ping 8.8.8.8 What is the source IP?

[JustTakeTheFirstStep]

Switch is using a loopback IP and multiple VLANs.
All VLANs are pingable as next hops.
If ping to an external DNS, what is the source IP?

[MHM Cisco World · Accepted solution]

Nearest interface to destination SW use it IP

Mostly is the IP of interfaces use in default route

MHM

[Joseph W. Doherty · Accepted solution]

On a L3 switch, correct?

If so, its default is as already noted by @MHM Cisco World , i.e. the switch's egress interface IP.

BTW, some services, e.g. FTP, support a configuration command to designate a source IP.  This overrides, the above, default behavior.  (Don't recall this being a config option for ping, but I recall a switch's ping may support a source option.)

[Martin L · Accepted solution]

To add, U can check show ip cef  also/and/or using show ip route 

also, u can try debug ip icmp  

Regards, ML
**Please Rate All Helpful Responses **