netdev - Re: Toggling link state breaks network connectivity

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Message-ID: <aef8dfb4-d11a-2859-3589-f477cd150071@neratec.com>
Date:   Tue, 13 Jun 2017 11:39:31 +0200
From:   Matthias May <matthias.may@...atec.com>
To:     Mason <slash.tmp@...e.fr>, netdev <netdev@...r.kernel.org>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>, Mans Rullgard <mans@...sr.com>,
        Thibaud Cornic <thibaud_cornic@...madesigns.com>
Subject: Re: Toggling link state breaks network connectivity

On 12/06/17 15:22, Mason wrote:
> Hello,
> 
> I am using the following drivers for Ethernet connectivity.
> drivers/net/ethernet/aurora/nb8800.c
> drivers/net/phy/at803x.c
> 
> Pulling the cable and plugging it back works as expected.
> (I can ping both before and after.)
> 
> However, if I toggle the link state in software (using ip link set),
> the board loses network connectivity.
> 
> # Statically assign IP address
> ip addr add 172.27.64.77/18 brd 172.27.127.255 dev eth0
> # Set link state to "up"
> ip link set eth0 up
> # ping -c 3 172.27.64.1 > /tmp/v1
> 
> PING 172.27.64.1 (172.27.64.1): 56 data bytes
> 64 bytes from 172.27.64.1: seq=0 ttl=64 time=18.321 ms
> 
> --- 172.27.64.1 ping statistics ---
> 3 packets transmitted, 1 packets received, 66% packet loss
> round-trip min/avg/max = 18.321/18.321/18.321 ms
> 
> 
> 172.27.64.1 is a desktop system.
> Running
> % tcpdump -n -i eth1-boards ether host 00:16:e8:4d:7f:c4
> on the desktop, I get:
> 
> 15:01:45.187346 ARP, Request who-has 172.27.64.1 tell 172.27.64.77, length 46
> 15:01:45.187359 ARP, Reply 172.27.64.1 is-at 00:15:17:24:e0:81, length 28
> 15:01:45.194633 IP 172.27.64.77 > 172.27.64.1: ICMP echo request, id 41219, seq 0, length 64
> 15:01:45.194662 IP 172.27.64.1 > 172.27.64.77: ICMP echo reply, id 41219, seq 0, length 64
> 15:01:50.198564 ARP, Request who-has 172.27.64.77 tell 172.27.64.1, length 28
> 15:01:50.205929 IP 172.27.64.77 > 172.27.64.1: ICMP echo request, id 41219, seq 1, length 64
> 15:01:50.205951 IP 172.27.64.1 > 172.27.64.77: ICMP echo reply, id 41219, seq 1, length 64
> 15:01:50.213217 IP 172.27.64.77 > 172.27.64.1: ICMP echo request, id 41219, seq 2, length 64
> 15:01:50.213232 IP 172.27.64.1 > 172.27.64.77: ICMP echo reply, id 41219, seq 2, length 64
> 15:01:51.198563 ARP, Request who-has 172.27.64.77 tell 172.27.64.1, length 28
> 15:01:51.209586 ARP, Reply 172.27.64.77 is-at 00:16:e8:4d:7f:c4, length 46
> 15:01:51.209598 ARP, Reply 172.27.64.77 is-at 00:16:e8:4d:7f:c4, length 46
> 
> Packet #1: the board asks for the desktop's MAC address
> Packet #2: the desktop replies instantly
> Packet #3: the board sends the first ping
> Packet #4: the desktop replies instantly
> Then the board goes quiet for a long time (why???)
> Packet #5: the desktop asks for the board's MAC address (doesn't it have it already?)
> Packet #6: this seems to unwedge the board, which sends the second ping
> Packet #7: the desktop replies instantly
> Packet #8: the board sends the third ping
> Packet #9: the desktop replies instantly
> Packet #10: the desktop asks again for the board's MAC address
> Packet #11 and #12: the board answers twice (for the old and new requests?)
> 
> Some oddities, but it seems to work.
> 
> Now toggle the link state:
> 
> % ip link set eth0 down
> % ip link set eth0 up
> % ping -c 3 172.27.64.1 > /tmp/v2
> 
> PING 172.27.64.1 (172.27.64.1): 56 data bytes
> 
> --- 172.27.64.1 ping statistics ---
> 3 packets transmitted, 0 packets received, 100% packet loss
> 
> 
> On the desktop, I see
> 
> 15:14:03.900162 ARP, Request who-has 172.27.64.1 tell 172.27.64.77, length 46
> 15:14:03.900175 ARP, Reply 172.27.64.1 is-at 00:15:17:24:e0:81, length 28
> 15:14:05.017189 ARP, Request who-has 172.27.64.1 tell 172.27.64.77, length 46
> 15:14:05.017200 ARP, Reply 172.27.64.1 is-at 00:15:17:24:e0:81, length 28
> 15:14:06.030531 ARP, Request who-has 172.27.64.1 tell 172.27.64.77, length 46
> 15:14:06.030541 ARP, Reply 172.27.64.1 is-at 00:15:17:24:e0:81, length 28
> 
> So basically, the board is asking the desktop for its MAC address,
> and the desktop is answering immediately. But the board doesn't seem
> to be getting the replies... Any ideas, or words of wisdom, as they say?
> 
> Regards.
> 

Hi
You might want to read this thread:
https://www.mail-archive.com/netdev@vger.kernel.org/msg133896.html
The symptoms you describe are pretty much what we had at one point.

BR
Matthias