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Old 03-17-2002, 09:55 AM   #1
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Registered: Mar 2002
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Strange DHCPcd behavior

Hi all,

I'm running Redhat 7.2. If I run dhcpcd -n (renew license) I expect that I will send out a packet to my dhcp server and receive one back. However, if I run tcpdump and then run dhcpcd -n - I see:

[user]# tcpdump -n host yyy.yyy.yyy.yyy
tcpdump: listening on eth0
13:20:32.720462 > yyy.yyy.yyy.yyy.bootps: xid:0x54496739 secs:3 [|bootp]
13:20:32.754394 yyy.yyy.yyy.yyy.bootps > xid:0x54496739 [|bootp] (DF)
13:20:32.754859 > yyy.yyy.yyy.yyy: icmp: udp port bootpc unreachable [tos 0xc0]

Which seems to show me sending one out, getting one back and then (unexpectedly) sending out an ICMP packet (which turns out to be port unreachable).

So my first issue is why am I sending out a port unreachable? Does this indicate a problem with dhcp?

Then, if I look at my iptables log all I see is:

[user]# tail /var/log/messages
Mar 15 13:20:32 pokey kernel: INPUT:IN=eth0 OUT= MAC=00:00:00:00:00:00:00:00:00:00:00:00:00:00 SRC=yyy.yyy.yyy.yyy LEN=359 TOS=0x00 PREC=0x00 TTL=253 ID=32883 DF PROTO=UDP SPT=67 DPT=68 LEN=339
Mar 15 13:20:32 pokey kernel: OUTPUT:IN= OUT=eth0 DST=yyy.yyy.yyy.yyy LEN=387 TOS=0x00 PREC=0xC0 TTL=255 ID=1645 PROTO=ICMP TYPE=3 CODE=3 [SRC=yyy.yyy.yyy.yyy LEN=359 TOS=0x00 PREC=0x00 TTL=253 ID=32883 DF PROTO=UDP SPT=67 DPT=68 LEN=339 ]

Which seems to show me receiving a packet and sending out the port unreachable but never sending out the initial packet. Here are my rules:
#Log anything in other than loopback
$iptables -A INPUT -i ! lo -j LOG --log-prefix "INPUT:"

#Log anything in other than loopback
$iptables -A OUTPUT -o ! lo -j LOG --log-prefix "OUTPUT:"

So my second question is: why does iptables only show 2 of the 3 packets?

Thanks so much for any help,


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