This article will focus on the LDP protocol. Although this protocol is quite simple, I often had some doubts about some LDP Junos commands and behaviours. This is the aim of this new article: clarify basic LDP stuffs.
To speak about LDP configuration on Junos, we will use this very simple and atypical topology. The IGP is OSPF (a single area) and LDP is activated only on physical interfaces.
In this article we will configure an ISIS multi-area network and also explain some part of the ISIS theory.
For network guys ISIS is not a goddess in Ancient Egyptian religious beliefs but rather, the Intra Domain routing protocol specified by the IEC and then extended by the IETF.
IS-IS was first developed for the DECNET project Phase V by ISO:IEC. It was the first Intra AS (Autonomous System) network protocol, but only for network equipment that supported the OSI model and thus a CLNP stack (CLNS systems) : Connectionless Network Protocol. IS-IS was not designed by default for IP. The first version was published in 1987: ISO10589, then a second version in 2002 : ISO10589:version 2. At the beginning of the 90th : the IETF ISIS Working Group specified IP support for ISIS in RFC 1195. Other RFCs after that have been published to enrich the RFC 1195. IP support for IS-IS is also referred to as Integrated IS-IS. ISIS stack’s :
- IS-IS is conveyed directly at Layer 2
- Even though IS-IS was not initially designed for IP, it provides a simple way to add new extensions by using TLV (Type Length Value) fields.
- Indeed, ISIS data is conveyed by using the TLV method : That was the case for IPv4 and then IPv6 extension and recently for SPB. The concept is: Just adding new TLVs for a new protocol family and If you don’t support a given TLV just silently ignore it. Note: TLV has been also extended with sub-TLV.
The Basis :
In the whole article we’ll speak about:
- IS: Intermediate System (This is the router)
- Circuit: it’s a link between 2 IS
- Neighbor: a directly connected IS on a Circuit
- LSP: Link State PDU (packets that transport the IS-IS database of a router)
- Adjacency: IS-IS “session” established between 2 IS directly connected allowing LSP exchanges.
- Point to Point (P2P) link: implicit P2P link like for example Sonet or Frame Relay (not multipoint) but also a multipoint link (Ethernet) configured explicitly in Point to Point (useful when only 2 routers are connected on an Ethernet segment).
- Pseudo-Node: One specific router on a LAN.
- Area : Like OSPF, this is a group of routers that are in the same ISIS flooding domain.
- Level : Hierarchical level. Only 2 Levels in IS-IS
- Leaking : ISIS routes leaked from an IS-IS level to another.
- Redistribution : Injected routes into IS-IS (coming from other protocols: static, RIP, BGP…)