switch killing connection to router

[John Huthmaker]

I'm working on my cisco lab.  Every device is plugged in to my switch (computer, router, firewall).  Whenever I telnet from my computer direct to my router, it works for a second and then disconnects.  I cant then reconnect.  If I telnet to my switch first, and then telnet from my switch to my router, it works fine. I tried connecting my router to different ports on the switch.  Why does it do this?

[John Huthmaker]

Does anybody know what is causing the above?

[fb_webuser]

Does everything have a unique IP address?

do show ip arp on the routers and arp -a on your PC perhaps the arp tables are getting messed up.

If you connect by telnet while monitoring the serial port do you get any messages ?

---

Posted by WebUser Stuart Gall

[John Huthmaker]

Everything does have a unique IP Address.  I will run the above commands tonight when I have a chance.

I just want to be clear on the last sentence.  You want me to console in to the router, and then also connect over telnet and see if the console gives me a message.  Is that right?

[jas2061461]

Can you ping the router interface from your PC. Sometimes being connect to a WAP while plugged into a different network, such as your switched network, can cause issues; disable secondary network connections.  Sometimes Windows firewall can cause issues; disable that.  Post any configs you have available.

[John Huthmaker]

Here is a breakdown of my network.

Fortigate Fortinet 200a Firewall 10.0.0.1 (Running DHCP Services)

Cisco 3548XM Switch 10.0.0.2 (VLAN1)

Cisco 2611 Router 10.0.0.3

My computer 10.0.0.100 (recieved from DHCP - Directly plugged in to switch)

If I telnet to 10.0.0.3 it makes a connection and prompts me to login.  Before I can complete the login it disconnects me, and I cannot reconnect.  I can ping 10.0.0.3 just fine.  I can then telnet to 10.0.0.2 and login, and then telnet from there to 10.0.0.3 and it works fine.

[ebarticel]

You default gateway on PC is the firewall at 10.0.0.1 since it gives the DHCP address, I assume.

I would suggest you check the settings on that firewall. Also check the encapsulation on both the firewall and router.

It works between switch and router because the are from same family

[John Huthmaker]

I'm following what your saying, but that still doesnt answer why I can successfully telnet the switch and not the router.  How would I check the "encapsulation" on the firewall and switch?  An ip address is an ip address.  I dont see why my computer recieving it via DHCP from the firewall would make any sort of difference.

[ebarticel]

Have you tried just for testing, to give vlan 1 on router an IP address on same subnet and try to telnet to it?

Please let us know of the results.

Eugen