BGP Cores Sample Network

• Geographically distributed

• Hierarchical

• Media independent

• A clearly identifiable core

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• Geographically distributed

• Hierarchical

• Media independent

• A clearly identifiable core

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iBGP Core Migration Plan

• Configure BGP in all the core routers

Transit path

Turn synchronization off

• Route Generation

Use static routes to create summaries

Redistribution from the IGP is NOT recommended as it may cause instability

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iBGP Core ^^ Migration Plan (Cont)

• Route Generation—Example: 1

router bgp 109

network 200.200.200.0

network 201.201.0.0 mask 255.255.0.0

ip route 200.200.200.0 255.255.255.0 null0

ip route 201.201.0.0 255.255.0.0 null0

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iBGP Core Migration Plan (Cont.) ^

• Verify consistency of routing information

Compare the routing table against the BGP table—they must match!

• Change the distance parameters so that the BGP routes are preferred

distance bgp 20 20 20

All IGPs have a higher administrative distance

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iBGP Core Migration Plan (Cont.)

• Filter "non-core" IGP routes

Method will depend on the IGP used

May require the use of a different IGP process in the core if using a link state protocol

The routes to reach all the core links plus the BGP peering addresses must be carried by the IGP

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IGP carries all the routes

The core routers may be stressed due to the large number of routes

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iBGP Core After...

Core:

IGP carries only core links plus peering address information

BGP carries all the routes

Increased Stability!

Increased Stability!

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iBGP Core Results

• The routes from the core cannot be redistributed back into the IGP

Non-core areas need a default route

Amount of routing information in non-core areas has been reduced!

• Full logical iBGP mesh

• External connections must be located in the core

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Scaling Issues

• Full mesh core

High number of neighbors

Update generation

• Complex topologies

Not a "simple" hierarchical network

Multiple external and/or inter-region connections

Policy definition and enforcement

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• Reduce the number of updates

Peer groups

• Reduce the number of neighbors

Confederations Route reflectors

• Use additional information to effectively apply policies eBGP provides extra granularity Confederations

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