Unable to ping Internet / Shared Network

[Fons de Jongh]

Hi Barry,
 
I have the following suggestion. Please follow each step:
 
1) Bind an IP address from subnet 192.168.100.0/24 to the interface of the router, where you have already bound 192.168.1.1 to. This IP address must not exist in the pool range (so it cannot be an address from 192.168.100.2 through 192.168.100.6)
 
2) In subnet 192.168.1.0/24, configure 'option routers' to 192.168.1.1
 
3) In subnet 192.168.100.0, configure  'option routers' to the IP address from subnet 192.168.100.0/24 that you have bound to the router's interface.
 
4) You can remove the 'option routers' from the global DHCP configuration.
 
Explanation:
Hosts in subnet 192.168.100.0/24 will consider 192.168.1.1 an IP address in a remote subnet that can only be reached through a router. They will not try to resolve the hardware address of 192.168.1.1 per ARP, and hence will not be able to send IP datagrams to IP addresses in remote subnets via the router's interface. Hosts in subnet 192.168.100.0/24 will consider any other IP address in 192.168.100.0/24 an address in the local subnet, so if you bind an IP address from 192.168.100.0/24 to the same interface of the router as where you have bound 192.168.1.1 to, and configure 'option routers' in subnet 192.168.100.0/24 to that IP address, then DHCP clients with an address from 192.168.100.0/24 will be able to use the router also.
 
Thanks and kind regards,
 
Fons
 

>>> Barry Stear <bstear at gmail.com> 7/6/2011 12:37 AM >>>
Hi,

I have my isc-dhcp-server setup as a shared network with two subnets that are using the same interface (eth0). ETH0 is connected to a 5 port switch which connects Linksys router. The problem I have is that I cannot ping anything on the internet when I receive an IP address in the 192.168.100.X subnet. I am unable to ping 192.168.1.2 from the 192.168.100.X subnet.
I tried changing the 'options routers' for the 192.168.100.X subnet to 192.168.1.2 and that didn't make a difference. 
Network Topology
------------------------ 
Linkysys router (192.168.1.1) ---> 5 Port Hub ---- > NIC Eth0 (192.168.1.2) / ETH0:1 (192.168.100.1)
Snippet from my configuration

DHCP.CONF
----------------------

option routers 192.168.1.1;
one-lease-per-client true;
get-lease-hostnames true;

shared-network MYNET {

# trusted subnet
subnet 192.168.1.0 netmask 255.255.255.0 {
max-lease-time 172800;
default-lease-time 28800;

pool {
range 192.168.1.10 192.168.1.39;
option routers 192.168.1.1;
option domain-name-servers 192.168.1.2;
option subnet-mask 255.255.255.0;
deny unknown-clients;
}
}

# untrustedhosts
subnet 192.168.100.0 netmask 255.255.255.0 {
max-lease-time 28800;
default-lease-time 14400;

pool {

range 192.168.100.2 192.168.100.6;
option routers 192.168.1.1;
option domain-name-servers 192.168.100.1;
option subnet-mask 255.255.255.0
allow unknown-clients;
}
}
}


My NIC is setup as follows : 

eth0 
ipv4 address : 192.168.1.2
netmask 255.255.255.0
broadbase 192.168.1.255

eth0:1 Virtual 
ipv4 address : 192.168.100.1
netmask 255.255.255.0
broadcast 192.168.100.255 

According to a book I have called The DHCP Handbook I should not have to setup a route since it is setup as a shared network using a single NIC, i am unsure what I need to do to route the traffic to my Linksys router (192.168.1.1)

Let me know if you need any other information.. 

Any help is appreciated.

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