Esoteric question

Simon Hobson simon at thehobsons.co.uk
Wed Sep 18 20:47:34 UTC 2019


Gregory Sloop <gregs at sloop.net> wrote:

>Packet caps from the new router show that the router/DHCP server IS
>seeing all the DHCP protocol handshake. [When it's having the
>"problem."]
>The client does a DISCOVER
>Server responds with OFFER
>The client responds with REQUEST
>Then there's a LONG pause. [like 90s+ worth.]
>The Server responds with ACK. [It actually appears to send several
>ACKS.

Ah, about 90s you say ?
Have a look on the external interface and/or in the logs and see if it's trying to do any DNS lookups or updates. Over the years I've seen lots of threads related to 90s delays - a common one being SSH logins - which have come down to the device attempting a DNS lookup and waiting for it to time out.

Anyway, what I theorise could be happening is :
With WAN connected, "something" (dhcpd) is trying to do "something" with an outside service and timing out.
When the WAN is link-up but not connected to the modem, such attempts fail very quickly as the device has no ARP entry for it's default route and so the network stack quickly reports "no route to host".

BTW, when I first read your post I was thinking WTF ! It was only after reading the other replies that this idea came to mind.

Simon
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