How does DHCP Work?

[mrschafer]

Due to packet forwarding on my router I must disable DHCP and use static IPs on my LAN. This has always worked fine in the past but recently I have been experimenting with SLAX, a server live CD based on slackware, as a mobile demo environment for my php scripts.

The distro configures itself properly when I enable DHCP. But when I disable it I am unable to browse the web or connect to any im clients. However, I can ping local nodes, preform name resolution, and access my web based router config. This problem has arisen on multiple PCs and on two seperate networks.

I contacted Tomas, the one man band for the project, who said nothing had changed and seems to have little motivation to help.

I guess all I really need to know is how dhcp works and what files it modifies.

[stokes]

Are you saying you can see PC's on your internal network but you can't see anything on the Internet? Sounds like a DNS resolution problem.

Go to your router status page and make a note of the DNS servers allocated by your ISP. Then edit your /etc/resolv.conf and add the DNS servers in there.

nameserver 204.xxx.yyy.1
nameserver 204.xxx.yyy.2

The only problem is, you would lose these changes when you restart because Slax is a live distro. There may be some way of making these changes permenant, I really don't know with Slax, but I hope this helps ....

[farslayer]

Also check to make sure you have a default route set.. The default route would be the IP address of your Router.. usually something like 192.168.1.1. Without a default route, you will not be able to access anything outside your local network.

From your description I would say the problem is definately either the Default route or the DNS server settings if not both.

mail:/etc/network# route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.1.0     *               255.255.255.0   U     0      0        0 eth1
default         192.168.1.1     0.0.0.0         UG    0      0        0 eth1

http://www.slackware.com/config/network.php

http://slax.linux-live.org/doc_using...ax.php#network

[mrschafer]

I have already added a route/gateway and name servers. I cannot get past my router unless it is in dhcp mode. Not even to ping. However, I can preform name resolution when my router is set as the DNS server.

I have a linksys router if that makes any difference.

[farslayer]

DHCP or Static IP's should make absolutely NO difference when it comes to IP communications.. having the right addressess in the right locations will make all the difference in the world..


Internet
|
|
<internet IP address set via DHCP from ISP>
LINKSYS ROUTER
<192.168.1.1> -internal Interface DHCP Server disabled
|
|
|
Workstation
IP Address 192.168.1.2
Netmask 255.255.255.0
Broadcast Address 192.168.1.255
Gateway 192.168.1.1
DNS 192.168.1.1


to check the addressing on your machine
ifconfig -a

mail:~# ifconfig -a
eth1 Link encap:Ethernet HWaddr 00:02:B3:EE:5B:FD
inet addr:192.168.1.2 Bcast:192.168.1.255 Mask:255.255.255.0
inet6 addr: fe80::202:b3ff:feee:5bfd/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:550718 errors:0 dropped:0 overruns:0 frame:0
TX packets:16154 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:84637889 (80.7 MiB) TX bytes:1263922 (1.2 MiB)
Base address:0xdf80 Memory:ff8a0000-ff8c0000

to check the default route
route

mail:~# route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
192.168.1.0 * 255.255.255.0 U 0 0 0 eth1
default 192.168.1.1 0.0.0.0 UG 0 0 0 eth1

to check dns

more /etc/resolv.conf

itg-debian:/etc# more /etc/resolv.conf
nameserver 192.168.1.1

to test connectivity

Ping local address 192.168.1.2
ping gateway 192.168.1.1
ping internet host..

imail:~# ping -c 3 72.14.205.99
PING 72.14.205.99 (72.14.205.99) 56(84) bytes of data.
64 bytes from 72.14.205.99: icmp_seq=1 ttl=255 time=2.49 ms
64 bytes from 72.14.205.99: icmp_seq=2 ttl=255 time=1.50 ms
64 bytes from 72.14.205.99: icmp_seq=3 ttl=255 time=1.29 ms

--- 72.14.205.99 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2002ms
rtt min/avg/max/mdev = 1.293/1.762/2.495/0.526 ms

to test name resolution use dig to resolve some names..

dig www.google.com
mail:~# dig www.google.com

; <<>> DiG 9.2.4 <<>> www.google.com
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 36732
;; flags: qr rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;www.google.com. IN A

;; ANSWER SECTION:
www.google.com. 53507 IN CNAME www.l.google.com.
www.l.google.com. 300 IN A 72.14.205.99
www.l.google.com. 300 IN A 72.14.205.104

;; Query time: 40 msec
;; SERVER: 192.168.1.1#53(192.168.1.1)
;; WHEN: Tue Apr 11 16:16:13 2006
;; MSG SIZE rcvd: 84

you need to figure out where the breakdown in your network is..

DHCP is really irrelevant if your network settings are correct.

[mrschafer]

I just recieved a reply from the project manager for the distro and apparently it has been documented as a bug. So I guess I wasn't doing anything wrong after all. Now the only question is can anyone tell me how to fix it?

[farslayer]

http://slax.linux-live.org/forum/viewtopic.php?t=9963

Yep it's listed as a bug.. looks like you will have to wait until the y figure it out, or configure your box to use DHCP.


You are aware that you can usually configure a DHCP server to give aspecific IP address to a Certain machine on the network right ? IT's almost the same as having a static IP, since the box would always get the same address.


Look into DHCP Reservations in your DHCP server. you will need the MAC address from the workstation you wish to assign a specific address to .

Basically what you are doing is telling the DHCP server, When you see a DHCP request from this MAC address always give him THIS SPECIFIC IP Address..

[BallisticPain]

http://slax.linux-live.org/forum/viewtopic.php?t=9963

Yep it's listed as a bug.. looks like you will have to wait until the y figure it out, or configure your box to use DHCP.


You are aware that you can usually configure a DHCP server to give aspecific IP address to a Certain machine on the network right ? IT's almost the same as having a static IP, since the box would always get the same address.


Look into DHCP Reservations in your DHCP server. you will need the MAC address from the workstation you wish to assign a specific address to .

Basically what you are doing is telling the DHCP server, When you see a DHCP request from this MAC address always give him THIS SPECIFIC IP Address..

I have seen this functionality on a few different routers, but never on a linksys. I wish they would add it for ease of use, but I had a friend that explained to me why it would be redundant to have it there. I just dont remember the explanation or I would offer it here.

IMHO,
JS