Hey!
Starting from kernel 4.11 (commit beb1afac518d), IPv6 are now notified
using RTA_MULTIPATH, like IPv4 routes. Those routes are not handled
correctly by BIRD. We handle them correctly. This also enable to parse
alien routes correctly. Route modifications is still done in the old
way as for insertion/deletion, this is not helpful to optimize in those
cases and for replace, IPv4 case is not optimized either. It should be
possible to detect appropriate support for RTA_MULTIPATH when receiving
an IPv6 route with this attribute, but I don't see how it would be
helpful, so I didn't do it (simpler code this way).
I did some quick tests and routes are removed/added correctly:
Deleted 2001:db8:a3::/64 proto bird metric 1024
nexthop via 2001:db8:ff::5 dev vti5 weight 1
nexthop via 2001:db8:ff::7 dev vti6 weight 1
2001:db8:a3::/64 via 2001:db8:ff::7 dev vti6 proto bird metric 1024 pref medium
Deleted 2001:db8:a3::/64 via 2001:db8:ff::7 dev vti6 proto bird metric 1024
pref medium
2001:db8:a3::/64 via 2001:db8:ff::5 dev vti5 proto bird metric 1024 pref medium
2001:db8:a3::/64 proto bird metric 1024
nexthop via 2001:db8:ff::7 dev vti6 weight 1
nexthop via 2001:db8:ff::5 dev vti5 weight 1
Also, alien routes are correctly parsed when next-hops are correctly
ordered (I didn't check if this restriction is also present for IPv4 or
if Linux is always sending IPv4 multipath routes with next-hops
correctly ordered):
2001:db8:a4::/64 metric 1024
nexthop via 2001:db8:ff::5 dev vti5 weight 1
nexthop via 2001:db8:ff::7 dev vti6 weight 1
2001:db8:a4::/64 multipath [kernel1 22:30:54] * (10)
via 2001:db8:ff::5 on vti5 weight 1
via 2001:db8:ff::7 on vti6 weight 1
I'll try to investigate that unless someone already knows the answer.
>From 705d3b93f0527a693cab38357a68c7598a4039cc Mon Sep 17 00:00:00 2001
From: Vincent Bernat <[email protected]>
Date: Thu, 31 Aug 2017 21:47:52 +0200
Subject: [PATCH] KRT: Fix IPv6 ECMP with 4.11+ kernels
Starting from kernel 4.11 (commit beb1afac518d), IPv6 are now notified
using RTA_MULTIPATH, like IPv4 routes. Those routes are not handled
correctly by BIRD. We handle them correctly. This also enable to parse
alien routes correctly. Route modifications is still done in the old
way.
---
sysdep/linux/netlink.c | 51 ++++++++++++++++++++++++++++++++++++--------------
1 file changed, 37 insertions(+), 14 deletions(-)
diff --git a/sysdep/linux/netlink.c b/sysdep/linux/netlink.c
index 22313f439977..6a3972faea2a 100644
--- a/sysdep/linux/netlink.c
+++ b/sysdep/linux/netlink.c
@@ -59,22 +59,26 @@
/*
* Structure nl_parse_state keeps state of received route processing. Ideally,
* we could just independently parse received Netlink messages and immediately
- * propagate received routes to the rest of BIRD, but Linux kernel represents
- * and announces IPv6 ECMP routes not as one route with multiple next hops (like
- * RTA_MULTIPATH in IPv4 ECMP), but as a set of routes with the same prefix.
+ * propagate received routes to the rest of BIRD, but older Linux kernel (before
+ * 4.11) represents and announces IPv6 ECMP routes not as one route with
+ * multiple next hops (like RTA_MULTIPATH in IPv4 ECMP), but as a set of routes
+ * with the same prefix. More recent kernels work as with IPv4.
*
* Therefore, BIRD keeps currently processed route in nl_parse_state structure
* and postpones its propagation until we expect it to be final; i.e., when
* non-matching route is received or when the scan ends. When another matching
* route is received, it is merged with the already processed route to form an
* ECMP route. Note that merging is done only for IPv6 (merge == 1), but the
- * postponing is done in both cases (for simplicity). All IPv4 routes are just
- * considered non-matching.
+ * postponing is done in both cases (for simplicity). All IPv4 routes or IPv6
+ * routes with RTA_MULTIPATH set are just considered non-matching.
*
* This is ignored for asynchronous notifications (every notification is handled
* as a separate route). It is not an issue for our routes, as we ignore such
* notifications anyways. But importing alien IPv6 ECMP routes does not work
- * properly.
+ * properly with older kernels.
+ *
+ * Whatever the kernel version is, IPv6 ECMP routes are sent as multiple routes
+ * for the same prefix.
*/
struct nl_parse_state
@@ -320,9 +324,15 @@ static struct nl_want_attrs ifa_attr_want6[BIRD_IFA_MAX] = {
#define BIRD_RTA_MAX (RTA_TABLE+1)
+#ifndef IPV6
static struct nl_want_attrs mpnh_attr_want4[BIRD_RTA_MAX] = {
[RTA_GATEWAY] = { 1, 1, sizeof(ip4_addr) },
};
+#else
+static struct nl_want_attrs mpnh_attr_want6[BIRD_RTA_MAX] = {
+ [RTA_GATEWAY] = { 1, 1, sizeof(ip6_addr) },
+};
+#endif
#ifndef IPV6
static struct nl_want_attrs rtm_attr_want4[BIRD_RTA_MAX] = {
@@ -345,6 +355,7 @@ static struct nl_want_attrs rtm_attr_want6[BIRD_RTA_MAX] = {
[RTA_PRIORITY] = { 1, 1, sizeof(u32) },
[RTA_PREFSRC] = { 1, 1, sizeof(ip6_addr) },
[RTA_METRICS] = { 1, 0, 0 },
+ [RTA_MULTIPATH] = { 1, 0, 0 },
[RTA_FLOW] = { 1, 1, sizeof(u32) },
[RTA_TABLE] = { 1, 1, sizeof(u32) },
};
@@ -477,7 +488,7 @@ nl_add_multipath(struct nlmsghdr *h, unsigned bufsize, struct mpnh *nh)
}
static struct mpnh *
-nl_parse_multipath(struct krt_proto *p, struct rtattr *ra)
+nl_parse_multipath(struct krt_proto *p, struct rtattr *ra, u8 family)
{
/* Temporary buffer for multicast nexthops */
static struct mpnh *nh_buffer;
@@ -515,10 +526,21 @@ nl_parse_multipath(struct krt_proto *p, struct rtattr *ra)
/* Nonexistent RTNH_PAYLOAD ?? */
nl_attr_len = nh->rtnh_len - RTNH_LENGTH(0);
- nl_parse_attrs(RTNH_DATA(nh), mpnh_attr_want4, a, sizeof(a));
+ switch (family)
+ {
+#ifndef IPV6
+ case AF_INET:
+ nl_parse_attrs(RTNH_DATA(nh), mpnh_attr_want4, a, sizeof(a));
+ break;
+#else
+ case AF_INET6:
+ nl_parse_attrs(RTNH_DATA(nh), mpnh_attr_want6, a, sizeof(a));
+ break;
+#endif
+ }
if (a[RTA_GATEWAY])
{
- memcpy(&rv->gw, RTA_DATA(a[RTA_GATEWAY]), sizeof(ip_addr));
+ memcpy(&rv->gw, RTA_DATA(a[RTA_GATEWAY]), sizeof(rv->gw));
ipa_ntoh(rv->gw);
neighbor *ng = neigh_find2(&p->p, &rv->gw, rv->iface,
@@ -1240,10 +1262,10 @@ nl_parse_route(struct nl_parse_state *s, struct nlmsghdr *h)
{
case RTN_UNICAST:
- if (a[RTA_MULTIPATH] && (i->rtm_family == AF_INET))
+ if (a[RTA_MULTIPATH])
{
ra->dest = RTD_MULTIPATH;
- ra->nexthops = nl_parse_multipath(p, a[RTA_MULTIPATH]);
+ ra->nexthops = nl_parse_multipath(p, a[RTA_MULTIPATH], i->rtm_family);
if (!ra->nexthops)
{
log(L_ERR "KRT: Received strange multipath route %I/%d",
@@ -1384,9 +1406,10 @@ nl_parse_route(struct nl_parse_state *s, struct nlmsghdr *h)
}
/*
- * Ideally, now we would send the received route to the rest of kernel code.
- * But IPv6 ECMP routes are sent as a sequence of routes, so we postpone it
- * and merge next hops until the end of the sequence.
+ * Ideally, now we would send the received route to the rest of
+ * kernel code. But IPv6 ECMP routes before 4.11 are sent as a
+ * sequence of routes, so we postpone it and merge next hops until
+ * the end of the sequence.
*/
if (!s->net)
--
2.14.1
--
Make input easy to proofread.
- The Elements of Programming Style (Kernighan & Plauger)
