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can see the neighbors but cant Telnet or ping

Unanswered Question
Nov 21st, 2005
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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.

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spremkumar Mon, 11/21/2005 - 02:50
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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..


benetxpert Mon, 11/21/2005 - 02:59
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Router 1700 :e0, ip address:

Router 2500 :e0, ip address:

Router 2600: f0/0, ip address:

martin_tsang Mon, 11/21/2005 - 03:06
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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, so unless you have set the subnet mask to, you wont get layer 3 connectivity.

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

Good luck

spremkumar Mon, 11/21/2005 - 03:08
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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.,, 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..


leonvd79 Mon, 11/21/2005 - 02:52
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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.



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