ISIS Continued(Wireshark walkthrough)…..

ISIS Hello has information like as shown below in screen capture. Below are few of them which are frequently used.

  • Circuit type L1 or L2 or L1 and L2 ? In this case it is L1 and L2
  • System ID: This 48 bit value is taken from the NET string we entered (49.0001.0000.0001.00)
  • System ID of DIS
  • Area address, in this case 49.0001
  • IP interfaces associated with the ISIS enabled interface
  • Supported protocols, in this case it is IP. If you have the experience working with Avaya SPBM you would see the protocol supported field as SPBM.


ISIS Hello
ISIS hello

CSNP: This packet has the summarized information of the LSPs the device has and also the remaining lifetime after which LSP would expire. It also has the sequence number like ospf which is used to identify the most valid or new LSP.


LSP: LSP is used to send the complete routing table to other ISIS routers. It has two important components the IP reachability and IS reachability information.

ISIS LSP (Link State Protocol)
ISIS LSP (Link State Protocol)

ISIS LSP Data Unit

The above two images of LSPs are of a single packet, would not accommodate in a single screen to take screen capture.

Thank You. As I have covered some basics of the ISIS till now the next post would cover the implementation of ISIS on Cisco devices.

Here are related ISIS posts : ISIS1, ISIS2 , ISIS Tasks and Solution

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