Home » Mounir Mohamed

Mounir Mohamed

Over a decade of experince in networking business, ranging from service provider to networking vendors, Specialized in IP routing protocols and MPLS applications. CCIE(SP&RS) and JNCIE-SP.

IS-IS DIS in Practice

In the previous post IS-IS Neighbor Discovery we have discussed how IS-IS automatically discovers neighbors, in this post we will discuss the DIS role in broadcast networks. After the adjacency state reached the UP state the DIS election process take place, the router with the highest priority value (0-127 specified in the Priority field of the IIH PDU) win the election, if multiple routers have the same priority which is the case in most scenarios due to the default value “64” of most implementations, the router with the highest SNPA (MAC address discovered from the MAC header of the received …

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IS-IS Neighbor Discovery

Like other routing and signaling protocols IS-IS has built-in automatic neighbor discovery mechanism which is known by IIHs (IS-IS Hello PDUs), because IS-IS is not IP based protocol the IIH PDUs and all other IS-IS PDUs are directly encapsulated on the data-link layer. IS-IS has two hierarchical levels (L1 and L2) and two network types (Point-to-Point and Broadcast) so it’s essential to have different types of hello messages or PDUs for serve these networks since the data-link layer for broadcast and P2P links have different style of addressing so they need different treatment, due to this differences  there are three …

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IS-IS MTU Mismatch

IS-IS is a link-state routing protocol, it uses the concept of distributed map/database and local computation , each router originates an LSP to describes himself , this LSP carries links and topological information, reach router on the domain generates its own LSP and relays other routers LSPs untouched (With respect to the Level that the LSP originated in) this information is used to build up the distributed map, a local computation is then performed on the database to extract IP reachability information to formalize the forwarding plane. What is the problem? IS-IS is an extended protocol by nature, Initially it …

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BGP 4-Byte ASN

The internet growth is awesome, day by day people recognizes how  internet is important in their daily personal  and business life and even for their culture, so the internet has a good bit of newbie everyday which depleted some internet resources such as IPv4 address space and the BGP AS numbers (IPv4 exhaustion dilemma is more severe than the BGP ASN dilemma). The BGP AS number space is a finite amount of address space. It is defined as a 16 bit integer and hence limited to 65535 unique AS numbers. Not all can be used!! Out of the AS number …

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MPLS Special Labels

MPLS label range from 0 to 1,048,575 (configurable on Cisco IOS) Labels 0 through 15 are reserved labels. An LSR cannot use them in the normal case for forwarding packets, the labels from 16 through 1,048,575 are used for normal packet forwarding. In Cisco IOS, the default range is 16 through 100,000. This number is more than enough for labeling all the IGP prefixes in large routing table, but in very large scale networks this number might be insufficient, so we can change the label range with the mpls label range min max command LSR1(config)#mpls label range ? <16-1048575>  Minimum …

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Static Routes Label Binding

In this post we will be discussing the label binding for static routes and the forwarding of labeled packets destined to these destinations. IP routing protocols build the IP routing table, and each LSR assigns a label to every destination in its IP routing table independently (Independent LSP Control – Connected, static or learned dynamically via IGP) , afterwards the LSRs announce their assigned labels to all other LSRs (Unsolicited Downstream Label Distribution), then every LSR receives the label binding information from the downstream LSRs and store it in the LIB table (Liberal Label Retention Mode), then each LSR picks …

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