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Serial interface is up? No ping

Hi,

Please see the below pic. there are two Router  R2 and R3.

I set the IP on R2 and R3 interface is up but no IP address.

R2 Interface Status and PORT. is up

R2#show ip interface brief | include up
Serial0/0                  1.1.1.1         YES manual up                    up

Now I ping from R2 to R2 no ping I want to know why.???

R2#ping 1.1.1.1

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
R2#
RTRSE.jpg

2 ACCEPTED SOLUTIONS

Accepted Solutions
Hall of Fame Super Blue

Re: Serial interface is up? No ping

When you ping a serial interface the ping is actually sent down the P2P link to the remote router and back again. Because you have not set an IP address on R3 when R3 receives the packet it does not know how to send it back because it's serial interface is not in the same subnet as the serial interface on R2.

So you need to assign an IP to R3 serial interface in the same subnet as the IP address on the serial interface on R2.

Jon

VIP Super Bronze

Re: Serial interface is up? No ping

Jon is correct.  When you ping you own IP address on a point-to-point serial interface the ICMP packet goes over the wire to the other side and back. So you need to have an IP address on the same subnet on the other router (r3) in order to ping your own interface (r2).

HTH

Reza

9 REPLIES
Hall of Fame Super Blue

Re: Serial interface is up? No ping

When you ping a serial interface the ping is actually sent down the P2P link to the remote router and back again. Because you have not set an IP address on R3 when R3 receives the packet it does not know how to send it back because it's serial interface is not in the same subnet as the serial interface on R2.

So you need to assign an IP to R3 serial interface in the same subnet as the IP address on the serial interface on R2.

Jon

New Member

Re: Serial interface is up? No ping

Res. Sir,

I want to ping in R2 to R2 not to R3 so no matter to send a ICMP to R3.

R2 want to ping local serail interface so interface is up but cant ping.

R2#sh ip int brief | in up
Serial0/0                  1.1.1.1         YES manual up                    up 

R2#ping 1.1.1.1

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
R2#

VIP Super Bronze

Re: Serial interface is up? No ping

Jon is correct.  When you ping you own IP address on a point-to-point serial interface the ICMP packet goes over the wire to the other side and back. So you need to have an IP address on the same subnet on the other router (r3) in order to ping your own interface (r2).

HTH

Reza

New Member

Re: Serial interface is up? No ping

Yes Sir,

I agreee but why??....if ICMP goes to there then data also can flood....

Hall of Fame Super Silver

Re: Serial interface is up? No ping

I do not understand your concern about allowing IP traffic to go over the serial interface. But Jon and Reza are quite correct that ping over a serial interface is implemented by Cisco to go over the serial lnk and be sent back by the neighbor router. If there is no IP address on the serial interface of the neighbor router then ping will not work.

I also am puzzled why you would configure an IP address on the serial interface of one router but not on the serial interface of the other router. With no IP address on the neighbor router then any IP traffic sent out your serial interface will fail. And if all traffic out the serial interface will fail then why put an IP address on the interface?

HTH

Rick

Re: Serial interface is up? No ping

Abhinay,

Are you using frame relay encap on your circuits ?

If yes, then we need to follow some rules and more configs are expected !

New Member

Re: Serial interface is up? No ping

no any other tech. or protocol using excp. to P2P.

One Router is Connect to ANother Router simple IP set and ping its done.

then remove one IP address from R3 as per diag. and confirm port. and status is must up at both  router.

come in the R2 and ping it self (ping 1.1.1.1) we cant not ping.

Hall of Fame Super Blue

Re: Serial interface is up? No ping

Not sure what else we can say. It's been explained to you that that is how ping works on serial interfaces ie. it must go to the other end of the link and back. That is how it is implemented. So if there is no IP address on the other end ie. R3 then R3 does not know how to send the ping packet back.

So even though R2 serial is up with an IP address you will only be able to ping it from R2 if R3 serial interface is up and has an IP address from the same subnet as R2 serial IP address.

Jon

New Member

Re: Serial interface is up? No ping

John and Reza are right. if you do not beilieve try trace route your own interface, it will go to other end and come back. In your case if fails because there is no ip address on other side.

to confirm, try to assign ip address on both end and traceroute your own ip address.

HTH

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