Netflow evolution

The term netflow is very confusing. Because it means two different things. It means first the exporting process and also the metering process. When we speak about traditional netflow, flexible netflow or metric mediation agent that is for metering. When we speak about netflow v5, v9 or IPFIX that is just protocol for exporting the  Full Article…

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Netflow overview

Netflow classify packets arriving to device interface into the flows and once a flow has ended or reached maximum limit it is exported to the collector. So with flows you have a view of everything what is happening in your network. How the router classify the flows? Based on key attributes which are for example  Full Article…

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VRF, Route Distinguisher, Route Target

VRF means Virtual Routing Forwarding and it allows you to create more than one routing tables inside one physical routers, hence creating many virtual routers. You can then assign specific interfaces to related VRFs. The Route-Distinguisher (RD) & Route-Target (RT) are two different concepts that are both used in an MPLS VPN. The RD is  Full Article…

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MPLS L3 VPN

Here are basic steps how to configure MPLS L3 VPN: Configure IGP inside SP Core Configure MPLS LDP inside SP Core Create VRF, RD and RT for customer Configure VPNv4 peering between PE routers Configure routing between PE and CE – you provide whatever customer requires here (OSPF, static, BGP, ISIS, RIP,…) Configure redistribution on  Full Article…

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Introduction to EIGRP

To be completed…

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EIGRP over NBMA

NBMA is for most network engineers „cloudy“ concept. Lets review little bit  what it is. When we talk about NBMA in cisco world you are most probably refering to Frame relay network. Not because Frame relay is the best technology or newest, but its kind of the foundation technology. To have some overview read the  Full Article…

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IPv6 Address Types

Unicast – One to One Multicast – One to Many Anycast – new concept and means One to Nearest (based on routing) In IPv4 broadcasts caused problems like interupts in every node in network and in some cases triggering broadcast storms. BC is not anymore used in IPv6 instead multicast is used. IPv6 Global unicast  Full Article…

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Interface identifiers in IPv6

Interface identifiers (IDs) are used to uniquely identify interface on a link. To be unique on a link is a requirement. They can be unique also at a global scope. When interface ID is derived directly from the data link layer address of a interface, the scope is assumed to be globally unique. IDs are  Full Article…

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Virtual links

OSPF two layer hierarchy requires that every non backbone area must connect to backbone area to be able to communicate with other areas. Virtual link is a link that allows discontiguous areas 0 to connect together. Or to to connect non backbone area to backbone area via transit area. The OSPF virtual link feature should  Full Article…

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passive-interface in OSPF

Passive-interface command can be used with all routing protocols except BGP. In general, it prevents from sending the routing updates but it behaves differently in every routing protocol. In OSPF the specified interface appears as a STUB network in OSPF domain and OSPF information is neigher sent nor received through the specified interface. When you  Full Article…

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OSPF Metric Calculation

OSPF use cost as a metric. On Cisco routers cost is nothing more than calculated cumulative bandwidth on the path from source to destination. However we are just using bandwidth, there is a formula for calculating the cost. The lower the metric the better the path. More bandwidth means better right? Thats why the formula  Full Article…

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OSPF over NBMA an overview

OSPF over NBMA is weird. You will see 😉 We must know some foundation concept to know how this weirdness works. So lets hop into it OSPF supports many network types like: Broadcast, multi access networks Ethernet, Token ring single operation mode DR/BDR election, 10 sec hellos Point-to-Point networks T1, ISDN BRI/PRI single operation mode  Full Article…

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Structure of the OSPF packet

OSPF packet is solely encapsulated by IP and data-link headers. OSPF does not define a way to fragment its protocol headers, IP fragmentation is used when large DBD needs to be send over medium. OSPF can use multicast. OSPF is IP protocol number 89. Two distinct IP addresses are used: ALLSPFRouters – 224.0.0.5, All OSPF routers  Full Article…

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OSPF area concept

In small networks, there not too much routers, there are not too much updates, the LSDB is small so the Djisktra calculation is quick and it doesn’t consume much resources. However in huge networks we can face precise opposite situation: Frequent SPF algorithm calculations – in large networks, changes are inevitable. So the OSPF consume  Full Article…

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Introduction to OSPFv2

OSPF is one of the most commonly used routing protocol nowadays. It is an OPEN standard protocol, so you can read everything about it in RFC2328. I recommend to look at it if you have problem to grab facts and are still asking why it behaves like this. Or read my blog and maybe it  Full Article…

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MPLS LDP troubleshooting

When your MPLS neighbors are not forming the neighborship, you may have these possible issues: MPLS IP not enabled on interface protocol missmatch (TDP, LDP globaly or at interface level) higher loopback ID is taken as a router ID which is not advertised via IGP missmatch authentication if configured filtering udp port 646 for LDP  Full Article…

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Penultimate Hop Popping (PHP)

Penultimate Hop Popping optimizes MPLS performance by removing the requirement for double lookup to be performed on PE router. The LIB table will show the value of imp-null. When PHP is turned on the penultimate router remove the label (POP) from the packet if he sees that the destination packet is directly connected for the  Full Article…

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MPLS Packet flow and label distribution protocol

First the router build routing table for IGP routing in MPLS domain and put it to FIB in CEF Every LSR assign a local label for each route learned Every LSR assign implicit null label for its local connected interface networks. Every LSR will share its label with its direct neighbors using LDP Every LSR  Full Article…

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Configuring MPLS LDP inside SP Core

Pre-requirements CEF must be enabled – without CEF the MPLS just doesnt work IGP routing – for router to be able to map label to network the route must exist in routing table for that network. Router build from routing table the FIB in CEF and once you configure label binding it will configure also  Full Article…

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MPLS labels

MPLS label got 4 bytes and is inserted between L2 and L3. It encapsulates the L2 frame. the first 20 bits is label itself, which is assigned to each packet. next 3 bites is EXP filed which contain QoS or IPPresence values. next one bit is bottom of stack indicator. This indicates if the label  Full Article…

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