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bridge sending out DHCP queries
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javeree
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Joined: 29 Jan 2006
Posts: 349

PostPosted: Tue Sep 29, 2015 12:31 pm    Post subject: bridge sending out DHCP queries Reply with quote

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
wlanu


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
4 1322 LOG udp -- br0 any anywhere anywhere udp dpt:bootps LOG level warning prefix "unhandled DHCP-related: "
144 51661 LOG udp -- br0 any anywhere anywhere udp spt:bootps LOG level warning prefix "unhandled DHCP-related: "


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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