[bug #56136] The netif->mtu6 was updated by Router Advertisement abnomally

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[bug #56136] The netif->mtu6 was updated by Router Advertisement abnomally

Wilfred
URL:
  <https://savannah.nongnu.org/bugs/?56136>

                 Summary: The netif->mtu6 was updated by Router Advertisement
abnomally
                 Project: lwIP - A Lightweight TCP/IP stack
            Submitted by: kevingao
            Submitted on: Sun 14 Apr 2019 01:45:19 PM UTC
                Category: IPv6
                Severity: 3 - Normal
              Item Group: Faulty Behaviour
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: None
            lwIP version: git head

    _______________________________________________________

Details:

Let's assume there are two routers in the network, we named them router A and
B. The MTU announced in RA message from Router A is 1280, and the MTU from
Router B is 1500. If the RA msg from Router A received by lwip before Router
B, what's the netif->mtu6 in this scenario. The answer is the netif->mtu6 is
1500, and it is abnormal as we do IPv6 fragmentation using wrong MTU.
so the correct method is to make netif->mtu6 equals the minimum value of all
the RA message, pls refer the attached patch.



    _______________________________________________________

File Attachments:


-------------------------------------------------------
Date: Sun 14 Apr 2019 01:45:19 PM UTC  Name: update-netif-mtu6.patch  Size:
555B   By: kevingao

<http://savannah.nongnu.org/bugs/download.php?file_id=46770>

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[bug #56136] The netif->mtu6 was updated by Router Advertisement abnomally

Wilfred
Follow-up Comment #1, bug #56136 (project lwip):

Additional TODO to avoid MTU getting smaller: On link down, MTU should be
reset to initial value of netif->mtu (see netif->add())

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[bug #56136] The netif->mtu6 was updated by Router Advertisement abnomally

Wilfred
Update of bug #56136 (project lwip):

                  Status:                    None => Fixed                  
             Open/Closed:                    Open => Closed                

    _______________________________________________________

Follow-up Comment #2:

Pushed your patch, thanks for reporting!

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