Re: Configuring pppd to accept link-local IPv6 interface id from remote peer
Benjamin Cama <[email protected]>
| Newsgroups | gmane.linux.ppp |
|---|---|
| Message-ID | <[email protected]> |
Hello James, Nicholas & others, Please allow me to join the conversation: Le dimanche 14 février 2021 à 11:23 -0500, James Carlson a écrit : > RFC 2472 is a little weird with respect to the Interface-Identifier > option. It's possible to send an all-zero identifier, but we're really > in uncharted waters if the peer can't give us an address or rejects the > option. Could I suggest that then IPv6CP just fails? > This sort of makes sense given that IPv6 itself just doesn't > work at all (no ICMPv6 ND means no work gets done) without a local > address, so it's not something anyone has really explored. Well, I actually sent last year a patch (attached again to this message) to Paul and Cc'ed here about sending a zero identifier to do exactly (to my understanding) what Nicholas is intending to do: let the “server”-side choose the interface identifier. It is a very small change that is basically activated on the “client”- side with: ipv6 ::, thus sending a zero identifier for our side. It worked quite well for my work case (virtual serial links), where having short addresses when autoconfiguring helps a lot, too. I couldn't resist also citing the “stability to global scope addresses” argument from the RFC, which is indeed relevant to me, at least. What do you think about it? Regards, -- Benjamin
0001-pppd-Allow-for-a-zero-interface-identifier-in-ConfRe.patch
(text/x-patch, 1.6 KB)
From 59ee72be9b6dba56b5422c0bec88842d61c9c56f Mon Sep 17 00:00:00 2001 From: Benjamin Cama <[email protected]> Date: Wed, 17 Jun 2020 14:30:01 +0200 Subject: [PATCH] pppd: Allow for a zero interface identifier in ConfReq RFC 5072 allows a peer to send a zero interface identifier in an IPv6CP Configure-Request, signifying it wants the other side to choose one for it. Allow this by passing "::" to the classic "ipv6" option. --- Quoting section 4.1 of RFC 5072 <https://tools.ietf.org/html/rfc5072#section-4.1>: If neither a unique number nor a random number can be generated, it is recommended that a zero value be used for the interface identifier transmitted in the Configure-Request. In this case, the PPP peer may provide a valid non-zero interface identifier in its response as described below. It can be useful to have non-random identifiers, to help having short and stable ids, furthermote assigned from one place only. It helps providing “stability to global scope addresses”, as put by the RFC authors. pppd/ipv6cp.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/pppd/ipv6cp.c b/pppd/ipv6cp.c index bda91e9..1e4fd2b 100644 --- a/pppd/ipv6cp.c +++ b/pppd/ipv6cp.c @@ -346,8 +346,7 @@ setifaceid(argv) struct in6_addr addr; static int prio_local, prio_remote; -#define VALIDID(a) ( (((a).s6_addr32[0] == 0) && ((a).s6_addr32[1] == 0)) && \ - (((a).s6_addr32[2] != 0) || ((a).s6_addr32[3] != 0)) ) +#define VALIDID(a) ( ((a).s6_addr32[0] == 0) && ((a).s6_addr32[1] == 0) ) arg = *argv; if ((comma = strchr(arg, ',')) == NULL) -- 2.26.0