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Old 09-21-2003, 02:45 AM   #1
agl
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Registered: Sep 2003
Posts: 2

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DHCP: 1 hostname, 2 IP addresses, only 1 is reachable?


I recently set up an ADSL connection on my Debian Woody machine. I obtain an IP address via DHCP. This all appears to work fine - I can ping everywhere, receive email, and so forth. While playing around with setting up Apache, I noticed that my IP address as obtained by DHCP doesn't appear to match my hostname when I look it up with the host command. Moreover, I can ping my machine with one of my IP addresses, but not the 2nd or the hostname (which resolves to the 2nd address). The details:

> cat /etc/network/interfaces
# Loopback interface - always
#
auto lo
iface lo inet loopback

# use dhcp:
#
auto eth0
iface eth0 inet dhcp

---

> ifconfig
eth0 Link encap:Ethernet HWaddr 00:50:DA:05:B2:C3
inet addr:64.180.174.60 Bcast:64.180.191.255 Mask:255.255.224.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:34090 errors:0 dropped:0 overruns:0 frame:0
TX packets:25548 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:100
RX bytes:34243659 (32.6 MiB) TX bytes:2991102 (2.8 MiB)
Interrupt:11 Base address:0x6500

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:2353 errors:0 dropped:0 overruns:0 frame:0
TX packets:2353 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:783598 (765.2 KiB) TX bytes:783598 (765.2 KiB)

---

> iptables --list
Chain INPUT (policy ACCEPT)
target prot opt source destination

Chain FORWARD (policy ACCEPT)
target prot opt source destination

Chain OUTPUT (policy ACCEPT)
target prot opt source destination

---

> host 64.180.174.60
60.174.180.64.in-addr.arpa domain name pointer amgd22mjy327j.bc.hsia.telus.net

> host amgd22mjy327j.bc.hsia.telus.net
amgd22mjy327j.bc.hsia.telus.net has address 207.6.238.178

[note that the hostname doesn't resolve to the same IP]

> ping 64.180.174.60
PING 64.180.174.60 (64.180.174.60): 56 data bytes
64 bytes from 64.180.174.60: icmp_seq=0 ttl=255 time=0.3 ms
64 bytes from 64.180.174.60: icmp_seq=1 ttl=255 time=0.1 ms
...

> ping 207.6.238.178
PING 207.6.238.178 (207.6.238.178): 56 data bytes
[no further output]

> ping amgd22mjy327j.bc.hsia.telus.net
PING amgd22mjy327j.bc.hsia.telus.net (207.6.238.178): 56 data bytes
[no further output]

A friend elsewhere on the internet has the same results - she can ping the first IP, but the 2nd and the hostname are unreachable.

Soo.... what's going on here?
 
Old 09-21-2003, 06:06 AM   #2
peter_robb
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Registered: Feb 2002
Location: Szczecin, Poland
Distribution: Gentoo, Debian
Posts: 2,458

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The in-addr.arpa record came from your ISP registering the ip space so that mail servers can reverse lookup your ip number and validate your location.

The second record came from the dns servers of your ISP, which look to advertise a different name series...

It is quite common to have a domain name showing a different ip number (hopefully the correct one) from the reverse lookups in ARPA.
The ARPA records would show who the numbers are registered to and the dns would show who the names are registered to.

Last edited by peter_robb; 09-21-2003 at 06:09 AM.
 
Old 09-21-2003, 08:46 PM   #3
agl
LQ Newbie
 
Registered: Sep 2003
Posts: 2

Original Poster
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Guess I have some more reading to do. Thanks for the pointers.
 
  


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