IS-IS is very confusing..

• July 28, 2008
• Personal  
• Technology  
• BSCI  
• CCNP  
• IS-IS  

Well, at least some of it. Adjacencies and how IS’s update other IS’s is the thing that nobody can give me an answer to. According to all the material IS’s maintain adjacencies to all others, but still elect a DIS.

When doing the labs on this, the only thing I can see the DIS doing is sending out CSNP’s (Complete Sequence Network PDU’s). The DIS is also sending out hello’s every 3.3 seconds by default. However, LSP (Link State PDU’s (packets)) will get sent from every router that has something to say, directly to all other routers, not the DIS. So its role is somewhat different than a DR/BDR in OSPF.

Also, according to material, the DIS should send out a pseudonode-LSP on behalf of the broadcast medium. I havent seen this on labs either.