Re: [PATCH] ndp: Extend lifetime of prefix, router, RDNSS and search list

[David Gibson <david@gibson.dropbear.id.au>]

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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.
> 
> 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.
> 
> 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.
> 
> Set prefix and DNS information lifetime to infinity. This is allowed
> by RFC 4861 and RFC 8319.
> 
> 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(-)
> 
> 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 = RA;
>  		ihr->icmp6_code = 0;
>  		ihr->icmp6_hop_limit = 255;
> -		ihr->icmp6_rt_lifetime = htons(9000);
> +		ihr->icmp6_rt_lifetime = htons(65535); /* RFC 8319 */
>  		ihr->icmp6_addrconf_managed = 1;
>  
>  		p = (unsigned char *)(ihr + 1);
> @@ -103,9 +103,9 @@ int ndp(struct ctx *c, const struct icmp6hdr *ih, const struct in6_addr *saddr)
>  		*p++ = 4;			/* length */
>  		*p++ = 64;			/* prefix length */
>  		*p++ = 0xc0;			/* prefix flags: L, A */
> -		*(uint32_t *)p = htonl(3600);	/* lifetime */
> +		*(uint32_t *)p = (uint32_t)~0U;	/* lifetime */
>  		p += 4;
> -		*(uint32_t *)p = htonl(3600);	/* preferred lifetime */
> +		*(uint32_t *)p = (uint32_t)~0U;	/* preferred lifetime */
>  		p += 8;
>  		memcpy(p, &c->ip6.addr, 8);	/* prefix */
>  		p += 16;
> @@ -126,7 +126,7 @@ int ndp(struct ctx *c, const struct icmp6hdr *ih, const struct in6_addr *saddr)
>  			*p++ = 25;				/* RDNSS */
>  			*p++ = 1 + 2 * n;			/* length */
>  			p += 2;					/* reserved */
> -			*(uint32_t *)p = htonl(60);		/* lifetime */
> +			*(uint32_t *)p = (uint32_t)~0U;		/* lifetime */
>  			p += 4;
>  
>  			for (i = 0; i < n; i++) {
> @@ -142,7 +142,7 @@ int ndp(struct ctx *c, const struct icmp6hdr *ih, const struct in6_addr *saddr)
>  			*p++ = 31;				/* DNSSL */
>  			*p++ = (dns_s_len + 8 - 1) / 8 + 1;	/* length */
>  			p += 2;					/* reserved */
> -			*(uint32_t *)p = htonl(60);		/* lifetime */
> +			*(uint32_t *)p = (uint32_t)~0U;		/* lifetime */
>  			p += 4;
>  
>  			for (i = 0; i < n; i++) {

-- 
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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