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Community Member

can see the neighbors but cant Telnet or ping

i connected three Routers by using a hub

1700 Router

2500 Router

2600 Router

i go to 1700 Router and want to access the two other routers. by using sh cdp neighbors command i can see just Router2500 but cant ping or telnet it....what could be the reason?!

Note: i already put a password to the vty line in all Routers.

7 REPLIES

Re: can see the neighbors but cant Telnet or ping

Hi

Since all the three boxes are connected in a same hub u need to check the ip connectivity to those respective boxes from 1700.

i feel you might be having the ethernet of all three boxes configured under the same subnet if not you need to do the same before trying something in line with telnet or ping.

Show cdp will display the details of neighboring devices but still u wont be able to ping or telnet them up the reason out here is CDP and telnet/ping works in different OSI layers.

if u need more info do post out the config of all the three boxes here..

regds

Community Member

Re: can see the neighbors but cant Telnet or ping

Router 1700 :e0, ip address: 192.168.3.1

Router 2500 :e0, ip address: 192.168.2.1

Router 2600: f0/0, ip address: 192.168.1.1

Community Member

Re: can see the neighbors but cant Telnet or ping

1. CDP works on Layer 2 so you can see them.

2. Ping requires Layer 3 connectivity, and you have configured IP's incorrectly if you used 255.255.255.0, so unless you have set the subnet mask to 255.255.0.0, you wont get layer 3 connectivity.

You should read up on subnetting if you arnet sure what i'm rambling on about :-)

Good luck

Re: can see the neighbors but cant Telnet or ping

Hi

As per the ip addressing scheme being mentioned in ur post u need to have a static route in 1700 for those networks i.e.,192.168.2.0,192.168.1.0 towards your ethernet 0 interface.

If u get the static routes for these networks pointing ur ethernet interface u will get the connectivity for other boxes..

regds

Community Member

Re: can see the neighbors but cant Telnet or ping

can some one help to understand what will happen in OSI layers while we trying to connect a switch in telnet .....?

Hall of Fame Super Gold

Re: can see the neighbors but cant Telnet or ping

Why did you add your question to this very old discussion, which does not really relate to the question that you are asking? It would have been more effective if you had started a new discussion and had been able to give it a title which reflected what you want to ask.

 

I hope that you will find this explanation helpful:

- your telnet client will formulate a packet to initiate telnet to the switch (application layer) and pass the data to the transport layer which builds a layer 4 leader and selects 23 as the destination port and selects some value as the source port.

- it passes the packet to the network layer which builds a layer 3 header and puts the switch IP address as the destination and puts your IP address as the source.

- it passes the packet to layer 2 which will build a layer 2 header and put the switch MAC address as the destination MAC and put your MAC as the source MAC. If layer 2 does not yet know the MAC for the switch then it will do an ARP request for the switch.

- it passes the frame to layer 1 which transmits the data on the physical media.

- the switch layer 1 receives the data and passes the frame to layer 2.

- layer 2 verifies that the destination MAC is found on that device and then strips the layer 2 header and passes the packet to layer 3.

- layer 3 verifies that the destination IP address is a local address and then strips the layer 3 header and passes the packet to layer 4.

- layer 4 evaluates the header, strips the header, and based on the destination protocol being 23 will pass the data to the telnet server application.

 

HTH

 

Rick

Silver

Re: can see the neighbors but cant Telnet or ping

CDP works on layer 2 of the OSI model. Both ping and telnet work on layer 3 a.k.a. network layer.

Connect console cable to both 2500 and 2600 router and review your IP configuration. Issue a show ip interfaces brief to see if your interfaces are up.

You can use debug ip icmp to see what happens when you ping your routers.

HTH

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