[LEDE-DEV] umdns - TTL restricted to 255

[Philipp Meier]

OK - I provided a patch for this change ([PATCH] Remove ttl==255 
restriction for queries).

Additionally I sent two other patches:
1. [PATCH] umdns: Remove incorrect comma in hhtp service json config
2. [PATCH] umdns: Add debug output for service_timeout

Philipp

On 09/25/2017 06:45 PM, John Crispin wrote:
> in that case its a bug and the code should be changed to only have that 
> restriction on queries
> 
>      John
> 
> 
> On 25/09/17 17:21, Philipp Meier wrote:
>> My question is about query (not response). LEDE is ignoring query when 
>> TTL != 255.
>>
>> Philipp
>>
>>
>> On 09/25/2017 05:16 PM, John Crispin wrote:
>>> Hi,
>>>
>>> rfc6762 has the following ...
>>>
>>> 11.  Source Address Check
>>>
>>>    All Multicast DNS responses (including responses sent via unicast)
>>>    SHOULD be sent with IP TTL set to 255.  This is recommended to
>>>    provide backwards-compatibility with older Multicast DNS queriers
>>>    (implementing a draft version of this document, posted in February
>>>    2004) that check the IP TTL on reception to determine whether the
>>>    packet originated on the local link.  These older queriers discard
>>>    all packets with TTLs other than 255.
>>>
>>>     John
>>>
>>>
>>>
>>> On 25/09/17 16:44, Philipp Meier wrote:
>>>> Hi,
>>>>
>>>> When using umdns I was wondering why my mDNS query did not get any 
>>>> answer.
>>>>
>>>> I found the following reason:
>>>>
>>>> My mDNS query has TTL field set to 1. But LEDE umdns package expects 
>>>> a TTL value of 255 (see interface.c function read_socket4).
>>>>
>>>> According 
>>>> https://www.systutorials.com/docs/linux/man/5-avahi-daemon.conf/ 
>>>> (see check-response-ttl) this was necessary security behavior in 
>>>> older mDNS versions but will be incompatible with newer versions of 
>>>> mDNS implementations.
>>>>
>>>> Therefore my question here is: Is this by purpose restricted to 255 
>>>> by LEDE umdns package or could this be changed?
>>>>
>>>> Regards
>>>> Philipp
>>>>
>>>>
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>>>
>>>
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>>
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