Ping only works on extended ping with different vlan

Answered Question
Aug 22nd, 2012
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Hi all,


My ping works using extended vlans but not when I ping from the switch (ip 192.168.77.129)


3750#ping

Protocol [ip]:

Target IP address: 192.168.2.16

Repeat count [5]:

Datagram size [100]:

Timeout in seconds [2]:

Extended commands [n]: y

Source address or interface: vlan 888

Type of service [0]:

Set DF bit in IP header? [no]:

Validate reply data? [no]:

Data pattern [0xABCD]:

Loose, Strict, Record, Timestamp, Verbose[none]:

Sweep range of sizes [n]:

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 192.168.2.16, timeout is 2 seconds:

Packet sent with a source address of 192.168.81.1

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 1/3/8 ms


Now clearly the routing to and from source to destination device is correct for this ping to work from the switch so why not for 192.168.77.129? Please advise.

Correct Answer by Alessio Andreoli about 4 years 12 months ago

Hi Zahan,

to verify connectivity you should use:


ping 192.168.2.16 source vlan 888


and the same test with other IP addresses. I would say you should understand with which source IP the ICMP is encapsulated and checking if this IP is properly routed. In this case, when in your extended ping you specify vlan 888 the source address will be the ip address you stated in


int vlan 888

ip address 192.168.81.1 255.255.255.0


If you understand which ip address the switch use as source ip address when you do NOT specify anithing (like vlan 888) you can easily find out your issue


Take Care

Alessio

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Correct Answer
Alessio Andreoli Wed, 08/22/2012 - 05:09
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Hi Zahan,

to verify connectivity you should use:


ping 192.168.2.16 source vlan 888


and the same test with other IP addresses. I would say you should understand with which source IP the ICMP is encapsulated and checking if this IP is properly routed. In this case, when in your extended ping you specify vlan 888 the source address will be the ip address you stated in


int vlan 888

ip address 192.168.81.1 255.255.255.0


If you understand which ip address the switch use as source ip address when you do NOT specify anithing (like vlan 888) you can easily find out your issue


Take Care

Alessio

Zahan Al-Rashid Wed, 08/22/2012 - 05:24
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Thanks for your response.


Your right, if I specify the source address as 192.168.77.129 ping also works. so it appears that this address was not being used to ping by default. is there anyway to know which IP address the switch assumes when pinging?


thanks for your assist.

Alessio Andreoli Wed, 08/22/2012 - 05:37
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Difficult question

I would issue


show cdp nei det


from a cisco device directly connected!!!


Take Care


Alessio

cadet alain Wed, 08/22/2012 - 06:27
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Hi,


sh ip route x.x.x.x and recursion will tell you which address is used if there ain't no PBR overriding the routing behaviour.


Regards.


Alain


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