can not ping the access switch but can putty to it

[q-le]

Hi All,

We have an access 3750 switch connect to the 7K nexus Core - we can putty to it and ping it from other access Cisco switches 

but we cannot ping it from my PC or from any Server.

what tools or commands we can run from the PC or the switch itself to troubleshoot?

Please advise

ThanksQl

[Emmanouil Patiniotakis]

Hello,

is there the necessary routing information for the switch to return traffic to the PCs/Servers?

Another possible cause could be an ACL. 

Enable debug ip icmp at the switch and check if the pings from the PCs arrive. If yes then check the routing for the return path.

Let us know about the results. 

[q-le]

Hi,

Turn on debug and ping from my PC (172.17.53.125) to switch (172.18.111.148) and I get

the following result:

Sep 24 09:40:38.735 AEST: ICMP: echo reply sent, src 172.18.111.148, dst 172.17.                                                     53.125, topology BASE, dscp 0 topoid 0
Sep 24 09:40:43.286 AEST: ICMP: echo reply sent, src 172.18.111.148, dst 172.17.                                                     53.125, topology BASE, dscp 0 topoid 0
Sep 24 09:40:48.283 AEST: ICMP: echo reply sent, src 172.18.111.148, dst 172.17.                                                     53.125, topology BASE, dscp 0 topoid 0

Can you please explain what the result means? and how to fix it.

Thanks

Ql

[Richard Burts]

Ql

The output of debug confirms that the ping from your PC was received by the switch and that the switch (172.18.111.148) is sending a response to your PC (172.17.53.125). If the response does not get to your PC then something has happened to the ping response packet.

Can you help us understand the topology of this network? Your PC connects to what? The devices between your PC and this access switch are what?

Perhaps it would be helpful to do a traceroute from the access switch to your PC. If the traceroute does complete it will show us the devices along the data path and help us know what we might need to investigate. If the traceroute does not complete then it will identify the last successful device and that will help us know what we need to investigate further.

HTH

Rick

[q-le]

Hi  Rick,

Please see below:

For ease of configuration.
I used my server (172.18.100.191) to ping switch(172.18.111.148) because my PC is on a remote site.
The topology is a simple star network.
Access switch(172.18.111.148) connect to Core(172.18.111.1 or 172.18.111.2 HSRP run here) and the server is connect to the Core.

Tracerouter from the access switch to the server result:
172.18.111.148#traceroute 172.18.100.191
Type escape sequence to abort.
Tracing the route to 172.18.100.191

  1  *  *
    172.18.111.1 0 msec
  2 172.18.100.191 0 msec 0 msec *

ping is not successfully from Access switch:
172.18.111.148#ping 172.18.100.191

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.18.100.191, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)

CRT-01(CORE)# ping 172.18.100.191
PING 172.18.100.191 (172.18.100.191): 56 data bytes
64 bytes from 172.18.100.191: icmp_seq=0 ttl=126 time=1.158 ms
64 bytes from 172.18.100.191: icmp_seq=1 ttl=126 time=0.583 ms
64 bytes from 172.18.100.191: icmp_seq=2 ttl=126 time=0.537 ms
64 bytes from 172.18.100.191: icmp_seq=3 ttl=126 time=0.571 ms
64 bytes from 172.18.100.191: icmp_seq=4 ttl=126 time=0.607 ms

--- 172.18.100.191 ping statistics ---
5 packets transmitted, 5 packets received, 0.00% packet loss
round-trip min/avg/max = 0.537/0.691/1.158 ms

CRT-01(CORE)# traceroute 172.18.100.191
traceroute to 172.18.100.191 (172.18.100.191), 30 hops max, 40 byte packets
 1  hastings.com (172.18.100.191) (AS 640)  0.519 ms  0.464 ms  0.385 ms
CRT-01(CORE)# traceroute 172.18.100.191
traceroute to 172.18.100.191 (172.18.100.191), 30 hops max, 40 byte packets
 1  hastings.com (172.18.100.191) (AS 640)  1.193 ms  0.621 ms  0.565 ms

Ping and tracert result from Server(172.18.100.191) to access switch (172.18.111.148):

C:\Users\ql>ping 172.18.111.148

Pinging 172.18.111.148 with 32 bytes of data:
Request timed out.
Request timed out.
Request timed out.
Request timed out.

Ping statistics for 172.18.111.148:
    Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),

C:\Users\ql>tracert 172.18.111.148

Tracing route to comvision.com [172.18.111.148]
over a maximum of 30 hops:

  1    <1 ms    <1 ms    <1 ms  172.18.100.2
  2     *        *        *     Request timed out.
  3     *        *        *     Request timed out.
  4     *     ^C
C:\Users\ql>

Tahnks

Ql

[q-le]

Hi Rick,

Our Core is  2 x cisco Nexus7000 C7009 ios version 6.1(3).

and we think maybe there is some weird issues with this IOS version and vpc.

Any suggestion is much appreciated.

Thanks

[Richard Burts]

Ql

I find it especially odd that traceroute from the access switch does get through and get a response but that the ping fails. The traceroute from the switch is using UDP packets while ping is using ICMP. I do not have an explanation of why the core seems to have issues with the ICMP but not with UDP. Perhaps it is something with the code?

HTH

Rick