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Webcast-Catalyst9k
New Member

Ping Trivia

Hello fellow netpros!

Just want to ask if anyone recalls the technical reason why, in a point-to-point WAN connection between two routers - RouterA and RouterB, pinging the remote WAN IP (say, of RouterB) returns a lower round-trip time than when pinging the local WAN interface (of RouterA) from RouterA itself. I knew that this is normal but I sort of have forgotten the exact explanation.

Appreciate anyone's reply! Many thanks.

RICO

4 REPLIES
New Member

Re: Ping Trivia

Hi.

When you ping your own router interface the ICMP echo packets go to the other end of the link and the router there sends them back. The same happens with the ICMP echo reply packets that your own router generates. This is why it takes twice as long as doing a ping to the router on the other end of the link.

Rgds.

NM

New Member

Re: Ping Trivia

Thanks NM! But why should the echo packets go to the other end instead of going directly to the ping source-address. And speaking of source-address, if we ping the local WAN interface, is it sourced from the Ethernet address or from the same WAN interface's address?

Rgds,

RICO

Gold

Re: Ping Trivia

Because on serial interfaces, you can't hear packets you send--you have to send them to the other end, where they can be reflected back to you. All locally generated packets are sourced from the exit interface towards the destination, so in this case, you will source from the serial interface. You can change this through the extended options in the ping command.

Russ

New Member

Re: Ping Trivia

Many thanks, Russ and NM! I really appreciate your time. :-)

Best regards,

RICO

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