feat: Support more addresses in RDNSS section #245
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This is based on PR#193, with significant cleanups & safety checks added. - RFC 6106 section 5.3.1 recommended that the number of RDNSS addresses should be limited to three, however that was for clients, not servers. - RFC 8106 section 5.3.1 clarified the recommendation to at least 3 from multiple sources. Based on this, set the limit for a single RDNSS section to 127 servers in radvd, based on the size of the length field. Note that it may cause fragmentation as the single option exceeds usable RA option space (MTU less headers); and server configurations should generally use fewer. See also the RFC6106 errata & RFC6980 section 2 for behaviors of very large RA options. Reference: https://www.rfc-editor.org/errata/rfc6106 Reference: https://datatracker.ietf.org/doc/html/rfc6980#section-2 Reference: https://datatracker.ietf.org/doc/html/rfc6106#section-5.3.1 Reference: https://datatracker.ietf.org/doc/html/rfc8106#section-5.3.1 Based-on: radvd-project#193 Based-on-work-by: WenChao1Hou <[email protected]> Signed-off-by: Robin H. Johnson <[email protected]>
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What I missed: --- a/radvd.conf.5.man
+++ b/radvd.conf.5.man
@@ -83,11 +83,24 @@ advertise more specific routes to the hosts.
RDNSS (Recursive DNS server) definitions are of the form:
.nf
-.BR "RDNSS " "ip [ip] [ip] " {
+.BR "RDNSS " "ip [ip] [ip] ..." {
list of rdnss specific options
.B };
.fi
+For your consideration:
+
+* RFC 6106 section 5.3.1 recommended that the number of RDNSS addresses
+ should be limited to three, however that was for clients, not servers.
+* RFC 8106 section 5.3.1 clarified the recommendation to at least 3 from
+ multiple sources.
+
+Based on this, set the limit for a single RDNSS section to 127 servers
+in radvd, based on the size of the length field. Note that it may cause
+fragmentation as the single option exceeds usable RA option space (MTU
+less headers); and server configurations should generally use fewer.
+
+
DNSSL (DNS Search List) definitions are of the form:
.nfPlease make such minimalistic change the manual page of the configuration file. The word minimalistic is for expressing "it is okay to make a non perfect formatted change, better formatting can be done in a follow-up change". |
mpontillo
approved these changes
Dec 29, 2024
| // too many DNS servers could exceed it | ||
| // https://datatracker.ietf.org/doc/html/rfc8106#section-5.1 | ||
| if (bytes > (255 * 8)) { | ||
| flog(LOG_ERR, "RDNSS too long for RA option, must be < 2032 bytes. Skipping option."); |
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Same comment as the other PR - shouldn't this be <= 2040 bytes? Or am I not understanding the math?
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This is based on PR#193, with significant cleanups & safety checks added.
Based on this, set the limit for a single RDNSS section to 127 servers in radvd, based on the size of the length field. Note that it may cause fragmentation as the single option exceeds usable RA option space (MTU less headers); and server configurations should generally use fewer.
See also the RFC6106 errata & RFC6980 section 2 for behaviors of very large RA options.
Reference: https://www.rfc-editor.org/errata/rfc6106
Reference: https://datatracker.ietf.org/doc/html/rfc6980#section-2
Reference: https://datatracker.ietf.org/doc/html/rfc6106#section-5.3.1
Reference: https://datatracker.ietf.org/doc/html/rfc8106#section-5.3.1
Based-on: #193
Based-on-work-by: WenChao1Hou [email protected]