Tuesday, May 8, 2012

Cisco to Cisco IPsec-manual Decrypt packets - Part 2

Now let's get into decrypting ICMP packets between R1 and R2.

First let's capture some packets between R1 and R2.
  • Right click on the line between R1 and R2
  • Choose R1 f1/0 
  • Click "OK"

Now you should be able to ping across from R1.

  • Right click again on the line between R1 and R2
  • Select Start Wireshark

Notice that the ICMP packets are encrypted and all you see is the ESP. 

  • Click Edit --> Preferences
  • Expand protocols

  • Scroll to ESP
  • Check Attempt to detect/decode encrypted ESP payload
  • Input 2 SA one inbound and one outbound
  • Choose des and hmac-sha
  • Input the session-keys which we manually set earlier in the crypto-map in part 1
  • Click Apply and OK.

Notice that the ESP packets are now gone and you see the encrypted payload which are the ICMP packets.

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