diff options
Diffstat (limited to 'src/dhcpv6-ia.c')
| -rw-r--r-- | src/dhcpv6-ia.c | 25 |
1 files changed, 25 insertions, 0 deletions
diff --git a/src/dhcpv6-ia.c b/src/dhcpv6-ia.c index 99fd2fd..41c9f30 100644 --- a/src/dhcpv6-ia.c +++ b/src/dhcpv6-ia.c @@ -1332,6 +1332,31 @@ ssize_t dhcpv6_ia_handle_IAs(uint8_t *buf, size_t buflen, struct interface *ifac if (reqlen > 64) reqlen = 64; + + /* + * A requesting router can include a desired prefix length for its + * delegation. The delegating router (us) is not required to honor + * the hint (RFC3633, section 11.2, we MAY choose to use the + * information in the option; RFC8168, section 3.2 has several SHOULDs + * about desired choices for selecting a prefix to delegate). + * + * We support a policy setting to conserve prefix space, which purposely + * assigns prefixes that might not match the requesting router's hint. + * + * If the minimum prefix length is set in this interface's + * configuration, we use it as a floor for the requested (hinted) + * prefix length. This allows us to conserve prefix space so that + * any single router can't grab too much of it. Consider if we have + * an interface with a /56 prefix. A requesting router could ask for + * a /58 and take 1/4 of our total address space. But if we set a + * minimum of /60, we can limit each requesting router to get only + * 1/16 of our total address space. + */ + if (iface->dhcpv6_pd_min_len && reqlen < iface->dhcpv6_pd_min_len) { + syslog(LOG_INFO, "clamping requested PD from %d to %d", + reqlen, iface->dhcpv6_pd_min_len); + reqlen = iface->dhcpv6_pd_min_len; + } } else if (is_na) { uint8_t *sdata; uint16_t stype, slen; |