ISIS Authentication types (packet captures)
In this post i would like to highlight a couple of “features” of ISIS.
More specifically the authentication mechanism used and how it looks in the data plane.
I will do this by configuring a couple of routers and configure the 2 authentication types available. I will then look at packet captures taken from the link between them and illustrate how its used by the ISIS process.
The 2 types of Authentication are link-level authentication of the Hello messages used to establish an adjacency and the second type is the authentication used to authenticate the LSP’s (Link State Packet) themselves.
First off, here is the extremely simple topology, but its all thats required for this purpose:
Simple, right? 2 routers with 1 link between them on Gig1. They are both running ISIS level-2-only mode, which means they will only try and establish a L2 adjacency with their neighbors. Each router has a loopback interface, which is also advertised into ISIS.
First off, lets look at the relevant configuration of CSR-02 for the Link-level authentication:
key chain MY-CHAIN key 1 key-string WIPPIE ! interface GigabitEthernet1 ip address 10.1.2.2 255.255.255.0 ip router isis 1 negotiation auto no Continue reading


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