BGP Local Preference (LOCAL_PREF)

BGP LOCAL_PREF is the Second BGP attribute if we dive deep into BGP’s algorithm of best path selection followed by aggregate (detailed in my first post in BGP section).  When an AS (autonomous system) has multiple routes to another AS, the LOCAL_PREF indicates the degree of preference for one route over the other routes. The […]

BGP Weight

BGP Weight is the first BGP attribute if we dive deep into BGP’s algorithm of best path selection followed by Local_Preference & aggregate (detailed in my first post in BGP section). Weight is vendor specific (Cisco proprietary) so it is found only on Cisco routers. Weight is always local on a router and it is […]

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 […]

MP-BGP and Address Families

BGP originally only supports normal IPv4 unicast prefixes. With the passage of time & advancement in Network Technology, the need for support of more prefix types arose. There were two solutions to this problem: First, to invent a whole new protocol or a new version of BGP, Second, to add the extra functionality in the […]


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 […]