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642-691 BGP+MPLS

A collection of 6 posts

Difference between Router Descriptor (RD) and Route Target (RT)

642-691 BGP+MPLS

Difference between Router Descriptor (RD) and Route Target (RT)

Studying towards the SPEDGE (great word Cisco!) tonight and couldn't quite define exactly Route Descriptors and Route Targets. So lets try First off it might be important (and obvious) to note both RT and RDs will only ever be configured and used on PE nodes! P and CE

%BGP-4-VPNV4NH_MASK and OSPF advertising loopback as /32 by default

642-691 BGP+MPLS

%BGP-4-VPNV4NH_MASK and OSPF advertising loopback as /32 by default

Recently when doing some MPLS VPN lab work I came across the error %BGP-4-VPNV4NH_MASK: Nexthop 4.4.4.4 may not be reachable from neigbor 2.2.2.2 - not /32 mask It occurs because by default OSPF advertises loopback interfaces with a /32 mask even if you

642-691 BGP+MPLS

BGP Route Reflectors (GNS3 lab)

One problem of having a large number of routers running IBGP with each other in a full mesh is the volume of IBGP connections needed. The formula to see the number of connections needed for a full IBGP mesh is n(n-1)/2 so with 20 routers we would end

BGP Confederations (GNS3 Lab)

Similar to using route reflectors confederations are usually used to reduce the amount of IBGP connections needed for a full mesh. They do this by splitting an AS into multiple sub ASs. In the sub ASs created by the confederation all the normal rules of IBGP apply e.g. Fully

Changing MED value in BGP (GNS3 lab)

642-691 BGP+MPLS

Changing MED value in BGP (GNS3 lab)

BGP Multiexit Discriminator (MED or MULTI_EXIT_DISC) is an optional nontransative attribute (Type code Value 4). It is usually used to exchange info about a preferred to external BGP neighbours. MED is passed between ASs unlike LOCAL_PREF but each time it is passed to another new AS it

BGP Attributes

When BGP sends an UPDATE packet to a peer it sends path attributes associated with the prefix. These path attributes are then used by BGP to pick the best route to a destination. BGP attributes are similar to metrics in OSPF and EIGRP in the way it uses them to