[lwip-devel] [bug #64791] Router flag in NA packets will never set.

[Zhang Wenxu]

URL:
  <https://savannah.nongnu.org/bugs/?64791>

                 Summary: Router flag in NA packets will never set.
                   Group: lwIP - A Lightweight TCP/IP stack
               Submitter: zwx1995esp
               Submitted: Thu 19 Oct 2023 07:13:04 AM UTC
                Category: IPv6
                Severity: 3 - Normal
              Item Group: Feature Request
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: None
            lwIP version: 2.1.3


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Follow-up Comments:


-------------------------------------------------------
Date: Thu 19 Oct 2023 07:13:04 AM UTC By: Zhang Wenxu <zwx1995esp>
topology: 

WH <---> Router <-----> BR <===> Device

WH: windows host, connected to Router using Wi-Fi
Router: A Wi-Fi router.
BR: A border router, which can forward the packets between wifi network and
some other networks.
Device: Other network device, connect to BR using other protocol.


A LWIP based BR device in a network will send RA packets periodically. In the
RA packets, there is a RIO which cantain the router information between Wi-Fi
network and other network. WH will receive this RA and add this RIO to its
router table. When WH want to ping Device, it will first look up route
table,and find the target address has a gateway `BR`, so it will send NS for
getting the MAC address for BR. BR received this NS, and generate a NA to send
back, for LWIP implementation, route flag will never set, WH receive this
packet and then it will remove the router entry in the router table. Then WH
can never ping Device untill next RA received.

Also, I read some Linux source code, and I found that in the Linux
implementations: before send NA, it will look up the neighbor able to
determine that the router flag is ture or not :
https://github.com/torvalds/linux/blob/master/net/ipv6/ndisc.c#L957C55-L957C55
and then send NA. But I did not see some related neighbor table in LWIP.

Should this a bug for LWIP?







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