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I have been troubleshooting using ping on both 2600 and 3700 series Cisco routers. The ping is done on interfaces that have status of up, line protocol up. On FastEthernet interfaces, if status is up and line protocol is up, the router can successfully ping the ip address of its own FastEthernet interface. For Serial interfaces, if status is up and line protocol is up, in some cases the router cannot ping its own serial interface IP address.

Can someone give any explanation as to why a ping on the router's own interface should fail for a Serial interface in an up/up state?

R4#show ip interface brief
Interface                  IP-Address      OK? Method Status                Protocol
FastEthernet0/0      YES NVRAM  up                    up
Serial0/0             YES NVRAM  up                    up
FastEthernet0/1            unassigned      YES NVRAM  administratively down down
Serial0/1             YES NVRAM  up                    up

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to, timeout is 2 seconds:
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1 Answer 1

Are the serial interfaces frame-relay? If so, you'll need to map the local interface IP to one of the active DLCIs in order to ping the interface.

interface Serial0/0
 ip address
 frame-relay map ip 102 broadcast
 frame-relay map ip 102
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They are all PPP. All router interfaces are configured encapsulation ppp – T. Webster Apr 19 '13 at 22:09
Any of them PPPoE? I've seem some issues with pinging the local dialer/virtual-template interface for an up/up interface. Can you give us the full router config and specify the ping that doesn't work (via pastebin)? – Keller G Apr 19 '13 at 22:18 – T. Webster Apr 19 '13 at 22:46
the output I get at the terminal is in the EDIT. – T. Webster Apr 19 '13 at 22:46
I've seen instances where PPP interfaces are up/up but they are failing negotiation in some other way, which doesn't allow the interface to become functional. Is this on real hardware or a emulator? What does the other end's interface look like? Does the remote router show up as a CDP neighbor? – Keller G Apr 22 '13 at 20:58

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