# bridge sending out DHCP queries

## javeree

I have a PC running as NAT router, with dnsmasq as dhcp/dns server

the WAN side is ppp1, the LAN side consists of a wired and a wireless interface, that I bridge together. 

 *Quote:*   

> brctl show
> 
> bridge name     bridge id               STP enabled     interfaces
> 
> br0             8000.000000006b52       yes             ethu
> ...

 

br0 is assigned a static IP address 192.168.4.1, dnsmasq assigns addresses in the 192.168.4.5x region.

I wanted to make sure that all dhcp requests reached dnsmasq, and none came from the WAN side, so I put up some IPtables looking for unexpected DHCP.

 *Quote:*   

>   884  359K ACCEPT     udp  --  br0    any     0.0.0.0              255.255.255.255      udp spt:bootpc dpt:bootps
> 
>   506  166K ACCEPT     udp  --  br0    any     anywhere             255.255.255.255      udp spt:bootpc dpt:bootps
> 
>  1259  478K ACCEPT     udp  --  br0    any     anywhere             ROUTER.home  udp spt:bootpc dpt:bootps
> ...

 

with this setup I regularly see dhcp queries coming not from some internal PC, but from the bridge itself !

 *Quote:*   

> [787708.676250] unhandled DHCP-related: IN=br0 OUT= MAC= SRC=192.168.4.1 DST=255.255.255.255 LEN=377 TOS=0x00 PREC=0xC0 TTL=64 ID=51814 PROTO=UDP SPT=67 DPT=68 LEN=357 

 

What could possibly cause this message ? AFAIK, the br0 interface or its children ethu or wlanu should never ask for an IP address or do any other DHCP query, or am I mistaken ?

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