if (!rtnh_ok(rtnh, remaining))
goto errout;
/* neither weighted multipath nor any flags
* are supported
if (rtnh->rtnh_hops || rtnh->rtnh_flags)
goto errout;
attrlen = rtnh_attrlen(rtnh);
if (attrlen > 0) {
struct nlattr *attrs = rtnh_attrs(rtnh);
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