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SubjectRe: [PATCH net-next v3] net/ipv6: Introduce accept_unsolicited_na knob to implement router-side changes for RFC9131
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On 5/20/22 1:19 AM, Arun Ajith S wrote:
> On Thu, Apr 14, 2022 at 3:37 AM David Ahern <dsahern@kernel.org> wrote:
>>
>> On 4/13/22 8:34 AM, Arun Ajith S wrote:
>>> diff --git a/tools/testing/selftests/net/ndisc_unsolicited_na_test.py b/tools/testing/selftests/net/ndisc_unsolicited_na_test.py
>>> new file mode 100755
>>> index 000000000000..f508657ee126
>>> --- /dev/null
>>> +++ b/tools/testing/selftests/net/ndisc_unsolicited_na_test.py
>>> @@ -0,0 +1,255 @@
>>> +#!/bin/bash
>>
>> that file name suffix should be .sh since it is a bash script; not .py
>>
>> other than that looks good to me.
>>
>> Reviewed-by: David Ahern <dsahern@kernel.org>
>
> Hi David,
>
> It has been pointed out to me that I might have read RFC9131 in a
> narrower sense than what was intended.
> The behavior of adding a new entry in the neighbour cache on receiving
> a NA if none exists presently
> shouldn't be limited to unsolicited NAs like in my original patch,
> rather it should extend to all NAs.
>
> I am quoting from the RFC below
>
> | When a valid Neighbor Advertisement is received (either solicited
> | or unsolicited), the Neighbor Cache is searched for the target's
> | entry. If no entry exists:
> |
> | * Hosts SHOULD silently discard the advertisement. There is no
> | need to create an entry if none exists, since the recipient has
> | apparently not initiated any communication with the target.
> |
> | * Routers SHOULD create a new entry for the target address with
> | the link-layer address set to the Target Link-Layer Address
> | Option (if supplied). The entry's reachability state MUST be
> | set to STALE. If the received Neighbor Advertisement does not
> | contain the Target Link-Layer Address Option, the advertisement
> | SHOULD be silently discarded.
>
> I want to fix this, but this would mean the sysctl name
> accept_unsolicited_na is no longer appropriate
> I see that the net-next window for 5.19 is still open and changing the
> sysctl name
> wouldn't mean changing an existing interface.
> I was thinking of renaming the sysctl to accept_untracked_na to
> highlight that we are accepting NAs even if there is
> no corresponding entry tracked in the neighbor cache.
>
> Also, there's an error in my comment, where I say "pass up the stack"
> as we don't pass NAs up the stack.
> The comment can be updated as:
> /* RFC 9131 updates original Neighbour Discovery RFC 4861.
> * NAs with Target LL Address option without a corresponding
> * entry in the neighbour cache can now create a STALE neighbour
> * cache entry on routers.
> *
> * entry accept fwding solicited behaviour
> * ------- ------ ------ --------- ----------------------
> * present X X 0 Set state to STALE
> * present X X 1 Set state to REACHABLE
> * absent 0 X X Do nothing
> * absent 1 0 X Do nothing
> * absent 1 1 X Add a new STALE entry
> */
>
> In summary
> 1. accept=0 keeps original(5.18) behavior for all cases.
> 2. accept=1 changes original behavior for entry=asbent, fwding=1 case
> provided the NA had specified target link-layer address.
>
> Please let me know what you think.
>

Changes can be made until it is in a released kernel to users. This
feature has many weeks before it hits that level.

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