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MINOR: sock-inet: detect apparent IPv6 connectivity

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In order to ease dual-stack deployments, we could at least try to
check if ipv6 seems to be reachable. For this we're adding a test
based on a UDP connect (no traffic) on port 53 to the base of
public addresses (2001::) and see if the connect() is permitted,
indicating that the routing table knows how to reach it, or fails.
Based on this result we're setting a global variable that other
subsystems might use to preset their defaults.
This commit is contained in:
Willy Tarreau 2025-04-24 17:05:14 +02:00
parent 2c46c2c042
commit 5d41d476f3
2 changed files with 22 additions and 0 deletions
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1
include/haproxy/sock_inet.h
View File

@ -30,6 +30,7 @@
extern int sock_inet6_v6only_default;
extern int sock_inet_tcp_maxseg_default;
extern int sock_inet6_tcp_maxseg_default;
extern int sock_inet6_seems_reachable;
#ifdef HA_HAVE_MPTCP
extern int sock_inet_mptcp_maxseg_default;

21
src/sock_inet.c
View File

@ -79,6 +79,9 @@ int sock_inet6_v6only_default = 0;
int sock_inet_tcp_maxseg_default = -1;
int sock_inet6_tcp_maxseg_default = -1;
/* indicate whether v6 looks reachable (this is only a hint) */
int sock_inet6_seems_reachable = 0;
/* Default MPTCPv4/MPTCPv6 MSS settings. -1=unknown. */
#ifdef HA_HAVE_MPTCP
int sock_inet_mptcp_maxseg_default = -1;
@ -526,6 +529,24 @@ static void sock_inet_prepare()
close(fd);
}
#endif
/* detect IPv6 reachability: for this we perform a UDP connect to
* address 2001:: on port 53. No packet will be sent, it will just
* check the routing table towards this prefix for the majority of
* public addresses. In case of error we assume no IPv6 connectivity.
*/
fd = socket(AF_INET6, SOCK_DGRAM, 0);
if (fd >= 0) {
struct sockaddr_in6 dest = { };
dest.sin6_family = AF_INET6;
dest.sin6_addr.s6_addr[0] = 0x20;
dest.sin6_addr.s6_addr[1] = 0x01;
dest.sin6_port = htons(53);
if (connect(fd, (struct sockaddr*)&dest, sizeof(dest)) == 0)
sock_inet6_seems_reachable = 1;
close(fd);
}
}
INITCALL0(STG_PREPARE, sock_inet_prepare);