CCS/TM4C1294NCPDT: lwIP problem with tcp socket on different subnets tiva

Hi Lukasz,
I tend to think that this is not a LwIP problem. But if you are in doubt I will suggest you seek support from the LwIP forum. The DHCP client request involves sending broadcasting address to the LAN. If the DHCP server is in the same subnet it will lease the IP address to the client. I think for the DHCP to work across different subnets, you will need to have some type of DHCP relay agents. The DHCP client broadcasts on the local network and the relay agent receives the broadcast and transmits it to one or more DHCP servers using unicast. I'm not a network expert so please also consult with your IT department.

Hi Charles,

Of course I don't claim it is Lwip problem. I seek an advice and expertise to debug the problem.
You have made a good point. But if I have other devices with DHCP assigned IP they work without additional treatment, once packet arrives to correct subnet router based on broadcasting knows the IPs and MACs of devices in the subnet.


Lukasz

Hi Lukasz,

EMAC0 supports multiple 802.1Q VLANs when configured, otherwise a (router) is required to make IP connections across different subnets or VLANS. Windows 2008 server and other Microsoft products act as a router when properly configured.

Cisco routers support IP helper for DCHP clients to connect across VLANS to a DHCP server on a specific VLAN. One can enable multiple VLANS to a NIC if 802.1Q protocol is enabled.

Hi,

Thank you a lot. I will check the data sheet for proper EMAC configuration. Any hints?

In case of inter VLAN communication or between different subnets of LAN router has to be involved. When server and client are in different LANs I can ping to my server but similarly no acknowledgement of synchronization and it fails. This case with both hosts connected to different gateway points is actually my biggest problem. I wasn’t clear enough.

Can this be relatated to EMAC configuration? Or more router block?

Thanks again for discussion.

Lukasz Huchel said:

. When server and client are in different LANs I can ping to my server but similarly no acknowledgement of synchronization and it fails.

Assuming both network addresses are the same, e.g. (192.168.x.x) ?  That ICMP ping echo response is a broadcast yet if the subnet masks are different that might cause LWIP ARP router issues. As you are aware broadcast typically stop at the router, layer 3. Cisco's EIGRP routing encapsulates IP, seem to recall layer 3 broadcasts are captured via IP encapsulation or at least the endpoint VLANS would return ICMP broadcasts over 802.1Q.

Hi Charles,

I actually had hands on years ago setting up a network for Intel 802.1Q trunking on all sever NICS. Was managed by a Cisco Catalyst 6503 gigabit switch, 12 VLANS.

Hi,

I can use ICMP (ping ,trace route) in case of both devices at the same subnet or at completely different network addresses (server in 18.62.x.x, client in 18.111.x.x) . I get the ping response and I can trace the particular hops using trace route command.

Here is the moment which I cannot explain to myself. When my devices are in one LAN (have the same subnet, same gateway addresses) my application works ok and telnet command allows me to open the port that server is listening at. Now when I try to use my application from different network addresses (server in 18.62.x.x, client in 18.111.x.x) it fails (telnet also fails to open the port where the server is listening to). However, all commands of ICMP protocol can still reach correctly.

My server is listening for tcp connection at a chosen port from any ip address.

Can I narrow down potential reasons? Or contact network administrator to make sure my device is correctly registered and can talk to remote locations in different network addresses.

Thanks a lot for the discussion.

Hi BP101, Charles,

Thank you a lot for the discussion. I have benefited from that. The final solution was registering my device. Network administrator created appropriate rule on my default gateway. I can access desired server from a different subnet or gateway. 

Thanks again.