BGP Local Preference and Multi Exit Disc

The LOCAL_PREF attribute affects only traffic leaving the AS. To influence incoming traffic, the MULTI_EXIT_DISC attribute, known as the MED for short, is used.

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OSPF Virtual Link

OSPF Virtual Link OSPF virtual link is use for that area far from backbone area 0. At this figure 1.1 area 2 is far from area 0 so area 2 can't reach other area. Figure 1.1 After configure OSPF, neighbor is up but router 2 don't see 3.3.3.0/24 network. R3#sh ip ospf nei Neighbor ID Pri State Dead Time Address Interface 2.2.2.2 1 FULL/DR 00:00:39 10.1.2.1 FastEthernet0/0 R2#sh ip route 10.0.0.0/30 is subnetted, 2 subnets C 10.1.2.0 is directly connected, FastEthernet1/0 C 10.1.1.0 is directly connected, FastEthernet0/0 One of OSPF rule all area must connect to area 0.In this cause we can use virtual link at area 1. R2 router ospf 1 router-id 2.2.2.2 log-adjace...

OSPF Stub

The following restrictions apply to stub areas: You cannot create a virtual link through a stub area. A stub area cannot contain an AS boundary router. You cannot configure the backbone as a stub area. You cannot configure an area as both a stub area and an not-so-stubby area (NSSA). Ref : Juniper.net

Why does OSPF need backbone area?

Why does OSPF require all traffic between non-backbone areas to pass through a backbone area (area 0)? Because inter-area OSPF is distance vector, it is vulnerable to routing loops. It avoids loops by mandating a loop-free inter-area topology, in which traffic from one area can only reach another area through area 0. Ref : Jeff Doyle article at Network world http://www.networkworld.com/article/2348778/cisco-subnet/my-favorite-interview-question.html

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