Changes between Version 49 and Version 50 of GENIExperimenter/Tutorials/ClickExample/Execute


Ignore:
Timestamp:
07/16/14 14:58:16 (5 years ago)
Author:
sedwards@bbn.com
Comment:

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  • GENIExperimenter/Tutorials/ClickExample/Execute

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     360=== Monitoring your core network ===
     361
     362Let's watch how the packets travel through the network.
     363
     364
     365i. In a local terminal type:
     366{{{
     367#!div style="background: #ffd; border: 3px ridge; width: 685px;"
     368   {{{
     369ssh -A top "tail -f /tmp/click.log"
     370   }}}
     371}}}
     372
     373ii. Go to your window for '''hostA''', where your '''nc''' command is still running. Type a message into this window. You should see a log message in three of your four router windows.
     374{{{
     375#!div style="background: #ddf; border: 2px ridge; width: 685px;"
     376   {{{
     377[mberman@hostb ~]$ nc -ul 24565
     378your message here
     379   }}}
     380}}}
     381iii. In the local terminal you will see:
     382{{{
     383#!div style="background: #ffd; border: 3px ridge; width: 685px;"
     384  {{{
     385outR:   76 | 000423b7 192e0004 23b71ce0 7744416c 69636557 61734865
     386  }}}
     387}}}
     388  This log entry says that the '''top''' router received a packet from '''hostA''', modified it, and sent it out to the '''right''' router. If the entry started with '''outL''', that would indicate that it sent the packet out to the '''left''' router. Let's look a bit at the start of the packet (the first 24 bytes are logged). It starts with an Ethernet header. The first six bytes are the MAC address of the destination interface, that's 00:04:23:B7:19:2E, the MAC address of '''eth4''' on '''right'''. The next six bytes are the MAC address of the source interface, 00:04:23:B7:1C:E0, or '''eth4''' on '''top'''. Next comes your ether type, 0x7744. The remaining bytes, "416c 69636557 61734865" are the start of the first field in your new protocol, "!AliceWasHe" in ASCII.
     389
     390iv. Try typing a few different lines to '''hostA'''.
     391{{{
     392#!div style="background: #ddf; border: 2px ridge; width: 685px;"
     393   {{{
     394[mberman@hostb ~]$ nc -ul 24565
     395four score
     396and
     397seven years
     398ago
     399   }}}
     400}}}
     401v. In the local terminal you should see some packets routed to the left and some to the right. The routing decision is based on the '''route :: Classifier(27/01%01,-);''' entry in the '''top''' router configuration. Here, the router is looking at the low-order bit of the checksum on the initial IP packet (now at byte position 27 with the addition of the new sixteen byte field at the start of the header). Packets with odd checksums go to the left; those with even checksums go right.
     402
     403
     404
    360405= [wiki:GENIExperimenter/Tutorials/ClickExample/Finish Next: Teardown] =