buglwIP - A Lightweight TCP/IP stack - Bugs: bug #64791, Router flag in NA packets will...


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bug #64791: Router flag in NA packets will never set.

Submitter:  Zhang Wenxu <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 Planned Release:  None
lwIP version:  2.1.3

Thu 19 Oct 2023 07:13:04 AM UTC, original submission:  


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?

Zhang Wenxu <zwx1995esp>


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