Dropping reply received on <downstream interface> when using -iu/-id

Patrick Cervicek patrick at freifunk-stuttgart.spamtrap.hs-esslingen.de
Tue Jan 2 23:47:15 UTC 2018

Am 2. Januar 2018 15:55:52 MEZ schrieb "Brian J. Murrell" <brian at interlinx.bc.ca>:
>On Tue, 2017-12-12 at 09:54 -0500, Brian J. Murrell wrote:
>> I want to use the -iu/-id options with dhcrelay to prevent relays
>> from
>> relaying (and thus duplicating) requests coming from the network that
>> the DHCP server is on[1]:
>> # /usr/sbin/dhcrelay -4 -d -pf /var/run/dhcrelay4.pid -id br-guest
>> -iu br-lan
>> When I do this, DHCP Discover requests coming from clients on the br-
>> guest interface have their Relay agent IP address set to the address
>> of
>> the br-guest interface.  When the DHCP server sends back an DHCP
>> Offer
>> it sends it to the IP address of the br-guest interface on the relay
>> machine.  dhcrelay then proceeds to drop that reply:
>> Dropping reply received on br-guest

To me it looks like DHCP Offer did come in via br-guest (and not br-lan)
Are this interfaces seperated or somehow bridged together? Locally or on the same switch/vlan
The server should be reachable only via br-lan

Could you provide:
brctl show br-guest
brctl show br-lan
ip addr 

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