Because ISPs tend to run EBGP-4 and IBGP-4 extensively, they tend to run these exclusively for exterior routes, using an IGP only for internal routes. This requires no redistribution, which is easier for the routers and means the following:
• Redistribution is not necessary, and the resources are spared.
• The IGP routing table is spared.
• BGP-4 can converge faster because it does not have to wait for a hello.
The synchronization command does not apply in this type of network because IBGP-4 is running in a fully meshed environment. With either a fully meshed network or carefully designed route reflectors, the synchronization rule can be turned off.
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