Pinging Issue

Answered Question
Nov 12th, 2007

I am trying to communicate to my 2621XM router from my 3620 router by serial cable, and I am getting this result:

"

eastrouter#ping 200.100.11.6

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 200.100.11.6, timeout is 2 seconds:

.!.!.

Success rate is 40 percent (2/5), round-trip min/avg/max = 28/28/28 ms

eastrouter#ping 200.100.11.6

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 200.100.11.6, timeout is 2 seconds:

!.!.!

Success rate is 60 percent (3/5), round-trip min/avg/max = 28/29/32 ms

eastrouter#

"

I can telnet from the 3620 to the 2621XM.

I have doublechecked my DCE clockrate & "no shutdown" in my interfaces and I have ruled these out.

Please have a look at the extract of the pinging result that I have pasted, I would be greatful for any help.

Regards

Bob.

I have this problem too.
0 votes
Correct Answer by Richard Burts about 9 years 2 weeks ago

Bob

I do not believe that erasing startup-config is necessary. I suspect the problem is in the way that you are attempting to change the addresses. When you try to change the mask are you getting an error message about invalid mask? If so the reason is that the IP address you are attempting to configure on the interface is either the subnet address or is the subnet broadcast address. If that is not the issue then can you tell us what you are trying to configure and what error message you get when you try to change the config?

To make this discussion a bit easier can you post the addressing that you are trying to use on both serial interfaces and the addressing of the devices connected on each of the serial interfaces? They perhaps we can help you choose and implement addresses that will work?

HTH

Rick

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Richard Burts Mon, 11/12/2007 - 14:33

Bob

What you are showing here is a classic example of what happens when the router believes that it has 2 paths that get to the destination but only 1 of the paths works correctly. would you post the output of show ip route 200.100.11.6 ? I am guessing that there will be 2 paths.

HTH

Rick

bvsnarayana03 Tue, 11/13/2007 - 00:09

Rick is right. I encountered it many a times. There are 2 paths for ur switch, while only 1 is active or reachable.

"sh ip route 200.100.11.6" will confirm.

reb999000 Tue, 11/13/2007 - 09:51

Rick & bvsnarayana03,

I have went into my 2621XM router which it's hostname is called "southrouter" and I done "show ip route 200.100.11.6" and got this result and pasted this below:

"

southrouter#show ip route 200.100.11.6

Routing entry for 200.100.11.0/24

Known via "connected", distance 0, metric 0 (connected, via interface)

Redistributing via rip

Advertised by rip

Routing Descriptor Blocks:

* directly connected, via Serial0/0

Route metric is 0, traffic share count is 1

southrouter#

"

I look forward to your reply fellows,

Many Thanks

Regards

Bob.

Richard Burts Tue, 11/13/2007 - 10:12

Bob

Thanks for the additional information. If southrouter does not have 2 paths then perhaps the other router does. Can you post the output of show ip route from the other router (and perhaps the output of show ip route from this router so we can see the complete table).

HTH

Rick

reb999000 Tue, 11/13/2007 - 11:00

Rick,

I have went into my 3620 router which is called "eastrouter" and placed the "show ip route" and recieved this result:

"

eastrouter#show ip route

Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP

D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP

i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area

* - candidate default, U - per-user static route, o - ODR

P - periodic downloaded static route

Gateway of last resort is not set

C 200.100.11.0/24 is directly connected, Serial1/0

is directly connected, Serial1/1

eastrouter#

Regards

Bob.

Richard Burts Tue, 11/13/2007 - 11:21

Bob

Thanks for the additional information. The symptom still looks like some device has more than one path that it is trying to use. Could you post the output of show ip interface brief and of show cdp neighbor detail from both routers?

HTH

Rick

Richard Burts Tue, 11/13/2007 - 11:28

Bob

After posting my response I took a closer look at what you posted and see that I overlooked something very important. Here is part of what you posted:

C 200.100.11.0/24 is directly connected, Serial1/0

is directly connected, Serial1/1

eastrouter#

note that eastrouter believes that the subnet is directly connected on serial1/0 and believes that the subnet is also directly connected on serial1/1. There are the 2 paths that we are talking about. eastrouter is sending one packet to serial1/0, the next to serial1/1, the next to serial 1/0, and so on.

Perhaps you can post the configuration of serial 1/0 and of serial 1/1? I believe that this will show us what is causing the confusion.

HTH

Rick

reb999000 Wed, 11/14/2007 - 09:52

Rick,

this is the output from "show interface brief" which I done on both routers:

"

eastrouter#show ip interface brief

Interface IP-Address OK? Method Status Protocol

BRI0/0 unassigned YES NVRAM administratively down down

FastEthernet0/0 unassigned YES NVRAM administratively down down

BRI0/0:1 unassigned YES unset administratively down down

BRI0/0:2 unassigned YES unset administratively down down

Serial1/0 200.100.11.4 YES NVRAM up up

Serial1/1 200.100.11.7 YES NVRAM up up

Serial1/2 unassigned YES NVRAM administratively down down

Serial1/3 unassigned YES NVRAM administratively down down

eastrouter#telnet 200.100.11.6

Trying 200.100.11.6 ... Open

User Access Verification

Password:

southrouter>

southrouter>en

Password:

southrouter#show ip interface brief

Interface IP-Address OK? Method Status Protocol

FastEthernet0/0 unassigned YES NVRAM up down

Serial0/0 200.100.11.6 YES NVRAM up up

BRI0/0 unassigned YES NVRAM administratively down down

BRI0/0:1 unassigned YES unset administratively down down

BRI0/0:2 unassigned YES unset administratively down down

FastEthernet0/1 unassigned YES NVRAM administratively down down

southrouter#

Regards

Bob.

reb999000 Wed, 11/14/2007 - 10:00

Rick,

This is the output from "show cdp neighbours detail" from both routers:

"

southrouter#show cdp ne

southrouter#show cdp neighbors detail

-------------------------

Device ID: eastrouter

Entry address(es):

IP address: 200.100.11.7

Platform: cisco 3620, Capabilities: Router

Interface: Serial0/0, Port ID (outgoing port): Serial1/1

Holdtime : 161 sec

Version :

Cisco Internetwork Operating System Software

IOS (tm) 3600 Software (C3620-I-M), Version 12.2(5d), RELEASE SOFTWARE (fc1)

Copyright (c) 1986-2002 by cisco Systems, Inc.

Compiled Sat 02-Feb-02 01:51 by kellythw

advertisement version: 2

southrouter#logout

[Connection to 200.100.11.6 closed by foreign host]

eastrouter#show cdp nei

eastrouter#show cdp neighbors detail

Device ID: southrouter

Entry address(es):

IP address: 200.100.11.6

Platform: Cisco 2621XM, Capabilities: Router Switch IGMP

Interface: Serial1/1, Port ID (outgoing port): Serial0/0

Holdtime : 140 sec

Version :

Cisco IOS Software, C2600 Software (C2600-ENTBASE-M), Version 12.4(5), RELEASE SOFTWARE (fc3)

Technical Support: http://www.cisco.com/techsupport

Copyright (c) 1986-2005 by Cisco Systems, Inc.

Compiled Mon 31-Oct-05 20:06 by alnguyen

advertisement version: 2

VTP Management Domain: ''

eastrouter#

Regards

Bob.

Richard Burts Wed, 11/14/2007 - 10:15

Bob

We have clear evidence here of the fact that there the router believes that it has 2 paths to the destination:

Serial1/0 200.100.11.4 YES NVRAM up up

Serial1/1 200.100.11.7 YES NVRAM up up

If you want absolute proof you can do show ip route 200.100.11.6 on eastrouter and I believe that it will show that it can get to that address using serial 1/0 and also using serial 1/1. This is the explanation of the odd ping performance. Probably the easy fix for this is to change the subnet mask on the interfaces from /24 to /30.

HTH

Rick

bhallanaveen Thu, 11/15/2007 - 00:44

Hi Bob,

Try doing traceroute to 200.100.11.6 from eastrouter. This should show two next hops for each packet. Also please send configuration of both the interfaces Serial1/0 & Serial1/1 of eastrouter. From show CDP output, I understand that Serial1/0 has been assigned IP Address which is not required on it.

Thanks

NaveB

reb999000 Thu, 11/15/2007 - 09:14

NaveB,

I have placed the out put of "eastrouter#traceroute 200.100.11.6"

"

eastrouter#traceroute 200.100.11.6

Type escape sequence to abort.

Tracing the route to 200.100.11.6

1 200.100.11.3 36 msec 32 msec 16 msec

2 200.100.11.2 28 msec

00:02:06: %LINK-3-UPDOWN: Interface Serial1/1, changed state to up

00:02:07: %LINEPROTO-5-UPDOWN: Line protocol on Interface Serial1/1, changed state to up200.100.11.4 32 msec *

3 * * *

4 * * *

5 * * *

6 * * *

7 * * *

8 * * *

9 * * *

10 * * *

11 * * *

12 * * *

13 * * *

14 * * *

15 * * *

16 * * *

17 * * *

18 * * *

19 * * *

20 * * *

21 * * *

22 * * *

23 * * *

24 * * *

25 * * *

26 * * *

27 * * *

28 * * *

29 * * *

30 * * *

eastrouter#

Regards

Bob.

Richard Burts Thu, 11/15/2007 - 09:37

Bob

If this discussion is going to continue then please do show ip route 200.100.11.6 on eastrouter and post the output.

HTH

Rick

reb999000 Thu, 11/15/2007 - 09:53

Rick,

I have placed the out put of "eastrouter#show ip route 200.100.11.6"

"

eastrouter#show ip route 200.100.11.6

Routing entry for 200.100.11.0/24

Known via "connected", distance 0, metric 0 (connected, via interface)

Redistributing via rip

Advertised by rip

Routing Descriptor Blocks:

* directly connected, via Serial1/0

Route metric is 0, traffic share count is 1

directly connected, via Serial1/1

Route metric is 0, traffic share count is 1

eastrouter#

"

As I have changed the ip address on southrouter to 200.100.11.6 255.255.255.252

Regards

Bob.

Richard Burts Thu, 11/15/2007 - 10:00

Bob

You are on the right track to change the mask on southrouter to /30 but it is not enough. The real problem is on eastrouter. As long as both serial1/0 and serial1/1 have /24 masks the router will believe that it has 2 paths to 200.100.11.6 and your ping problem will continue. What you need to do is to change the mask on both serial interefaces on eastrouter.

HTH

Rick

reb999000 Thu, 11/15/2007 - 10:12

Rick,

I may have to "erase start-up config" on eastrouter and reconfigure the NVRAM for /30 addresses, as the current NVRAM is not accepting the /30 addresses. I know there is a quicker way around this.

Bob.

Correct Answer
Richard Burts Thu, 11/15/2007 - 10:26

Bob

I do not believe that erasing startup-config is necessary. I suspect the problem is in the way that you are attempting to change the addresses. When you try to change the mask are you getting an error message about invalid mask? If so the reason is that the IP address you are attempting to configure on the interface is either the subnet address or is the subnet broadcast address. If that is not the issue then can you tell us what you are trying to configure and what error message you get when you try to change the config?

To make this discussion a bit easier can you post the addressing that you are trying to use on both serial interfaces and the addressing of the devices connected on each of the serial interfaces? They perhaps we can help you choose and implement addresses that will work?

HTH

Rick

reb999000 Sat, 12/08/2007 - 03:37

Rick,

I am only restricting the use of RIP/RIPv2 on the 2500 series routers as the /24 & /30 addresses communicates very well using RIPv2 as this supports VLSM.

Thank you very much for all your help!

Regards

Bob.

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