Re: [lwip-users] Delay at startup to answer with gateway

[Jeff Barber]

This sounds a lot like a Spanning Tree Protocol (STP) effect.
However, that doesn't exactly match your description of the topology
so I'm not sure.

I have an lwIP device on a remote network segment and each time it's
rebooted (and hence, loses and regains link), it's inaccessible for a
fixed period until the switch to which it attaches moves the port to
'forwarding' mode.  We were able to reduce but not eliminate the
duration by reconfiguring the switch (maybe changing from ordinary STP
to RSTP ["Rapid" STP] -- something like that; I didn't actually do it
myself so I'm not sure).  As I recall, the time went from about 35
seconds to about 20.

Jeff

On Wed, Mar 3, 2010 at 7:51 AM, Stéphane Lesage <address@hidden> wrote:
> Hi,
>
> My LwIP devices work fine in general,
> but I discovered a problem recently in an environment where we use gateways.
>
> After powering-up, we have a delay of about 35 seconds before they are
> reachable.
> When using the same device from the same network, we have no problem.
> At first I suspected a problem with the switch/routers ARP cache.
>
> I asked my colleagues to do a wireshark capture (port mirroring)
>
> - packets 12-14: LwIP starts and sends ARP gratuitous and IGMP reports
> - a pc (192.168.245.14) pings the LwIP device (192.168.241.226),
> we can see the packets arriving on the wire, so the router already knows the
> MAC address of the device.
> - another PC (192.168.245.11) is trying to connect to TCP port 12302...
> - no answer for 34 seconds
> - packets 48-51: the LwIP answers to a TCP SYN (arp request to find a
> gateway MAC and SYN ACK)
>
> What's wrong ?
> Did someone else meet the same problem ?
>
> I cannot reproduce in my office (no routeur)... next week I'll be able to
> debug.
>
> --
> Stephane Lesage
>
>
>
>
>
>
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