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For router with route switch processor (RSP), if an IP address is configured for the RSP interface and the IP is pinged, is the ping forwarded to the main CPU (control plane)? Or the CPU of RSP will not forward to the main CPU and reply the ICMP itself?

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  • You say "RSP", several of Cisco's router models use that designation for the RP (Cisco 7500, Cisco 7600, Cisco 12000, ASR 9000), and the behavior is not the same. Which specific platform are you asking about? – Mike Pennington Mar 25 '15 at 10:05
  • @MikePennington I don't have particular models in mind. – Ron Vince Mar 26 '15 at 8:13
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As Mike correctly states, it depends on the specific platform you're asking about. On the 7500, VIP2/VIP4 cards will reply to ICMP packets locally on the VIP. On non-VIP 7500 linecards, the ICMP will be forwarded to the RSP and processed there.
The GSR (Cisco 12000) did all ICMP processing on the linecards, and to be really pedantic only had an "RP" (route processor) and not an RSP (route-switch processor).

On the ASR 9000, ICMP was handled strictly on the linecards.

I don't have enough background on the 7600 to answer authoritatively, but the general answer is that any linecard that has its own CPU and runs its own instance of IOS/IOS-XR would handle ICMP locally on those linecard.

I should say here that to be super super accurate there were almost always some very unique or specific cases where you could force packets to be punted all the way to the main RSP (or RP) but on more recent platforms those cases are more and more rare.

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  • "On non-VIP 7500 linecards, the ICMP will be forwarded to the RSP and processed there.". What kind of cards? – Ron Vince Mar 26 '15 at 10:20
  • The 7500 had two broad types of linecards - the "VIPs" were fully distributed and ran a local copy of IOS on each card and did fully autonomous forwarding. The other (i.e. non-VIP) linecards used the RSP to do all packet forwarding – ljwobker Mar 27 '15 at 16:42

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