not getting a default gateway through dhcp

From: Amadeus W. M. (amadeus84_at_cablespeed.com)
Date: 07/06/05 

Date: Tue, 05 Jul 2005 20:50:15 -0400

Ever since I moved to this ISP I've been having network problems, and I
need a little help.

They gave me an antique motorolla cable modem, and usually I have a
linksys router plugged into the router, but right now I have my FC4 pc
plugged in directly into the modem, to rule out any problems with the
router.

For the last couple of days the connection was ok, but this afternoon it
rained, and, since my ISP's service depends on the weather, the network
went down. If it rains, it goes down, if it's windy, it goes down, if
there's lightening, you guessed it, it goes down. It's an ISP from hell.

Now I've configured eth0 with dhcp. It does get an IP address, but when I
try to connect anywhere, it says no route to something (I can't check
exactly what it says right now, because I'm trying to send this).

I see network activity in gkrellm and I see ARP packets with ethereal,
so the link is ok. So I look at the routing table, and I see no default
gateway. But I did see some DHCP packets coming in, so I figured that must
be the gateway. I do

route add default gateway xx.xx.xx.xx

and then voila! I'm online.

Now that I got this far, I want to pinpoint where the problem is.
Why am I not getting the default gateway? Is it some bug in my FC4 dhcp
client, or is my stupid ISP that's not sending it. Is it possible to tell?

As a matter of fact, I installed the dhcp server on this machine, and my
other machines as well as the router got all the required info just fine.
I do want to go out through the router though, and I want it to get all
the info, as it should. I am positive my hardware is ok, except possibly
the motorolla cable modem, which is from the ISP.

Below is the DHCP packet I saw with ethereal. Please someone help, before
I end up in a mad house.

No. Time Source Destination Protocol Info
   4693 186.355671 24.35.40.1 255.255.255.255 DHCP DHCP Offer - Transaction ID 0x33d1a0

Frame 4693 (363 bytes on wire, 363 bytes captured)
    Arrival Time: Jul 5, 2005 19:52:47.244828000
    Time delta from previous packet: 0.120903000 seconds
    Time since reference or first frame: 186.355671000 seconds
    Frame Number: 4693
    Packet Length: 363 bytes
    Capture Length: 363 bytes
    Protocols in frame: eth:ip:udp:bootp
Ethernet II, Src: 00:50:57:00:99:a6, Dst: ff:ff:ff:ff:ff:ff
    Destination: ff:ff:ff:ff:ff:ff (Broadcast)
    Source: 00:50:57:00:99:a6 (Broadban_00:99:a6)
    Type: IP (0x0800)
Internet Protocol, Src Addr: 24.35.40.1 (24.35.40.1), Dst Addr: 255.255.255.255
(255.255.255.255)
    Version: 4
    Header length: 20 bytes
    Differentiated Services Field: 0x07 (DSCP 0x01: Unknown DSCP; ECN: 0x03)
        0000 01.. = Differentiated Services Codepoint: Unknown (0x01)
        .... ..1. = ECN-Capable Transport (ECT): 1
        .... ...1 = ECN-CE: 1
    Total Length: 349
    Identification: 0x0000 (0)
    Flags: 0x00
        0... = Reserved bit: Not set
        .0.. = Don't fragment: Not set
        ..0. = More fragments: Not set
    Fragment offset: 0
    Time to live: 16
    Protocol: UDP (0x11)
    Header checksum: 0x6966 (correct)
    Source: 24.35.40.1 (24.35.40.1)
    Destination: 255.255.255.255 (255.255.255.255)
User Datagram Protocol, Src Port: bootps (67), Dst Port: bootpc (68)
    Source port: bootps (67)
    Destination port: bootpc (68)
    Length: 329
    Checksum: 0x6b77 (correct)
Bootstrap Protocol
    Message type: Boot Reply (2)
    Hardware type: Ethernet
    Hardware address length: 6
    Hops: 0
    Transaction ID: 0x0033d1a0
    Seconds elapsed: 0
    Bootp flags: 0x8000 (Broadcast)
        1... .... .... .... = Broadcast flag: Broadcast
        .000 0000 0000 0000 = Reserved flags: 0x0000
    Client IP address: 0.0.0.0 (0.0.0.0)
    Your (client) IP address: 24.35.42.93 (24.35.42.93)
    Next server IP address: 0.0.0.0 (0.0.0.0)
    Relay agent IP address: 24.35.40.1 (24.35.40.1)
    Client MAC address: 00:12:17:32:ea:79 (Cisco-Li_32:ea:79)
    Server host name not given
    Boot file name not given
    Magic cookie: (OK)
    Option 53: DHCP Message Type = DHCP Offer
    Option 54: Server Identifier = 24.35.0.42
    Option 51: IP Address Lease Time = 6 days, 23 hours, 59 minutes, 55 seconds
    Option 1: Subnet Mask = 255.255.248.0
    Option 5: Name Server
        IP Address: 24.35.0.12
        IP Address: 24.35.0.13
    Option 23: Default IP Time-to-Live = 64
    Option 27: All Subnets are Local = No
    Option 28: Broadcast Address = 255.255.255.255
    Option 31: Perform Router Discover = Enabled
    Option 35: ARP Cache Timeout = 1 minute
    Option 37: TCP Default TTL = 64
    Option 3: Router = 24.35.40.1
    Option 6: Domain Name Server
        IP Address: 24.35.0.12
        IP Address: 24.35.0.13
    Option 44: NetBIOS over TCP/IP Name Server = 127.0.0.1
    Option 46: NetBIOS over TCP/IP Node Type = H-node
    End Option

Relevant Pages

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