Wireshark Operators

Wireshark is the most useful & popular tool for packet Level deep Network Analysis & Troubleshooting. Most importantly, it is open source. It is like a measuring meter or device to find and examine what is going on inside a network cable or port just like a multimeter is used by an electrician to examine […]


TLV (Type-Length-Value or Tag-Length-Value) is an encoding scheme used for optional information element in a certain protocol. The type and length are fixed in size (typically 1-4 bytes), and the value field is of variable size. Type: It is simply the data being processed, a binary code, often simply alphanumeric, which indicates the kind of field that this […]

IS-IS Levels & Relationships

IS-IS creates flooding boundaries logical by breaking the network into routing domain levels i.e. A level2 routing domain and multiple level1 routing domains. The single Level 2 routing domain could be analogous to OSPF Area0 and multiple Level 1 routing domains are analogous to other OSPF Areas. Basically, IS-IS has two layer hierarchy: Level-2 (the backbone) Level-1 […]

A brief flashback of IS-IS – Part II

Hello PDU’s of IS-IS: IS-IS has three types of Hello PDUs: i. ESH (ES Hello – sent by ES to an IS) ii. ISH (IS Hello – sent by IS to an ES) iii. IIH (IS-IS Hello – sent between two ISs)     Routing Levels Level0: Used to locate end systems Level1: Routing within an area […]

Adjacencies in IS-IS

IS-IS Protocol has two types of nodes (since the roots of IS-IS are based on ISO Connectionless Network Protocol) i.e. IS & ES. ES (End System): A workstation or network host (limited routing capability) IS (Intermediate Systems): Network devices such as routers with full packet-forwarding capabilities. The word intermediate refers to the capabilities of routers as intermediate forwarding or relay […]

Yet another difference b/w IS-IS and OSPF

Neighbour is someone who lives nearby, normally in a house or apartment that is next door or, in the case of houses, across the street. Some neighbors are adjacent while some are not. People form friendships with their neighbours, and help them by sharing their information & tasks. Similarly, in Network & routing world there […]

A brief flashback of IS-IS – Part I

IS-IS is categorised under Link State type of protocols & it is based on Dijkstra Algorithm same as OSPF. Admin Distance defaults to 115 & metric is 10 for all type of links (contrast to OSPF which has different cost for different type of media). It was originally standardized by ISO in 1987 (ISO10589) which was […]