I've got a server that I've set up, as mentioned in recent posts. It is
acting as the NAT gateway for my network, and I've configured the iptables
stuff via shorewall. It is running SSH on both interfaces, and DHCP, DNS,
NTP and Samba on the internal interface.

eth0: 75.148.79.37, 255.255.255.252
eth1: 192.168.0.1, 255.255.0.0
host name: server

Both interfaces on the server are running static IPs of course, but all
other machines on the internal network configure their interfaces via DHCP.
For the computer lab, each of the 12 computers have host names of lab1,
lab2... etc.

Running tcpdump on lab3 while pinging lab5 (which works just fine) gives me
the following output:

20:14:05.426473 IP lab3.55559 > 192.168.0.1.domain: 5488+ A? lab5. (22)
20:14:05.426498 IP lab3.55559 > 192.168.0.1.domain: 5488+ A? lab5. (22)
20:14:05.429513 arp who-has lab5 tell lab3
20:14:05.429520 arp who-has lab5 tell lab3
20:14:10.431332 arp who-has lab3 tell lab5

As a side note, any of the DHCP configured desktops can ping the server with
it's host name, without any problems. However, I cannot ping any of the lab
computers from the server with their host names. When I ran tcpdump on the
server while trying to ping lab3, here is what I got. Please note the
highlighted line.

20:41:08.546663 IP 75-148-79-37-Jacksonville.hfc.comcastbusiness.net.49946 >
chAdmin.hsd1.fl.comcast.net.domain: 31782+ PTR? 37.79.148.75.in-addr.arpa.
(43)
20:41:08.659553 IP chAdmin.hsd1.fl.comcast.net.domain >
75-148-79-37-Jacksonville.hfc.comcastbusiness.net.49946: 31782 1/0/0 (114)
20:41:08.659755 IP 75-148-79-37-Jacksonville.hfc.comcastbusiness.net.52151 >
chAdmin.hsd1.fl.comcast.net.domain: 62637+ PTR? 9.162.106.76.in-addr.arpa.
(43)
20:41:08.711983 IP chAdmin.hsd1.fl.comcast.net.domain >
75-148-79-37-Jacksonville.hfc.comcastbusiness.net.52151: 62637 1/0/0 (99)
20:41:08.712183 IP 75-148-79-37-Jacksonville.hfc.comcastbusiness.net.41542 >
chAdmin.hsd1.fl.comcast.net.domain: 22514+ PTR? 1.10.1.10.in-addr.arpa. (40)
20:41:08.722986 IP chAdmin.hsd1.fl.comcast.net.domain >
75-148-79-37-Jacksonville.hfc.comcastbusiness.net.41542: 22514* 1/0/0
PTR[|domain]
20:41:10.118574 IP 75-148-79-37-Jacksonville.hfc.comcastbusiness.net.52671 >
chAdmin.hsd1.fl.comcast.net.domain: 40171+ A? eth1.hsd1.fl.comcast.net. (42)
20:41:11.728485 IP 192.168.0.1.ntp > 192.168.0.0.ntp: NTPv4, Broadcast,
length 48
20:41:11.728676 IP 75-148-79-37-Jacksonville.hfc.comcastbusiness.net.53047 >
chAdmin.hsd1.fl.comcast.net.domain: 52022+ PTR? 0.0.168.192.in-addr.arpa.
(42)
20:41:15.115556 IP 75-148-79-37-Jacksonville.hfc.comcastbusiness.net.52671 >
chAdmin.hsd1.fl.comcast.net.domain: 40171+ A? eth1.hsd1.fl.comcast.net. (42)
20:41:16.521816 IP 75-148-79-37-Jacksonville.hfc.comcastbusiness.net.41471 >
chAdmin.hsd1.fl.comcast.net.domain: 5694+ A? lab3.hsd1.fl.comcast.net. (42)
20:41:16.725544 IP 75-148-79-37-Jacksonville.hfc.comcastbusiness.net.53047 >
chAdmin.hsd1.fl.comcast.net.domain: 52022+ PTR? 0.0.168.192.in-addr.arpa.
(42)
20:41:17.845241 IP nf-in-f17.google.com.www >
75-148-79-37-Jacksonville.hfc.comcastbusiness.net.56993: P
1837939960:1837939982(22) ack 3047802026 win 266 <nop,nop,timestamp
2119125004 19019018>
20:41:17.845283 IP 75-148-79-37-Jacksonville.hfc.comcastbusiness.net.56993 >
nf-in-f17.google.com.www: . ack 22 win 541 <nop,nop,timestamp 19021568
2119125004>
20:41:17.845346 IP nf-in-f18.google.com.www > 192.168.0.231.2343: P
3037914064:3037914086(22) ack 2815779179 win 17520

I am certainly no expert with this stuff, but it looks to me like my server
is taking the ARP request meant for my local network, and sending it to
chAdmin.hsd1.fl.comcast.net. My question is: why? I figure that I probably
have mis-configured something, therefore causing this problem. However, I've
been doing quite a bit of googling this afternoon and evening, but have only
seen bits that hinted at the ARP problem, but without a solution. Does
anyone know what I might be doing wrong?


Douglass Clem
crashsystems.net
Public Key: http://crashsystems.net/pubkey.asc

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