2

Sorry for the newb question, I am trying to figure out how to best link up an subinterface on a Cisco 1921 router, with an external network, by connecting the router and the cable from the external network, to a Cisco Catalyst 2960 switch and isolating them into their own VLAN. The external network recommended I use a 172.A.A.102 255.255.252 for my router IP, and ping 172.A.A.101 on their network. I was able to ping successfully by connecting the external network's cable to my laptop and configuring their IP information, but I cant ping from my router after what I setup:

  1. I created the subinterface for the external network on my router with:

    interface GigabitEthernet0/0.3 encapsulation dot1Q 802 ip address 172.A.A.102 255.255.255.252

  2. On the switch I configured two ports: f0/5 for the router, and f0/6 for the external network cable with:

!
interface FastEthernet0/5 switchport mode trunk spanning-tree portfast !
interface FastEthernet0/6 switchport access vlan 802 switchport mode access spanning-tree portfast But unfortunately I cannot ping 172.A.A.101. Please what am I doing wrong?

Improve this question
4
  • Is the VLAN 802 up? What is the result of a "show vlan" on the switch? Is the interface GigabitEthernet0/0.3 on the router up?
    – JFL
    Commented Jun 26, 2017 at 8:59
  • Yes VLAN 802 is up, show vlan presents 802 VLAN_NAME active Fa0/6, interface is up on the router: GigabitEthernet0/0.3 172.A.A.102 YES manual up up
    – Unpossible
    Commented Jun 26, 2017 at 9:05
  • Wow. Seems to have worked, I can ping the external network IP from the router now. main1#ping 172.31.63.101 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 172.A.A.101, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/4 ms But from the catalyst switch, I can't ping 172.A.A.101 or 172.A.A.102, is this normal?
    – Unpossible
    Commented Jun 26, 2017 at 9:19
  • The switch doesn't have an IP in this network, and it can't since it's a /30 network which allow only 2 IPs - a waste, since the provider could use a /31 for the same result. So yes , it is normal. Glad you found out. You could post what you did as an answer and accept it so the question doesn't pop up for ever.
    – JFL
    Commented Jun 26, 2017 at 9:25

1 Answer 1

Reset to default
1

Actually I did the right thing, I suppose I wasn't patient enough for the switch to start accepting packets. Everything works as expected.

Improve this answer
1
  • you should accept your answer so that the question doesn't keep popping up forever, looking for an answer.
    – Ron Maupin ♦
    Commented Jul 26, 2017 at 9:44

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.