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2.2 IPv4 Routing

OSPF LSAs

1. LSA components Sequence number InitialSequenceNumber = 0x80000001 MaxSequenceNumber= 0x7FFFFFFF When MaxSequnceNumber is reached, and a new update must be sent, the LSA is flushed by setting the Age to MaxAge and reflooding it over all adjacencies. Then, a new version of the LSA is sent with sequence number set …

OSPF Areas

Areas are identified by a 32 bit Area ID. This can be represented as a number in decimal or in dotted decimal format. Area 0 (0.0.0.0) is reserved for backbone. The backbone is responsible for summarizing the topologies of each area to every other area => all inter-area traffic must …

OSPF 101

1. Starting the routing process OSPF can be configured inside the routing process or on the interface. Even a combination of those will be a valid option. The interface configuration will override the routing process configuration. 1.1 Inside the routing process R(config)# router ospf PROCESS R(config-router)# network NETWORK-ADDR WILDCARD area …

More EIGRP Features

1. Router ID The router ID is a 32 bit number, usually represented as a dotted decimal (like an IP address). The Router ID is determined when the routing process is started by the following algorithm: Use the configured value R(config-router)# eigrp router-id ROUTER-ID Use the highest up/up loopback ip …

EIGRP Metric

[pmath size=12]K5!=0, doubleright Metric_EIGRP = [(K1B+K2B/{256-L}+K3D)*{K5/{R+K4}}]*256[/pmath] [pmath size=12]K5=0, doubleright Metric_EIGRP = (K1B+K2B/{256-L}+K3D)*256[/pmath] you will have to round down to the nearest integer default K valus: (K1,K2,K3,K4,K5) = (1,0,1,0,0) default EIGRP metric: B+D remember it as BuiLDeR 20 The EIGRP metric is 256 times larger than IGRP metric. 1. Metric Components …

EIGRP 101

1. Starting the routing process R(config)# router eigrp AS-NUMBER ! AS Number mast match between neighbors R(config-router)# network NETWORK-ADDR [WILDCARD] !If no wildcard is specified, the network is considered classful EIGRP will advertise routes learned by the EIGRP process and all routes that appear directly connected on the interfaces that …

RIP 101

1. Starting the routing process R(config)# router rip R(config-router)# network NETWORK-ADDR In RIP there is no wildcard option when configuring the network command. The NETWORK-ADDR will always be considered a classful address and will match all interfaces that are in the same classful network: R(config-router)#network 172.16.23.45 R1(config-router)#do sh run | …

How the routing table is built

1. The Routing Process The routing mechanism involves three different processes: the routing protocols that build the routing table, the routing process that looks up the routing table and the forwarding process that inquires the routing process what to do with a packet. Several routing protocols can run on one …

Policy based Routing

1. In Theory Policy Routing is a feature on Cisco routers that offers greater control over paths in a network. Normal routing is done based on the routing table. The router looks up the destination address of a packet and finds out the next hop or the outgoing interface. With …

ODR

1. What is ODR? ODR(On Demand Routing) is a routing protocol that runs on top of CDP and that is best suited for a hub and spoke topology. If the CDP traffic is already active between the routers on a Hub and Spoke network, the use of ODR makes sense …