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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