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Date: Mon, 11 Dec 2023 13:09:15 +1100
From: David Gibson <david@gibson.dropbear.id.au>
To: Stefano Brivio <sbrivio@redhat.com>
Subject: Re: [PATCH] ndp: Extend lifetime of prefix, router, RDNSS and search
list
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On Fri, Dec 08, 2023 at 06:49:12PM +0100, Stefano Brivio wrote:
> Currently, we have no mechanism to dynamically update IPv6
> addressing, routing or DNS information (which should eventually be
> implemented via netlink monitor), so it makes no sense to limit
> lifetimes of NDP information to any particular value.
>=20
> If we do, with common configurations of systemd-networkd in a guest,
> we can end up in a situation where we have a /128 address assigned
> via DHCPv6, the NDP-assigned prefix expires, and the default route
> also expires. However, as there's a valid address, the prefix is
> not renewed. As a result, the default route becomes invalid and we
> lose it altogether, which implies that the guest loses IPv6
> connectivity except for link-local communication.
>=20
> Set the router lifetime to the maximum allowed by RFC 8319, that is,
> 65535 seconds (about 18 hours). RFC 4861 limited this value to 9000
> seconds, but RFC 8319 later updated this limit.
>=20
> Set prefix and DNS information lifetime to infinity. This is allowed
> by RFC 4861 and RFC 8319.
>=20
> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
> ---
> ndp.c | 10 +++++-----
> 1 file changed, 5 insertions(+), 5 deletions(-)
>=20
> diff --git a/ndp.c b/ndp.c
> index adab1d2..4c85ab8 100644
> --- a/ndp.c
> +++ b/ndp.c
> @@ -94,7 +94,7 @@ int ndp(struct ctx *c, const struct icmp6hdr *ih, const=
struct in6_addr *saddr)
> ihr->icmp6_type =3D RA;
> ihr->icmp6_code =3D 0;
> ihr->icmp6_hop_limit =3D 255;
> - ihr->icmp6_rt_lifetime =3D htons(9000);
> + ihr->icmp6_rt_lifetime =3D htons(65535); /* RFC 8319 */
> ihr->icmp6_addrconf_managed =3D 1;
> =20
> p =3D (unsigned char *)(ihr + 1);
> @@ -103,9 +103,9 @@ int ndp(struct ctx *c, const struct icmp6hdr *ih, con=
st struct in6_addr *saddr)
> *p++ =3D 4; /* length */
> *p++ =3D 64; /* prefix length */
> *p++ =3D 0xc0; /* prefix flags: L, A */
> - *(uint32_t *)p =3D htonl(3600); /* lifetime */
> + *(uint32_t *)p =3D (uint32_t)~0U; /* lifetime */
> p +=3D 4;
> - *(uint32_t *)p =3D htonl(3600); /* preferred lifetime */
> + *(uint32_t *)p =3D (uint32_t)~0U; /* preferred lifetime */
> p +=3D 8;
> memcpy(p, &c->ip6.addr, 8); /* prefix */
> p +=3D 16;
> @@ -126,7 +126,7 @@ int ndp(struct ctx *c, const struct icmp6hdr *ih, con=
st struct in6_addr *saddr)
> *p++ =3D 25; /* RDNSS */
> *p++ =3D 1 + 2 * n; /* length */
> p +=3D 2; /* reserved */
> - *(uint32_t *)p =3D htonl(60); /* lifetime */
> + *(uint32_t *)p =3D (uint32_t)~0U; /* lifetime */
> p +=3D 4;
> =20
> for (i =3D 0; i < n; i++) {
> @@ -142,7 +142,7 @@ int ndp(struct ctx *c, const struct icmp6hdr *ih, con=
st struct in6_addr *saddr)
> *p++ =3D 31; /* DNSSL */
> *p++ =3D (dns_s_len + 8 - 1) / 8 + 1; /* length */
> p +=3D 2; /* reserved */
> - *(uint32_t *)p =3D htonl(60); /* lifetime */
> + *(uint32_t *)p =3D (uint32_t)~0U; /* lifetime */
> p +=3D 4;
> =20
> for (i =3D 0; i < n; i++) {
--=20
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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