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MINOR: resolvers: add "dns-accept-family auto" to rely on detected IPv6

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Instead of always having to force IPv4 or IPv6, let's now also offer
"auto" which will only enable IPv6 if the system has a default gateway
for it. This means that properly configured dual-stack systems will
default to "ipv4,ipv6" while those lacking a gateway will only use
"ipv4". Note that no real connectivity test is performed, so firewalled
systems may still get it wrong and might prefer to rely on a manual
"ipv4" assignment.
This commit is contained in:
Willy Tarreau 2025-04-24 17:18:06 +02:00
parent 5d41d476f3
commit 69b051d1dc
3 changed files with 19 additions and 0 deletions
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1
doc/configuration.txt
View File

@ -2179,6 +2179,7 @@ dns-accept-family <family>[,...]
of the following words:
- "ipv4": query and accept IPv4 addresses ("A" records)
- "ipv6": query and accept IPv6 addresses ("AAAA" records)
- "auto": use IPv4, and IPv6 if the system has a default gateway for it.
When a single family is used, no request will be sent to resolvers for the
other family, and any response for the othe family will be ignored. The

1
include/haproxy/resolvers-t.h
View File

@ -98,6 +98,7 @@ enum {
RSLV_ACCEPT_IPV6 = 0x02,
RSLV_ACCEPT_MASK = RSLV_ACCEPT_IPV4 | RSLV_ACCEPT_IPV6,
RSLV_FORCED_FAMILY = 0x04,
RSLV_AUTO_FAMILY = 0x08,
};
/* NOTE: big endian structure */

17
src/resolvers.c
View File

@ -40,6 +40,7 @@
#include <haproxy/sample.h>
#include <haproxy/sc_strm.h>
#include <haproxy/server.h>
#include <haproxy/sock_inet.h>
#include <haproxy/stats.h>
#include <haproxy/stconn.h>
#include <haproxy/task.h>
@ -3935,6 +3936,19 @@ int cfg_post_parse_resolvers()
return err_code;
}
/* called once the config was fully parsed */
static int resolvers_late_init(void)
{
if (resolv_accept_families & RSLV_AUTO_FAMILY) {
/* Let's adjust our default resolver families based on apparent IPv6 connectivity */
if (sock_inet6_seems_reachable)
resolv_accept_families = RSLV_ACCEPT_IPV4 | RSLV_ACCEPT_IPV6;
else
resolv_accept_families = RSLV_ACCEPT_IPV4;
}
return 0;
}
/* config parser for global "dns-accept-family", accepts "ipv4", "ipv6" or both delimited by a comma */
static int cfg_parse_dns_accept_family(char **args, int section_type, struct proxy *curpx,
const struct proxy *defpx, const char *file, int line,
@ -3958,6 +3972,8 @@ static int cfg_parse_dns_accept_family(char **args, int section_type, struct pro
accept_families |= RSLV_ACCEPT_IPV4;
else if (strcmp(arg, "ipv6") == 0)
accept_families |= RSLV_ACCEPT_IPV6;
else if (strcmp(arg, "auto") == 0)
accept_families |= RSLV_AUTO_FAMILY;
else
goto usage;
}
@ -3985,6 +4001,7 @@ REGISTER_CONFIG_SECTION("resolvers", cfg_parse_resolvers, cfg_post_parse_re
REGISTER_POST_DEINIT(resolvers_deinit);
REGISTER_CONFIG_POSTPARSER("dns runtime resolver", resolvers_finalize_config);
REGISTER_PRE_CHECK(resolvers_create_default);
REGISTER_POST_CHECK(resolvers_late_init);
#if defined(USE_PROMEX)