kernel/linux.git/Documentation/networking/ip-sysctl.rst, branch v6.12.80

Documentation: networking: Add a caveat to nexthop_compat_mode sysctl

2024-12-19T17:13:16+00:00

[ Upstream commit bbe4b41259a3e255a16d795486d331c1670b4e75 ] net.ipv4.nexthop_compat_mode was added when nexthop objects were added to provide the view of nexthop objects through the usual lens of the route UAPI. As nexthop objects evolved, the information provided through this lens became incomplete. For example, details of resilient nexthop groups are obviously omitted. Now that 16-bit nexthop group weights are a thing, the 8-bit UAPI cannot convey the >8-bit weight accurately. Instead of inventing workarounds for an obsolete interface, just document the expectations of inaccuracy. Fixes: b72a6a7ab957 ("net: nexthop: Increase weight to u16") Signed-off-by: Petr Machata Reviewed-by: Ido Schimmel Reviewed-by: David Ahern Link: https://patch.msgid.link/b575e32399ccacd09079b2a218255164535123bd.1733740749.git.petrm@nvidia.com Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin

Add support for PIO p flag

2024-07-31T12:49:48+00:00

draft-ietf-6man-pio-pflag is adding a new flag to the Prefix Information Option to signal that the network can allocate a unique IPv6 prefix per client via DHCPv6-PD (see draft-ietf-v6ops-dhcp-pd-per-device). When ra_honor_pio_pflag is enabled, the presence of a P-flag causes SLAAC autoconfiguration to be disabled for that particular PIO. An automated test has been added in Android (r.android.com/3195335) to go along with this change. Cc: Maciej Żenczykowski Cc: Lorenzo Colitti Cc: David Lamparter Cc: Simon Horman Signed-off-by: Patrick Rohr Reviewed-by: Maciej Żenczykowski Signed-off-by: David S. Miller

net: ipv4: Add a sysctl to set multipath hash seed

2024-06-12T23:42:11+00:00

When calculating hashes for the purpose of multipath forwarding, both IPv4 and IPv6 code currently fall back on flow_hash_from_keys(). That uses a randomly-generated seed. That's a fine choice by default, but unfortunately some deployments may need a tighter control over the seed used. In this patch, make the seed configurable by adding a new sysctl key, net.ipv4.fib_multipath_hash_seed to control the seed. This seed is used specifically for multipath forwarding and not for the other concerns that flow_hash_from_keys() is used for, such as queue selection. Expose the knob as sysctl because other such settings, such as headers to hash, are also handled that way. Like those, the multipath hash seed is a per-netns variable. Despite being placed in the net.ipv4 namespace, the multipath seed sysctl is used for both IPv4 and IPv6, similarly to e.g. a number of TCP variables. The seed used by flow_hash_from_keys() is a 128-bit quantity. However it seems that usually the seed is a much more modest value. 32 bits seem typical (Cisco, Cumulus), some systems go even lower. For that reason, and to decouple the user interface from implementation details, go with a 32-bit quantity, which is then quadruplicated to form the siphash key. Signed-off-by: Petr Machata Reviewed-by: Ido Schimmel Reviewed-by: Nikolay Aleksandrov Reviewed-by: David Ahern Link: https://lore.kernel.org/r/20240607151357.421181-3-petrm@nvidia.com Signed-off-by: Jakub Kicinski

tcp: add sysctl_tcp_rto_min_us

2024-06-05T12:42:54+00:00

Adding a sysctl knob to allow user to specify a default rto_min at socket init time, other than using the hard coded 200ms default rto_min. Note that the rto_min route option has the highest precedence for configuring this setting, followed by the TCP_BPF_RTO_MIN socket option, followed by the tcp_rto_min_us sysctl. Signed-off-by: Kevin Yang Reviewed-by: Neal Cardwell Reviewed-by: Yuchung Cheng Reviewed-by: Eric Dumazet Reviewed-by: Tony Lu Reviewed-by: Jakub Kicinski Signed-off-by: David S. Miller

net: ipv6/addrconf: clamp preferred_lft to the minimum required

2024-02-15T14:34:40+00:00

If the preferred lifetime was less than the minimum required lifetime, ipv6_create_tempaddr would error out without creating any new address. On my machine and network, this error happened immediately with the preferred lifetime set to 5 seconds or less, after a few minutes with the preferred lifetime set to 6 seconds, and not at all with the preferred lifetime set to 7 seconds. During my investigation, I found a Stack Exchange post from another person who seems to have had the same problem: They stopped getting new addresses if they lowered the preferred lifetime below 3 seconds, and they didn't really know why. The preferred lifetime is a preference, not a hard requirement. The kernel does not strictly forbid new connections on a deprecated address, nor does it guarantee that the address will be disposed of the instant its total valid lifetime expires. So rather than disable IPv6 privacy extensions altogether if the minimum required lifetime swells above the preferred lifetime, it is more in keeping with the user's intent to increase the temporary address's lifetime to the minimum necessary for the current network conditions. With these fixes, setting the preferred lifetime to 5 or 6 seconds "just works" because the extra fraction of a second is practically unnoticeable. It's even possible to reduce the time before deprecation to 1 or 2 seconds by setting /proc/sys/net/ipv6/conf/*/regen_min_advance and /proc/sys/net/ipv6/conf/*/dad_transmits to 0. I realize that that is a pretty niche use case, but I know at least one person who would gladly sacrifice performance and convenience to be sure that they are getting the maximum possible level of privacy. Link: https://serverfault.com/a/1031168/310447 Signed-off-by: Alex Henrie Reviewed-by: David Ahern Signed-off-by: Paolo Abeni

net: ipv6/addrconf: introduce a regen_min_advance sysctl

2024-02-15T14:34:40+00:00

In RFC 8981, REGEN_ADVANCE cannot be less than 2 seconds, and the RFC does not permit the creation of temporary addresses with lifetimes shorter than that: > When processing a Router Advertisement with a > Prefix Information option carrying a prefix for the purposes of > address autoconfiguration (i.e., the A bit is set), the host MUST > perform the following steps: > 5. A temporary address is created only if this calculated preferred > lifetime is greater than REGEN_ADVANCE time units. However, some users want to change their IPv6 address as frequently as possible regardless of the RFC's arbitrary minimum lifetime. For the benefit of those users, add a regen_min_advance sysctl parameter that can be set to below or above 2 seconds. Link: https://datatracker.ietf.org/doc/html/rfc8981 Signed-off-by: Alex Henrie Reviewed-by: David Ahern Signed-off-by: Paolo Abeni

net: ipv6/addrconf: ensure that regen_advance is at least 2 seconds

2024-02-15T14:34:40+00:00

RFC 8981 defines REGEN_ADVANCE as follows: REGEN_ADVANCE = 2 + (TEMP_IDGEN_RETRIES * DupAddrDetectTransmits * RetransTimer / 1000) Thus, allowing it to be less than 2 seconds is technically a protocol violation. Link: https://datatracker.ietf.org/doc/html/rfc8981#name-defined-protocol-parameters Signed-off-by: Alex Henrie Reviewed-by: David Ahern Signed-off-by: Paolo Abeni

Revert "net: ipv6/addrconf: clamp preferred_lft to the minimum required"

2024-01-02T22:58:46+00:00

The commit had a bug and might not have been the right approach anyway. Fixes: 629df6701c8a ("net: ipv6/addrconf: clamp preferred_lft to the minimum required") Fixes: ec575f885e3e ("Documentation: networking: explain what happens if temp_prefered_lft is too small or too large") Reported-by: Dan Moulding Closes: https://lore.kernel.org/netdev/20231221231115.12402-1-dan@danm.net/ Link: https://lore.kernel.org/netdev/CAMMLpeTdYhd=7hhPi2Y7pwdPCgnnW5JYh-bu3hSc7im39uxnEA@mail.gmail.com/ Signed-off-by: Alex Henrie Reviewed-by: David Ahern Link: https://lore.kernel.org/r/20231230043252.10530-1-alexhenrie24@gmail.com Signed-off-by: Jakub Kicinski

Documentation: networking: explain what happens if temp_prefered_lft is too small or too large

2023-10-26T01:23:07+00:00

Signed-off-by: Alex Henrie Reviewed-by: David Ahern Link: https://lore.kernel.org/r/20231024212312.299370-5-alexhenrie24@gmail.com Signed-off-by: Jakub Kicinski

Documentation: networking: explain what happens if temp_valid_lft is too small

2023-10-26T01:23:07+00:00

Signed-off-by: Alex Henrie Reviewed-by: David Ahern Link: https://lore.kernel.org/r/20231024212312.299370-4-alexhenrie24@gmail.com Signed-off-by: Jakub Kicinski